draft-ietf-cbor-7049bis-16.txt   rfc8949.txt 
Network Working Group C. Bormann Internet Engineering Task Force (IETF) C. Bormann
Internet-Draft Universitaet Bremen TZI Request for Comments: 8949 Universität Bremen TZI
Obsoletes: 7049 (if approved) P. Hoffman STD: 94 P. Hoffman
Intended status: Standards Track ICANN Obsoletes: 7049 ICANN
Expires: 3 April 2021 30 September 2020 Category: Standards Track December 2020
ISSN: 2070-1721
Concise Binary Object Representation (CBOR) Concise Binary Object Representation (CBOR)
draft-ietf-cbor-7049bis-16
Abstract Abstract
The Concise Binary Object Representation (CBOR) is a data format The Concise Binary Object Representation (CBOR) is a data format
whose design goals include the possibility of extremely small code whose design goals include the possibility of extremely small code
size, fairly small message size, and extensibility without the need size, fairly small message size, and extensibility without the need
for version negotiation. These design goals make it different from for version negotiation. These design goals make it different from
earlier binary serializations such as ASN.1 and MessagePack. earlier binary serializations such as ASN.1 and MessagePack.
This document is a revised edition of RFC 7049, with editorial This document obsoletes RFC 7049, providing editorial improvements,
improvements, added detail, and fixed errata. This revision formally new details, and errata fixes while keeping full compatibility with
obsoletes RFC 7049, while keeping full compatibility of the the interchange format of RFC 7049. It does not create a new version
interchange format from RFC 7049. It does not create a new version
of the format. of the format.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
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Internet Standards is available in Section 2 of RFC 7841.
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and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8949.
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document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
1.1. Objectives . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Objectives
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Terminology
2. CBOR Data Models . . . . . . . . . . . . . . . . . . . . . . 8 2. CBOR Data Models
2.1. Extended Generic Data Models . . . . . . . . . . . . . . 9 2.1. Extended Generic Data Models
2.2. Specific Data Models . . . . . . . . . . . . . . . . . . 9 2.2. Specific Data Models
3. Specification of the CBOR Encoding . . . . . . . . . . . . . 10 3. Specification of the CBOR Encoding
3.1. Major Types . . . . . . . . . . . . . . . . . . . . . . . 11 3.1. Major Types
3.2. Indefinite Lengths for Some Major Types . . . . . . . . . 14 3.2. Indefinite Lengths for Some Major Types
3.2.1. The "break" Stop Code . . . . . . . . . . . . . . . . 14 3.2.1. The "break" Stop Code
3.2.2. Indefinite-Length Arrays and Maps . . . . . . . . . . 14 3.2.2. Indefinite-Length Arrays and Maps
3.2.3. Indefinite-Length Byte Strings and Text Strings . . . 16 3.2.3. Indefinite-Length Byte Strings and Text Strings
3.2.4. Summary of indefinite-length use of major types . . . 17 3.2.4. Summary of Indefinite-Length Use of Major Types
3.3. Floating-Point Numbers and Values with No Content . . . . 18 3.3. Floating-Point Numbers and Values with No Content
3.4. Tagging of Items . . . . . . . . . . . . . . . . . . . . 20 3.4. Tagging of Items
3.4.1. Standard Date/Time String . . . . . . . . . . . . . . 23 3.4.1. Standard Date/Time String
3.4.2. Epoch-based Date/Time . . . . . . . . . . . . . . . . 23 3.4.2. Epoch-Based Date/Time
3.4.3. Bignums . . . . . . . . . . . . . . . . . . . . . . . 24 3.4.3. Bignums
3.4.4. Decimal Fractions and Bigfloats . . . . . . . . . . . 25 3.4.4. Decimal Fractions and Bigfloats
3.4.5. Content Hints . . . . . . . . . . . . . . . . . . . . 26 3.4.5. Content Hints
3.4.5.1. Encoded CBOR Data Item . . . . . . . . . . . . . 27 3.4.5.1. Encoded CBOR Data Item
3.4.5.2. Expected Later Encoding for CBOR-to-JSON 3.4.5.2. Expected Later Encoding for CBOR-to-JSON Converters
Converters . . . . . . . . . . . . . . . . . . . . 27 3.4.5.3. Encoded Text
3.4.5.3. Encoded Text . . . . . . . . . . . . . . . . . . 28 3.4.6. Self-Described CBOR
3.4.6. Self-Described CBOR . . . . . . . . . . . . . . . . . 29 4. Serialization Considerations
4. Serialization Considerations . . . . . . . . . . . . . . . . 29 4.1. Preferred Serialization
4.1. Preferred Serialization . . . . . . . . . . . . . . . . . 29 4.2. Deterministically Encoded CBOR
4.2. Deterministically Encoded CBOR . . . . . . . . . . . . . 31 4.2.1. Core Deterministic Encoding Requirements
4.2.1. Core Deterministic Encoding Requirements . . . . . . 31 4.2.2. Additional Deterministic Encoding Considerations
4.2.2. Additional Deterministic Encoding Considerations . . 32 4.2.3. Length-First Map Key Ordering
4.2.3. Length-first Map Key Ordering . . . . . . . . . . . . 34 5. Creating CBOR-Based Protocols
5. Creating CBOR-Based Protocols . . . . . . . . . . . . . . . . 35 5.1. CBOR in Streaming Applications
5.1. CBOR in Streaming Applications . . . . . . . . . . . . . 35 5.2. Generic Encoders and Decoders
5.2. Generic Encoders and Decoders . . . . . . . . . . . . . . 36 5.3. Validity of Items
5.3. Validity of Items . . . . . . . . . . . . . . . . . . . . 37 5.3.1. Basic validity
5.3.1. Basic validity . . . . . . . . . . . . . . . . . . . 37 5.3.2. Tag validity
5.3.2. Tag validity . . . . . . . . . . . . . . . . . . . . 37 5.4. Validity and Evolution
5.5. Numbers
5.4. Validity and Evolution . . . . . . . . . . . . . . . . . 38 5.6. Specifying Keys for Maps
5.5. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.6.1. Equivalence of Keys
5.6. Specifying Keys for Maps . . . . . . . . . . . . . . . . 40 5.7. Undefined Values
5.6.1. Equivalence of Keys . . . . . . . . . . . . . . . . . 42 6. Converting Data between CBOR and JSON
5.7. Undefined Values . . . . . . . . . . . . . . . . . . . . 43 6.1. Converting from CBOR to JSON
6. Converting Data between CBOR and JSON . . . . . . . . . . . . 43 6.2. Converting from JSON to CBOR
6.1. Converting from CBOR to JSON . . . . . . . . . . . . . . 43 7. Future Evolution of CBOR
6.2. Converting from JSON to CBOR . . . . . . . . . . . . . . 44 7.1. Extension Points
7. Future Evolution of CBOR . . . . . . . . . . . . . . . . . . 46 7.2. Curating the Additional Information Space
7.1. Extension Points . . . . . . . . . . . . . . . . . . . . 46 8. Diagnostic Notation
7.2. Curating the Additional Information Space . . . . . . . . 47 8.1. Encoding Indicators
8. Diagnostic Notation . . . . . . . . . . . . . . . . . . . . . 47 9. IANA Considerations
8.1. Encoding Indicators . . . . . . . . . . . . . . . . . . . 49 9.1. CBOR Simple Values Registry
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49 9.2. CBOR Tags Registry
9.1. Simple Values Registry . . . . . . . . . . . . . . . . . 50 9.3. Media Types Registry
9.2. Tags Registry . . . . . . . . . . . . . . . . . . . . . . 50 9.4. CoAP Content-Format Registry
9.3. Media Type ("MIME Type") . . . . . . . . . . . . . . . . 51 9.5. Structured Syntax Suffix Registry
9.4. CoAP Content-Format . . . . . . . . . . . . . . . . . . . 51 10. Security Considerations
9.5. The +cbor Structured Syntax Suffix Registration . . . . . 52 11. References
10. Security Considerations . . . . . . . . . . . . . . . . . . . 53 11.1. Normative References
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 55 11.2. Informative References
11.1. Normative References . . . . . . . . . . . . . . . . . . 55 Appendix A. Examples of Encoded CBOR Data Items
11.2. Informative References . . . . . . . . . . . . . . . . . 57 Appendix B. Jump Table for Initial Byte
Appendix A. Examples of Encoded CBOR Data Items . . . . . . . . 59 Appendix C. Pseudocode
Appendix B. Jump Table for Initial Byte . . . . . . . . . . . . 63 Appendix D. Half-Precision
Appendix C. Pseudocode . . . . . . . . . . . . . . . . . . . . . 66
Appendix D. Half-Precision . . . . . . . . . . . . . . . . . . . 69
Appendix E. Comparison of Other Binary Formats to CBOR's Design Appendix E. Comparison of Other Binary Formats to CBOR's Design
Objectives . . . . . . . . . . . . . . . . . . . . . . . 70 Objectives
E.1. ASN.1 DER, BER, and PER . . . . . . . . . . . . . . . . . 71 E.1. ASN.1 DER, BER, and PER
E.2. MessagePack . . . . . . . . . . . . . . . . . . . . . . . 71 E.2. MessagePack
E.3. BSON . . . . . . . . . . . . . . . . . . . . . . . . . . 72 E.3. BSON
E.4. MSDTP: RFC 713 . . . . . . . . . . . . . . . . . . . . . 72 E.4. MSDTP: RFC 713
E.5. Conciseness on the Wire . . . . . . . . . . . . . . . . . 72 E.5. Conciseness on the Wire
Appendix F. Well-formedness errors and examples . . . . . . . . 73 Appendix F. Well-Formedness Errors and Examples
F.1. Examples for CBOR data items that are not well-formed . . 74 F.1. Examples of CBOR Data Items That Are Not Well-Formed
Appendix G. Changes from RFC 7049 . . . . . . . . . . . . . . . 76 Appendix G. Changes from RFC 7049
G.1. Errata processing, clerical changes . . . . . . . . . . . 76 G.1. Errata Processing and Clerical Changes
G.2. Changes in IANA considerations . . . . . . . . . . . . . 77 G.2. Changes in IANA Considerations
G.3. Changes in suggestions and other informational G.3. Changes in Suggestions and Other Informational Components
components . . . . . . . . . . . . . . . . . . . . . . . 77 Acknowledgements
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 79 Authors' Addresses
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79
1. Introduction 1. Introduction
There are hundreds of standardized formats for binary representation There are hundreds of standardized formats for binary representation
of structured data (also known as binary serialization formats). Of of structured data (also known as binary serialization formats). Of
those, some are for specific domains of information, while others are those, some are for specific domains of information, while others are
generalized for arbitrary data. In the IETF, probably the best-known generalized for arbitrary data. In the IETF, probably the best-known
formats in the latter category are ASN.1's BER and DER [ASN.1]. formats in the latter category are ASN.1's BER and DER [ASN.1].
The format defined here follows some specific design goals that are The format defined here follows some specific design goals that are
skipping to change at page 4, line 26 skipping to change at line 155
to note that this is not a proposal that the grammar in RFC 8259 be to note that this is not a proposal that the grammar in RFC 8259 be
extended in general, since doing so would cause a significant extended in general, since doing so would cause a significant
backwards incompatibility with already deployed JSON documents. backwards incompatibility with already deployed JSON documents.
Instead, this document simply defines its own data model that starts Instead, this document simply defines its own data model that starts
from JSON. from JSON.
Appendix E lists some existing binary formats and discusses how well Appendix E lists some existing binary formats and discusses how well
they do or do not fit the design objectives of the Concise Binary they do or do not fit the design objectives of the Concise Binary
Object Representation (CBOR). Object Representation (CBOR).
This document is a revised edition of [RFC7049], with editorial This document obsoletes [RFC7049], providing editorial improvements,
improvements, added detail, and fixed errata. This revision formally new details, and errata fixes while keeping full compatibility with
obsoletes RFC 7049, while keeping full compatibility of the the interchange format of RFC 7049. It does not create a new version
interchange format from RFC 7049. It does not create a new version
of the format. of the format.
1.1. Objectives 1.1. Objectives
The objectives of CBOR, roughly in decreasing order of importance, The objectives of CBOR, roughly in decreasing order of importance,
are: are:
1. The representation must be able to unambiguously encode most 1. The representation must be able to unambiguously encode most
common data formats used in Internet standards. common data formats used in Internet standards.
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3. Data must be able to be decoded without a schema description. 3. Data must be able to be decoded without a schema description.
* Similar to JSON, encoded data should be self-describing so * Similar to JSON, encoded data should be self-describing so
that a generic decoder can be written. that a generic decoder can be written.
4. The serialization must be reasonably compact, but data 4. The serialization must be reasonably compact, but data
compactness is secondary to code compactness for the encoder and compactness is secondary to code compactness for the encoder and
decoder. decoder.
* "Reasonable" here is bounded by JSON as an upper bound in * "Reasonable" here is bounded by JSON as an upper bound in size
size, and by the implementation complexity limiting how much and by the implementation complexity, which limits the amount
effort can go into achieving that compactness. Using either of effort that can go into achieving that compactness. Using
general compression schemes or extensive bit-fiddling violates either general compression schemes or extensive bit-fiddling
the complexity goals. violates the complexity goals.
5. The format must be applicable to both constrained nodes and high- 5. The format must be applicable to both constrained nodes and high-
volume applications. volume applications.
* This means it must be reasonably frugal in CPU usage for both * This means it must be reasonably frugal in CPU usage for both
encoding and decoding. This is relevant both for constrained encoding and decoding. This is relevant both for constrained
nodes and for potential usage in applications with a very high nodes and for potential usage in applications with a very high
volume of data. volume of data.
6. The format must support all JSON data types for conversion to and 6. The format must support all JSON data types for conversion to and
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The term "byte" is used in its now-customary sense as a synonym for The term "byte" is used in its now-customary sense as a synonym for
"octet". All multi-byte values are encoded in network byte order "octet". All multi-byte values are encoded in network byte order
(that is, most significant byte first, also known as "big-endian"). (that is, most significant byte first, also known as "big-endian").
This specification makes use of the following terminology: This specification makes use of the following terminology:
Data item: A single piece of CBOR data. The structure of a data Data item: A single piece of CBOR data. The structure of a data
item may contain zero, one, or more nested data items. The term item may contain zero, one, or more nested data items. The term
is used both for the data item in representation format and for is used both for the data item in representation format and for
the abstract idea that can be derived from that by a decoder; the the abstract idea that can be derived from that by a decoder; the
former can be addressed specifically by using "encoded data item". former can be addressed specifically by using the term "encoded
data item".
Decoder: A process that decodes a well-formed encoded CBOR data item Decoder: A process that decodes a well-formed encoded CBOR data item
and makes it available to an application. Formally speaking, a and makes it available to an application. Formally speaking, a
decoder contains a parser to break up the input using the syntax decoder contains a parser to break up the input using the syntax
rules of CBOR, as well as a semantic processor to prepare the data rules of CBOR, as well as a semantic processor to prepare the data
in a form suitable to the application. in a form suitable to the application.
Encoder: A process that generates the (well-formed) representation Encoder: A process that generates the (well-formed) representation
format of a CBOR data item from application information. format of a CBOR data item from application information.
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Stream decoder: A process that decodes a data stream and makes each Stream decoder: A process that decodes a data stream and makes each
of the data items in the sequence available to an application as of the data items in the sequence available to an application as
they are received. they are received.
Terms and concepts for floating-point values such as Infinity, NaN Terms and concepts for floating-point values such as Infinity, NaN
(not a number), negative zero, and subnormal are defined in (not a number), negative zero, and subnormal are defined in
[IEEE754]. [IEEE754].
Where bit arithmetic or data types are explained, this document uses Where bit arithmetic or data types are explained, this document uses
the notation familiar from the programming language C [C], except the notation familiar from the programming language C [C], except
that "**" denotes exponentiation and ".." denotes a range that that ".." denotes a range that includes both ends given, and
includes both ends given. Examples and pseudocode assume that signed superscript notation denotes exponentiation. For example, 2 to the
integers use two's complement representation and that right shifts of power of 64 is notated: 2^(64). In the plain-text version of this
signed integers perform sign extension; these assumptions are also specification, superscript notation is not available and therefore is
specified in Sections 6.8.2 and 7.6.7 of the 2020 version of C++, rendered by a surrogate notation. That notation is not optimized for
successor of [Cplusplus17]. this RFC; it is unfortunately ambiguous with C's exclusive-or (which
is only used in the appendices, which in turn do not use
exponentiation) and requires circumspection from the reader of the
plain-text version.
Examples and pseudocode assume that signed integers use two's
complement representation and that right shifts of signed integers
perform sign extension; these assumptions are also specified in
Sections 6.8.1 (basic.fundamental) and 7.6.7 (expr.shift) of the 2020
version of C++ (currently available as a final draft, [Cplusplus20]).
Similar to the "0x" notation for hexadecimal numbers, numbers in Similar to the "0x" notation for hexadecimal numbers, numbers in
binary notation are prefixed with "0b". Underscores can be added to binary notation are prefixed with "0b". Underscores can be added to
a number solely for readability, so 0b00100001 (0x21) might be a number solely for readability, so 0b00100001 (0x21) might be
written 0b001_00001 to emphasize the desired interpretation of the written 0b001_00001 to emphasize the desired interpretation of the
bits in the byte; in this case, it is split into three bits and five bits in the byte; in this case, it is split into three bits and five
bits. Encoded CBOR data items are sometimes given in the "0x" or bits. Encoded CBOR data items are sometimes given in the "0x" or
"0b" notation; these values are first interpreted as numbers as in C "0b" notation; these values are first interpreted as numbers as in C
and are then interpreted as byte strings in network byte order, and are then interpreted as byte strings in network byte order,
including any leading zero bytes expressed in the notation. including any leading zero bytes expressed in the notation.
Words may be _italicized_ for emphasis; in the plain text form of Words may be _italicized_ for emphasis; in the plain text form of
this specification this is indicated by surrounding words with this specification, this is indicated by surrounding words with
underscore characters. Verbatim text (e.g., names from a programming underscore characters. Verbatim text (e.g., names from a programming
language) may be set in "monospace" type; in plain text this is language) may be set in "monospace" type; in plain text, this is
approximated somewhat ambiguously by surrounding the text in double approximated somewhat ambiguously by surrounding the text in double
quotes (which also retain their usual meaning). quotes (which also retain their usual meaning).
2. CBOR Data Models 2. CBOR Data Models
CBOR is explicit about its generic data model, which defines the set CBOR is explicit about its generic data model, which defines the set
of all data items that can be represented in CBOR. Its basic generic of all data items that can be represented in CBOR. Its basic generic
data model is extensible by the registration of "simple values" and data model is extensible by the registration of "simple values" and
tags. Applications can then subset the resulting extended generic tags. Applications can then create a subset of the resulting
data model to build their specific data models. extended generic data model to build their specific data models.
Within environments that can represent the data items in the generic Within environments that can represent the data items in the generic
data model, generic CBOR encoders and decoders can be implemented data model, generic CBOR encoders and decoders can be implemented
(which usually involves defining additional implementation data types (which usually involves defining additional implementation data types
for those data items that do not already have a natural for those data items that do not already have a natural
representation in the environment). The ability to provide generic representation in the environment). The ability to provide generic
encoders and decoders is an explicit design goal of CBOR; however encoders and decoders is an explicit design goal of CBOR; however,
many applications will provide their own application-specific many applications will provide their own application-specific
encoders and/or decoders. encoders and/or decoders.
In the basic (un-extended) generic data model defined in Section 3, a In the basic (unextended) generic data model defined in Section 3, a
data item is one of: data item is one of the following:
* an integer in the range -2**64..2**64-1 inclusive * an integer in the range -2^(64)..2^(64)-1 inclusive
* a simple value, identified by a number between 0 and 255, but * a simple value, identified by a number between 0 and 255, but
distinct from that number itself distinct from that number itself
* a floating-point value, distinct from an integer, out of the set * a floating-point value, distinct from an integer, out of the set
representable by IEEE 754 binary64 (including non-finites) representable by IEEE 754 binary64 (including non-finites)
[IEEE754] [IEEE754]
* a sequence of zero or more bytes ("byte string") * a sequence of zero or more bytes ("byte string")
* a sequence of zero or more Unicode code points ("text string") * a sequence of zero or more Unicode code points ("text string")
* a sequence of zero or more data items ("array") * a sequence of zero or more data items ("array")
* a mapping (mathematical function) from zero or more data items * a mapping (mathematical function) from zero or more data items
("keys") each to a data item ("values"), ("map") ("keys") each to a data item ("values"), ("map")
* a tagged data item ("tag"), comprising a tag number (an integer in * a tagged data item ("tag"), comprising a tag number (an integer in
the range 0..2**64-1) and the tag content (a data item) the range 0..2^(64)-1) and the tag content (a data item)
Note that integer and floating-point values are distinct in this Note that integer and floating-point values are distinct in this
model, even if they have the same numeric value. model, even if they have the same numeric value.
Also note that serialization variants are not visible at the generic Also note that serialization variants are not visible at the generic
data model level, including the number of bytes of the encoded data model level. This deliberate absence of visibility includes the
floating-point value or the choice of one of the ways in which an number of bytes of the encoded floating-point value. It also
integer, the length of a text or byte string, the number of elements includes the choice of encoding for an "argument" (see Section 3)
in an array or pairs in a map, or a tag number, (collectively "the such as the encoding for an integer, the encoding for the length of a
argument", see Section 3) can be encoded. text or byte string, the encoding for the number of elements in an
array or pairs in a map, or the encoding for a tag number.
2.1. Extended Generic Data Models 2.1. Extended Generic Data Models
This basic generic data model comes pre-extended by the registration This basic generic data model has been extended in this document by
of a number of simple values and tag numbers right in this document, the registration of a number of simple values and tag numbers, such
such as: as:
* "false", "true", "null", and "undefined" (simple values identified * "false", "true", "null", and "undefined" (simple values identified
by 20..23) by 20..23, Section 3.3)
* integer and floating-point values with a larger range and * integer and floating-point values with a larger range and
precision than the above (tag numbers 2 to 5) precision than the above (tag numbers 2 to 5, Section 3.4)
* application data types such as a point in time or an RFC 3339 * application data types such as a point in time or date/time string
date/time string (tag numbers 1, 0) defined in RFC 3339 (tag numbers 1 and 0, Section 3.4)
Further elements of the extended generic data model can be (and have Additional elements of the extended generic data model can be (and
been) defined via the IANA registries created for CBOR. Even if such have been) defined via the IANA registries created for CBOR. Even if
an extension is unknown to a generic encoder or decoder, data items such an extension is unknown to a generic encoder or decoder, data
using that extension can be passed to or from the application by items using that extension can be passed to or from the application
representing them at the interface to the application within the by representing them at the application interface within the basic
basic generic data model, i.e., as generic simple values or generic generic data model, i.e., as generic simple values or generic tags.
tags.
In other words, the basic generic data model is stable as defined in In other words, the basic generic data model is stable as defined in
this document, while the extended generic data model expands by the this document, while the extended generic data model expands by the
registration of new simple values or tag numbers, but never shrinks. registration of new simple values or tag numbers, but never shrinks.
While there is a strong expectation that generic encoders and While there is a strong expectation that generic encoders and
decoders can represent "false", "true", and "null" ("undefined" is decoders can represent "false", "true", and "null" ("undefined" is
intentionally omitted) in the form appropriate for their programming intentionally omitted) in the form appropriate for their programming
environment, implementation of the data model extensions created by environment, the implementation of the data model extensions created
tags is truly optional and a matter of implementation quality. by tags is truly optional and a matter of implementation quality.
2.2. Specific Data Models 2.2. Specific Data Models
The specific data model for a CBOR-based protocol usually subsets the The specific data model for a CBOR-based protocol usually takes a
extended generic data model and assigns application semantics to the subset of the extended generic data model and assigns application
data items within this subset and its components. When documenting semantics to the data items within this subset and its components.
such specific data models, where it is desired to specify the types When documenting such specific data models and specifying the types
of data items, it is preferred to identify the types by the names of data items, it is preferable to identify the types by their
they have in the generic data model ("negative integer", "array") generic data model names ("negative integer", "array") instead of
instead of by referring to aspects of their CBOR representation referring to aspects of their CBOR representation ("major type 1",
("major type 1", "major type 4"). "major type 4").
Specific data models can also specify what values (including values Specific data models can also specify value equivalency (including
of different types) are equivalent for the purposes of map keys and values of different types) for the purposes of map keys and encoder
encoder freedom. For example, in the generic data model, a valid map freedom. For example, in the generic data model, a valid map MAY
MAY have both "0" and "0.0" as keys, and an encoder MUST NOT encode have both "0" and "0.0" as keys, and an encoder MUST NOT encode "0.0"
"0.0" as an integer (major type 0, Section 3.1). However, if a as an integer (major type 0, Section 3.1). However, if a specific
specific data model declares that floating-point and integer data model declares that floating-point and integer representations
representations of integral values are equivalent, using both map of integral values are equivalent, using both map keys "0" and "0.0"
keys "0" and "0.0" in a single map would be considered duplicates, in a single map would be considered duplicates, even while encoded as
even while encoded as different major types, and so invalid; and an different major types, and so invalid; and an encoder could encode
encoder could encode integral-valued floats as integers or vice integral-valued floats as integers or vice versa, perhaps to save
versa, perhaps to save encoded bytes. encoded bytes.
3. Specification of the CBOR Encoding 3. Specification of the CBOR Encoding
A CBOR data item (Section 2) is encoded to or decoded from a byte A CBOR data item (Section 2) is encoded to or decoded from a byte
string carrying a well-formed encoded data item as described in this string carrying a well-formed encoded data item as described in this
section. The encoding is summarized in Table 7 in Appendix B, section. The encoding is summarized in Table 7 in Appendix B,
indexed by the initial byte. An encoder MUST produce only well- indexed by the initial byte. An encoder MUST produce only well-
formed encoded data items. A decoder MUST NOT return a decoded data formed encoded data items. A decoder MUST NOT return a decoded data
item when it encounters input that is not a well-formed encoded CBOR item when it encounters input that is not a well-formed encoded CBOR
data item (this does not detract from the usefulness of diagnostic data item (this does not detract from the usefulness of diagnostic
skipping to change at page 11, line 6 skipping to change at line 470
are not used as an integer argument, but as a floating-point value are not used as an integer argument, but as a floating-point value
(see Section 3.3). (see Section 3.3).
28, 29, 30: These values are reserved for future additions to the 28, 29, 30: These values are reserved for future additions to the
CBOR format. In the present version of CBOR, the encoded item is CBOR format. In the present version of CBOR, the encoded item is
not well-formed. not well-formed.
31: No argument value is derived. If the major type is 0, 1, or 6, 31: No argument value is derived. If the major type is 0, 1, or 6,
the encoded item is not well-formed. For major types 2 to 5, the the encoded item is not well-formed. For major types 2 to 5, the
item's length is indefinite, and for major type 7, the byte does item's length is indefinite, and for major type 7, the byte does
not constitute a data item at all but terminates an indefinite not constitute a data item at all but terminates an indefinite-
length item; all are described in Section 3.2. length item; all are described in Section 3.2.
The initial byte and any additional bytes consumed to construct the The initial byte and any additional bytes consumed to construct the
argument are collectively referred to as the "head" of the data item. argument are collectively referred to as the _head_ of the data item.
The meaning of this argument depends on the major type. For example, The meaning of this argument depends on the major type. For example,
in major type 0, the argument is the value of the data item itself in major type 0, the argument is the value of the data item itself
(and in major type 1 the value of the data item is computed from the (and in major type 1, the value of the data item is computed from the
argument); in major type 2 and 3 it gives the length of the string argument); in major type 2 and 3, it gives the length of the string
data in bytes that follows; and in major types 4 and 5 it is used to data in bytes that follow; and in major types 4 and 5, it is used to
determine the number of data items enclosed. determine the number of data items enclosed.
If the encoded sequence of bytes ends before the end of a data item, If the encoded sequence of bytes ends before the end of a data item,
that item is not well-formed. If the encoded sequence of bytes still that item is not well-formed. If the encoded sequence of bytes still
has bytes remaining after the outermost encoded item is decoded, that has bytes remaining after the outermost encoded item is decoded, that
encoding is not a single well-formed CBOR item; depending on the encoding is not a single well-formed CBOR item. Depending on the
application, the decoder may either treat the encoding as not well- application, the decoder may either treat the encoding as not well-
formed or just identify the start of the remaining bytes to the formed or just identify the start of the remaining bytes to the
application. application.
A CBOR decoder implementation can be based on a jump table with all A CBOR decoder implementation can be based on a jump table with all
256 defined values for the initial byte (Table 7). A decoder in a 256 defined values for the initial byte (Table 7). A decoder in a
constrained implementation can instead use the structure of the constrained implementation can instead use the structure of the
initial byte and following bytes for more compact code (see initial byte and following bytes for more compact code (see
Appendix C for a rough impression of how this could look). Appendix C for a rough impression of how this could look).
3.1. Major Types 3.1. Major Types
The following lists the major types and the additional information The following lists the major types and the additional information
and other bytes associated with the type. and other bytes associated with the type.
Major type 0: an unsigned integer in the range 0..2**64-1 inclusive. Major type 0:
The value of the encoded item is the argument itself. For An unsigned integer in the range 0..2^(64)-1 inclusive. The value
example, the integer 10 is denoted as the one byte 0b000_01010 of the encoded item is the argument itself. For example, the
(major type 0, additional information 10). The integer 500 would integer 10 is denoted as the one byte 0b000_01010 (major type 0,
be 0b000_11001 (major type 0, additional information 25) followed additional information 10). The integer 500 would be 0b000_11001
by the two bytes 0x01f4, which is 500 in decimal. (major type 0, additional information 25) followed by the two
bytes 0x01f4, which is 500 in decimal.
Major type 1: a negative integer in the range -2**64..-1 inclusive. Major type 1:
The value of the item is -1 minus the argument. For example, the A negative integer in the range -2^(64)..-1 inclusive. The value
integer -500 would be 0b001_11001 (major type 1, additional of the item is -1 minus the argument. For example, the integer
information 25) followed by the two bytes 0x01f3, which is 499 in -500 would be 0b001_11001 (major type 1, additional information
decimal. 25) followed by the two bytes 0x01f3, which is 499 in decimal.
Major type 2: a byte string. The number of bytes in the string is Major type 2:
equal to the argument. For example, a byte string whose length is A byte string. The number of bytes in the string is equal to the
5 would have an initial byte of 0b010_00101 (major type 2, argument. For example, a byte string whose length is 5 would have
additional information 5 for the length), followed by 5 bytes of an initial byte of 0b010_00101 (major type 2, additional
binary content. A byte string whose length is 500 would have 3 information 5 for the length), followed by 5 bytes of binary
initial bytes of 0b010_11001 (major type 2, additional information content. A byte string whose length is 500 would have 3 initial
25 to indicate a two-byte length) followed by the two bytes 0x01f4 bytes of 0b010_11001 (major type 2, additional information 25 to
for a length of 500, followed by 500 bytes of binary content. indicate a two-byte length) followed by the two bytes 0x01f4 for a
length of 500, followed by 500 bytes of binary content.
Major type 3: a text string (Section 2), encoded as UTF-8 Major type 3:
([RFC3629]). The number of bytes in the string is equal to the A text string (Section 2) encoded as UTF-8 [RFC3629]. The number
argument. A string containing an invalid UTF-8 sequence is well- of bytes in the string is equal to the argument. A string
formed but invalid (Section 1.2). This type is provided for containing an invalid UTF-8 sequence is well-formed but invalid
systems that need to interpret or display human-readable text, and (Section 1.2). This type is provided for systems that need to
allows the differentiation between unstructured bytes and text interpret or display human-readable text, and allows the
that has a specified repertoire (that of Unicode) and encoding differentiation between unstructured bytes and text that has a
(UTF-8). In contrast to formats such as JSON, the Unicode specified repertoire (that of Unicode) and encoding (UTF-8). In
characters in this type are never escaped. Thus, a newline contrast to formats such as JSON, the Unicode characters in this
character (U+000A) is always represented in a string as the byte type are never escaped. Thus, a newline character (U+000A) is
0x0a, and never as the bytes 0x5c6e (the characters "\" and "n") always represented in a string as the byte 0x0a, and never as the
nor as 0x5c7530303061 (the characters "\", "u", "0", "0", "0", and bytes 0x5c6e (the characters "\" and "n") nor as 0x5c7530303061
"a"). (the characters "\", "u", "0", "0", "0", and "a").
Major type 4: an array of data items. In other formats, arrays are Major type 4:
also called lists, sequences, or tuples (a "CBOR sequence" is An array of data items. In other formats, arrays are also called
something slightly different, though [RFC8742]). The argument is lists, sequences, or tuples (a "CBOR sequence" is something
the number of data items in the array. Items in an array do not slightly different, though [RFC8742]). The argument is the number
need to all be of the same type. For example, an array that of data items in the array. Items in an array do not need to all
contains 10 items of any type would have an initial byte of be of the same type. For example, an array that contains 10 items
0b100_01010 (major type 4, additional information 10 for the of any type would have an initial byte of 0b100_01010 (major type
length) followed by the 10 remaining items. 4, additional information 10 for the length) followed by the 10
remaining items.
Major type 5: a map of pairs of data items. Maps are also called Major type 5:
tables, dictionaries, hashes, or objects (in JSON). A map is A map of pairs of data items. Maps are also called tables,
comprised of pairs of data items, each pair consisting of a key dictionaries, hashes, or objects (in JSON). A map is comprised of
that is immediately followed by a value. The argument is the pairs of data items, each pair consisting of a key that is
number of _pairs_ of data items in the map. For example, a map immediately followed by a value. The argument is the number of
that contains 9 pairs would have an initial byte of 0b101_01001 _pairs_ of data items in the map. For example, a map that
(major type 5, additional information 9 for the number of pairs) contains 9 pairs would have an initial byte of 0b101_01001 (major
followed by the 18 remaining items. The first item is the first type 5, additional information 9 for the number of pairs) followed
key, the second item is the first value, the third item is the by the 18 remaining items. The first item is the first key, the
second key, and so on. Because items in a map come in pairs, second item is the first value, the third item is the second key,
their total number is always even: A map that contains an odd and so on. Because items in a map come in pairs, their total
number of items (no value data present after the last key data number is always even: a map that contains an odd number of items
item) is not well-formed. A map that has duplicate keys may be (no value data present after the last key data item) is not well-
well-formed, but it is not valid, and thus it causes indeterminate formed. A map that has duplicate keys may be well-formed, but it
decoding; see also Section 5.6. is not valid, and thus it causes indeterminate decoding; see also
Section 5.6.
Major type 6: a tagged data item ("tag") whose tag number, an Major type 6:
integer in the range 0..2**64-1 inclusive, is the argument and A tagged data item ("tag") whose tag number, an integer in the
whose enclosed data item ("tag content") is the single encoded range 0..2^(64)-1 inclusive, is the argument and whose enclosed
data item that follows the head. See Section 3.4. data item (_tag content_) is the single encoded data item that
follows the head. See Section 3.4.
Major type 7: floating-point numbers and simple values, as well as Major type 7:
the "break" stop code. See Section 3.3. Floating-point numbers and simple values, as well as the "break"
stop code. See Section 3.3.
These eight major types lead to a simple table showing which of the These eight major types lead to a simple table showing which of the
256 possible values for the initial byte of a data item are used 256 possible values for the initial byte of a data item are used
(Table 7). (Table 7).
In major types 6 and 7, many of the possible values are reserved for In major types 6 and 7, many of the possible values are reserved for
future specification. See Section 9 for more information on these future specification. See Section 9 for more information on these
values. values.
Table 1 summarizes the major types defined by CBOR, ignoring the next Table 1 summarizes the major types defined by CBOR, ignoring
section for now. The number N in this table stands for the argument, Section 3.2 for now. The number N in this table stands for the
mt for the major type. argument.
+====+=======================+=================================+ +============+=======================+=========================+
| mt | Meaning | Content | | Major Type | Meaning | Content |
+====+=======================+=================================+ +============+=======================+=========================+
| 0 | unsigned integer N | - | | 0 | unsigned integer N | - |
+----+-----------------------+---------------------------------+ +------------+-----------------------+-------------------------+
| 1 | negative integer -1-N | - | | 1 | negative integer -1-N | - |
+----+-----------------------+---------------------------------+ +------------+-----------------------+-------------------------+
| 2 | byte string | N bytes | | 2 | byte string | N bytes |
+----+-----------------------+---------------------------------+ +------------+-----------------------+-------------------------+
| 3 | text string | N bytes (UTF-8 text) | | 3 | text string | N bytes (UTF-8 text) |
+----+-----------------------+---------------------------------+ +------------+-----------------------+-------------------------+
| 4 | array | N data items (elements) | | 4 | array | N data items (elements) |
+----+-----------------------+---------------------------------+ +------------+-----------------------+-------------------------+
| 5 | map | 2N data items (key/value pairs) | | 5 | map | 2N data items (key/ |
+----+-----------------------+---------------------------------+ | | | value pairs) |
| 6 | tag of number N | 1 data item | +------------+-----------------------+-------------------------+
+----+-----------------------+---------------------------------+ | 6 | tag of number N | 1 data item |
| 7 | simple/float | - | +------------+-----------------------+-------------------------+
+----+-----------------------+---------------------------------+ | 7 | simple/float | - |
+------------+-----------------------+-------------------------+
Table 1: Overview over the definite-length use of CBOR major Table 1: Overview over the Definite-Length Use of CBOR Major
types (mt = major type, N = argument) Types (N = Argument)
3.2. Indefinite Lengths for Some Major Types 3.2. Indefinite Lengths for Some Major Types
Four CBOR items (arrays, maps, byte strings, and text strings) can be Four CBOR items (arrays, maps, byte strings, and text strings) can be
encoded with an indefinite length using additional information value encoded with an indefinite length using additional information value
31. This is useful if the encoding of the item needs to begin before 31. This is useful if the encoding of the item needs to begin before
the number of items inside the array or map, or the total length of the number of items inside the array or map, or the total length of
the string, is known. (The ability to start sending a data item the string, is known. (The ability to start sending a data item
before all of it is known is often referred to as "streaming" within before all of it is known is often referred to as "streaming" within
that data item.) that data item.)
Indefinite-length arrays and maps are dealt with differently than Indefinite-length arrays and maps are dealt with differently than
indefinite-length strings (byte strings and text strings). indefinite-length strings (byte strings and text strings).
3.2.1. The "break" Stop Code 3.2.1. The "break" Stop Code
The "break" stop code is encoded with major type 7 and additional The "break" stop code is encoded with major type 7 and additional
information value 31 (0b111_11111). It is not itself a data item: it information value 31 (0b111_11111). It is not itself a data item: it
is just a syntactic feature to close an indefinite-length item. is just a syntactic feature to close an indefinite-length item.
If the "break" stop code appears anywhere where a data item is If the "break" stop code appears where a data item is expected, other
expected, other than directly inside an indefinite-length string, than directly inside an indefinite-length string, array, or map --
array, or map -- for example directly inside a definite-length array for example, directly inside a definite-length array or map -- the
or map -- the enclosing item is not well-formed. enclosing item is not well-formed.
3.2.2. Indefinite-Length Arrays and Maps 3.2.2. Indefinite-Length Arrays and Maps
Indefinite-length arrays and maps are represented using their major Indefinite-length arrays and maps are represented using their major
type with the additional information value of 31, followed by an type with the additional information value of 31, followed by an
arbitrary-length sequence of zero or more items for an array or key/ arbitrary-length sequence of zero or more items for an array or key/
value pairs for a map, followed by the "break" stop code value pairs for a map, followed by the "break" stop code
(Section 3.2.1). In other words, indefinite-length arrays and maps (Section 3.2.1). In other words, indefinite-length arrays and maps
look identical to other arrays and maps except for beginning with the look identical to other arrays and maps except for beginning with the
additional information value of 31 and ending with the "break" stop additional information value of 31 and ending with the "break" stop
skipping to change at page 17, line 25 skipping to change at line 775
5F -- Start indefinite-length byte string 5F -- Start indefinite-length byte string
44 -- Byte string of length 4 44 -- Byte string of length 4
aabbccdd -- Bytes content aabbccdd -- Bytes content
43 -- Byte string of length 3 43 -- Byte string of length 3
eeff99 -- Bytes content eeff99 -- Bytes content
FF -- "break" FF -- "break"
After decoding, this results in a single byte string with seven After decoding, this results in a single byte string with seven
bytes: 0xaabbccddeeff99. bytes: 0xaabbccddeeff99.
3.2.4. Summary of indefinite-length use of major types 3.2.4. Summary of Indefinite-Length Use of Major Types
Table 2 summarizes the major types defined by CBOR as used for Table 2 summarizes the major types defined by CBOR as used for
indefinite length encoding (with additional information set to 31). indefinite-length encoding (with additional information set to 31).
mt stands for the major type.
+====+===================+==================================+ +============+===================+==================================+
| mt | Meaning | enclosed up to "break" stop code | | Major Type | Meaning | Enclosed up to "break" Stop Code |
+====+===================+==================================+ +============+===================+==================================+
| 0 | (not well-formed) | - | | 0 | (not well- | - |
+----+-------------------+----------------------------------+ | | formed) | |
| 1 | (not well-formed) | - | +------------+-------------------+----------------------------------+
+----+-------------------+----------------------------------+ | 1 | (not well- | - |
| 2 | byte string | definite-length byte strings | | | formed) | |
+----+-------------------+----------------------------------+ +------------+-------------------+----------------------------------+
| 3 | text string | definite-length text strings | | 2 | byte string | definite-length byte strings |
+----+-------------------+----------------------------------+ +------------+-------------------+----------------------------------+
| 4 | array | data items (elements) | | 3 | text string | definite-length text strings |
+----+-------------------+----------------------------------+ +------------+-------------------+----------------------------------+
| 5 | map | data items (key/value pairs) | | 4 | array | data items (elements) |
+----+-------------------+----------------------------------+ +------------+-------------------+----------------------------------+
| 6 | (not well-formed) | - | | 5 | map | data items (key/value pairs) |
+----+-------------------+----------------------------------+ +------------+-------------------+----------------------------------+
| 7 | "break" stop code | - | | 6 | (not well- | - |
+----+-------------------+----------------------------------+ | | formed) | |
+------------+-------------------+----------------------------------+
| 7 | "break" stop | - |
| | code | |
+------------+-------------------+----------------------------------+
Table 2: Overview over the indefinite-length use of CBOR Table 2: Overview of the Indefinite-Length Use of CBOR Major
major types (mt = major type, additional information = Types (Additional Information = 31)
31)
3.3. Floating-Point Numbers and Values with No Content 3.3. Floating-Point Numbers and Values with No Content
Major type 7 is for two types of data: floating-point numbers and Major type 7 is for two types of data: floating-point numbers and
"simple values" that do not need any content. Each value of the "simple values" that do not need any content. Each value of the
5-bit additional information in the initial byte has its own separate 5-bit additional information in the initial byte has its own separate
meaning, as defined in Table 3. Like the major types for integers, meaning, as defined in Table 3. Like the major types for integers,
items of this major type do not carry content data; all the items of this major type do not carry content data; all the
information is in the initial bytes (the head). information is in the initial bytes (the head).
skipping to change at page 19, line 37 skipping to change at line 848
byte extension: it is followed by an additional byte to represent the byte extension: it is followed by an additional byte to represent the
simple value. (To minimize confusion, only the values 32 to 255 are simple value. (To minimize confusion, only the values 32 to 255 are
used.) This maintains the structure of the initial bytes: as for the used.) This maintains the structure of the initial bytes: as for the
other major types, the length of these always depends on the other major types, the length of these always depends on the
additional information in the first byte. Table 4 lists the numeric additional information in the first byte. Table 4 lists the numeric
values assigned and available for simple values. values assigned and available for simple values.
+=========+==============+ +=========+==============+
| Value | Semantics | | Value | Semantics |
+=========+==============+ +=========+==============+
| 0..19 | (Unassigned) | | 0..19 | (unassigned) |
+---------+--------------+ +---------+--------------+
| 20 | False | | 20 | false |
+---------+--------------+ +---------+--------------+
| 21 | True | | 21 | true |
+---------+--------------+ +---------+--------------+
| 22 | Null | | 22 | null |
+---------+--------------+ +---------+--------------+
| 23 | Undefined | | 23 | undefined |
+---------+--------------+ +---------+--------------+
| 24..31 | (Reserved) | | 24..31 | (reserved) |
+---------+--------------+ +---------+--------------+
| 32..255 | (Unassigned) | | 32..255 | (unassigned) |
+---------+--------------+ +---------+--------------+
Table 4: Simple Values Table 4: Simple Values
An encoder MUST NOT issue two-byte sequences that start with 0xf8 An encoder MUST NOT issue two-byte sequences that start with 0xf8
(major type 7, additional information 24) and continue with a byte (major type 7, additional information 24) and continue with a byte
less than 0x20 (32 decimal). Such sequences are not well-formed. less than 0x20 (32 decimal). Such sequences are not well-formed.
(This implies that an encoder cannot encode false, true, null, or (This implies that an encoder cannot encode "false", "true", "null",
undefined in two-byte sequences, and that only the one-byte variants or "undefined" in two-byte sequences and that only the one-byte
of these are well-formed; more generally speaking, each simple value variants of these are well-formed; more generally speaking, each
only has a single representation variant). simple value only has a single representation variant).
The 5-bit values of 25, 26, and 27 are for 16-bit, 32-bit, and 64-bit The 5-bit values of 25, 26, and 27 are for 16-bit, 32-bit, and 64-bit
IEEE 754 binary floating-point values [IEEE754]. These floating- IEEE 754 binary floating-point values [IEEE754]. These floating-
point values are encoded in the additional bytes of the appropriate point values are encoded in the additional bytes of the appropriate
size. (See Appendix D for some information about 16-bit floating- size. (See Appendix D for some information about 16-bit floating-
point numbers.) point numbers.)
3.4. Tagging of Items 3.4. Tagging of Items
In CBOR, a data item can be enclosed by a tag to give it some In CBOR, a data item can be enclosed by a tag to give it some
additional semantics, as uniquely identified by a "tag number". The additional semantics, as uniquely identified by a _tag number_. The
tag is major type 6, its argument (Section 3) indicates the tag tag is major type 6, its argument (Section 3) indicates the tag
number, and it contains a single enclosed data item, the "tag number, and it contains a single enclosed data item, the _tag
content". (If a tag requires further structure to its content, this content_. (If a tag requires further structure to its content, this
structure is provided by the enclosed data item.) We use the term structure is provided by the enclosed data item.) We use the term
"tag" for the entire data item consisting of both a tag number and _tag_ for the entire data item consisting of both a tag number and
the tag content: the tag content is the data item that is being the tag content: the tag content is the data item that is being
tagged. tagged.
For example, assume that a byte string of length 12 is marked with a For example, assume that a byte string of length 12 is marked with a
tag of number 2 to indicate it is a positive "bignum" tag of number 2 to indicate it is an unsigned _bignum_
(Section 3.4.3). The encoded data item would start with a byte (Section 3.4.3). The encoded data item would start with a byte
0b110_00010 (major type 6, additional information 2 for the tag 0b110_00010 (major type 6, additional information 2 for the tag
number) followed by the encoded tag content: 0b010_01100 (major type number) followed by the encoded tag content: 0b010_01100 (major type
2, additional information of 12 for the length) followed by the 12 2, additional information 12 for the length) followed by the 12 bytes
bytes of the bignum. of the bignum.
The definition of a tag number describes the additional semantics In the extended generic data model, a tag number's definition
conveyed for tags with this tag number in the extended generic data describes the additional semantics conveyed with the tag number.
model. These semantics may include equivalence of some tagged data These semantics may include equivalence of some tagged data items
items with other data items, including some that can already be with other data items, including some that can be represented in the
represented in the basic generic data model. For instance, 0xc24101, basic generic data model. For instance, 0xc24101, a bignum the tag
a bignum the tag content of which is the byte string with the single content of which is the byte string with the single byte 0x01, is
byte 0x01, is equivalent to an integer 1, which could also be encoded equivalent to an integer 1, which could also be encoded as 0x01,
for instance as 0x01, 0x1801, or 0x190001. The tag definition may 0x1801, or 0x190001. The tag definition may specify a preferred
include the definition of a preferred serialization (Section 4.1) serialization (Section 4.1) that is recommended for generic encoders;
that is recommended for generic encoders; this may prefer basic this may prefer basic generic data model representations over ones
generic data model representations over ones that employ a tag. that employ a tag.
The tag definition usually restricts what kinds of nested data item The tag definition usually defines which nested data items are valid
or items are valid for such tags. Tag definitions may restrict their for such tags. Tag definitions may restrict their content to a very
content to a very specific syntactic structure, as the tags defined specific syntactic structure, as the tags defined in this document
in this document do, or they may aim at a more semantically defined do, or they may define their content more semantically. An example
definition of their content, as for instance tags 40 and 1040 do for the latter is how tags 40 and 1040 accept multiple ways to
[RFC8746]: These accept a number of different ways of representing represent arrays [RFC8746].
arrays.
As a matter of convention, many tags do not accept null or undefined As a matter of convention, many tags do not accept "null" or
values as tag content; instead, the expectation is that a null or "undefined" values as tag content; instead, the expectation is that a
undefined value can be used in place of the entire tag; Section 3.4.2 "null" or "undefined" value can be used in place of the entire tag;
provides some further considerations for one specific tag about the Section 3.4.2 provides some further considerations for one specific
handling of this convention in application protocols and in mapping tag about the handling of this convention in application protocols
to platform types. and in mapping to platform types.
Decoders do not need to understand tags of every tag number, and tags Decoders do not need to understand tags of every tag number, and tags
may be of little value in applications where the implementation may be of little value in applications where the implementation
creating a particular CBOR data item and the implementation decoding creating a particular CBOR data item and the implementation decoding
that stream know the semantic meaning of each item in the data flow. that stream know the semantic meaning of each item in the data flow.
Their primary purpose in this specification is to define common data The primary purpose of tags in this specification is to define common
types such as dates. A secondary purpose is to provide conversion data types such as dates. A secondary purpose is to provide
hints when it is foreseen that the CBOR data item needs to be conversion hints when it is foreseen that the CBOR data item needs to
translated into a different format, requiring hints about the content be translated into a different format, requiring hints about the
of items. Understanding the semantics of tags is optional for a content of items. Understanding the semantics of tags is optional
decoder; it can simply present both the tag number and the tag for a decoder; it can simply present both the tag number and the tag
content to the application, without interpreting the additional content to the application, without interpreting the additional
semantics of the tag. semantics of the tag.
A tag applies semantics to the data item it encloses. Tags can nest: A tag applies semantics to the data item it encloses. Tags can nest:
If tag A encloses tag B, which encloses data item C, tag A applies to if tag A encloses tag B, which encloses data item C, tag A applies to
the result of applying tag B on data item C. the result of applying tag B on data item C.
IANA maintains a registry of tag numbers as described in Section 9.2. IANA maintains a registry of tag numbers as described in Section 9.2.
Table 5 provides a list of tag numbers that were defined in Table 5 provides a list of tag numbers that were defined in [RFC7049]
[RFC7049], with definitions in the rest of this section. (Tag number with definitions in the rest of this section. (Tag number 35 was
35 was also defined in [RFC7049]; a discussion of this tag number also defined in [RFC7049]; a discussion of this tag number follows in
follows in Section 3.4.5.3.) Note that many other tag numbers have Section 3.4.5.3.) Note that many other tag numbers have been defined
been defined since the publication of [RFC7049]; see the registry since the publication of [RFC7049]; see the registry described at
described at Section 9.2 for the complete list. Section 9.2 for the complete list.
+============+=============+==================================+ +=======+=============+==================================+
| Tag Number | Data Item | Tag Content Semantics | | Tag | Data Item | Semantics |
+============+=============+==================================+ +=======+=============+==================================+
| 0 | text string | Standard date/time string; see | | 0 | text string | Standard date/time string; see |
| | | Section 3.4.1 | | | | Section 3.4.1 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 1 | integer or | Epoch-based date/time; see | | 1 | integer or | Epoch-based date/time; see |
| | float | Section 3.4.2 | | | float | Section 3.4.2 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 2 | byte string | Positive bignum; see | | 2 | byte string | Unsigned bignum; see |
| | | Section 3.4.3 | | | | Section 3.4.3 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 3 | byte string | Negative bignum; see | | 3 | byte string | Negative bignum; see |
| | | Section 3.4.3 | | | | Section 3.4.3 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 4 | array | Decimal fraction; see | | 4 | array | Decimal fraction; see |
| | | Section 3.4.4 | | | | Section 3.4.4 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 5 | array | Bigfloat; see Section 3.4.4 | | 5 | array | Bigfloat; see Section 3.4.4 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 21 | (any) | Expected conversion to base64url | | 21 | (any) | Expected conversion to base64url |
| | | encoding; see Section 3.4.5.2 | | | | encoding; see Section 3.4.5.2 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 22 | (any) | Expected conversion to base64 | | 22 | (any) | Expected conversion to base64 |
| | | encoding; see Section 3.4.5.2 | | | | encoding; see Section 3.4.5.2 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 23 | (any) | Expected conversion to base16 | | 23 | (any) | Expected conversion to base16 |
| | | encoding; see Section 3.4.5.2 | | | | encoding; see Section 3.4.5.2 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 24 | byte string | Encoded CBOR data item; see | | 24 | byte string | Encoded CBOR data item; see |
| | | Section 3.4.5.1 | | | | Section 3.4.5.1 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 32 | text string | URI; see Section 3.4.5.3 | | 32 | text string | URI; see Section 3.4.5.3 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 33 | text string | base64url; see Section 3.4.5.3 | | 33 | text string | base64url; see Section 3.4.5.3 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 34 | text string | base64; see Section 3.4.5.3 | | 34 | text string | base64; see Section 3.4.5.3 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 36 | text string | MIME message; see | | 36 | text string | MIME message; see |
| | | Section 3.4.5.3 | | | | Section 3.4.5.3 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
| 55799 | (any) | Self-described CBOR; see | | 55799 | (any) | Self-described CBOR; see |
| | | Section 3.4.6 | | | | Section 3.4.6 |
+------------+-------------+----------------------------------+ +-------+-------------+----------------------------------+
Table 5: Tag numbers defined in RFC 7049 Table 5: Tag Numbers Defined in RFC 7049
Conceptually, tags are interpreted in the generic data model, not at Conceptually, tags are interpreted in the generic data model, not at
(de-)serialization time. A small number of tags (at this time, tag (de-)serialization time. A small number of tags (at this time, tag
number 25 and tag number 29 [IANA.cbor-tags]) have been registered number 25 and tag number 29 [IANA.cbor-tags]) have been registered
with semantics that may require processing at (de-)serialization with semantics that may require processing at (de-)serialization
time: The decoder needs to be aware and the encoder needs to be in time: the decoder needs to be aware of, and the encoder needs to be
control of the exact sequence in which data items are encoded into in control of, the exact sequence in which data items are encoded
the CBOR data item. This means these tags cannot be implemented on into the CBOR data item. This means these tags cannot be implemented
top of an arbitrary generic CBOR encoder/decoder (which might not on top of an arbitrary generic CBOR encoder/decoder (which might not
reflect the serialization order for entries in a map at the data reflect the serialization order for entries in a map at the data
model level and vice versa); their implementation therefore typically model level and vice versa); their implementation therefore typically
needs to be integrated into the generic encoder/decoder. The needs to be integrated into the generic encoder/decoder. The
definition of new tags with this property is NOT RECOMMENDED. definition of new tags with this property is NOT RECOMMENDED.
IANA allocated tag numbers 65535, 4294967295, and IANA allocated tag numbers 65535, 4294967295, and
18446744073709551615 (binary all-ones in 16-bit, 32-bit, and 64-bit). 18446744073709551615 (binary all-ones in 16-bit, 32-bit, and 64-bit).
These can be used as a convenience for implementers that want a These can be used as a convenience for implementers who want a
single integer data structure to indicate either that a specific tag single-integer data structure to indicate either the presence of a
is present, or the absence of a tag. That allocation is described in specific tag or absence of a tag. That allocation is described in
Section 10 of [I-D.bormann-cbor-notable-tags]. These tags are not Section 10 of [CBOR-TAGS]. These tags are not intended to occur in
intended to occur in actual CBOR data items; implementations MAY flag actual CBOR data items; implementations MAY flag such an occurrence
such an occurrence as an error. as an error.
Protocols using tag numbers 0 and 1 extend the generic data model Protocols can extend the generic data model (Section 2) with data
(Section 2) with data items representing points in time; tag numbers items representing points in time by using tag numbers 0 and 1, with
2 and 3, with arbitrarily sized integers; and tag numbers 4 and 5, arbitrarily sized integers by using tag numbers 2 and 3, and with
with floating-point values of arbitrary size and precision. floating-point values of arbitrary size and precision by using tag
numbers 4 and 5.
3.4.1. Standard Date/Time String 3.4.1. Standard Date/Time String
Tag number 0 contains a text string in the standard format described Tag number 0 contains a text string in the standard format described
by the "date-time" production in [RFC3339], as refined by Section 3.3 by the "date-time" production in [RFC3339], as refined by Section 3.3
of [RFC4287], representing the point in time described there. A of [RFC4287], representing the point in time described there. A
nested item of another type or a text string that doesn't match the nested item of another type or a text string that doesn't match the
[RFC4287] format is invalid. format described in [RFC4287] is invalid.
3.4.2. Epoch-based Date/Time 3.4.2. Epoch-Based Date/Time
Tag number 1 contains a numerical value counting the number of Tag number 1 contains a numerical value counting the number of
seconds from 1970-01-01T00:00Z in UTC time to the represented point seconds from 1970-01-01T00:00Z in UTC time to the represented point
in civil time. in civil time.
The tag content MUST be an unsigned or negative integer (major types The tag content MUST be an unsigned or negative integer (major types
0 and 1), or a floating-point number (major type 7 with additional 0 and 1) or a floating-point number (major type 7 with additional
information 25, 26, or 27). Other contained types are invalid. information 25, 26, or 27). Other contained types are invalid.
Non-negative values (major type 0 and non-negative floating-point Nonnegative values (major type 0 and nonnegative floating-point
numbers) stand for time values on or after 1970-01-01T00:00Z UTC and numbers) stand for time values on or after 1970-01-01T00:00Z UTC and
are interpreted according to POSIX [TIME_T]. (POSIX time is also are interpreted according to POSIX [TIME_T]. (POSIX time is also
known as "UNIX Epoch time".) Leap seconds are handled specially by known as "UNIX Epoch time".) Leap seconds are handled specially by
POSIX time and this results in a 1 second discontinuity several times POSIX time, and this results in a 1-second discontinuity several
per decade. Note that applications that require the expression of times per decade. Note that applications that require the expression
times beyond early 2106 cannot leave out support of 64-bit integers of times beyond early 2106 cannot leave out support of 64-bit
for the tag content. integers for the tag content.
Negative values (major type 1 and negative floating-point numbers) Negative values (major type 1 and negative floating-point numbers)
are interpreted as determined by the application requirements as are interpreted as determined by the application requirements as
there is no universal standard for UTC count-of-seconds time before there is no universal standard for UTC count-of-seconds time before
1970-01-01T00:00Z (this is particularly true for points in time that 1970-01-01T00:00Z (this is particularly true for points in time that
precede discontinuities in national calendars). The same applies to precede discontinuities in national calendars). The same applies to
non-finite values. non-finite values.
To indicate fractional seconds, floating-point values can be used To indicate fractional seconds, floating-point values can be used
within tag number 1 instead of integer values. Note that this within tag number 1 instead of integer values. Note that this
generally requires binary64 support, as binary16 and binary32 provide generally requires binary64 support, as binary16 and binary32 provide
non-zero fractions of seconds only for a short period of time around nonzero fractions of seconds only for a short period of time around
early 1970. An application that requires tag number 1 support may early 1970. An application that requires tag number 1 support may
restrict the tag content to be an integer (or a floating-point value) restrict the tag content to be an integer (or a floating-point value)
only. only.
Note that platform types for date/time may include null or undefined Note that platform types for date/time may include "null" or
values, which may also be desirable at an application protocol level. "undefined" values, which may also be desirable at an application
While emitting tag number 1 values with non-finite tag content values protocol level. While emitting tag number 1 values with non-finite
(e.g., with NaN for undefined date/time values or with Infinite for tag content values (e.g., with NaN for undefined date/time values or
an expiry date that is not set) may seem an obvious way to handle with Infinity for an expiry date that is not set) may seem an obvious
this, using untagged null or undefined avoids the use of non-finites way to handle this, using untagged "null" or "undefined" avoids the
and results in a shorter encoding. Application protocol designers use of non-finites and results in a shorter encoding. Application
are encouraged to consider these cases and include clear guidelines protocol designers are encouraged to consider these cases and include
for handling them. clear guidelines for handling them.
3.4.3. Bignums 3.4.3. Bignums
Protocols using tag numbers 2 and 3 extend the generic data model Protocols using tag numbers 2 and 3 extend the generic data model
(Section 2) with "bignums" representing arbitrarily sized integers. (Section 2) with "bignums" representing arbitrarily sized integers.
In the basic generic data model, bignum values are not equal to In the basic generic data model, bignum values are not equal to
integers from the same model, but the extended generic data model integers from the same model, but the extended generic data model
created by this tag definition defines equivalence based on numeric created by this tag definition defines equivalence based on numeric
value, and preferred serialization (Section 4.1) never makes use of value, and preferred serialization (Section 4.1) never makes use of
bignums that also can be expressed as basic integers (see below). bignums that also can be expressed as basic integers (see below).
skipping to change at page 25, line 12 skipping to change at line 1102
leading zeroes (note that this means the preferred serialization for leading zeroes (note that this means the preferred serialization for
n = 0 is the empty byte string, but see below). Decoders that n = 0 is the empty byte string, but see below). Decoders that
understand these tags MUST be able to decode bignums that do have understand these tags MUST be able to decode bignums that do have
leading zeroes. The preferred serialization of an integer that can leading zeroes. The preferred serialization of an integer that can
be represented using major type 0 or 1 is to encode it this way be represented using major type 0 or 1 is to encode it this way
instead of as a bignum (which means that the empty string never instead of as a bignum (which means that the empty string never
occurs in a bignum when using preferred serialization). Note that occurs in a bignum when using preferred serialization). Note that
this means the non-preferred choice of a bignum representation this means the non-preferred choice of a bignum representation
instead of a basic integer for encoding a number is not intended to instead of a basic integer for encoding a number is not intended to
have application semantics (just as the choice of a longer basic have application semantics (just as the choice of a longer basic
integer representation than needed, such as 0x1800 for 0x00 does integer representation than needed, such as 0x1800 for 0x00, does
not). not).
For example, the number 18446744073709551616 (2**64) is represented For example, the number 18446744073709551616 (2^(64)) is represented
as 0b110_00010 (major type 6, tag number 2), followed by 0b010_01001 as 0b110_00010 (major type 6, tag number 2), followed by 0b010_01001
(major type 2, length 9), followed by 0x010000000000000000 (one byte (major type 2, length 9), followed by 0x010000000000000000 (one byte
0x01 and eight bytes 0x00). In hexadecimal: 0x01 and eight bytes 0x00). In hexadecimal:
C2 -- Tag 2 C2 -- Tag 2
49 -- Byte string of length 9 49 -- Byte string of length 9
010000000000000000 -- Bytes content 010000000000000000 -- Bytes content
3.4.4. Decimal Fractions and Bigfloats 3.4.4. Decimal Fractions and Bigfloats
Protocols using tag number 4 extend the generic data model with data Protocols using tag number 4 extend the generic data model with data
items representing arbitrary-length decimal fractions of the form items representing arbitrary-length decimal fractions of the form
m*(10**e). Protocols using tag number 5 extend the generic data m*(10^(e)). Protocols using tag number 5 extend the generic data
model with data items representing arbitrary-length binary fractions model with data items representing arbitrary-length binary fractions
of the form m*(2**e). As with bignums, values of different types are of the form m*(2^(e)). As with bignums, values of different types
not equal in the generic data model. are not equal in the generic data model.
Decimal fractions combine an integer mantissa with a base-10 scaling Decimal fractions combine an integer mantissa with a base-10 scaling
factor. They are most useful if an application needs the exact factor. They are most useful if an application needs the exact
representation of a decimal fraction such as 1.1 because there is no representation of a decimal fraction such as 1.1 because there is no
exact representation for many decimal fractions in binary floating- exact representation for many decimal fractions in binary floating-
point representations. point representations.
"Bigfloats" combine an integer mantissa with a base-2 scaling factor. "Bigfloats" combine an integer mantissa with a base-2 scaling factor.
They are binary floating-point values that can exceed the range or They are binary floating-point values that can exceed the range or
the precision of the three IEEE 754 formats supported by CBOR the precision of the three IEEE 754 formats supported by CBOR
(Section 3.3). Bigfloats may also be used by constrained (Section 3.3). Bigfloats may also be used by constrained
applications that need some basic binary floating-point capability applications that need some basic binary floating-point capability
without the need for supporting IEEE 754. without the need for supporting IEEE 754.
A decimal fraction or a bigfloat is represented as a tagged array A decimal fraction or a bigfloat is represented as a tagged array
that contains exactly two integer numbers: an exponent e and a that contains exactly two integer numbers: an exponent e and a
mantissa m. Decimal fractions (tag number 4) use base-10 exponents; mantissa m. Decimal fractions (tag number 4) use base-10 exponents;
the value of a decimal fraction data item is m*(10**e). Bigfloats the value of a decimal fraction data item is m*(10^(e)). Bigfloats
(tag number 5) use base-2 exponents; the value of a bigfloat data (tag number 5) use base-2 exponents; the value of a bigfloat data
item is m*(2**e). The exponent e MUST be represented in an integer item is m*(2^(e)). The exponent e MUST be represented in an integer
of major type 0 or 1, while the mantissa can also be a bignum of major type 0 or 1, while the mantissa can also be a bignum
(Section 3.4.3). Contained items with other structures are invalid. (Section 3.4.3). Contained items with other structures are invalid.
An example of a decimal fraction is that the number 273.15 could be An example of a decimal fraction is the representation of the number
represented as 0b110_00100 (major type 6 for tag, additional 273.15 as 0b110_00100 (major type 6 for tag, additional information 4
information 4 for the tag number), followed by 0b100_00010 (major for the tag number), followed by 0b100_00010 (major type 4 for the
type 4 for the array, additional information 2 for the length of the array, additional information 2 for the length of the array),
array), followed by 0b001_00001 (major type 1 for the first integer, followed by 0b001_00001 (major type 1 for the first integer,
additional information 1 for the value of -2), followed by additional information 1 for the value of -2), followed by
0b000_11001 (major type 0 for the second integer, additional 0b000_11001 (major type 0 for the second integer, additional
information 25 for a two-byte value), followed by 0b0110101010110011 information 25 for a two-byte value), followed by 0b0110101010110011
(27315 in two bytes). In hexadecimal: (27315 in two bytes). In hexadecimal:
C4 -- Tag 4 C4 -- Tag 4
82 -- Array of length 2 82 -- Array of length 2
21 -- -2 21 -- -2
19 6ab3 -- 27315 19 6ab3 -- 27315
An example of a bigfloat is that the number 1.5 could be represented An example of a bigfloat is the representation of the number 1.5 as
as 0b110_00101 (major type 6 for tag, additional information 5 for 0b110_00101 (major type 6 for tag, additional information 5 for the
the tag number), followed by 0b100_00010 (major type 4 for the array, tag number), followed by 0b100_00010 (major type 4 for the array,
additional information 2 for the length of the array), followed by additional information 2 for the length of the array), followed by
0b001_00000 (major type 1 for the first integer, additional 0b001_00000 (major type 1 for the first integer, additional
information 0 for the value of -1), followed by 0b000_00011 (major information 0 for the value of -1), followed by 0b000_00011 (major
type 0 for the second integer, additional information 3 for the value type 0 for the second integer, additional information 3 for the value
of 3). In hexadecimal: of 3). In hexadecimal:
C5 -- Tag 5 C5 -- Tag 5
82 -- Array of length 2 82 -- Array of length 2
20 -- -1 20 -- -1
03 -- 3 03 -- 3
skipping to change at page 27, line 38 skipping to change at line 1218
therefore wants to say what it believes is the proper way to convert therefore wants to say what it believes is the proper way to convert
binary strings to JSON. binary strings to JSON.
The data item tagged can be a byte string or any other data item. In The data item tagged can be a byte string or any other data item. In
the latter case, the tag applies to all of the byte string data items the latter case, the tag applies to all of the byte string data items
contained in the data item, except for those contained in a nested contained in the data item, except for those contained in a nested
data item tagged with an expected conversion. data item tagged with an expected conversion.
These three tag numbers suggest conversions to three of the base data These three tag numbers suggest conversions to three of the base data
encodings defined in [RFC4648]. Tag number 21 suggests conversion to encodings defined in [RFC4648]. Tag number 21 suggests conversion to
base64url encoding (Section 5 of RFC 4648), where padding is not used base64url encoding (Section 5 of [RFC4648]) where padding is not used
(see Section 3.2 of RFC 4648); that is, all trailing equals signs (see Section 3.2 of [RFC4648]); that is, all trailing equals signs
("=") are removed from the encoded string. Tag number 22 suggests ("=") are removed from the encoded string. Tag number 22 suggests
conversion to classical base64 encoding (Section 4 of RFC 4648), with conversion to classical base64 encoding (Section 4 of [RFC4648]) with
padding as defined in RFC 4648. For both base64url and base64, padding as defined in RFC 4648. For both base64url and base64,
padding bits are set to zero (see Section 3.5 of RFC 4648), and the padding bits are set to zero (see Section 3.5 of [RFC4648]), and the
conversion to alternate encoding is performed on the contents of the conversion to alternate encoding is performed on the contents of the
byte string (that is, without adding any line breaks, whitespace, or byte string (that is, without adding any line breaks, whitespace, or
other additional characters). Tag number 23 suggests conversion to other additional characters). Tag number 23 suggests conversion to
base16 (hex) encoding, with uppercase alphabetics (see Section 8 of base16 (hex) encoding with uppercase alphabetics (see Section 8 of
RFC 4648). Note that, for all three tag numbers, the encoding of the [RFC4648]). Note that, for all three tag numbers, the encoding of
empty byte string is the empty text string. the empty byte string is the empty text string.
3.4.5.3. Encoded Text 3.4.5.3. Encoded Text
Some text strings hold data that have formats widely used on the Some text strings hold data that have formats widely used on the
Internet, and sometimes those formats can be validated and presented Internet, and sometimes those formats can be validated and presented
to the application in appropriate form by the decoder. There are to the application in appropriate form by the decoder. There are
tags for some of these formats. tags for some of these formats.
* Tag number 32 is for URIs, as defined in [RFC3986]. If the text * Tag number 32 is for URIs, as defined in [RFC3986]. If the text
string doesn't match the "URI-reference" production, the string is string doesn't match the "URI-reference" production, the string is
invalid. invalid.
* Tag numbers 33 and 34 are for base64url- and base64-encoded text * Tag numbers 33 and 34 are for base64url- and base64-encoded text
strings, respectively, as defined in [RFC4648]. If any of: strings, respectively, as defined in [RFC4648]. If any of the
following apply:
- the encoded text string contains non-alphabet characters or - the encoded text string contains non-alphabet characters or
only 1 alphabet character in the last block of 4 (where only 1 alphabet character in the last block of 4 (where
alphabet is defined by Section 5 of [RFC4648] for tag number 33 alphabet is defined by Section 5 of [RFC4648] for tag number 33
and Section 4 of [RFC4648] for tag number 34), or and Section 4 of [RFC4648] for tag number 34), or
- the padding bits in a 2- or 3-character block are not 0, or - the padding bits in a 2- or 3-character block are not 0, or
- the base64 encoding has the wrong number of padding characters, - the base64 encoding has the wrong number of padding characters,
or or
- the base64url encoding has padding characters, - the base64url encoding has padding characters,
the string is invalid. the string is invalid.
* Tag number 36 is for MIME messages (including all headers), as * Tag number 36 is for MIME messages (including all headers), as
defined in [RFC2045]. A text string that isn't a valid MIME defined in [RFC2045]. A text string that isn't a valid MIME
message is invalid. (For this tag, validity checking may be message is invalid. (For this tag, validity checking may be
particularly onerous for a generic decoder and might therefore not particularly onerous for a generic decoder and might therefore not
be offered. Note that many MIME messages are general binary data be offered. Note that many MIME messages are general binary data
and can therefore not be represented in a text string; and therefore cannot be represented in a text string;
[IANA.cbor-tags] lists a registration for tag number 257 that is [IANA.cbor-tags] lists a registration for tag number 257 that is
similar to tag number 36 but uses a byte string as its tag similar to tag number 36 but uses a byte string as its tag
content.) content.)
Note that tag numbers 33 and 34 differ from 21 and 22 in that the Note that tag numbers 33 and 34 differ from 21 and 22 in that the
data is transported in base-encoded form for the former and in raw data is transported in base-encoded form for the former and in raw
byte string form for the latter. byte string form for the latter.
[RFC7049] also defined a tag number 35, for regular expressions that [RFC7049] also defined a tag number 35 for regular expressions that
are in Perl Compatible Regular Expressions (PCRE/PCRE2) form [PCRE] are in Perl Compatible Regular Expressions (PCRE/PCRE2) form [PCRE]
or in JavaScript regular expression syntax [ECMA262]. The state of or in JavaScript regular expression syntax [ECMA262]. The state of
the art in these regular expression specifications has since advanced the art in these regular expression specifications has since advanced
and is continually advancing, so the present specification does not and is continually advancing, so this specification does not attempt
attempt to update the references to a snapshot that is current at the to update the references. Instead, this tag remains available (as
time of writing. Instead, this tag remains available (as registered registered in [RFC7049]) for applications that specify the particular
in [RFC7049]) for applications that specify the particular regular regular expression variant they use out-of-band (possibly by limiting
expression variant they use out-of-band (possibly by limiting the the usage to a defined common subset of both PCRE and ECMA262). As
usage to a defined common subset of both PCRE and ECMA262). As the this specification clarifies tag validity beyond [RFC7049], we note
present specification clarifies tag validity beyond [RFC7049], we that due to the open way the tag was defined in [RFC7049], any
note that due to the open way the tag was defined in [RFC7049], any
contained string value needs to be valid at the CBOR tag level (but contained string value needs to be valid at the CBOR tag level (but
may then not be "expected" at the application level). then may not be "expected" at the application level).
3.4.6. Self-Described CBOR 3.4.6. Self-Described CBOR
In many applications, it will be clear from the context that CBOR is In many applications, it will be clear from the context that CBOR is
being employed for encoding a data item. For instance, a specific being employed for encoding a data item. For instance, a specific
protocol might specify the use of CBOR, or a media type is indicated protocol might specify the use of CBOR, or a media type is indicated
that specifies its use. However, there may be applications where that specifies its use. However, there may be applications where
such context information is not available, such as when CBOR data is such context information is not available, such as when CBOR data is
stored in a file that does not have disambiguating metadata. Here, stored in a file that does not have disambiguating metadata. Here,
it may help to have some distinguishing characteristics for the data it may help to have some distinguishing characteristics for the data
skipping to change at page 29, line 51 skipping to change at line 1326
which will never be found at the beginning of a JSON text. which will never be found at the beginning of a JSON text.
4. Serialization Considerations 4. Serialization Considerations
4.1. Preferred Serialization 4.1. Preferred Serialization
For some values at the data model level, CBOR provides multiple For some values at the data model level, CBOR provides multiple
serializations. For many applications, it is desirable that an serializations. For many applications, it is desirable that an
encoder always chooses a preferred serialization (preferred encoder always chooses a preferred serialization (preferred
encoding); however, the present specification does not put the burden encoding); however, the present specification does not put the burden
of enforcing this preference on either encoder or decoder. of enforcing this preference on either the encoder or decoder.
Some constrained decoders may be limited in their ability to decode Some constrained decoders may be limited in their ability to decode
non-preferred serializations: For example, if only integers below non-preferred serializations: for example, if only integers below
1_000_000_000 (one billion) are expected in an application, the 1_000_000_000 (one billion) are expected in an application, the
decoder may leave out the code that would be needed to decode 64-bit decoder may leave out the code that would be needed to decode 64-bit
arguments in integers. An encoder that always uses preferred arguments in integers. An encoder that always uses preferred
serialization ("preferred encoder") interoperates with this decoder serialization ("preferred encoder") interoperates with this decoder
for the numbers that can occur in this application. More generally for the numbers that can occur in this application. Generally
speaking, it therefore can be said that a preferred encoder is more speaking, a preferred encoder is more universally interoperable (and
universally interoperable (and also less wasteful) than one that, also less wasteful) than one that, say, always uses 64-bit integers.
say, always uses 64-bit integers.
Similarly, a constrained encoder may be limited in the variety of Similarly, a constrained encoder may be limited in the variety of
representation variants it supports in such a way that it does not representation variants it supports such that it does not emit
emit preferred serializations ("variant encoder"): Say, it could be preferred serializations ("variant encoder"). For instance, a
designed to always use the 32-bit variant for an integer that it constrained encoder could be designed to always use the 32-bit
encodes even if a short representation is available (again, assuming variant for an integer that it encodes even if a short representation
that there is no application need for integers that can only be is available (assuming that there is no application need for integers
represented with the 64-bit variant). A decoder that does not rely that can only be represented with the 64-bit variant). A decoder
on only ever receiving preferred serializations ("variation-tolerant that does not rely on receiving only preferred serializations
decoder") can therefore be said to be more universally interoperable ("variation-tolerant decoder") can therefore be said to be more
(it might very well optimize for the case of receiving preferred universally interoperable (it might very well optimize for the case
serializations, though). Full implementations of CBOR decoders are of receiving preferred serializations, though). Full implementations
by definition variation-tolerant; the distinction is only relevant if of CBOR decoders are by definition variation tolerant; the
a constrained implementation of a CBOR decoder meets a variant distinction is only relevant if a constrained implementation of a
encoder. CBOR decoder meets a variant encoder.
The preferred serialization always uses the shortest form of The preferred serialization always uses the shortest form of
representing the argument (Section 3); it also uses the shortest representing the argument (Section 3); it also uses the shortest
floating-point encoding that preserves the value being encoded. floating-point encoding that preserves the value being encoded.
The preferred serialization for a floating-point value is the The preferred serialization for a floating-point value is the
shortest floating-point encoding that preserves its value, e.g., shortest floating-point encoding that preserves its value, e.g.,
0xf94580 for the number 5.5, and 0xfa45ad9c00 for the number 5555.5. 0xf94580 for the number 5.5, and 0xfa45ad9c00 for the number 5555.5.
For NaN values, a shorter encoding is preferred if zero-padding the For NaN values, a shorter encoding is preferred if zero-padding the
shorter significand towards the right reconstitutes the original NaN shorter significand towards the right reconstitutes the original NaN
value (for many applications, the single NaN encoding 0xf97e00 will value (for many applications, the single NaN encoding 0xf97e00 will
suffice). suffice).
Definite length encoding is preferred whenever the length is known at Definite-length encoding is preferred whenever the length is known at
the time the serialization of the item starts. the time the serialization of the item starts.
4.2. Deterministically Encoded CBOR 4.2. Deterministically Encoded CBOR
Some protocols may want encoders to only emit CBOR in a particular Some protocols may want encoders to only emit CBOR in a particular
deterministic format; those protocols might also have the decoders deterministic format; those protocols might also have the decoders
check that their input is in that deterministic format. Those check that their input is in that deterministic format. Those
protocols are free to define what they mean by a "deterministic protocols are free to define what they mean by a "deterministic
format" and what encoders and decoders are expected to do. This format" and what encoders and decoders are expected to do. This
section defines a set of restrictions that can serve as the base of section defines a set of restrictions that can serve as the base of
skipping to change at page 31, line 38 skipping to change at line 1401
- 24 to 255 and -25 to -256 MUST be expressed only with an - 24 to 255 and -25 to -256 MUST be expressed only with an
additional uint8_t; additional uint8_t;
- 256 to 65535 and -257 to -65536 MUST be expressed only with an - 256 to 65535 and -257 to -65536 MUST be expressed only with an
additional uint16_t; additional uint16_t;
- 65536 to 4294967295 and -65537 to -4294967296 MUST be expressed - 65536 to 4294967295 and -65537 to -4294967296 MUST be expressed
only with an additional uint32_t. only with an additional uint32_t.
Floating-point values also MUST use the shortest form that Floating-point values also MUST use the shortest form that
preserves the value, e.g. 1.5 is encoded as 0xf93e00 (binary16) preserves the value, e.g., 1.5 is encoded as 0xf93e00 (binary16)
and 1000000.5 as 0xfa49742408 (binary32). (One implementation of and 1000000.5 as 0xfa49742408 (binary32). (One implementation of
this is to have all floats start as a 64-bit float, then do a test this is to have all floats start as a 64-bit float, then do a test
conversion to a 32-bit float; if the result is the same numeric conversion to a 32-bit float; if the result is the same numeric
value, use the shorter form and repeat the process with a test value, use the shorter form and repeat the process with a test
conversion to a 16-bit float. This also works to select 16-bit conversion to a 16-bit float. This also works to select 16-bit
float for positive and negative Infinity as well.) float for positive and negative Infinity as well.)
* Indefinite-length items MUST NOT appear. They can be encoded as * Indefinite-length items MUST NOT appear. They can be encoded as
definite-length items instead. definite-length items instead.
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4. "z", encoded as 0x617a. 4. "z", encoded as 0x617a.
5. "aa", encoded as 0x626161. 5. "aa", encoded as 0x626161.
6. [100], encoded as 0x811864. 6. [100], encoded as 0x811864.
7. [-1], encoded as 0x8120. 7. [-1], encoded as 0x8120.
8. false, encoded as 0xf4. 8. false, encoded as 0xf4.
(Implementation note: the self-delimiting nature of the CBOR | Implementation note: the self-delimiting nature of the CBOR
encoding means that there are no two well-formed CBOR encoded data | encoding means that there are no two well-formed CBOR encoded
items where one is a prefix of the other. The bytewise | data items where one is a prefix of the other. The bytewise
lexicographic comparison of deterministic encodings of different | lexicographic comparison of deterministic encodings of
map keys therefore always ends in a position where the byte | different map keys therefore always ends in a position where
differs between the keys, before the end of a key is reached.) | the byte differs between the keys, before the end of a key is
| reached.
4.2.2. Additional Deterministic Encoding Considerations 4.2.2. Additional Deterministic Encoding Considerations
CBOR tags present additional considerations for deterministic CBOR tags present additional considerations for deterministic
encoding. If a CBOR-based protocol were to provide the same encoding. If a CBOR-based protocol were to provide the same
semantics for the presence and absence of a specific tag (e.g., by semantics for the presence and absence of a specific tag (e.g., by
allowing both tag 1 data items and raw numbers in a date/time allowing both tag 1 data items and raw numbers in a date/time
position, treating the latter as if they were tagged), the position, treating the latter as if they were tagged), the
deterministic format would not allow the presence of the tag, based deterministic format would not allow the presence of the tag, based
on the "shortest form" principle. For example, a protocol might give on the "shortest form" principle. For example, a protocol might give
encoders the choice of representing a URL as either a text string or, encoders the choice of representing a URL as either a text string or,
using Section 3.4.5.3, tag number 32 containing a text string. This using Section 3.4.5.3, tag number 32 containing a text string. This
protocol's deterministic encoding needs to either require that the protocol's deterministic encoding needs either to require that the
tag is present or require that it is absent, not allow either one. tag is present or to require that it is absent, not allow either one.
In a protocol that does require tags in certain places to obtain In a protocol that does require tags in certain places to obtain
specific semantics, the tag needs to appear in the deterministic specific semantics, the tag needs to appear in the deterministic
format as well. Deterministic encoding considerations also apply to format as well. Deterministic encoding considerations also apply to
the content of tags. the content of tags.
If a protocol includes a field that can express integers with an If a protocol includes a field that can express integers with an
absolute value of 2^64 or larger using tag numbers 2 or 3 absolute value of 2^(64) or larger using tag numbers 2 or 3
(Section 3.4.3), the protocol's deterministic encoding needs to (Section 3.4.3), the protocol's deterministic encoding needs to
specify whether smaller integers are also expressed using these tags specify whether smaller integers are also expressed using these tags
or using major types 0 and 1. Preferred serialization uses the or using major types 0 and 1. Preferred serialization uses the
latter choice, which is therefore recommended. latter choice, which is therefore recommended.
Protocols that include floating-point values, whether represented Protocols that include floating-point values, whether represented
using basic floating-point values (Section 3.3) or using tags (or using basic floating-point values (Section 3.3) or using tags (or
both), may need to define extra requirements on their deterministic both), may need to define extra requirements on their deterministic
encodings, such as: encodings, such as:
skipping to change at page 33, line 21 skipping to change at line 1482
and negative zero as distinct values, the application might not and negative zero as distinct values, the application might not
distinguish these and might decide to represent all zero values distinguish these and might decide to represent all zero values
with a positive sign, disallowing negative zero. (The application with a positive sign, disallowing negative zero. (The application
may also want to restrict the precision of floating-point values may also want to restrict the precision of floating-point values
in such a way that there is never a need to represent 64-bit -- or in such a way that there is never a need to represent 64-bit -- or
even 32-bit -- floating-point values.) even 32-bit -- floating-point values.)
* If a protocol includes a field that can express floating-point * If a protocol includes a field that can express floating-point
values, with a specific data model that declares integer and values, with a specific data model that declares integer and
floating-point values to be interchangeable, the protocol's floating-point values to be interchangeable, the protocol's
deterministic encoding needs to specify whether (for example) the deterministic encoding needs to specify whether, for example, the
integer 1.0 is encoded as 0x01 (unsigned integer), 0xf93c00 integer 1.0 is encoded as 0x01 (unsigned integer), 0xf93c00
(binary16), 0xfa3f800000 (binary32), or 0xfb3ff0000000000000 (binary16), 0xfa3f800000 (binary32), or 0xfb3ff0000000000000
(binary64). Example rules for this are: (binary64). Example rules for this are:
1. Encode integral values that fit in 64 bits as values from 1. Encode integral values that fit in 64 bits as values from
major types 0 and 1, and other values as the preferred major types 0 and 1, and other values as the preferred
(smallest of 16-, 32-, or 64-bit) floating-point (smallest of 16-, 32-, or 64-bit) floating-point
representation that accurately represents the value, representation that accurately represents the value,
2. Encode all values as the preferred floating-point 2. Encode all values as the preferred floating-point
representation that accurately represents the value, even for representation that accurately represents the value, even for
integral values, or integral values, or
3. Encode all values as 64-bit floating-point representations. 3. Encode all values as 64-bit floating-point representations.
Rule 1 straddles the boundaries between integers and floating- Rule 1 straddles the boundaries between integers and floating-
point values, and Rule 3 does not use preferred serialization, so point values, and Rule 3 does not use preferred serialization, so
Rule 2 may be a good choice in many cases. Rule 2 may be a good choice in many cases.
* If NaN is an allowed value and there is no intent to support NaN * If NaN is an allowed value, and there is no intent to support NaN
payloads or signaling NaNs, the protocol needs to pick a single payloads or signaling NaNs, the protocol needs to pick a single
representation, typically 0xf97e00. If that simple choice is not representation, typically 0xf97e00. If that simple choice is not
possible, specific attention will be needed for NaN handling. possible, specific attention will be needed for NaN handling.
* Subnormal numbers (nonzero numbers with the lowest possible * Subnormal numbers (nonzero numbers with the lowest possible
exponent of a given IEEE 754 number format) may be flushed to zero exponent of a given IEEE 754 number format) may be flushed to zero
outputs or be treated as zero inputs in some floating-point outputs or be treated as zero inputs in some floating-point
implementations. A protocol's deterministic encoding may want to implementations. A protocol's deterministic encoding may want to
specifically accommodate such implementations while creating an specifically accommodate such implementations while creating an
onus on other implementations, by excluding subnormal numbers from onus on other implementations by excluding subnormal numbers from
interchange, interchanging zero instead. interchange, interchanging zero instead.
* The same number can be represented by different decimal fractions, * The same number can be represented by different decimal fractions,
by different bigfloats, and by different forms under other tags by different bigfloats, and by different forms under other tags
that may be defined to express numeric values. Depending on the that may be defined to express numeric values. Depending on the
implementation, it may not always be practical to determine implementation, it may not always be practical to determine
whether any of these forms (or forms in the basic generic data whether any of these forms (or forms in the basic generic data
model) are equivalent. An application protocol that presents model) are equivalent. An application protocol that presents
choices of this kind for the representation format of numbers choices of this kind for the representation format of numbers
needs to be explicit in how the formats are to be chosen for needs to be explicit about how the formats for deterministic
deterministic encoding. encoding are to be chosen.
4.2.3. Length-first Map Key Ordering 4.2.3. Length-First Map Key Ordering
The core deterministic encoding requirements (Section 4.2.1) sort map The core deterministic encoding requirements (Section 4.2.1) sort map
keys in a different order from the one suggested by Section 3.9 of keys in a different order from the one suggested by Section 3.9 of
[RFC7049] (called "Canonical CBOR" there). Protocols that need to be [RFC7049] (called "Canonical CBOR" there). Protocols that need to be
compatible with [RFC7049]'s order can instead be specified in terms compatible with the order specified in [RFC7049] can instead be
of this specification's "length-first core deterministic encoding specified in terms of this specification's "length-first core
requirements": deterministic encoding requirements":
A CBOR encoding satisfies the "length-first core deterministic A CBOR encoding satisfies the "length-first core deterministic
encoding requirements" if it satisfies the core deterministic encoding requirements" if it satisfies the core deterministic
encoding requirements except that the keys in every map MUST be encoding requirements except that the keys in every map MUST be
sorted such that: sorted such that:
1. If two keys have different lengths, the shorter one sorts 1. If two keys have different lengths, the shorter one sorts
earlier; earlier;
2. If two keys have the same length, the one with the lower value in 2. If two keys have the same length, the one with the lower value in
(byte-wise) lexical order sorts earlier. (bytewise) lexical order sorts earlier.
For example, under the length-first core deterministic encoding For example, under the length-first core deterministic encoding
requirements, the following keys are sorted correctly: requirements, the following keys are sorted correctly:
1. 10, encoded as 0x0a. 1. 10, encoded as 0x0a.
2. -1, encoded as 0x20. 2. -1, encoded as 0x20.
3. false, encoded as 0xf4. 3. false, encoded as 0xf4.
4. 100, encoded as 0x1864. 4. 100, encoded as 0x1864.
5. "z", encoded as 0x617a. 5. "z", encoded as 0x617a.
6. [-1], encoded as 0x8120. 6. [-1], encoded as 0x8120.
7. "aa", encoded as 0x626161. 7. "aa", encoded as 0x626161.
8. [100], encoded as 0x811864. 8. [100], encoded as 0x811864.
(Although [RFC7049] used the term "Canonical CBOR" for its form of | Although [RFC7049] used the term "Canonical CBOR" for its form
requirements on deterministic encoding, this document avoids this | of requirements on deterministic encoding, this document avoids
term because "canonicalization" is often associated with specific | this term because "canonicalization" is often associated with
uses of deterministic encoding only. The terms are essentially | specific uses of deterministic encoding only. The terms are
interchangeable, however, and the set of core requirements in this | essentially interchangeable, however, and the set of core
document could also be called "Canonical CBOR", while the length- | requirements in this document could also be called "Canonical
first-ordered version of that could be called "Old Canonical CBOR".) | CBOR", while the length-first-ordered version of that could be
| called "Old Canonical CBOR".
5. Creating CBOR-Based Protocols 5. Creating CBOR-Based Protocols
Data formats such as CBOR are often used in environments where there Data formats such as CBOR are often used in environments where there
is no format negotiation. A specific design goal of CBOR is to not is no format negotiation. A specific design goal of CBOR is to not
need any included or assumed schema: a decoder can take a CBOR item need any included or assumed schema: a decoder can take a CBOR item
and decode it with no other knowledge. and decode it with no other knowledge.
Of course, in real-world implementations, the encoder and the decoder Of course, in real-world implementations, the encoder and the decoder
will have a shared view of what should be in a CBOR data item. For will have a shared view of what should be in a CBOR data item. For
skipping to change at page 35, line 41 skipping to change at line 1601
based protocols MUST produce only valid items, that is, the protocol based protocols MUST produce only valid items, that is, the protocol
cannot be designed to make use of invalid items. An encoder can be cannot be designed to make use of invalid items. An encoder can be
capable of encoding as many or as few types of values as is required capable of encoding as many or as few types of values as is required
by the protocol in which it is used; a decoder can be capable of by the protocol in which it is used; a decoder can be capable of
understanding as many or as few types of values as is required by the understanding as many or as few types of values as is required by the
protocols in which it is used. This lack of restrictions allows CBOR protocols in which it is used. This lack of restrictions allows CBOR
to be used in extremely constrained environments. to be used in extremely constrained environments.
The rest of this section discusses some considerations in creating The rest of this section discusses some considerations in creating
CBOR-based protocols. With few exceptions, it is advisory only and CBOR-based protocols. With few exceptions, it is advisory only and
explicitly excludes any language from BCP 14 other than words that explicitly excludes any language from BCP 14 [RFC2119] [RFC8174]
could be interpreted as "MAY" in the sense of BCP 14. The exceptions other than words that could be interpreted as "MAY" in the sense of
aim at facilitating interoperability of CBOR-based protocols while BCP 14. The exceptions aim at facilitating interoperability of CBOR-
making use of a wide variety of both generic and application-specific based protocols while making use of a wide variety of both generic
encoders and decoders. and application-specific encoders and decoders.
5.1. CBOR in Streaming Applications 5.1. CBOR in Streaming Applications
In a streaming application, a data stream may be composed of a In a streaming application, a data stream may be composed of a
sequence of CBOR data items concatenated back-to-back. In such an sequence of CBOR data items concatenated back-to-back. In such an
environment, the decoder immediately begins decoding a new data item environment, the decoder immediately begins decoding a new data item
if data is found after the end of a previous data item. if data is found after the end of a previous data item.
Not all of the bytes making up a data item may be immediately Not all of the bytes making up a data item may be immediately
available to the decoder; some decoders will buffer additional data available to the decoder; some decoders will buffer additional data
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Generic CBOR encoders provide an application interface that allows Generic CBOR encoders provide an application interface that allows
the application to specify any well-formed value to be encoded as a the application to specify any well-formed value to be encoded as a
CBOR data item, including simple values and tags unknown to the CBOR data item, including simple values and tags unknown to the
encoder. encoder.
Even though CBOR attempts to minimize these cases, not all well- Even though CBOR attempts to minimize these cases, not all well-
formed CBOR data is valid: for example, the encoded text string formed CBOR data is valid: for example, the encoded text string
"0x62c0ae" does not contain valid UTF-8 (because [RFC3629] requires "0x62c0ae" does not contain valid UTF-8 (because [RFC3629] requires
always using the shortest form) and so is not a valid CBOR item. always using the shortest form) and so is not a valid CBOR item.
Also, specific tags may make semantic constraints that may be Also, specific tags may make semantic constraints that may be
violated, for instance by a bignum tag enclosing another tag, or by violated, for instance, by a bignum tag enclosing another tag or by
an instance of tag number 0 containing a byte string, or containing a an instance of tag number 0 containing a byte string or containing a
text string with contents that do not match [RFC3339]'s "date-time" text string with contents that do not match the "date-time"
production. There is no requirement that generic encoders and production of [RFC3339]. There is no requirement that generic
decoders make unnatural choices for their application interface to encoders and decoders make unnatural choices for their application
enable the processing of invalid data. Generic encoders and decoders interface to enable the processing of invalid data. Generic encoders
are expected to forward simple values and tags even if their specific and decoders are expected to forward simple values and tags even if
codepoints are not registered at the time the encoder/decoder is their specific codepoints are not registered at the time the encoder/
written (Section 5.4). decoder is written (Section 5.4).
5.3. Validity of Items 5.3. Validity of Items
A well-formed but invalid CBOR data item (Section 1.2) presents a A well-formed but invalid CBOR data item (Section 1.2) presents a
problem with interpreting the data encoded in it in the CBOR data problem with interpreting the data encoded in it in the CBOR data
model. A CBOR-based protocol could be specified in several layers, model. A CBOR-based protocol could be specified in several layers,
in which the lower layers don't process the semantics of some of the in which the lower layers don't process the semantics of some of the
CBOR data they forward. These layers can't notice any validity CBOR data they forward. These layers can't notice any validity
errors in data they don't process and MUST forward that data as-is. errors in data they don't process and MUST forward that data as-is.
The first layer that does process the semantics of an invalid CBOR The first layer that does process the semantics of an invalid CBOR
item MUST take one of two choices: item MUST pick one of two choices:
1. Replace the problematic item with an error marker and continue 1. Replace the problematic item with an error marker and continue
with the next item, or with the next item, or
2. Issue an error and stop processing altogether. 2. Issue an error and stop processing altogether.
A CBOR-based protocol MUST specify which of these options its A CBOR-based protocol MUST specify which of these options its
decoders take, for each kind of invalid item they might encounter. decoders take for each kind of invalid item they might encounter.
Such problems might occur at the basic validity level of CBOR or in Such problems might occur at the basic validity level of CBOR or in
the context of tags (tag validity). the context of tags (tag validity).
5.3.1. Basic validity 5.3.1. Basic validity
Two kinds of validity errors can occur in the basic generic data Two kinds of validity errors can occur in the basic generic data
model: model:
Duplicate keys in a map: Generic decoders (Section 5.2) make data Duplicate keys in a map: Generic decoders (Section 5.2) make data
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that the sequence of bytes in a UTF-8 string (major type 3) is that the sequence of bytes in a UTF-8 string (major type 3) is
actually valid UTF-8 and react appropriately. actually valid UTF-8 and react appropriately.
5.3.2. Tag validity 5.3.2. Tag validity
Two additional kinds of validity errors are introduced by adding tags Two additional kinds of validity errors are introduced by adding tags
to the basic generic data model: to the basic generic data model:
Inadmissible type for tag content: Tag numbers (Section 3.4) specify Inadmissible type for tag content: Tag numbers (Section 3.4) specify
what type of data item is supposed to be used as their tag what type of data item is supposed to be used as their tag
content; for example, the tag numbers for positive or negative content; for example, the tag numbers for unsigned or negative
bignums are supposed to be put on byte strings. A decoder that bignums are supposed to be put on byte strings. A decoder that
decodes the tagged data item into a native representation (a decodes the tagged data item into a native representation (a
native big integer in this example) is expected to check the type native big integer in this example) is expected to check the type
of the data item being tagged. Even decoders that don't have such of the data item being tagged. Even decoders that don't have such
native representations available in their environment may perform native representations available in their environment may perform
the check on those tags known to them and react appropriately. the check on those tags known to them and react appropriately.
Inadmissible value for tag content: The type of data item may be Inadmissible value for tag content: The type of data item may be
admissible for a tag's content, but the specific value may not be; admissible for a tag's content, but the specific value may not be;
e.g., a value of "yesterday" is not acceptable for the content of e.g., a value of "yesterday" is not acceptable for the content of
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would present a tag with an unknown tag number (Section 5.4). would present a tag with an unknown tag number (Section 5.4).
5.4. Validity and Evolution 5.4. Validity and Evolution
A decoder with validity checking will expend the effort to reliably A decoder with validity checking will expend the effort to reliably
detect data items with validity errors. For example, such a decoder detect data items with validity errors. For example, such a decoder
needs to have an API that reports an error (and does not return data) needs to have an API that reports an error (and does not return data)
for a CBOR data item that contains any of the validity errors listed for a CBOR data item that contains any of the validity errors listed
in the previous subsection. in the previous subsection.
The set of tags defined in the tag registry (Section 9.2), as well as The set of tags defined in the "Concise Binary Object Representation
the set of simple values defined in the simple values registry (CBOR) Tags" registry (Section 9.2), as well as the set of simple
(Section 9.1), can grow at any time beyond the set understood by a values defined in the "Concise Binary Object Representation (CBOR)
generic decoder. A validity-checking decoder can do one of two Simple Values" registry (Section 9.1), can grow at any time beyond
things when it encounters such a case that it does not recognize: the set understood by a generic decoder. A validity-checking decoder
can do one of two things when it encounters such a case that it does
not recognize:
* It can report an error (and not return data). Note that treating * It can report an error (and not return data). Note that treating
this case as an error can cause ossification, and is thus not this case as an error can cause ossification and is thus not
encouraged. This error is not a validity error per se. This kind encouraged. This error is not a validity error, per se. This
of error is more likely to be raised by a decoder that would be kind of error is more likely to be raised by a decoder that would
performing validity checking if this were a known case. be performing validity checking if this were a known case.
* It can emit the unknown item (type, value, and, for tags, the * It can emit the unknown item (type, value, and, for tags, the
decoded tagged data item) to the application calling the decoder, decoded tagged data item) to the application calling the decoder,
with an indication that the decoder did not recognize that tag and then give the application an indication that the decoder did
number or simple value. not recognize that tag number or simple value.
The latter approach, which is also appropriate for decoders that do The latter approach, which is also appropriate for decoders that do
not support validity checking, provides forward compatibility with not support validity checking, provides forward compatibility with
newly registered tags and simple values without the requirement to newly registered tags and simple values without the requirement to
update the encoder at the same time as the calling application. (For update the encoder at the same time as the calling application. (For
this, the API for the decoder needs to have a way to mark unknown this, the decoder's API needs the ability to mark unknown items so
items so that the calling application can handle them in a manner that the calling application can handle them in a manner appropriate
appropriate for the program.) for the program.)
Since some of the processing needed for validity checking may have an Since some of the processing needed for validity checking may have an
appreciable cost (in particular with duplicate detection for maps), appreciable cost (in particular with duplicate detection for maps),
support of validity checking is not a requirement placed on all CBOR support of validity checking is not a requirement placed on all CBOR
decoders. decoders.
Some encoders will rely on their applications to provide input data Some encoders will rely on their applications to provide input data
in such a way that valid CBOR results from the encoder. A generic in such a way that valid CBOR results from the encoder. A generic
encoder may also want to provide a validity-checking mode where it encoder may also want to provide a validity-checking mode where it
reliably limits its output to valid CBOR, independent of whether or reliably limits its output to valid CBOR, independent of whether or
not its application is indeed providing API-conformant data. not its application is indeed providing API-conformant data.
5.5. Numbers 5.5. Numbers
CBOR-based protocols should take into account that different language CBOR-based protocols should take into account that different language
environments pose different restrictions on the range and precision environments pose different restrictions on the range and precision
of numbers that are representable. For example, the basic JavaScript of numbers that are representable. For example, the basic JavaScript
number system treats all numbers as floating-point values, which may number system treats all numbers as floating-point values, which may
result in silent loss of precision in decoding integers with more result in the silent loss of precision in decoding integers with more
than 53 significant bits. Another example is that, since CBOR keeps than 53 significant bits. Another example is that, since CBOR keeps
the sign bit for its integer representation in the major type, it has the sign bit for its integer representation in the major type, it has
one bit more for signed numbers of a certain length (e.g., one bit more for signed numbers of a certain length (e.g.,
-2**64..2**64-1 for 1+8-byte integers) than the typical platform -2^(64)..2^(64)-1 for 1+8-byte integers) than the typical platform
signed integer representation of the same length (-2**63..2**63-1 for signed integer representation of the same length (-2^(63)..2^(63)-1
8-byte int64_t). A protocol that uses numbers should define its for 8-byte int64_t). A protocol that uses numbers should define its
expectations on the handling of non-trivial numbers in decoders and expectations on the handling of nontrivial numbers in decoders and
receiving applications. receiving applications.
A CBOR-based protocol that includes floating-point numbers can A CBOR-based protocol that includes floating-point numbers can
restrict which of the three formats (half-precision, single- restrict which of the three formats (half-precision, single-
precision, and double-precision) are to be supported. For an precision, and double-precision) are to be supported. For an
integer-only application, a protocol may want to completely exclude integer-only application, a protocol may want to completely exclude
the use of floating-point values. the use of floating-point values.
A CBOR-based protocol designed for compactness may want to exclude A CBOR-based protocol designed for compactness may want to exclude
specific integer encodings that are longer than necessary for the specific integer encodings that are longer than necessary for the
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compact application that does not require deterministic encoding compact application that does not require deterministic encoding
should accept values that use a longer-than-needed encoding (such as should accept values that use a longer-than-needed encoding (such as
encoding "0" as 0b000_11001 followed by two bytes of 0x00) as long as encoding "0" as 0b000_11001 followed by two bytes of 0x00) as long as
the application can decode an integer of the given size. Similar the application can decode an integer of the given size. Similar
considerations apply to floating-point values; decoding both considerations apply to floating-point values; decoding both
preferred serializations and longer-than-needed ones is recommended. preferred serializations and longer-than-needed ones is recommended.
CBOR-based protocols for constrained applications that provide a CBOR-based protocols for constrained applications that provide a
choice between representing a specific number as an integer and as a choice between representing a specific number as an integer and as a
decimal fraction or bigfloat (such as when the exponent is small and decimal fraction or bigfloat (such as when the exponent is small and
non-negative), might express a quality-of-implementation expectation nonnegative) might express a quality-of-implementation expectation
that the integer representation is used directly. that the integer representation is used directly.
5.6. Specifying Keys for Maps 5.6. Specifying Keys for Maps
The encoding and decoding applications need to agree on what types of The encoding and decoding applications need to agree on what types of
keys are going to be used in maps. In applications that need to keys are going to be used in maps. In applications that need to
interwork with JSON-based applications, conversion is simplified by interwork with JSON-based applications, conversion is simplified by
limiting keys to text strings only; otherwise, there has to be a limiting keys to text strings only; otherwise, there has to be a
specified mapping from the other CBOR types to text strings, and this specified mapping from the other CBOR types to text strings, and this
often leads to implementation errors. In applications where keys are often leads to implementation errors. In applications where keys are
numeric in nature and numeric ordering of keys is important to the numeric in nature, and numeric ordering of keys is important to the
application, directly using the numbers for the keys is useful. application, directly using the numbers for the keys is useful.
If multiple types of keys are to be used, consideration should be If multiple types of keys are to be used, consideration should be
given to how these types would be represented in the specific given to how these types would be represented in the specific
programming environments that are to be used. For example, in programming environments that are to be used. For example, in
JavaScript Maps [ECMA262], a key of integer 1 cannot be distinguished JavaScript Maps [ECMA262], a key of integer 1 cannot be distinguished
from a key of floating-point 1.0. This means that, if integer keys from a key of floating-point 1.0. This means that, if integer keys
are used, the protocol needs to avoid use of floating-point keys the are used, the protocol needs to avoid the use of floating-point keys
values of which happen to be integer numbers in the same map. the values of which happen to be integer numbers in the same map.
Decoders that deliver data items nested within a CBOR data item Decoders that deliver data items nested within a CBOR data item
immediately on decoding them ("streaming decoders") often do not keep immediately on decoding them ("streaming decoders") often do not keep
the state that is necessary to ascertain uniqueness of a key in a the state that is necessary to ascertain uniqueness of a key in a
map. Similarly, an encoder that can start encoding data items before map. Similarly, an encoder that can start encoding data items before
the enclosing data item is completely available ("streaming encoder") the enclosing data item is completely available ("streaming encoder")
may want to reduce its overhead significantly by relying on its data may want to reduce its overhead significantly by relying on its data
source to maintain uniqueness. source to maintain uniqueness.
A CBOR-based protocol MUST define what to do when a receiving A CBOR-based protocol MUST define what to do when a receiving
application does see multiple identical keys in a map. The resulting application sees multiple identical keys in a map. The resulting
rule in the protocol MUST respect the CBOR data model: it cannot rule in the protocol MUST respect the CBOR data model: it cannot
prescribe a specific handling of the entries with the identical keys, prescribe a specific handling of the entries with the identical keys,
except that it might have a rule that having identical keys in a map except that it might have a rule that having identical keys in a map
indicates a malformed map and that the decoder has to stop with an indicates a malformed map and that the decoder has to stop with an
error. When processing maps that exhibit entries with duplicate error. When processing maps that exhibit entries with duplicate
keys, a generic decoder might do one of the following: keys, a generic decoder might do one of the following:
* Not accept maps with duplicate keys (that is, enforce validity for * Not accept maps with duplicate keys (that is, enforce validity for
maps, see also Section 5.4). These generic decoders are maps, see also Section 5.4). These generic decoders are
universally useful. An application may still need to do perform universally useful. An application may still need to perform its
its own duplicate checking based on application rules (for own duplicate checking based on application rules (for instance,
instance if the application equates integers and floating-point if the application equates integers and floating-point values in
values in map key positions for specific maps). map key positions for specific maps).
* Pass all map entries to the application, including ones with * Pass all map entries to the application, including ones with
duplicate keys. This requires the application to handle (check duplicate keys. This requires that the application handle (check
against) duplicate keys, even if the application rules are against) duplicate keys, even if the application rules are
identical to the generic data model rules. identical to the generic data model rules.
* Lose some entries with duplicate keys, e.g. by only delivering the * Lose some entries with duplicate keys, e.g., deliver only the
final (or first) entry out of the entries with the same key. With final (or first) entry out of the entries with the same key. With
such a generic decoder, applications may get different results for such a generic decoder, applications may get different results for
a specific key on different runs and with different generic a specific key on different runs, and with different generic
decoders as which value is returned is based on generic decoder decoders, which value is returned is based on generic decoder
implementation and the actual order of keys in the map. In implementation and the actual order of keys in the map. In
particular, applications cannot validate key uniqueness on their particular, applications cannot validate key uniqueness on their
own as they do not necessarily see all entries; they may not be own as they do not necessarily see all entries; they may not be
able to use such a generic decoder if they do need to validate key able to use such a generic decoder if they need to validate key
uniqueness. These generic decoders can only be used in situations uniqueness. These generic decoders can only be used in situations
where the data source and transfer can be relied upon to always where the data source and transfer always provide valid maps; this
provide valid maps; this is not possible if the data source and is not possible if the data source and transfer can be attacked.
transfer can be attacked.
Generic decoders need to document which of these three approaches Generic decoders need to document which of these three approaches
they implement. they implement.
The CBOR data model for maps does not allow ascribing semantics to The CBOR data model for maps does not allow ascribing semantics to
the order of the key/value pairs in the map representation. Thus, a the order of the key/value pairs in the map representation. Thus, a
CBOR-based protocol MUST NOT specify that changing the key/value pair CBOR-based protocol MUST NOT specify that changing the key/value pair
order in a map would change the semantics, except to specify that order in a map changes the semantics, except to specify that some
some orders are disallowed, for example where they would not meet the orders are disallowed, for example, where they would not meet the
requirements of a deterministic encoding (Section 4.2). (Any requirements of a deterministic encoding (Section 4.2). (Any
secondary effects of map ordering such as on timing, cache usage, and secondary effects of map ordering such as on timing, cache usage, and
other potential side channels are not considered part of the other potential side channels are not considered part of the
semantics but may be enough reason on their own for a protocol to semantics but may be enough reason on their own for a protocol to
require a deterministic encoding format.) require a deterministic encoding format.)
Applications for constrained devices that have maps where a small Applications for constrained devices should consider using small
number of frequently used keys can be identified should consider integers as keys if they have maps with a small number of frequently
using small integers as keys; for instance, a set of 24 or fewer used keys; for instance, a set of 24 or fewer keys can be encoded in
frequent keys can be encoded in a single byte as unsigned integers, a single byte as unsigned integers, up to 48 if negative integers are
up to 48 if negative integers are also used. Less frequently also used. Less frequently occurring keys can then use integers with
occurring keys can then use integers with longer encodings. longer encodings.
5.6.1. Equivalence of Keys 5.6.1. Equivalence of Keys
The specific data model applying to a CBOR data item is used to The specific data model that applies to a CBOR data item is used to
determine whether keys occurring in maps are duplicates or distinct. determine whether keys occurring in maps are duplicates or distinct.
At the generic data model level, numerically equivalent integer and At the generic data model level, numerically equivalent integer and
floating-point values are distinct from each other, as they are from floating-point values are distinct from each other, as they are from
the various big numbers (Tags 2 to 5). Similarly, text strings are the various big numbers (Tags 2 to 5). Similarly, text strings are
distinct from byte strings, even if composed of the same bytes. A distinct from byte strings, even if composed of the same bytes. A
tagged value is distinct from an untagged value or from a value tagged value is distinct from an untagged value or from a value
tagged with a different tag number. tagged with a different tag number.
Within each of these groups, numeric values are distinct unless they Within each of these groups, numeric values are distinct unless they
are numerically equal (specifically, -0.0 is equal to 0.0); for the are numerically equal (specifically, -0.0 is equal to 0.0); for the
purpose of map key equivalence, NaN (not a number) values are purpose of map key equivalence, NaN values are equivalent if they
equivalent if they have the same significand after zero-extending have the same significand after zero-extending both significands at
both significands at the right to 64 bits. the right to 64 bits.
(Byte and text) strings are compared byte by byte, arrays element by Both byte strings and text strings are compared byte by byte, arrays
element, and are equal if they have the same number of bytes/elements are compared element by element, and are equal if they have the same
and the same values at the same positions. Two maps are equal if number of bytes/elements and the same values at the same positions.
they have the same set of pairs regardless of their order; pairs are Two maps are equal if they have the same set of pairs regardless of
equal if both the key and value are equal. their order; pairs are equal if both the key and value are equal.
Tagged values are equal if both the tag number and the tag content Tagged values are equal if both the tag number and the tag content
are equal. (Note that a generic decoder that provides processing for are equal. (Note that a generic decoder that provides processing for
a specific tag may not be able to distinguish some semantically a specific tag may not be able to distinguish some semantically
equivalent values, e.g. if leading zeroes occur in the content of tag equivalent values, e.g., if leading zeroes occur in the content of
2/3 (Section 3.4.3).) Simple values are equal if they simply have tag 2 or tag 3 (Section 3.4.3).) Simple values are equal if they
the same value. Nothing else is equal in the generic data model; a simply have the same value. Nothing else is equal in the generic
simple value 2 is not equivalent to an integer 2 and an array is data model; a simple value 2 is not equivalent to an integer 2, and
never equivalent to a map. an array is never equivalent to a map.
As discussed in Section 2.2, specific data models can make values As discussed in Section 2.2, specific data models can make values
equivalent for the purpose of comparing map keys that are distinct in equivalent for the purpose of comparing map keys that are distinct in
the generic data model. Note that this implies that a generic the generic data model. Note that this implies that a generic
decoder may deliver a decoded map to an application that needs to be decoder may deliver a decoded map to an application that needs to be
checked for duplicate map keys by that application (alternatively, checked for duplicate map keys by that application (alternatively,
the decoder may provide a programming interface to perform this the decoder may provide a programming interface to perform this
service for the application). Specific data models are not able to service for the application). Specific data models are not able to
distinguish values for map keys that are equal for this purpose at distinguish values for map keys that are equal for this purpose at
the generic data model level. the generic data model level.
5.7. Undefined Values 5.7. Undefined Values
In some CBOR-based protocols, the simple value (Section 3.3) of In some CBOR-based protocols, the simple value (Section 3.3) of
Undefined might be used by an encoder as a substitute for a data item "undefined" might be used by an encoder as a substitute for a data
with an encoding problem, in order to allow the rest of the enclosing item with an encoding problem, in order to allow the rest of the
data items to be encoded without harm. enclosing data items to be encoded without harm.
6. Converting Data between CBOR and JSON 6. Converting Data between CBOR and JSON
This section gives non-normative advice about converting between CBOR This section gives non-normative advice about converting between CBOR
and JSON. Implementations of converters MAY use whichever advice and JSON. Implementations of converters MAY use whichever advice
here they want. here they want.
It is worth noting that a JSON text is a sequence of characters, not It is worth noting that a JSON text is a sequence of characters, not
an encoded sequence of bytes, while a CBOR data item consists of an encoded sequence of bytes, while a CBOR data item consists of
bytes, not characters. bytes, not characters.
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6.2. Converting from JSON to CBOR 6.2. Converting from JSON to CBOR
All JSON values, once decoded, directly map into one or more CBOR All JSON values, once decoded, directly map into one or more CBOR
values. As with any kind of CBOR generation, decisions have to be values. As with any kind of CBOR generation, decisions have to be
made with respect to number representation. In a suggested made with respect to number representation. In a suggested
conversion: conversion:
* JSON numbers without fractional parts (integer numbers) are * JSON numbers without fractional parts (integer numbers) are
represented as integers (major types 0 and 1, possibly major type represented as integers (major types 0 and 1, possibly major type
6 tag number 2 and 3), choosing the shortest form; integers longer 6, tag number 2 and 3), choosing the shortest form; integers
than an implementation-defined threshold may instead be longer than an implementation-defined threshold may instead be
represented as floating-point values. The default range that is represented as floating-point values. The default range that is
represented as integer is -2**53+1..2**53-1 (fully exploiting the represented as integer is -2^(53)+1..2^(53)-1 (fully exploiting
range for exact integers in the binary64 representation often used the range for exact integers in the binary64 representation often
for decoding JSON [RFC7493]). A CBOR-based protocol, or a generic used for decoding JSON [RFC7493]). A CBOR-based protocol, or a
converter implementation, may choose -2**32..2**32-1 or generic converter implementation, may choose -2^(32)..2^(32)-1 or
-2**64..2**64-1 (fully using the integer ranges available in CBOR -2^(64)..2^(64)-1 (fully using the integer ranges available in
with uint32_t or uint64_t, respectively) or even -2**31..2**31-1 CBOR with uint32_t or uint64_t, respectively) or even
or -2**63..2**63-1 (using popular ranges for two's complement -2^(31)..2^(31)-1 or -2^(63)..2^(63)-1 (using popular ranges for
signed integers). (If the JSON was generated from a JavaScript two's complement signed integers). (If the JSON was generated
implementation, its precision is already limited to 53 bits from a JavaScript implementation, its precision is already limited
maximum.) to 53 bits maximum.)
* Numbers with fractional parts are represented as floating-point * Numbers with fractional parts are represented as floating-point
values, performing the decimal-to-binary conversion based on the values, performing the decimal-to-binary conversion based on the
precision provided by IEEE 754 binary64. The mathematical value precision provided by IEEE 754 binary64. The mathematical value
of the JSON number is converted to binary64 using the of the JSON number is converted to binary64 using the
roundTiesToEven procedure in Section 4.3.1 of [IEEE754]. Then, roundTiesToEven procedure in Section 4.3.1 of [IEEE754]. Then,
when encoding in CBOR, the preferred serialization uses the when encoding in CBOR, the preferred serialization uses the
shortest floating-point representation exactly representing this shortest floating-point representation exactly representing this
conversion result; for instance, 1.5 is represented in a 16-bit conversion result; for instance, 1.5 is represented in a 16-bit
floating-point value (not all implementations will be capable of floating-point value (not all implementations will be capable of
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protocol is designed to tolerate and embrace implementations that protocol is designed to tolerate and embrace implementations that
start using more codepoints than initially allocated. start using more codepoints than initially allocated.
Sizing the codepoint space may be difficult because the range Sizing the codepoint space may be difficult because the range
required may be hard to predict. Protocol designs should attempt to required may be hard to predict. Protocol designs should attempt to
make the codepoint space large enough so that it can slowly be filled make the codepoint space large enough so that it can slowly be filled
over the intended lifetime of the protocol. over the intended lifetime of the protocol.
CBOR has three major extension points: CBOR has three major extension points:
* the "simple" space (values in major type 7). Of the 24 efficient the "simple" space (values in major type 7): Of the 24 efficient
(and 224 slightly less efficient) values, only a small number have (and 224 slightly less efficient) values, only a small number have
been allocated. Implementations receiving an unknown simple data been allocated. Implementations receiving an unknown simple data
item may easily be able to process it as such, given that the item may easily be able to process it as such, given that the
structure of the value is indeed simple. The IANA registry in structure of the value is indeed simple. The IANA registry in
Section 9.1 is the appropriate way to address the extensibility of Section 9.1 is the appropriate way to address the extensibility of
this codepoint space. this codepoint space.
* the "tag" space (values in major type 6). The total codepoint the "tag" space (values in major type 6): The total codepoint space
space is abundant; only a tiny part of it has been allocated. is abundant; only a tiny part of it has been allocated. However,
However, not all of these codepoints are equally efficient: the not all of these codepoints are equally efficient: the first 24
first 24 only consume a single ("1+0") byte, and half of them have only consume a single ("1+0") byte, and half of them have already
already been allocated. The next 232 values only consume two been allocated. The next 232 values only consume two ("1+1")
("1+1") bytes, with nearly a quarter already allocated. These bytes, with nearly a quarter already allocated. These subspaces
subspaces need some curation to last for a few more decades. need some curation to last for a few more decades.
Implementations receiving an unknown tag number can choose to Implementations receiving an unknown tag number can choose to
process just the enclosed tag content or, preferably, to process process just the enclosed tag content or, preferably, to process
the tag as an unknown tag number wrapping the tag content. The the tag as an unknown tag number wrapping the tag content. The
IANA registry in Section 9.2 is the appropriate way to address the IANA registry in Section 9.2 is the appropriate way to address the
extensibility of this codepoint space. extensibility of this codepoint space.
* the "additional information" space. An implementation receiving the "additional information" space: An implementation receiving an
an unknown additional information value has no way to continue unknown additional information value has no way to continue
decoding, so allocating codepoints in this space is a major step decoding, so allocating codepoints in this space is a major step
beyond just exercising an extension point. There are also very beyond just exercising an extension point. There are also very
few codepoints left. See also Section 7.2. few codepoints left. See also Section 7.2.
7.2. Curating the Additional Information Space 7.2. Curating the Additional Information Space
The human mind is sometimes drawn to filling in little perceived gaps The human mind is sometimes drawn to filling in little perceived gaps
to make something neat. We expect the remaining gaps in the to make something neat. We expect the remaining gaps in the
codepoint space for the additional information values to be an codepoint space for the additional information values to be an
attractor for new ideas, just because they are there. attractor for new ideas, just because they are there.
The present specification does not manage the additional information The present specification does not manage the additional information
codepoint space by an IANA registry. Instead, allocations out of codepoint space by an IANA registry. Instead, allocations out of
this space can only be done by updating this specification. this space can only be done by updating this specification.
For an additional information value of n >= 24, the size of the For an additional information value of n >= 24, the size of the
additional data typically is 2**(n-24) bytes. Therefore, additional additional data typically is 2^(n-24) bytes. Therefore, additional
information values 28 and 29 should be viewed as candidates for information values 28 and 29 should be viewed as candidates for
128-bit and 256-bit quantities, in case a need arises to add them to 128-bit and 256-bit quantities, in case a need arises to add them to
the protocol. Additional information value 30 is then the only the protocol. Additional information value 30 is then the only
additional information value available for general allocation, and additional information value available for general allocation, and
there should be a very good reason for allocating it before assigning there should be a very good reason for allocating it before assigning
it through an update of the present specification. it through an update of the present specification.
8. Diagnostic Notation 8. Diagnostic Notation
CBOR is a binary interchange format. To facilitate documentation and CBOR is a binary interchange format. To facilitate documentation and
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The notation borrows the JSON syntax for numbers (integer and The notation borrows the JSON syntax for numbers (integer and
floating-point), True (>true<), False (>false<), Null (>null<), UTF-8 floating-point), True (>true<), False (>false<), Null (>null<), UTF-8
strings, arrays, and maps (maps are called objects in JSON; the strings, arrays, and maps (maps are called objects in JSON; the
diagnostic notation extends JSON here by allowing any data item in diagnostic notation extends JSON here by allowing any data item in
the key position). Undefined is written >undefined< as in the key position). Undefined is written >undefined< as in
JavaScript. The non-finite floating-point numbers Infinity, JavaScript. The non-finite floating-point numbers Infinity,
-Infinity, and NaN are written exactly as in this sentence (this is -Infinity, and NaN are written exactly as in this sentence (this is
also a way they can be written in JavaScript, although JSON does not also a way they can be written in JavaScript, although JSON does not
allow them). A tag is written as an integer number for the tag allow them). A tag is written as an integer number for the tag
number, followed by the tag content in parentheses; for instance, an number, followed by the tag content in parentheses; for instance, a
RFC 3339 (ISO 8601) date could be notated as: date in the format specified by RFC 3339 (ISO 8601) could be notated
as:
0("2013-03-21T20:04:00Z") 0("2013-03-21T20:04:00Z")
or the equivalent relative time as or the equivalent relative time as the following:
1(1363896240) 1(1363896240)
Byte strings are notated in one of the base encodings, without Byte strings are notated in one of the base encodings, without
padding, enclosed in single quotes, prefixed by >h< for base16, >b32< padding, enclosed in single quotes, prefixed by >h< for base16, >b32<
for base32, >h32< for base32hex, >b64< for base64 or base64url (the for base32, >h32< for base32hex, >b64< for base64 or base64url (the
actual encodings do not overlap, so the string remains unambiguous). actual encodings do not overlap, so the string remains unambiguous).
For example, the byte string 0x12345678 could be written h'12345678', For example, the byte string 0x12345678 could be written h'12345678',
b32'CI2FM6A', or b64'EjRWeA'. b32'CI2FM6A', or b64'EjRWeA'.
Unassigned simple values are given as "simple()" with the appropriate Unassigned simple values are given as "simple()" with the appropriate
integer in the parentheses. For example, "simple(42)" indicates integer in the parentheses. For example, "simple(42)" indicates
major type 7, value 42. major type 7, value 42.
A number of useful extensions to the diagnostic notation defined here A number of useful extensions to the diagnostic notation defined here
are provided in Appendix G of [RFC8610], "Extended Diagnostic are provided in Appendix G of [RFC8610], "Extended Diagnostic
Notation" (EDN). Similarly, an extension of this notation could be Notation" (EDN). Similarly, this notation could be extended in a
provided in a separate document to provide for the documentation of separate document to provide documentation for NaN payloads, which
NaN payloads, which are not covered in the present document. are not covered in this document.
8.1. Encoding Indicators 8.1. Encoding Indicators
Sometimes it is useful to indicate in the diagnostic notation which Sometimes it is useful to indicate in the diagnostic notation which
of several alternative representations were actually used; for of several alternative representations were actually used; for
example, a data item written >1.5< by a diagnostic decoder might have example, a data item written >1.5< by a diagnostic decoder might have
been encoded as a half-, single-, or double-precision float. been encoded as a half-, single-, or double-precision float.
The convention for encoding indicators is that anything starting with The convention for encoding indicators is that anything starting with
an underscore and all following characters that are alphanumeric or an underscore and all following characters that are alphanumeric or
underscore, is an encoding indicator, and can be ignored by anyone underscore is an encoding indicator, and can be ignored by anyone not
not interested in this information. For example, "_" or "_3". interested in this information. For example, "_" or "_3". Encoding
Encoding indicators are always optional. indicators are always optional.
A single underscore can be written after the opening brace of a map A single underscore can be written after the opening brace of a map
or the opening bracket of an array to indicate that the data item was or the opening bracket of an array to indicate that the data item was
represented in indefinite-length format. For example, [_ 1, 2] represented in indefinite-length format. For example, [_ 1, 2]
contains an indicator that an indefinite-length representation was contains an indicator that an indefinite-length representation was
used to represent the data item [1, 2]. used to represent the data item [1, 2].
An underscore followed by a decimal digit n indicates that the An underscore followed by a decimal digit n indicates that the
preceding item (or, for arrays and maps, the item starting with the preceding item (or, for arrays and maps, the item starting with the
preceding bracket or brace) was encoded with an additional preceding bracket or brace) was encoded with an additional
information value of 24+n. For example, 1.5_1 is a half-precision information value of 24+n. For example, 1.5_1 is a half-precision
floating-point number, while 1.5_3 is encoded as double precision. floating-point number, while 1.5_3 is encoded as double precision.
This encoding indicator is not shown in Appendix A. (Note that the This encoding indicator is not shown in Appendix A. (Note that the
encoding indicator "_" is thus an abbreviation of the full form "_7", encoding indicator "_" is thus an abbreviation of the full form "_7",
which is not used.) which is not used.)
The detailed chunk structure of byte and text strings of indefinite The detailed chunk structure of byte and text strings of indefinite
length can be notated in the form (_ h'0123', h'4567') and (_ "foo", length can be notated in the form (_ h'0123', h'4567') and (_ "foo",
"bar"). However, for an indefinite length string with no chunks "bar"). However, for an indefinite-length string with no chunks
inside, (_ ) would be ambiguous whether a byte string (0x5fff) or a inside, (_ ) would be ambiguous as to whether a byte string (0x5fff)
text string (0x7fff) is meant and is therefore not used. The basic or a text string (0x7fff) is meant and is therefore not used. The
forms ''_ and ""_ can be used instead and are reserved for the case basic forms ''_ and ""_ can be used instead and are reserved for the
with no chunks only -- not as short forms for the (permitted, but not case of no chunks only -- not as short forms for the (permitted, but
really useful) encodings with only empty chunks, which to preserve not really useful) encodings with only empty chunks, which need to be
the chunk structure need to be notated as (_ ''), (_ ""), etc. notated as (_ ''), (_ ""), etc., to preserve the chunk structure.
9. IANA Considerations 9. IANA Considerations
IANA has created two registries for new CBOR values. The registries IANA has created two registries for new CBOR values. The registries
are separate, that is, not under an umbrella registry, and follow the are separate, that is, not under an umbrella registry, and follow the
rules in [RFC8126]. IANA has also assigned a new MIME media type and rules in [RFC8126]. IANA has also assigned a new media type, an
an associated Constrained Application Protocol (CoAP) Content-Format associated CoAP Content-Format entry, and a structured syntax suffix.
entry.
9.1. Simple Values Registry 9.1. CBOR Simple Values Registry
IANA has created the "Concise Binary Object Representation (CBOR) IANA has created the "Concise Binary Object Representation (CBOR)
Simple Values" registry at [IANA.cbor-simple-values]. The initial Simple Values" registry at [IANA.cbor-simple-values]. The initial
values are shown in Table 4. values are shown in Table 4.
New entries in the range 0 to 19 are assigned by Standards Action. New entries in the range 0 to 19 are assigned by Standards Action
It is suggested that these Standards Actions allocate values starting [RFC8126]. It is suggested that IANA allocate values starting with
with the number 16 in order to reserve the lower numbers for the number 16 in order to reserve the lower numbers for contiguous
contiguous blocks (if any). blocks (if any).
New entries in the range 32 to 255 are assigned by Specification New entries in the range 32 to 255 are assigned by Specification
Required. Required.
9.2. Tags Registry 9.2. CBOR Tags Registry
IANA has created the "Concise Binary Object Representation (CBOR) IANA has created the "Concise Binary Object Representation (CBOR)
Tags" registry at [IANA.cbor-tags]. The tags that were defined in Tags" registry at [IANA.cbor-tags]. The tags that were defined in
[RFC7049] are described in detail in Section 3.4, and other tags have [RFC7049] are described in detail in Section 3.4, and other tags have
already been defined since then. already been defined since then.
New entries in the range 0 to 23 ("1+0") are assigned by Standards New entries in the range 0 to 23 ("1+0") are assigned by Standards
Action. New entries in the ranges 24 to 255 ("1+1") and 256 to 32767 Action. New entries in the ranges 24 to 255 ("1+1") and 256 to 32767
(lower half of "1+2") are assigned by Specification Required. New (lower half of "1+2") are assigned by Specification Required. New
entries in the range 32768 to 18446744073709551615 (upper half of entries in the range 32768 to 18446744073709551615 (upper half of
skipping to change at page 51, line 5 skipping to change at line 2302
* Description of semantics (URL) -- This description is optional; * Description of semantics (URL) -- This description is optional;
the URL can point to something like an Internet-Draft or a web the URL can point to something like an Internet-Draft or a web
page. page.
Applicants exercising the First Come First Served range and making a Applicants exercising the First Come First Served range and making a
suggestion for a tag number that is not representable in 32 bits suggestion for a tag number that is not representable in 32 bits
(i.e., larger than 4294967295) should be aware that this could reduce (i.e., larger than 4294967295) should be aware that this could reduce
interoperability with implementations that do not support 64-bit interoperability with implementations that do not support 64-bit
numbers. numbers.
9.3. Media Type ("MIME Type") 9.3. Media Types Registry
The Internet media type [RFC6838] for a single encoded CBOR data item The Internet media type [RFC6838] ("MIME type") for a single encoded
is application/cbor, as defined in [IANA.media-types]: CBOR data item is "application/cbor" as defined in the "Media Types"
registry [IANA.media-types]:
Type name: application Type name: application
Subtype name: cbor Subtype name: cbor
Required parameters: n/a Required parameters: n/a
Optional parameters: n/a Optional parameters: n/a
Encoding considerations: Binary Encoding considerations: Binary
Security considerations: See Section 10 of this document Security considerations: See Section 10 of RFC 8949.
Interoperability considerations: n/a Interoperability considerations: n/a
Published specification: This document Published specification: RFC 8949
Applications that use this media type: Many Applications that use this media type: Many
Additional information: Additional information:
* Magic number(s): n/a
* File extension(s): .cbor
* Macintosh file type code(s): n/a Magic number(s): n/a
File extension(s): .cbor
Macintosh file type code(s): n/a
Person & email address to contact for further information: IETF CBOR Person & email address to contact for further information: IETF CBOR
Working Group cbor@ietf.org (mailto:cbor@ietf.org) or IETF Working Group (cbor@ietf.org) or IETF Applications and Real-Time
Applications and Real-Time Area art@ietf.org (mailto:art@ietf.org) Area (art@ietf.org)
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: none Restrictions on usage: none
Author: IETF CBOR Working Group cbor@ietf.org (mailto:cbor@ietf.org) Author: IETF CBOR Working Group (cbor@ietf.org)
Change controller: The IESG iesg@ietf.org (mailto:iesg@ietf.org) Change controller: The IESG (iesg@ietf.org)
9.4. CoAP Content-Format 9.4. CoAP Content-Format Registry
The CoAP Content-Format for CBOR is registered in The CoAP Content-Format for CBOR has been registered in the "CoAP
[IANA.core-parameters]: Content-Formats" subregistry within the "Constrained RESTful
Environments (CoRE) Parameters" registry [IANA.core-parameters]:
Media Type: application/cbor Media Type: application/cbor
Encoding: -
Id: 60 Encoding: -
Reference: [RFCthis] ID: 60
9.5. The +cbor Structured Syntax Suffix Registration Reference: RFC 8949
The Structured Syntax Suffix [RFC6838] for media types based on a 9.5. Structured Syntax Suffix Registry
single encoded CBOR data item is +cbor, as defined in
[IANA.media-type-structured-suffix]:
Name: Concise Binary Object Representation (CBOR) The structured syntax suffix [RFC6838] for media types based on a
single encoded CBOR data item is +cbor, which IANA has registered in
the "Structured Syntax Suffixes" registry [IANA.structured-suffix]:
+suffix: +cbor Name: Concise Binary Object Representation (CBOR)
References: [RFCthis] +suffix: +cbor
Encoding Considerations: CBOR is a binary format. References: RFC 8949
Interoperability Considerations: n/a Encoding Considerations: CBOR is a binary format.
Interoperability Considerations: n/a
Fragment Identifier Considerations: The syntax and semantics of Fragment Identifier Considerations: The syntax and semantics of
fragment identifiers specified for +cbor SHOULD be as specified fragment identifiers specified for +cbor SHOULD be as specified
for "application/cbor". (At publication of this document, there for "application/cbor". (At publication of RFC 8949, there is no
is no fragment identification syntax defined for "application/ fragment identification syntax defined for "application/cbor".)
cbor".)
The syntax and semantics for fragment identifiers for a specific The syntax and semantics for fragment identifiers for a specific
"xxx/yyy+cbor" SHOULD be processed as follows: "xxx/yyy+cbor" SHOULD be processed as follows:
* For cases defined in +cbor, where the fragment identifier * For cases defined in +cbor, where the fragment identifier
resolves per the +cbor rules, then process as specified in resolves per the +cbor rules, then process as specified in
+cbor. +cbor.
* For cases defined in +cbor, where the fragment identifier does * For cases defined in +cbor, where the fragment identifier does
not resolve per the +cbor rules, then process as specified in not resolve per the +cbor rules, then process as specified in
"xxx/yyy+cbor". "xxx/yyy+cbor".
* For cases not defined in +cbor, then process as specified in * For cases not defined in +cbor, then process as specified in
"xxx/yyy+cbor". "xxx/yyy+cbor".
Security Considerations: See Section 10 of this document Security Considerations: See Section 10 of RFC 8949.
Contact: IETF CBOR Working Group cbor@ietf.org Contact: IETF CBOR Working Group (cbor@ietf.org) or IETF
(mailto:cbor@ietf.org) or IETF Applications and Real-Time Area Applications and Real-Time Area (art@ietf.org)
art@ietf.org (mailto:art@ietf.org)
Author/Change Controller: The IESG iesg@ietf.org Author/Change Controller: IETF
(mailto:iesg@ietf.org)
10. Security Considerations 10. Security Considerations
A network-facing application can exhibit vulnerabilities in its A network-facing application can exhibit vulnerabilities in its
processing logic for incoming data. Complex parsers are well known processing logic for incoming data. Complex parsers are well known
as a likely source of such vulnerabilities, such as the ability to as a likely source of such vulnerabilities, such as the ability to
remotely crash a node, or even remotely execute arbitrary code on it. remotely crash a node, or even remotely execute arbitrary code on it.
CBOR attempts to narrow the opportunities for introducing such CBOR attempts to narrow the opportunities for introducing such
vulnerabilities by reducing parser complexity, by giving the entire vulnerabilities by reducing parser complexity, by giving the entire
range of encodable values a meaning where possible. range of encodable values a meaning where possible.
skipping to change at page 53, line 43 skipping to change at line 2435
As discussed throughout this document, there are many values that can As discussed throughout this document, there are many values that can
be considered "equivalent" in some circumstances and "not equivalent" be considered "equivalent" in some circumstances and "not equivalent"
in others. As just one example, the numeric value for the number in others. As just one example, the numeric value for the number
"one" might be expressed as an integer or a bignum. A system "one" might be expressed as an integer or a bignum. A system
interpreting CBOR input might accept either form for the number interpreting CBOR input might accept either form for the number
"one", or might reject one (or both) forms. Such acceptance or "one", or might reject one (or both) forms. Such acceptance or
rejection can have security implications in the program that is using rejection can have security implications in the program that is using
the interpreted input. the interpreted input.
Hostile input may be constructed to overrun buffers, overflow or Hostile input may be constructed to overrun buffers, to overflow or
underflow integer arithmetic, or cause other decoding disruption. underflow integer arithmetic, or to cause other decoding disruption.
CBOR data items might have lengths or sizes that are intentionally CBOR data items might have lengths or sizes that are intentionally
extremely large or too short. Resource exhaustion attacks might extremely large or too short. Resource exhaustion attacks might
attempt to lure a decoder into allocating very big data items attempt to lure a decoder into allocating very big data items
(strings, arrays, maps, or even arbitrary precision numbers) or (strings, arrays, maps, or even arbitrary precision numbers) or
exhaust the stack depth by setting up deeply nested items. Decoders exhaust the stack depth by setting up deeply nested items. Decoders
need to have appropriate resource management to mitigate these need to have appropriate resource management to mitigate these
attacks. (Items for which very large sizes are given can also attacks. (Items for which very large sizes are given can also
attempt to exploit integer overflow vulnerabilities.) attempt to exploit integer overflow vulnerabilities.)
A CBOR decoder, by definition, only accepts well-formed CBOR; this is A CBOR decoder, by definition, only accepts well-formed CBOR; this is
the first step to its robustness. Input that is not well-formed CBOR the first step to its robustness. Input that is not well-formed CBOR
causes no further processing from the point where the lack of well- causes no further processing from the point where the lack of well-
formedness was detected. If possible, any data decoded up to this formedness was detected. If possible, any data decoded up to this
point should have no impact on the application using the CBOR point should have no impact on the application using the CBOR
decoder. decoder.
In addition to ascertaining well-formedness, a CBOR decoder might In addition to ascertaining well-formedness, a CBOR decoder might
also perform validity checks on the CBOR data. Alternatively, it can also perform validity checks on the CBOR data. Alternatively, it can
leave those checks to the application using the decoder. This choice leave those checks to the application using the decoder. This choice
skipping to change at page 55, line 6 skipping to change at line 2496
underflow of integer arithmetic, and other such errors that are aimed underflow of integer arithmetic, and other such errors that are aimed
to disrupt the encoder. to disrupt the encoder.
Protocols should be defined in such a way that potential multiple Protocols should be defined in such a way that potential multiple
interpretations are reliably reduced to a single interpretation. For interpretations are reliably reduced to a single interpretation. For
example, an attacker could make use of invalid input such as example, an attacker could make use of invalid input such as
duplicate keys in maps, or exploit different precision in processing duplicate keys in maps, or exploit different precision in processing
numbers to make one application base its decisions on a different numbers to make one application base its decisions on a different
interpretation than the one that will be used by a second interpretation than the one that will be used by a second
application. To facilitate consistent interpretation, encoder and application. To facilitate consistent interpretation, encoder and
decoder implementations should provide a validity checking mode of decoder implementations should provide a validity-checking mode of
operation (Section 5.4). Note, however, that a generic decoder operation (Section 5.4). Note, however, that a generic decoder
cannot know about all requirements that an application poses on its cannot know about all requirements that an application poses on its
input data; it is therefore not relieving the application from input data; it is therefore not relieving the application from
performing its own input checking. Also, since the set of defined performing its own input checking. Also, since the set of defined
tag numbers evolves, the application may employ a tag number that is tag numbers evolves, the application may employ a tag number that is
not yet supported for validity checking by the generic decoder it not yet supported for validity checking by the generic decoder it
uses. Generic decoders therefore need to provide documentation which uses. Generic decoders therefore need to document which tag numbers
tag numbers they support and what validity checking they can provide they support and what validity checking they provide for those tag
for each of them as well as for basic CBOR validity (UTF-8 checking, numbers as well as for basic CBOR (UTF-8 checking, duplicate map key
duplicate map key checking). checking).
Section 3.4.3 notes that using the non-preferred choice of a bignum Section 3.4.3 notes that using the non-preferred choice of a bignum
representation instead of a basic integer for encoding a number is representation instead of a basic integer for encoding a number is
not intended to have application semantics, but it can have such not intended to have application semantics, but it can have such
semantics if an application receiving CBOR data is using a decoder in semantics if an application receiving CBOR data is using a decoder in
the basic generic data model. This disparity causes a security issue the basic generic data model. This disparity causes a security issue
if the two sets of semantics differ. Thus, applications using CBOR if the two sets of semantics differ. Thus, applications using CBOR
need to specify the data model that they are using for each use of need to specify the data model that they are using for each use of
CBOR data. CBOR data.
It is common to convert CBOR data to other formats. In many cases, It is common to convert CBOR data to other formats. In many cases,
CBOR has more expressive types than other formats; this is CBOR has more expressive types than other formats; this is
particularly true for the common conversion to JSON. The loss of particularly true for the common conversion to JSON. The loss of
type information can cause security issues for the systems that are type information can cause security issues for the systems that are
processing the less-expressive data. processing the less-expressive data.
Section 6.2 describes a possibly-common usage scenario of converting Section 6.2 describes a possibly common usage scenario of converting
between CBOR and JSON that could allow an attack if the attcker knows between CBOR and JSON that could allow an attack if the attacker
that the application is performing the conversion. knows that the application is performing the conversion.
Security considerations for the use of base16 and base64 from Security considerations for the use of base16 and base64 from
[RFC4648], and the use of UTF-8 from [RFC3629], are relevant to CBOR [RFC4648], and the use of UTF-8 from [RFC3629], are relevant to CBOR
as well. as well.
11. References 11. References
11.1. Normative References 11.1. Normative References
[C] International Organization for Standardization, [C] International Organization for Standardization,
"Information technology — Programming languages — C", ISO/ "Information technology - Programming languages - C",
IEC 9899:2018, Fourth Edition, June 2018. Fourth Edition, ISO/IEC 9899:2018, June 2018,
<https://www.iso.org/standard/74528.html>.
[Cplusplus17] [Cplusplus20]
International Organization for Standardization, International Organization for Standardization,
"Programming languages — C++", ISO/IEC 14882:2017, Fifth "Programming languages - C++", Sixth Edition, ISO/IEC DIS
Edition, December 2017. 14882, ISO/IEC ISO/IEC JTC1 SC22 WG21 N 4860, March 2020,
<https://isocpp.org/files/papers/N4860.pdf>.
[IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE [IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE
Std 754-2019, DOI 10.1109/IEEESTD.2019.8766229, Std 754-2019, DOI 10.1109/IEEESTD.2019.8766229,
<https://ieeexplore.ieee.org/document/8766229>. <https://ieeexplore.ieee.org/document/8766229>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996, Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>. <https://www.rfc-editor.org/info/rfc2045>.
skipping to change at page 57, line 5 skipping to change at line 2590
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[TIME_T] The Open Group Base Specifications, "Open Group Standard: [TIME_T] The Open Group, "The Open Group Base Specifications",
Vol. 1: Base Definitions, Issue 7", Section 4.16 'Seconds Section 4.16, 'Seconds Since the Epoch', Issue 7, 2018
Since the Epoch', IEEE Std 1003.1, 2018 Edition, 2018, Edition, IEEE Std 1003.1, 2018,
<http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/ <https://pubs.opengroup.org/onlinepubs/9699919799/
V1_chap04.html#tag_04_16>. basedefs/V1_chap04.html#tag_04_16>.
11.2. Informative References 11.2. Informative References
[ASN.1] International Telecommunication Union, "Information [ASN.1] International Telecommunication Union, "Information
Technology — ASN.1 encoding rules: Specification of Basic Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994. X.690, 2015,
<https://www.itu.int/rec/T-REC-X.690-201508-I/en>.
[BSON] Various, "BSON - Binary JSON", 2013,
<http://bsonspec.org/>.
[ECMA262] Ecma International, "ECMAScript 2018 Language [BSON] Various, "BSON - Binary JSON", <http://bsonspec.org/>.
Specification", ECMA Standard ECMA-262, 9th Edition, June
2018, <https://www.ecma-
international.org/publications/files/ECMA-ST/Ecma-
262.pdf>.
[I-D.bormann-cbor-notable-tags] [CBOR-TAGS]
Bormann, C., "Notable CBOR Tags", Work in Progress, Bormann, C., "Notable CBOR Tags", Work in Progress,
Internet-Draft, draft-bormann-cbor-notable-tags-02, 25 Internet-Draft, draft-bormann-cbor-notable-tags-02, 25
June 2020, <http://www.ietf.org/internet-drafts/draft- June 2020, <https://tools.ietf.org/html/draft-bormann-
bormann-cbor-notable-tags-02.txt>. cbor-notable-tags-02>.
[ECMA262] Ecma International, "ECMAScript 2020 Language
Specification", Standard ECMA-262, 11th Edition, June
2020, <https://www.ecma-
international.org/publications/standards/Ecma-262.htm>.
[Err3764] RFC Errata, Erratum ID 3764, RFC 7049,
<https://www.rfc-editor.org/errata/eid3764>.
[Err3770] RFC Errata, Erratum ID 3770, RFC 7049,
<https://www.rfc-editor.org/errata/eid3770>.
[Err4294] RFC Errata, Erratum ID 4294, RFC 7049,
<https://www.rfc-editor.org/errata/eid4294>.
[Err4409] RFC Errata, Erratum ID 4409, RFC 7049,
<https://www.rfc-editor.org/errata/eid4409>.
[Err4963] RFC Errata, Erratum ID 4963, RFC 7049,
<https://www.rfc-editor.org/errata/eid4963>.
[Err4964] RFC Errata, Erratum ID 4964, RFC 7049,
<https://www.rfc-editor.org/errata/eid4964>.
[Err5434] RFC Errata, Erratum ID 5434, RFC 7049,
<https://www.rfc-editor.org/errata/eid5434>.
[Err5763] RFC Errata, Erratum ID 5763, RFC 7049,
<https://www.rfc-editor.org/errata/eid5763>.
[Err5917] RFC Errata, Erratum ID 5917, RFC 7049,
<https://www.rfc-editor.org/errata/eid5917>.
[IANA.cbor-simple-values] [IANA.cbor-simple-values]
IANA, "Concise Binary Object Representation (CBOR) Simple IANA, "Concise Binary Object Representation (CBOR) Simple
Values", Values",
<http://www.iana.org/assignments/cbor-simple-values>. <https://www.iana.org/assignments/cbor-simple-values>.
[IANA.cbor-tags] [IANA.cbor-tags]
IANA, "Concise Binary Object Representation (CBOR) Tags", IANA, "Concise Binary Object Representation (CBOR) Tags",
<http://www.iana.org/assignments/cbor-tags>. <https://www.iana.org/assignments/cbor-tags>.
[IANA.core-parameters] [IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE) IANA, "Constrained RESTful Environments (CoRE)
Parameters", Parameters",
<http://www.iana.org/assignments/core-parameters>. <https://www.iana.org/assignments/core-parameters>.
[IANA.media-type-structured-suffix]
IANA, "Structured Syntax Suffix Registry",
<http://www.iana.org/assignments/media-type-structured-
suffix>.
[IANA.media-types] [IANA.media-types]
IANA, "Media Types", IANA, "Media Types",
<http://www.iana.org/assignments/media-types>. <https://www.iana.org/assignments/media-types>.
[IANA.structured-suffix]
IANA, "Structured Syntax Suffixes",
<https://www.iana.org/assignments/media-type-structured-
suffix>.
[MessagePack] [MessagePack]
Furuhashi, S., "MessagePack", 2013, <http://msgpack.org/>. Furuhashi, S., "MessagePack", <https://msgpack.org/>.
[PCRE] Ho, A., "PCRE - Perl Compatible Regular Expressions", [PCRE] Hazel, P., "PCRE - Perl Compatible Regular Expressions",
2018, <http://www.pcre.org/>. <https://www.pcre.org/>.
[RFC0713] Haverty, J., "MSDTP-Message Services Data Transmission [RFC0713] Haverty, J., "MSDTP-Message Services Data Transmission
Protocol", RFC 713, DOI 10.17487/RFC0713, April 1976, Protocol", RFC 713, DOI 10.17487/RFC0713, April 1976,
<https://www.rfc-editor.org/info/rfc713>. <https://www.rfc-editor.org/info/rfc713>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
skipping to change at page 59, line 21 skipping to change at line 2727
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020, Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>. <https://www.rfc-editor.org/info/rfc8742>.
[RFC8746] Bormann, C., Ed., "Concise Binary Object Representation [RFC8746] Bormann, C., Ed., "Concise Binary Object Representation
(CBOR) Tags for Typed Arrays", RFC 8746, (CBOR) Tags for Typed Arrays", RFC 8746,
DOI 10.17487/RFC8746, February 2020, DOI 10.17487/RFC8746, February 2020,
<https://www.rfc-editor.org/info/rfc8746>. <https://www.rfc-editor.org/info/rfc8746>.
[SIPHASH_LNCS] [SIPHASH_LNCS]
Aumasson, J. and D. Bernstein, "SipHash: A Fast Short- Aumasson, J. and D. Bernstein, "SipHash: A Fast Short-
Input PRF", Lecture Notes in Computer Science pp. 489-508, Input PRF", Progress in Cryptology - INDOCRYPT 2012, pp.
DOI 10.1007/978-3-642-34931-7_28, 2012, 489-508, DOI 10.1007/978-3-642-34931-7_28, 2012,
<https://doi.org/10.1007/978-3-642-34931-7_28>. <https://doi.org/10.1007/978-3-642-34931-7_28>.
[SIPHASH_OPEN] [SIPHASH_OPEN]
Aumasson, J. and D.J. Bernstein, "SipHash: a fast short- Aumasson, J. and D.J. Bernstein, "SipHash: a fast short-
input PRF", <https://131002.net/siphash/siphash.pdf>. input PRF", <https://www.aumasson.jp/siphash/siphash.pdf>.
[YAML] Ben-Kiki, O., Evans, C., and I.d. Net, "YAML Ain't Markup [YAML] Ben-Kiki, O., Evans, C., and I.d. Net, "YAML Ain't Markup
Language (YAML[TM]) Version 1.2", 3rd Edition, October Language (YAML[TM]) Version 1.2", 3rd Edition, October
2009, <http://www.yaml.org/spec/1.2/spec.html>. 2009, <https://www.yaml.org/spec/1.2/spec.html>.
Appendix A. Examples of Encoded CBOR Data Items Appendix A. Examples of Encoded CBOR Data Items
The following table provides some CBOR-encoded values in hexadecimal The following table provides some CBOR-encoded values in hexadecimal
(right column), together with diagnostic notation for these values (right column), together with diagnostic notation for these values
(left column). Note that the string "\u00fc" is one form of (left column). Note that the string "\u00fc" is one form of
diagnostic notation for a UTF-8 string containing the single Unicode diagnostic notation for a UTF-8 string containing the single Unicode
character U+00FC, LATIN SMALL LETTER U WITH DIAERESIS (u umlaut). character U+00FC (LATIN SMALL LETTER U WITH DIAERESIS, "ü").
Similarly, "\u6c34" is a UTF-8 string in diagnostic notation with a Similarly, "\u6c34" is a UTF-8 string in diagnostic notation with a
single character U+6C34 (CJK UNIFIED IDEOGRAPH-6C34, often single character U+6C34 (CJK UNIFIED IDEOGRAPH-6C34, "水"), often
representing "water"), and "\ud800\udd51" is a UTF-8 string in representing "water", and "\ud800\udd51" is a UTF-8 string in
diagnostic notation with a single character U+10151 (GREEK ACROPHONIC diagnostic notation with a single character U+10151 (GREEK ACROPHONIC
ATTIC FIFTY STATERS). (Note that all these single-character strings ATTIC FIFTY STATERS, "𐅑"). (Note that all these single-character
could also be represented in native UTF-8 in diagnostic notation, strings could also be represented in native UTF-8 in diagnostic
just not in an ASCII-only specification.) In the diagnostic notation notation, just not if an ASCII-only specification is required.) In
provided for bignums, their intended numeric value is shown as a the diagnostic notation provided for bignums, their intended numeric
decimal number (such as 18446744073709551616) instead of showing a value is shown as a decimal number (such as 18446744073709551616)
tagged byte string (such as 2(h'010000000000000000')). instead of a tagged byte string (such as 2(h'010000000000000000')).
+==============================+====================================+ +==============================+====================================+
|Diagnostic | Encoded | |Diagnostic | Encoded |
+==============================+====================================+ +==============================+====================================+
|0 | 0x00 | |0 | 0x00 |
+------------------------------+------------------------------------+ +------------------------------+------------------------------------+
|1 | 0x01 | |1 | 0x01 |
+------------------------------+------------------------------------+ +------------------------------+------------------------------------+
|10 | 0x0a | |10 | 0x0a |
+------------------------------+------------------------------------+ +------------------------------+------------------------------------+
skipping to change at page 63, line 47 skipping to change at line 2944
Appendix B. Jump Table for Initial Byte Appendix B. Jump Table for Initial Byte
For brevity, this jump table does not show initial bytes that are For brevity, this jump table does not show initial bytes that are
reserved for future extension. It also only shows a selection of the reserved for future extension. It also only shows a selection of the
initial bytes that can be used for optional features. (All unsigned initial bytes that can be used for optional features. (All unsigned
integers are in network byte order.) integers are in network byte order.)
+============+================================================+ +============+================================================+
| Byte | Structure/Semantics | | Byte | Structure/Semantics |
+============+================================================+ +============+================================================+
| 0x00..0x17 | Unsigned integer 0x00..0x17 (0..23) | | 0x00..0x17 | unsigned integer 0x00..0x17 (0..23) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x18 | Unsigned integer (one-byte uint8_t follows) | | 0x18 | unsigned integer (one-byte uint8_t follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x19 | Unsigned integer (two-byte uint16_t follows) | | 0x19 | unsigned integer (two-byte uint16_t follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x1a | Unsigned integer (four-byte uint32_t follows) | | 0x1a | unsigned integer (four-byte uint32_t follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x1b | Unsigned integer (eight-byte uint64_t follows) | | 0x1b | unsigned integer (eight-byte uint64_t follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x20..0x37 | Negative integer -1-0x00..-1-0x17 (-1..-24) | | 0x20..0x37 | negative integer -1-0x00..-1-0x17 (-1..-24) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x38 | Negative integer -1-n (one-byte uint8_t for n | | 0x38 | negative integer -1-n (one-byte uint8_t for n |
| | follows) | | | follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x39 | Negative integer -1-n (two-byte uint16_t for n | | 0x39 | negative integer -1-n (two-byte uint16_t for n |
| | follows) | | | follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x3a | Negative integer -1-n (four-byte uint32_t for | | 0x3a | negative integer -1-n (four-byte uint32_t for |
| | n follows) | | | n follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x3b | Negative integer -1-n (eight-byte uint64_t for | | 0x3b | negative integer -1-n (eight-byte uint64_t for |
| | n follows) | | | n follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x40..0x57 | byte string (0x00..0x17 bytes follow) | | 0x40..0x57 | byte string (0x00..0x17 bytes follow) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x58 | byte string (one-byte uint8_t for n, and then | | 0x58 | byte string (one-byte uint8_t for n, and then |
| | n bytes follow) | | | n bytes follow) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0x59 | byte string (two-byte uint16_t for n, and then | | 0x59 | byte string (two-byte uint16_t for n, and then |
| | n bytes follow) | | | n bytes follow) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
skipping to change at page 65, line 43 skipping to change at line 3036
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xba | map (four-byte uint32_t for n, and then n | | 0xba | map (four-byte uint32_t for n, and then n |
| | pairs of data items follow) | | | pairs of data items follow) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xbb | map (eight-byte uint64_t for n, and then n | | 0xbb | map (eight-byte uint64_t for n, and then n |
| | pairs of data items follow) | | | pairs of data items follow) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xbf | map, pairs of data items follow, terminated by | | 0xbf | map, pairs of data items follow, terminated by |
| | "break" | | | "break" |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc0 | Text-based date/time (data item follows; see | | 0xc0 | text-based date/time (data item follows; see |
| | Section 3.4.1) | | | Section 3.4.1) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc1 | Epoch-based date/time (data item follows; see | | 0xc1 | epoch-based date/time (data item follows; see |
| | Section 3.4.2) | | | Section 3.4.2) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc2 | Positive bignum (data item "byte string" | | 0xc2 | unsigned bignum (data item "byte string" |
| | follows) | | | follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc3 | Negative bignum (data item "byte string" | | 0xc3 | negative bignum (data item "byte string" |
| | follows) | | | follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc4 | Decimal Fraction (data item "array" follows; | | 0xc4 | decimal Fraction (data item "array" follows; |
| | see Section 3.4.4) | | | see Section 3.4.4) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc5 | Bigfloat (data item "array" follows; see | | 0xc5 | bigfloat (data item "array" follows; see |
| | Section 3.4.4) | | | Section 3.4.4) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xc6..0xd4 | (tag) | | 0xc6..0xd4 | (tag) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xd5..0xd7 | Expected Conversion (data item follows; see | | 0xd5..0xd7 | expected conversion (data item follows; see |
| | Section 3.4.5.2) | | | Section 3.4.5.2) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xd8..0xdb | (more tags; 1/2/4/8 bytes of tag number and | | 0xd8..0xdb | (more tags; 1/2/4/8 bytes of tag number and |
| | then a data item follow) | | | then a data item follow) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xe0..0xf3 | (simple value) | | 0xe0..0xf3 | (simple value) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xf4 | False | | 0xf4 | false |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xf5 | True | | 0xf5 | true |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xf6 | Null | | 0xf6 | null |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xf7 | Undefined | | 0xf7 | undefined |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xf8 | (simple value, one byte follows) | | 0xf8 | (simple value, one byte follows) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xf9 | Half-Precision Float (two-byte IEEE 754) | | 0xf9 | half-precision float (two-byte IEEE 754) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xfa | Single-Precision Float (four-byte IEEE 754) | | 0xfa | single-precision float (four-byte IEEE 754) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xfb | Double-Precision Float (eight-byte IEEE 754) | | 0xfb | double-precision float (eight-byte IEEE 754) |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
| 0xff | "break" stop code | | 0xff | "break" stop code |
+------------+------------------------------------------------+ +------------+------------------------------------------------+
Table 7: Jump Table for Initial Byte Table 7: Jump Table for Initial Byte
Appendix C. Pseudocode Appendix C. Pseudocode
The well-formedness of a CBOR item can be checked by the pseudocode The well-formedness of a CBOR item can be checked by the pseudocode
in Figure 1. The data is well-formed if and only if: in Figure 1. The data is well-formed if and only if:
skipping to change at page 67, line 4 skipping to change at line 3091
+------------+------------------------------------------------+ +------------+------------------------------------------------+
Table 7: Jump Table for Initial Byte Table 7: Jump Table for Initial Byte
Appendix C. Pseudocode Appendix C. Pseudocode
The well-formedness of a CBOR item can be checked by the pseudocode The well-formedness of a CBOR item can be checked by the pseudocode
in Figure 1. The data is well-formed if and only if: in Figure 1. The data is well-formed if and only if:
* the pseudocode does not "fail"; * the pseudocode does not "fail";
* after execution of the pseudocode, no bytes are left in the input * after execution of the pseudocode, no bytes are left in the input
(except in streaming applications) (except in streaming applications).
The pseudocode has the following prerequisites: The pseudocode has the following prerequisites:
* take(n) reads n bytes from the input data and returns them as a * take(n) reads n bytes from the input data and returns them as a
byte string. If n bytes are no longer available, take(n) fails. byte string. If n bytes are no longer available, take(n) fails.
* uint() converts a byte string into an unsigned integer by * uint() converts a byte string into an unsigned integer by
interpreting the byte string in network byte order. interpreting the byte string in network byte order.
* Arithmetic works as in C. * Arithmetic works as in C.
* All variables are unsigned integers of sufficient range. * All variables are unsigned integers of sufficient range.
Note that "well_formed" returns the major type for well-formed Note that "well_formed" returns the major type for well-formed
definite length items, but 99 for an indefinite length item (or -1 definite-length items, but 99 for an indefinite-length item (or -1
for a "break" stop code, only if "breakable" is set). This is used for a "break" stop code, only if "breakable" is set). This is used
in "well_formed_indefinite" to ascertain that indefinite length in "well_formed_indefinite" to ascertain that indefinite-length
strings only contain definite length strings as chunks. strings only contain definite-length strings as chunks.
well_formed(breakable = false) { well_formed(breakable = false) {
// process initial bytes // process initial bytes
ib = uint(take(1)); ib = uint(take(1));
mt = ib >> 5; mt = ib >> 5;
val = ai = ib & 0x1f; val = ai = ib & 0x1f;
switch (ai) { switch (ai) {
case 24: val = uint(take(1)); break; case 24: val = uint(take(1)); break;
case 25: val = uint(take(2)); break; case 25: val = uint(take(2)); break;
case 26: val = uint(take(4)); break; case 26: val = uint(take(4)); break;
skipping to change at page 69, line 15 skipping to change at line 3169
Note that the remaining complexity of a complete CBOR decoder is Note that the remaining complexity of a complete CBOR decoder is
about presenting data that has been decoded to the application in an about presenting data that has been decoded to the application in an
appropriate form. appropriate form.
Major types 0 and 1 are designed in such a way that they can be Major types 0 and 1 are designed in such a way that they can be
encoded in C from a signed integer without actually doing an if-then- encoded in C from a signed integer without actually doing an if-then-
else for positive/negative (Figure 2). This uses the fact that else for positive/negative (Figure 2). This uses the fact that
(-1-n), the transformation for major type 1, is the same as ~n (-1-n), the transformation for major type 1, is the same as ~n
(bitwise complement) in C unsigned arithmetic; ~n can then be (bitwise complement) in C unsigned arithmetic; ~n can then be
expressed as (-1)^n for the negative case, while 0^n leaves n expressed as (-1)^n for the negative case, while 0^n leaves n
unchanged for non-negative. The sign of a number can be converted to unchanged for nonnegative. The sign of a number can be converted to
-1 for negative and 0 for non-negative (0 or positive) by arithmetic- -1 for negative and 0 for nonnegative (0 or positive) by arithmetic-
shifting the number by one bit less than the bit length of the number shifting the number by one bit less than the bit length of the number
(for example, by 63 for 64-bit numbers). (for example, by 63 for 64-bit numbers).
void encode_sint(int64_t n) { void encode_sint(int64_t n) {
uint64t ui = n >> 63; // extend sign to whole length uint64t ui = n >> 63; // extend sign to whole length
unsigned mt = ui & 0x20; // extract (shifted) major type unsigned mt = ui & 0x20; // extract (shifted) major type
ui ^= n; // complement negatives ui ^= n; // complement negatives
if (ui < 24) if (ui < 24)
*p++ = mt + ui; *p++ = mt + ui;
else if (ui < 256) { else if (ui < 256) {
skipping to change at page 73, line 27 skipping to change at line 3356
| | 00 00 04 31 00 13 00 00 00 | | | | 00 00 04 31 00 13 00 00 00 | |
| | 10 30 00 02 00 00 00 10 31 | | | | 10 30 00 02 00 00 00 10 31 | |
| | 00 03 00 00 00 00 00 | | | | 00 03 00 00 00 00 00 | |
+-------------+----------------------------+----------------+ +-------------+----------------------------+----------------+
| CBOR | 82 01 82 02 03 | 9f 01 82 02 03 | | CBOR | 82 01 82 02 03 | 9f 01 82 02 03 |
| | | ff | | | | ff |
+-------------+----------------------------+----------------+ +-------------+----------------------------+----------------+
Table 8: Examples for Different Levels of Conciseness Table 8: Examples for Different Levels of Conciseness
Appendix F. Well-formedness errors and examples Appendix F. Well-Formedness Errors and Examples
There are three basic kinds of well-formedness errors that can occur There are three basic kinds of well-formedness errors that can occur
in decoding a CBOR data item: in decoding a CBOR data item:
* Too much data: There are input bytes left that were not consumed. Too much data: There are input bytes left that were not consumed.
This is only an error if the application assumed that the input This is only an error if the application assumed that the input
bytes would span exactly one data item. Where the application bytes would span exactly one data item. Where the application
uses the self-delimiting nature of CBOR encoding to permit uses the self-delimiting nature of CBOR encoding to permit
additional data after the data item, as is for example done in additional data after the data item, as is done in CBOR sequences
CBOR sequences [RFC8742], the CBOR decoder can simply indicate [RFC8742], for example, the CBOR decoder can simply indicate which
what part of the input has not been consumed. part of the input has not been consumed.
* Too little data: The input data available would need additional Too little data: The input data available would need additional
bytes added at their end for a complete CBOR data item. This may bytes added at their end for a complete CBOR data item. This may
indicate the input is truncated; it is also a common error when indicate the input is truncated; it is also a common error when
trying to decode random data as CBOR. For some applications, trying to decode random data as CBOR. For some applications,
however, this may not actually be an error, as the application may however, this may not actually be an error, as the application may
not be certain it has all the data yet and can obtain or wait for not be certain it has all the data yet and can obtain or wait for
additional input bytes. Some of these applications may have an additional input bytes. Some of these applications may have an
upper limit for how much additional data can show up; here the upper limit for how much additional data can appear; here the
decoder may be able to indicate that the encoded CBOR data item decoder may be able to indicate that the encoded CBOR data item
cannot be completed within this limit. cannot be completed within this limit.
* Syntax error: The input data are not consistent with the Syntax error: The input data are not consistent with the
requirements of the CBOR encoding, and this cannot be remedied by requirements of the CBOR encoding, and this cannot be remedied by
adding (or removing) data at the end. adding (or removing) data at the end.
In Appendix C, errors of the first kind are addressed in the first In Appendix C, errors of the first kind are addressed in the first
paragraph/bullet list (requiring "no bytes are left"), and errors of paragraph and bullet list (requiring "no bytes are left"), and errors
the second kind are addressed in the second paragraph/bullet list of the second kind are addressed in the second paragraph/bullet list
(failing "if n bytes are no longer available"). Errors of the third (failing "if n bytes are no longer available"). Errors of the third
kind are identified in the pseudocode by specific instances of kind are identified in the pseudocode by specific instances of
calling fail(), in order: calling fail(), in order:
* a reserved value is used for additional information (28, 29, 30) * a reserved value is used for additional information (28, 29, 30)
* major type 7, additional information 24, value < 32 (incorrect) * major type 7, additional information 24, value < 32 (incorrect)
* incorrect substructure of indefinite length byte/text string (may * incorrect substructure of indefinite-length byte string or text
only contain definite length strings of the same major type) string (may only contain definite-length strings of the same major
type)
* "break" stop code (mt=7, ai=31) occurs in a value position of a * "break" stop code (major type 7, additional information 31) occurs
map or except at a position directly in an indefinite length item in a value position of a map or except at a position directly in
where also another enclosed data item could occur an indefinite-length item where also another enclosed data item
could occur
* additional information 31 used with major type 0, 1, or 6 * additional information 31 used with major type 0, 1, or 6
F.1. Examples for CBOR data items that are not well-formed F.1. Examples of CBOR Data Items That Are Not Well-Formed
This subsection shows a few examples for CBOR data items that are not This subsection shows a few examples for CBOR data items that are not
well-formed. Each example is a sequence of bytes each shown in well-formed. Each example is a sequence of bytes, each shown in
hexadecimal; multiple examples in a list are separated by commas. hexadecimal; multiple examples in a list are separated by commas.
Examples for well-formedness error kind 1 (too much data) can easily Examples for well-formedness error kind 1 (too much data) can easily
be formed by adding data to a well-formed encoded CBOR data item. be formed by adding data to a well-formed encoded CBOR data item.
Similarly, examples for well-formedness error kind 2 (too little Similarly, examples for well-formedness error kind 2 (too little
data) can be formed by truncating a well-formed encoded CBOR data data) can be formed by truncating a well-formed encoded CBOR data
item. In test suites, it may be beneficial to specifically test with item. In test suites, it may be beneficial to specifically test with
incomplete data items that would require large amounts of addition to incomplete data items that would require large amounts of addition to
be completed (for instance by starting the encoding of a string of a be completed (for instance by starting the encoding of a string of a
very large size). very large size).
A premature end of the input can occur in a head or within the A premature end of the input can occur in a head or within the
enclosed data, which may be bare strings or enclosed data items that enclosed data, which may be bare strings or enclosed data items that
are either counted or should have been ended by a "break" stop code. are either counted or should have been ended by a "break" stop code.
* End of input in a head: 18, 19, 1a, 1b, 19 01, 1a 01 02, 1b 01 02 End of input in a head: 18, 19, 1a, 1b, 19 01, 1a 01 02, 1b 01 02 03
03 04 05 06 07, 38, 58, 78, 98, 9a 01 ff 00, b8, d8, f8, f9 00, fa 04 05 06 07, 38, 58, 78, 98, 9a 01 ff 00, b8, d8, f8, f9 00, fa 00
00 00, fb 00 00 00 00, fb 00 00 00
* Definite length strings with short data: 41, 61, 5a ff ff ff ff Definite-length strings with short data: 41, 61, 5a ff ff ff ff 00,
00, 5b ff ff ff ff ff ff ff ff 01 02 03, 7a ff ff ff ff 00, 7b 7f 5b ff ff ff ff ff ff ff ff 01 02 03, 7a ff ff ff ff 00, 7b 7f ff
ff ff ff ff ff ff ff 01 02 03 ff ff ff ff ff ff 01 02 03
* Definite length maps and arrays not closed with enough items: 81, Definite-length maps and arrays not closed with enough items: 81, 81
81 81 81 81 81 81 81 81 81, 82 00, a1, a2 01 02, a1 00, a2 00 00 81 81 81 81 81 81 81 81, 82 00, a1, a2 01 02, a1 00, a2 00 00 00
00
* Tag number not followed by tag content: c0 Tag number not followed by tag content: c0
* Indefinite length strings not closed by a "break" stop code: 5f 41 Indefinite-length strings not closed by a "break" stop code: 5f 41
00, 7f 61 00 00, 7f 61 00
* Indefinite length maps and arrays not closed by a "break" stop Indefinite-length maps and arrays not closed by a "break" stop
code: 9f, 9f 01 02, bf, bf 01 02 01 02, 81 9f, 9f 80 00, 9f 9f 9f code: 9f, 9f 01 02, bf, bf 01 02 01 02, 81 9f, 9f 80 00, 9f 9f 9f 9f
9f 9f ff ff ff ff, 9f 81 9f 81 9f 9f ff ff ff 9f ff ff ff ff, 9f 81 9f 81 9f 9f ff ff ff
A few examples for the five subkinds of well-formedness error kind 3 A few examples for the five subkinds of well-formedness error kind 3
(syntax error) are shown below. (syntax error) are shown below.
Subkind 1: Subkind 1:
Reserved additional information values: 1c, 1d, 1e, 3c, 3d, 3e,
* Reserved additional information values: 1c, 1d, 1e, 3c, 3d, 3e, 5c, 5d, 5e, 7c, 7d, 7e, 9c, 9d, 9e, bc, bd, be, dc, dd, de, fc,
5c, 5d, 5e, 7c, 7d, 7e, 9c, 9d, 9e, bc, bd, be, dc, dd, de, fc, fd, fe,
fd, fe,
Subkind 2: Subkind 2:
Reserved two-byte encodings of simple values: f8 00, f8 01, f8
* Reserved two-byte encodings of simple values: f8 00, f8 01, f8 18, 18, f8 1f
f8 1f
Subkind 3: Subkind 3:
Indefinite-length string chunks not of the correct type: 5f 00
ff, 5f 21 ff, 5f 61 00 ff, 5f 80 ff, 5f a0 ff, 5f c0 00 ff, 5f
e0 ff, 7f 41 00 ff
* Indefinite length string chunks not of the correct type: 5f 00 ff, Indefinite-length string chunks not definite length: 5f 5f 41 00
5f 21 ff, 5f 61 00 ff, 5f 80 ff, 5f a0 ff, 5f c0 00 ff, 5f e0 ff, ff ff, 7f 7f 61 00 ff ff
7f 41 00 ff
* Indefinite length string chunks not definite length: 5f 5f 41 00
ff ff, 7f 7f 61 00 ff ff
Subkind 4: Subkind 4:
Break occurring on its own outside of an indefinite-length
item: ff
* Break occurring on its own outside of an indefinite length item: Break occurring in a definite-length array or map or a tag: 81
ff ff, 82 00 ff, a1 ff, a1 ff 00, a1 00 ff, a2 00 00 ff, 9f 81 ff,
9f 82 9f 81 9f 9f ff ff ff ff
* Break occurring in a definite length array or map or a tag: 81 ff,
82 00 ff, a1 ff, a1 ff 00, a1 00 ff, a2 00 00 ff, 9f 81 ff, 9f 82
9f 81 9f 9f ff ff ff ff
* Break in indefinite length map would lead to odd number of items Break in an indefinite-length map that would lead to an odd
(break in a value position): bf 00 ff, bf 00 00 00 ff number of items (break in a value position): bf 00 ff, bf 00 00
00 ff
Subkind 5: Subkind 5:
Major type 0, 1, 6 with additional information 31: 1f, 3f, df
* Major type 0, 1, 6 with additional information 31: 1f, 3f, df
Appendix G. Changes from RFC 7049 Appendix G. Changes from RFC 7049
As discussed in the introduction, this document is a revised edition As discussed in the introduction, this document formally obsoletes
of RFC 7049, with editorial improvements, added detail, and fixed RFC 7049 while keeping full compatibility with the interchange format
errata. This document formally obsoletes RFC 7049, while keeping from RFC 7049. This document provides editorial improvements, added
full compatibility of the interchange format from RFC 7049. This detail, and fixed errata. This document does not create a new
document does not create a new version of the format. version of the format.
G.1. Errata processing, clerical changes G.1. Errata Processing and Clerical Changes
The two verified errata on RFC 7049, EID 3764 and EID 3770, concerned The two verified errata on RFC 7049, [Err3764] and [Err3770],
two encoding examples in the text that have been corrected concerned two encoding examples in the text that have been corrected
(Section 3.4.3: "29" -> "49", Section 5.5: "0b000_11101" -> (Section 3.4.3: "29" -> "49", Section 5.5: "0b000_11101" ->
"0b000_11001"). Also, RFC 7049 contained an example using the "0b000_11001"). Also, RFC 7049 contained an example using the
numeric value 24 for a simple value (EID 5917), which is not well- numeric value 24 for a simple value [Err5917], which is not well-
formed; this example has been removed. Errata report 5763 pointed to formed; this example has been removed. Errata report 5763 [Err5763]
an accident in the wording of the definition of tags; this was pointed to an error in the wording of the definition of tags; this
resolved during a re-write of Section 3.4. Errata report 5434 was resolved during a rewrite of Section 3.4. Errata report 5434
pointed out that the UBJSON example in Appendix E no longer complied [Err5434] pointed out that the Universal Binary JSON (UBJSON) example
with the version of UBJSON current at the time of submitting the in Appendix E no longer complied with the version of UBJSON current
report. It turned out that the UBJSON specification had completely at the time of the errata report submission. It turned out that the
changed since 2013; this example therefore also was removed. Further UBJSON specification had completely changed since 2013; this example
errata reports (4409, 4963, 4964) complained that the map key sorting therefore was removed. Other errata reports [Err4409] [Err4963]
rules for canonical encoding were onerous; these led to a [Err4964] complained that the map key sorting rules for canonical
reconsideration of the canonical encoding suggestions and replacement encoding were onerous; these led to a reconsideration of the
by the deterministic encoding suggestions (described below). An canonical encoding suggestions and replacement by the deterministic
editorial suggestion in errata report 4294 was also implemented encoding suggestions (described below). An editorial suggestion in
(improved symmetry by adding "Second value" to a comment to the last errata report 4294 [Err4294] was also implemented (improved symmetry
example in Section 3.2.2). by adding "Second value" to a comment to the last example in
Section 3.2.2).
Other more clerical changes include: Other clerical changes include:
* use of new RFCXML functionality [RFC7991]; * the use of new xml2rfc functionality [RFC7991];
* explain some more of the notation used; * more explanation of the notation used;
* updated references, e.g. for RFC4627 to [RFC8259] in many places, * the update of references, e.g., from RFC 4627 to [RFC8259], from
for CNN-TERMS to [RFC7228]; added missing reference to [IEEE754] CNN-TERMS to [RFC7228], and from the 5.1 edition to the 11th
(importing required definitions) and updated to [ECMA262]; added a edition of [ECMA262]; the addition of a reference to [IEEE754] and
reference to [RFC8618] that further illustrates the discussion in importation of required definitions; the addition of references to
Appendix E; [C] and [Cplusplus20]; and the addition of a reference to
[RFC8618] that further illustrates the discussion in Appendix E;
* the discussion of diagnostic notation mentions the "Extended * in the discussion of diagnostic notation (Section 8), the
Diagnostic Notation" (EDN) defined in [RFC8610] as well as the gap "Extended Diagnostic Notation" (EDN) defined in [RFC8610] is now
diagnostic notation has in representing NaN payloads; an mentioned, the gap in representing NaN payloads is now
explanation was added on how to represent indefinite length highlighted, and an explanation of representing indefinite-length
strings with no chunks; strings with no chunks has been added (Section 8.1);
* the addition of this appendix. * the addition of this appendix.
G.2. Changes in IANA considerations G.2. Changes in IANA Considerations
The IANA considerations were generally updated (clerical changes, The IANA considerations were generally updated (clerical changes,
e.g., now pointing to the CBOR working group as the author of the e.g., now pointing to the CBOR Working Group as the author of the
specification). References to the respective IANA registries have specification). References to the respective IANA registries were
been added to the informative references. added to the informative references.
Tags in the space from 256 to 32767 (lower half of "1+2") are no In the "Concise Binary Object Representation (CBOR) Tags" registry
longer assigned by First Come First Served; this range is now [IANA.cbor-tags], tags in the space from 256 to 32767 (lower half of
Specification Required. "1+2") are no longer assigned by First Come First Served; this range
is now Specification Required.
G.3. Changes in suggestions and other informational components G.3. Changes in Suggestions and Other Informational Components
In revising the document, beyond processing errata reports, the WG While revising the document, beyond the addressing of the errata
could use nearly seven years of experience with the use of CBOR in a reports, the working group drew upon nearly seven years of experience
diverse set of applications. This led to a number of editorial with CBOR in a diverse set of applications. This led to a number of
changes, including adding tables for illustration, but also to editorial changes, including adding tables for illustration, but also
emphasizing some aspects and de-emphasizing others. emphasizing some aspects and de-emphasizing others.
A significant addition in this revision is Section 2, which discusses A significant addition is Section 2, which discusses the CBOR data
the CBOR data model and its small variations involved in the model and its small variations involved in the processing of CBOR.
processing of CBOR. Introducing terms for those (basic generic, The introduction of terms for those variations (basic generic,
extended generic, specific) enables more concise language in other extended generic, specific) enables more concise language in other
places of the document, but also helps in clarifying expectations on places of the document and also helps to clarify expectations of
implementations and on the extensibility features of the format. implementations and of the extensibility features of the format.
RFC 7049, as a format derived from the JSON ecosystem, was influenced As a format derived from the JSON ecosystem, RFC 7049 was influenced
by the JSON number system that was in turn inherited from JavaScript by the JSON number system that was in turn inherited from JavaScript
at the time. JSON does not provide distinct integers and floating- at the time. JSON does not provide distinct integers and floating-
point values (and the latter are decimal in the format). CBOR point values (and the latter are decimal in the format). CBOR
provides binary representations of numbers, which do differ between provides binary representations of numbers, which do differ between
integers and floating-point values. Experience from implementation integers and floating-point values. Experience from implementation
and use now suggested that the separation between these two number and use suggested that the separation between these two number
domains should be more clearly drawn in the document; language that domains should be more clearly drawn in the document; language that
suggested an integer could seamlessly stand in for a floating-point suggested an integer could seamlessly stand in for a floating-point
value was removed. Also, a suggestion (based on I-JSON [RFC7493]) value was removed. Also, a suggestion (based on I-JSON [RFC7493])
was added for handling these types when converting JSON to CBOR, and was added for handling these types when converting JSON to CBOR, and
the use of a specific rounding mechanism has been recommended. the use of a specific rounding mechanism has been recommended.
For a single value in the data model, CBOR often provides multiple For a single value in the data model, CBOR often provides multiple
encoding options. The revision adds a new section Section 4, which encoding options. A new section (Section 4) introduces the term
first introduces the term "preferred serialization" (Section 4.1) and "preferred serialization" (Section 4.1) and defines it for various
defines it for various kinds of data items. On the basis of this kinds of data items. On the basis of this terminology, the section
terminology, the section goes on to discuss how a CBOR-based protocol then discusses how a CBOR-based protocol can define "deterministic
can define "deterministic encoding" (Section 4.2), which now avoids encoding" (Section 4.2), which avoids terms "canonical" and
the RFC 7049 terms "canonical" and "canonicalization". The "canonicalization" from RFC 7049. The suggestion of "Core
suggestion of "Core Deterministic Encoding Requirements" Deterministic Encoding Requirements" (Section 4.2.1) enables generic
Section 4.2.1 enables generic support for such protocol-defined support for such protocol-defined encoding requirements. This
encoding requirements. The present revision further eases the document further eases the implementation of deterministic encoding
implementation of deterministic encoding by simplifying the map by simplifying the map ordering suggested in RFC 7049 to a simple
ordering suggested in RFC 7049 to simple lexicographic ordering of lexicographic ordering of encoded keys. A description of the older
encoded keys. A description of the older suggestion is kept as an suggestion is kept as an alternative, now termed "length-first map
alternative, now termed "length-first map key ordering" key ordering" (Section 4.2.3).
(Section 4.2.3).
The terminology for well-formed and valid data was sharpened and more The terminology for well-formed and valid data was sharpened and more
stringently used, avoiding less well-defined alternative terms such stringently used, avoiding less well-defined alternative terms such
as "syntax error", "decoding error" and "strict mode" outside as "syntax error", "decoding error", and "strict mode" outside of
examples. Also, a third level of requirements beyond CBOR-level examples. Also, a third level of requirements that an application
validity that an application has on its input data is now explicitly has on its input data beyond CBOR-level validity is now explicitly
called out. Well-formed (processable at all), valid (checked by a called out. Well-formed (processable at all), valid (checked by a
validity-checking generic decoder), and expected input (as checked by validity-checking generic decoder), and expected input (as checked by
the application) are treated as a hierarchy of layers of the application) are treated as a hierarchy of layers of
acceptability. acceptability.
The handling of non-well-formed simple values was clarified in text The handling of non-well-formed simple values was clarified in text
and pseudocode. Appendix F was added to discuss well-formedness and pseudocode. Appendix F was added to discuss well-formedness
errors and provide examples for them. The pseudocode was updated to errors and provide examples for them. The pseudocode was updated to
be more portable and some portability considerations were added. be more portable, and some portability considerations were added.
The discussion of validity has been sharpened in two areas. Map The discussion of validity has been sharpened in two areas. Map
validity (handling of duplicate keys) was clarified and the domain of validity (handling of duplicate keys) was clarified, and the domain
applicability of certain implementation choices explained. Also, of applicability of certain implementation choices explained. Also,
while streamlining the terminology for tags, tag numbers, and tag while streamlining the terminology for tags, tag numbers, and tag
content, discussion was added on tag validity, and the restrictions content, discussion was added on tag validity, and the restrictions
were clarified on tag content, in general and specifically for tag 1. were clarified on tag content, in general and specifically for tag 1.
An implementation note (and note for future tag definitions) was An implementation note (and note for future tag definitions) was
added to Section 3.4 about defining tags with semantics that depend added to Section 3.4 about defining tags with semantics that depend
on serialization order. on serialization order.
Tag 35 is no longer defined in this updated document; the Tag 35 is not defined by this document; the registration based on the
registration based on the definition in RFC 7049 remains in place. definition in RFC 7049 remains in place.
Terminology was introduced in Section 3 for "argument" and "head", Terminology was introduced in Section 3 for "argument" and "head",
simplifying further discussion. simplifying further discussion.
The security considerations were mostly rewritten and significantly The security considerations (Section 10) were mostly rewritten and
expanded; in multiple other places, the document is now more explicit significantly expanded; in multiple other places, the document is now
that a decoder cannot simply condone well-formedness errors. more explicit that a decoder cannot simply condone well-formedness
errors.
Acknowledgements Acknowledgements
CBOR was inspired by MessagePack. MessagePack was developed and CBOR was inspired by MessagePack. MessagePack was developed and
promoted by Sadayuki Furuhashi ("frsyuki"). This reference to promoted by Sadayuki Furuhashi ("frsyuki"). This reference to
MessagePack is solely for attribution; CBOR is not intended as a MessagePack is solely for attribution; CBOR is not intended as a
version of or replacement for MessagePack, as it has different design version of, or replacement for, MessagePack, as it has different
goals and requirements. design goals and requirements.
The need for functionality beyond the original MessagePack The need for functionality beyond the original MessagePack
Specification became obvious to many people at about the same time specification became obvious to many people at about the same time
around the year 2012. BinaryPack is a minor derivation of around the year 2012. BinaryPack is a minor derivation of
MessagePack that was developed by Eric Zhang for the binaryjs MessagePack that was developed by Eric Zhang for the binaryjs
project. A similar, but different, extension was made by Tim Caswell project. A similar, but different, extension was made by Tim Caswell
for his msgpack-js and msgpack-js-browser projects. Many people have for his msgpack-js and msgpack-js-browser projects. Many people have
contributed to the discussion about extending MessagePack to separate contributed to the discussion about extending MessagePack to separate
text string representation from byte string representation. text string representation from byte string representation.
The encoding of the additional information in CBOR was inspired by The encoding of the additional information in CBOR was inspired by
the encoding of length information designed by Klaus Hartke for CoAP. the encoding of length information designed by Klaus Hartke for CoAP.
skipping to change at page 79, line 42 skipping to change at line 3658
Richardson, Nico Williams, Peter Occil, Phillip Hallam-Baker, Ray Richardson, Nico Williams, Peter Occil, Phillip Hallam-Baker, Ray
Polk, Stuart Cheshire, Tim Bray, Tony Finch, Tony Hansen, and Yaron Polk, Stuart Cheshire, Tim Bray, Tony Finch, Tony Hansen, and Yaron
Sheffer. Benjamin Kaduk provided an extensive review during IESG Sheffer. Benjamin Kaduk provided an extensive review during IESG
processing. Éric Vyncke, Erik Kline, Robert Wilton, and Roman Danyliw processing. Éric Vyncke, Erik Kline, Robert Wilton, and Roman Danyliw
provided further IESG comments, which included an IoT directorate provided further IESG comments, which included an IoT directorate
review by Eve Schooler. review by Eve Schooler.
Authors' Addresses Authors' Addresses
Carsten Bormann Carsten Bormann
Universitaet Bremen TZI Universität Bremen TZI
Postfach 330440 Postfach 330440
D-28359 Bremen D-28359 Bremen
Germany Germany
Phone: +49-421-218-63921 Phone: +49-421-218-63921
Email: cabo@tzi.org Email: cabo@tzi.org
Paul Hoffman Paul Hoffman
ICANN ICANN
Email: paul.hoffman@icann.org Email: paul.hoffman@icann.org
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