--- 1/draft-ietf-httpbis-http2-13.txt 2014-07-30 17:14:31.103668355 -0700 +++ 2/draft-ietf-httpbis-http2-14.txt 2014-07-30 17:14:31.255672038 -0700 @@ -1,21 +1,21 @@ HTTPbis Working Group M. Belshe Internet-Draft Twist Intended status: Standards Track R. Peon -Expires: December 19, 2014 Google, Inc +Expires: January 31, 2015 Google, Inc M. Thomson, Ed. Mozilla - June 17, 2014 + July 30, 2014 Hypertext Transfer Protocol version 2 - draft-ietf-httpbis-http2-13 + draft-ietf-httpbis-http2-14 Abstract This specification describes an optimized expression of the syntax of the Hypertext Transfer Protocol (HTTP). HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent messages on the same connection. It also introduces unsolicited push of representations from servers to clients. @@ -39,21 +39,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on December 19, 2014. + This Internet-Draft will expire on January 31, 2015. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -71,72 +71,72 @@ 2.2. Conventions and Terminology . . . . . . . . . . . . . . . 6 3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. HTTP/2 Version Identification . . . . . . . . . . . . . . 8 3.2. Starting HTTP/2 for "http" URIs . . . . . . . . . . . . . 9 3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10 3.3. Starting HTTP/2 for "https" URIs . . . . . . . . . . . . 11 3.4. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . 11 3.5. HTTP/2 Connection Preface . . . . . . . . . . . . . . . . 11 4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . 12 - 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 13 + 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 14 4.3. Header Compression and Decompression . . . . . . . . . . 14 5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . 15 - 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 15 + 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 16 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 20 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21 - 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 21 - 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 21 - 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 22 + 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 22 + 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 22 + 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23 5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24 5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . 25 5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . 25 5.3.4. Prioritization State Management . . . . . . . . . . . 26 5.3.5. Default Priorities . . . . . . . . . . . . . . . . . 27 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 27 - 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 27 + 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 28 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28 - 5.4.3. Connection Termination . . . . . . . . . . . . . . . 28 - 5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 28 - 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 29 - 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 29 + 5.4.3. Connection Termination . . . . . . . . . . . . . . . 29 + 5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 29 + 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 30 + 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 33 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 34 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 35 6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 36 - 6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 36 - 6.5.3. Settings Synchronization . . . . . . . . . . . . . . 37 + 6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 37 + 6.5.3. Settings Synchronization . . . . . . . . . . . . . . 38 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 38 - 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 40 + 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 41 - 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 43 - 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 44 - 6.9.2. Initial Flow Control Window Size . . . . . . . . . . 45 - 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 46 - 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 47 - 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 47 - 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 49 - 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 49 - 8.1.1. Informational Responses . . . . . . . . . . . . . . . 50 + 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 44 + 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 45 + 6.9.2. Initial Flow Control Window Size . . . . . . . . . . 46 + 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 47 + 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 48 + 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 48 + 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 50 + 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 50 + 8.1.1. Upgrading From HTTP/2 . . . . . . . . . . . . . . . . 51 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . 51 8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . 55 - 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 58 - 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 59 + 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 57 + 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 58 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 59 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . 60 8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . 61 9. Additional HTTP Requirements/Considerations . . . . . . . . . 62 9.1. Connection Management . . . . . . . . . . . . . . . . . . 62 9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 63 - 9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 64 + 9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 63 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 64 9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . 64 9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 65 10. Security Considerations . . . . . . . . . . . . . . . . . . . 65 10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 65 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 66 10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 66 10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 67 10.5. Denial of Service Considerations . . . . . . . . . . . . 67 10.5.1. Limits on Header Block Size . . . . . . . . . . . . 68 @@ -147,38 +147,38 @@ 11.1. Registration of HTTP/2 Identification Strings . . . . . 70 11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . 71 11.3. Settings Registry . . . . . . . . . . . . . . . . . . . 72 11.4. Error Code Registry . . . . . . . . . . . . . . . . . . 72 11.5. HTTP2-Settings Header Field Registration . . . . . . . . 73 11.6. PRI Method Registration . . . . . . . . . . . . . . . . 74 11.7. The 421 Not Authoritative HTTP Status Code . . . . . . . 74 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 75 13.1. Normative References . . . . . . . . . . . . . . . . . . 75 - 13.2. Informative References . . . . . . . . . . . . . . . . . 76 - 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 77 - Appendix A. Change Log (to be removed by RFC Editor before - publication) . . . . . . . . . . . . . . . . . . . . 78 - A.1. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 78 - A.2. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 78 - A.3. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 78 - A.4. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 79 - A.5. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 79 - A.6. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 79 - A.7. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 79 - A.8. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 80 - A.9. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 80 - A.10. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 80 - A.11. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 81 - A.12. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 81 - A.13. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 82 - A.14. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 82 + 13.2. Informative References . . . . . . . . . . . . . . . . . 77 + 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 78 + Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 79 + A.1. Since draft-ietf-httpbis-http2-13 . . . . . . . . . . . . 79 + A.2. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 79 + A.3. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 79 + A.4. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 80 + A.5. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 80 + A.6. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 80 + A.7. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 81 + A.8. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 81 + A.9. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 81 + A.10. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 81 + A.11. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 82 + A.12. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 82 + A.13. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 82 + A.14. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 83 + A.15. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 83 1. Introduction The Hypertext Transfer Protocol (HTTP) is a wildly successful protocol. However, the HTTP/1.1 message format ([RFC7230], Section 3) was designed to be implemented with the tools at hand in the 1990s, not modern Web application performance. As such it has several characteristics that have a negative overall effect on application performance today. @@ -330,21 +330,21 @@ The means by which support for HTTP/2 is determined is different for "http" and "https" URIs. Discovery for "http" URIs is described in Section 3.2. Discovery for "https" URIs is described in Section 3.3. 3.1. HTTP/2 Version Identification The protocol defined in this document has two identifiers. o The string "h2" identifies the protocol where HTTP/2 uses TLS [TLS12]. This identifier is used in the TLS application layer - protocol negotiation extension (ALPN) [TLSALPN] field and any + protocol negotiation extension (ALPN) [TLS-ALPN] field and any place that HTTP/2 over TLS is identified. The "h2" string is serialized into an ALPN protocol identifier as the two octet sequence: 0x68, 0x32. o The string "h2c" identifies the protocol where HTTP/2 is run over cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade header field and any place that HTTP/2 over TCP is identified. Negotiating "h2" or "h2c" implies the use of the transport, security, @@ -467,40 +467,40 @@ implicit acknowledgment. Providing these values in the Upgrade request ensures that the protocol does not require default values for the above SETTINGS parameters, and gives a client an opportunity to provide other parameters prior to receiving any frames from the server. 3.3. Starting HTTP/2 for "https" URIs A client that makes a request to an "https" URI without prior knowledge about support for HTTP/2 uses TLS [TLS12] with the - application layer protocol negotiation extension [TLSALPN]. + application layer protocol negotiation extension [TLS-ALPN]. HTTP/2 over TLS uses the "h2" application token. The "h2c" token MUST NOT be sent by a client or selected by a server. Once TLS negotiation is complete, both the client and the server send a connection preface (Section 3.5). 3.4. Starting HTTP/2 with Prior Knowledge A client can learn that a particular server supports HTTP/2 by other means. For example, [ALT-SVC] describes a mechanism for advertising this capability. A client MAY immediately send HTTP/2 frames to a server that is known to support HTTP/2, after the connection preface (Section 3.5). A server can identify such a connection by the use of the "PRI" method in the connection preface. This only affects the establishment of HTTP/2 connections over cleartext TCP; implementations that support - HTTP/2 over TLS MUST use protocol negotiation in TLS [TLSALPN]. + HTTP/2 over TLS MUST use protocol negotiation in TLS [TLS-ALPN]. Prior support for HTTP/2 is not a strong signal that a given server will support HTTP/2 for future connections. It is possible for server configurations to change; for configurations to differ between instances in clustered server; or network conditions to change. 3.5. HTTP/2 Connection Preface Upon establishment of a TCP connection and determination that HTTP/2 will be used by both peers, each endpoint MUST send a connection @@ -530,58 +530,61 @@ SETTINGS frame (Section 6.5) that MUST be the first frame the server sends in the HTTP/2 connection. To avoid unnecessary latency, clients are permitted to send additional frames to the server immediately after sending the client connection preface, without waiting to receive the server connection preface. It is important to note, however, that the server connection preface SETTINGS frame might include parameters that necessarily alter how a client is expected to communicate with the server. Upon receiving the SETTINGS frame, the client is expected to - honor any parameters established. + honor any parameters established. In some configurations, it is + possible for the server to transmit SETTINGS before the client, + providing an opportunity to avoid this issue. Clients and servers MUST terminate the TCP connection if either peer does not begin with a valid connection preface. A GOAWAY frame (Section 6.8) can be omitted if it is clear that the peer is not using HTTP/2. 4. HTTP Frames Once the HTTP/2 connection is established, endpoints can begin exchanging frames. 4.1. Frame Format - All frames begin with a fixed 8-octet header followed by a payload of - between 0 and 16,383 octets. + All frames begin with a fixed 9-octet header followed by a variable- + length payload. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | R | Length (14) | Type (8) | Flags (8) | + | Length (24) | + +---------------+---------------+---------------+ + | Type (8) | Flags (8) | +-+-+-----------+---------------+-------------------------------+ |R| Stream Identifier (31) | +=+=============================================================+ | Frame Payload (0...) ... +---------------------------------------------------------------+ Frame Layout The fields of the frame header are defined as: - R: A reserved 2-bit field. The semantics of these bits are undefined - and the bits MUST remain unset (0) when sending and MUST be - ignored when receiving. - Length: The length of the frame payload expressed as an unsigned - 14-bit integer. The 8 octets of the frame header are not included - in this value. + 24-bit integer. Values greater than 2^14 (16,384) MUST NOT be + sent unless the receiver has set a larger value for + SETTINGS_MAX_FRAME_SIZE. + + The 9 octets of the frame header are not included in this value. Type: The 8-bit type of the frame. The frame type determines the format and semantics of the frame. Implementations MUST ignore and discard any frame that has a type that is unknown. Flags: An 8-bit field reserved for frame-type specific boolean flags. Flags are assigned semantics specific to the indicated frame type. Flags that have no defined semantics for a particular frame type @@ -593,62 +596,68 @@ Stream Identifier: A 31-bit stream identifier (see Section 5.1.1). The value 0 is reserved for frames that are associated with the connection as a whole as opposed to an individual stream. The structure and content of the frame payload is dependent entirely on the frame type. 4.2. Frame Size - The maximum size of a frame payload varies by frame type. The - absolute maximum size of a frame payload is 2^14-1 (16,383) octets, - meaning that the maximum frame size is 16,391 octets. All - implementations MUST be capable of receiving and minimally processing - frames up to this maximum size. + The size of a frame payload is limited by the maximum size that a + receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This + setting can have any value between 2^14 (16,384) and 2^24-1 + (16,777,215) octets, inclusive. - Certain frame types, such as PING (Section 6.7), impose additional - limits on the amount of payload data allowed. + All implementations MUST be capable of receiving and minimally + processing frames up to 2^14 octets in length, plus the 9 octet frame + header (Section 4.1). The size of the frame header is not included + when describing frame sizes. + + Note: Certain frame types, such as PING (Section 6.7), impose + additional limits on the amount of payload data allowed. If a frame size exceeds any defined limit, or is too small to contain mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR error. A frame size error in a frame that could alter the state of the entire connection MUST be treated as a connection error (Section 5.4.1); this includes any frame carrying a header block (Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), SETTINGS, and any WINDOW_UPDATE frame with a stream identifier of 0. + Endpoints are not obligated to use all available space in a frame. + Responsiveness can be improved by using frames that are smaller than + the permitted maximum size. Sending large frames can result in + delays in sending maintenance frames, such RST_STREAM, WINDOW_UPDATE, + or PRIORITY, which if blocked by the transmission of a large frame, + could affect performance. + 4.3. Header Compression and Decompression A header field in HTTP/2 is a name with one or more associated values. They are used within HTTP request and response messages as well as server push operations (see Section 8.2). - Header sets are collections of zero or more header fields. When - transmitted over a connection, a header set is serialized into a + Header lists are collections of zero or more header fields. When + transmitted over a connection, a header list is serialized into a header block using HTTP Header Compression [COMPRESSION]. The serialized header block is then divided into one or more octet sequences, called header block fragments, and transmitted within the payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or CONTINUATION (Section 6.10) frames. - HTTP Header Compression does not preserve the relative ordering of - header fields. Header fields with multiple values are encoded into a - single header field using a special delimiter (see Section 8.1.2.3), - this preserves the relative order of values for that header field. - The Cookie header field [COOKIE] is treated specially by the HTTP - mapping (see Section 8.1.2.4). + mapping (see Section 8.1.2.5). A receiving endpoint reassembles the header block by concatenating its fragments, then decompresses the block to reconstruct the header - set. + list. A complete header block consists of either: o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag set, or o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared and one or more CONTINUATION frames, where the last CONTINUATION frame has the END_HEADERS flag set. @@ -840,20 +849,25 @@ A stream that is "half closed (remote)" is no longer being used by the peer to send frames. In this state, an endpoint is no longer obligated to maintain a receiver flow control window if it performs flow control. If an endpoint receives additional frames for a stream that is in this state, other than WINDOW_UPDATE, PRIORITY or RST_STREAM, it MUST respond with a stream error (Section 5.4.2) of type STREAM_CLOSED. + A stream that is "half closed (remote)" can be used by the + endpoint to send frames of any type. In this state, the endpoint + continues to observe advertised stream level flow control limits + (Section 5.2). + A stream can transition from this state to "closed" by sending a frame that contains an END_STREAM flag, or when either peer sends a RST_STREAM frame. closed: The "closed" state is the terminal state. An endpoint MUST NOT send frames on a closed stream. An endpoint that receives any frame other than PRIORITY after receiving a RST_STREAM MUST treat that as a stream error (Section 5.4.2) of @@ -894,20 +908,25 @@ An endpoint might receive a PUSH_PROMISE frame after it sends RST_STREAM. PUSH_PROMISE causes a stream to become "reserved" even if the associated stream has been reset. Therefore, a RST_STREAM is needed to close an unwanted promised stream. In the absence of more specific guidance elsewhere in this document, implementations SHOULD treat the receipt of a message that is not expressly permitted in the description of a state as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. + An example of the state transitions for an HTTP request/response + exchange can be found in Section 8.1. An example of the state + transitions for server push can be found in Section 8.2.1 and + Section 8.2.2. + 5.1.1. Stream Identifiers Streams are identified with an unsigned 31-bit integer. Streams initiated by a client MUST use odd-numbered stream identifiers; those initiated by the server MUST use even-numbered stream identifiers. A stream identifier of zero (0x0) is used for connection control messages; the stream identifier zero cannot be used to establish a new stream. HTTP/1.1 requests that are upgraded to HTTP/2 (see Section 3.2) are @@ -1057,26 +1076,20 @@ it would prefer its peer allocate resources when managing concurrent streams. Most importantly, priority can be used to select streams for transmitting frames when there is limited capacity for sending. Streams can be prioritized by marking them as dependent on the completion of other streams (Section 5.3.1). Each dependency is assigned a relative weight, a number that is used to determine the relative proportion of available resources that are assigned to streams dependent on the same stream. - [[CREF2: Note that stream dependencies have not yet been validated in - practice. The theory might be fairly sound, but there are no - implementations currently sending these. If it turns out that they - are not useful, or actively harmful, implementations will be - requested to avoid creating stream dependencies.]] - Explicitly setting the priority for a stream is input to a prioritization process. It does not guarantee any particular processing or transmission order for the stream relative to any other stream. An endpoint cannot force a peer to process concurrent streams in a particular order using priority. Expressing priority is therefore only ever a suggestion. Prioritization information can be specified explicitly for streams as they are created using the HEADERS frame, or changed using the PRIORITY frame. Providing prioritization information is optional, so @@ -1087,25 +1100,28 @@ Each stream can be given an explicit dependency on another stream. Including a dependency expresses a preference to allocate resources to the identified stream rather than to the dependent stream. A stream that is not dependent on any other stream is given a stream dependency of 0x0. In other words, the non-existent stream 0 forms the root of the tree. A stream that depends on another stream is a dependent stream. The - stream upon which a stream is dependent is a parent stream. + stream upon which a stream is dependent is a parent stream. A + dependency on a stream that is not currently in the tree - such as a + stream in the "idle" state - results in the stream being given a + default priority (Section 5.3.5). When assigning a dependency on another stream, the stream is added as a new dependency of the parent stream. Dependent streams that share - the same parent are not order with respect to each other. For + the same parent are not ordered with respect to each other. For example, if streams B and C are dependent on stream A, and if stream D is created with a dependency on stream A, this results in a dependency order of A followed by B, C, and D in any order. A A / \ ==> /|\ B C B D C Example of Default Dependency Creation @@ -1228,23 +1244,23 @@ maintain state for at least as many streams as allowed by their setting for SETTINGS_MAX_CONCURRENT_STREAMS. An endpoint receiving a PRIORITY frame that changes the priority of a closed stream SHOULD alter the dependencies of the streams that depend on it, if it has retained enough state to do so. 5.3.5. Default Priorities Providing priority information is optional. Streams are assigned a - default dependency on stream 0x0. Pushed streams (Section 8.2) - initially depend on their associated stream. In both cases, streams - are assigned a default weight of 16. + non-exclusive dependency on stream 0x0 by default. Pushed streams + (Section 8.2) initially depend on their associated stream. In both + cases, streams are assigned a default weight of 16. 5.4. Error Handling HTTP/2 framing permits two classes of error: o An error condition that renders the entire connection unusable is a connection error. o An error in an individual stream is a stream error. @@ -1306,24 +1322,24 @@ 5.5. Extending HTTP/2 HTTP/2 permits extension of the protocol. Protocol extensions can be used to provide additional services or alter any aspect of the protocol, within the limitations described in this section. Extensions are effective only within the scope of a single HTTP/2 connection. Extensions are permitted to use new frame types (Section 4.1), new - settings (Section 6.5.2), new error codes (Section 7), or new header - fields that start with a colon (:). Of these, registries are - established for frame types (Section 11.2), settings (Section 11.3) - and error codes (Section 11.4). + settings (Section 6.5.2), or new error codes (Section 7). Registries + are established for managing these extension points: frame types + (Section 11.2), settings (Section 11.3) and error codes + (Section 11.4). Implementations MUST ignore unknown or unsupported values in all extensible protocol elements. Implementations MUST discard frames that have unknown or unsupported types. This means that any of these extension points can be safely used by extensions without prior arrangement or negotiation. However, extensions that could change the semantics of existing protocol components MUST be negotiated before being used. For example, an extension that changes the layout of the HEADERS frame @@ -1389,25 +1405,20 @@ Padding octets MUST be set to zero when sending and ignored when receiving. The DATA frame defines the following flags: END_STREAM (0x1): Bit 1 being set indicates that this frame is the last that the endpoint will send for the identified stream. Setting this flag causes the stream to enter one of the "half closed" states or the "closed" state (Section 5.1). - END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the - last for the current segment. Intermediaries MUST NOT coalesce - frames across a segment boundary and MUST preserve segment - boundaries when forwarding frames. - PADDED (0x8): Bit 4 being set indicates that the Pad Length field is present. DATA frames MUST be associated with a stream. If a DATA frame is received whose stream identifier field is 0x0, the recipient MUST respond with a connection error (Section 5.4.1) of type PROTOCOL_ERROR. DATA frames are subject to flow control and can only be sent when a stream is in the "open" or "half closed (remote)" states. The entire @@ -1477,25 +1488,20 @@ END_STREAM (0x1): Bit 1 being set indicates that the header block (Section 4.3) is the last that the endpoint will send for the identified stream. Setting this flag causes the stream to enter one of "half closed" states (Section 5.1). A HEADERS frame that is followed by CONTINUATION frames carries the END_STREAM flag that signals the end of a stream. A CONTINUATION frame cannot be used to terminate a stream. - END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the - last for the current segment. Intermediaries MUST NOT coalesce - frames across a segment boundary and MUST preserve segment - boundaries when forwarding frames. - END_HEADERS (0x4): Bit 3 being set indicates that this frame contains an entire header block (Section 4.3) and is not followed by any CONTINUATION frames. A HEADERS frame without the END_HEADERS flag set MUST be followed by a CONTINUATION frame for the same stream. A receiver MUST treat the receipt of any other type of frame or a frame on a different stream as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. @@ -1709,47 +1715,65 @@ A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be treated as special by endpoints. A zero value does prevent the creation of new streams, however this can also happen for any limit that is exhausted with active streams. Servers SHOULD only set a zero value for short durations; if a server does not wish to accept requests, closing the connection could be preferable. SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial window size (in bytes) for stream level flow control. The initial - value is 65,535. + value is 2^16-1 (65,535) octets. This setting affects the window size of all streams, including existing streams, see Section 6.9.2. Values above the maximum flow control window size of 2^31 - 1 MUST be treated as a connection error (Section 5.4.1) of type FLOW_CONTROL_ERROR. + SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest + frame payload that a receiver is willing to accept. + + The initial value is 2^14 (16,384) octets. The value advertised + by an endpoint MUST be between this initial value and the maximum + allowed frame size (2^24-1 or 16,777,215 octets), inclusive. + Values outside this range MUST be treated as a connection error + (Section 5.4.1) of type PROTOCOL_ERROR. + + SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a + peer of the maximum size of header list that the sender is + prepared to accept. The value is based on the uncompressed size + of header fields, including the length of the name and value in + octets plus an overhead of 32 octets for each header field. + + For any given request, a lower limit than what is advertised MAY + be enforced. The initial value of this setting is unlimited. + An endpoint that receives a SETTINGS frame with any unknown or unsupported identifier MUST ignore that setting. 6.5.3. Settings Synchronization Most values in SETTINGS benefit from or require an understanding of - when the peer has received and applied the changed the communicated - parameter values. In order to provide such synchronization - timepoints, the recipient of a SETTINGS frame in which the ACK flag - is not set MUST apply the updated parameters as soon as possible upon - receipt. + when the peer has received and applied the changed parameter values. + In order to provide such synchronization timepoints, the recipient of + a SETTINGS frame in which the ACK flag is not set MUST apply the + updated parameters as soon as possible upon receipt. - The values in the SETTINGS frame MUST be applied in the order they - appear, with no other frame processing between values. Once all - values have been applied, the recipient MUST immediately emit a - SETTINGS frame with the ACK flag set. Upon receiving a SETTINGS - frame with the ACK flag set, the sender of the altered parameters can - rely upon their application. + The values in the SETTINGS frame MUST be processed in the order they + appear, with no other frame processing between values. Unsupported + parameters MUST be ignored. Once all values have been processed, the + recipient MUST immediately emit a SETTINGS frame with the ACK flag + set. Upon receiving a SETTINGS frame with the ACK flag set, the + sender of the altered parameters can rely on the setting having been + applied. If the sender of a SETTINGS frame does not receive an acknowledgement within a reasonable amount of time, it MAY issue a connection error (Section 5.4.1) of type SETTINGS_TIMEOUT. 6.6. PUSH_PROMISE The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint in advance of streams the sender intends to initiate. The PUSH_PROMISE frame includes the unsigned 31-bit identifier of the @@ -1899,28 +1923,32 @@ streams on the connection, although a new connection can be established for new streams. The purpose of this frame is to allow an endpoint to gracefully stop accepting new streams, while still finishing processing of previously established streams. This enables administrative actions, like server maintainence. There is an inherent race condition between an endpoint starting new streams and the remote sending a GOAWAY frame. To deal with this - case, the GOAWAY contains the stream identifier of the last stream - which was or might be processed on the sending endpoint in this - connection. If the receiver of the GOAWAY has sent data on streams - with a higher stream identifier than what is indicated in the GOAWAY - frame, those streams are not or will not be processed. The receiver - of the GOAWAY frame can treat the streams as though they had never - been created at all, thereby allowing those streams to be retried - later on a new connection. + case, the GOAWAY contains the stream identifier of the last peer- + initiated stream which was or might be processed on the sending + endpoint in this connection. For instance, if the server sends a + GOAWAY frame, the identifed stream is the highest numbered stream + initiated by the client. + + If the receiver of the GOAWAY has sent data on streams with a higher + stream identifier than what is indicated in the GOAWAY frame, those + streams are not or will not be processed. The receiver of the GOAWAY + frame can treat the streams as though they had never been created at + all, thereby allowing those streams to be retried later on a new + connection. Endpoints SHOULD always send a GOAWAY frame before closing a connection so that the remote can know whether a stream has been partially processed or not. For example, if an HTTP client sends a POST at the same time that a server closes a connection, the client cannot know if the server started to process that POST request if the server does not send a GOAWAY frame to indicate what streams it might have acted on. An endpoint might choose to close a connection without sending GOAWAY @@ -2050,20 +2078,25 @@ The legal range for the increment to the flow control window is 1 to 2^31 - 1 (0x7fffffff) bytes. The WINDOW_UPDATE frame does not define any flags. The WINDOW_UPDATE frame can be specific to a stream or to the entire connection. In the former case, the frame's stream identifier indicates the affected stream; in the latter, the value "0" indicates that the entire connection is the subject of the frame. + A receiver MUST treat the recipt of a WINDOW_UPDATE frame with an + flow control window increment of 0 as a stream error (Section 5.4.2) + of type PROTOCOL_ERROR; errors on the connection flow control window + MUST be treated as a connection error (Section 5.4.1). + WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the END_STREAM flag. This means that a receiver could receive a WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream. A receiver MUST NOT treat this as an error, see Section 5.1. A receiver that receives a flow controlled frame MUST always account for its contribution against the connection flow control window, unless the receiver treats this as a connection error (Section 5.4.1). This is necessary even if the frame is in error. Since the sender counts the frame toward the flow control window, if @@ -2093,26 +2126,26 @@ available in both windows by the length of the transmitted frame. The receiver of a frame sends a WINDOW_UPDATE frame as it consumes data and frees up space in flow control windows. Separate WINDOW_UPDATE frames are sent for the stream and connection level flow control windows. A sender that receives a WINDOW_UPDATE frame updates the corresponding window by the amount specified in the frame. - A sender MUST NOT allow a flow control window to exceed 2^31 - 1 - bytes. If a sender receives a WINDOW_UPDATE that causes a flow - control window to exceed this maximum it MUST terminate either the - stream or the connection, as appropriate. For streams, the sender - sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code; - for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. + A sender MUST NOT allow a flow control window to exceed 2^31-1 bytes. + If a sender receives a WINDOW_UPDATE that causes a flow control + window to exceed this maximum it MUST terminate either the stream or + the connection, as appropriate. For streams, the sender sends a + RST_STREAM with the error code of FLOW_CONTROL_ERROR code; for the + connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. Flow controlled frames from the sender and WINDOW_UPDATE frames from the receiver are completely asynchronous with respect to each other. This property allows a receiver to aggressively update the window size kept by the sender to prevent streams from stalling. 6.9.2. Initial Flow Control Window Size When an HTTP/2 connection is first established, new streams are created with an initial flow control window size of 65,535 bytes. @@ -2289,150 +2322,132 @@ this protocol are defined in the sections below. 8.1. HTTP Request/Response Exchange A client sends an HTTP request on a new stream, using a previously unused stream identifier (Section 5.1.1). A server sends an HTTP response on the same stream as the request. An HTTP message (request or response) consists of: - 1. one HEADERS frame (followed by zero or more CONTINUATION frames) + 1. for a response only, zero or more HEADERS frames (each followed + by zero or more CONTINUATION frames) containing the message + headers of informational (1xx) HTTP responses (see [RFC7230], + Section 3.2 and [RFC7231], Section 6.2), and + + 2. one HEADERS frame (followed by zero or more CONTINUATION frames) containing the message headers (see [RFC7230], Section 3.2), and - 2. zero or more DATA frames containing the message payload (see + 3. zero or more DATA frames containing the message payload (see [RFC7230], Section 3.3), and - 3. optionally, one HEADERS frame, followed by zero or more + 4. optionally, one HEADERS frame, followed by zero or more CONTINUATION frames containing the trailer-part, if present (see [RFC7230], Section 4.1.2). The last frame in the sequence bears an END_STREAM flag, noting that a HEADERS frame bearing the END_STREAM flag can be followed by CONTINUATION frames that carry any remaining portions of the header block. Other frames (from any stream) MUST NOT occur between either HEADERS frame and any CONTINUATION frames that might follow. - Otherwise, frames MAY be interspersed on the stream between these - frames, but those frames do not carry HTTP semantics. In particular, - HEADERS frames (and any CONTINUATION frames that follow) other than - the first and optional last frames in this sequence do not carry HTTP - semantics. + A HEADERS frame (and associated CONTINUATION frames) can only appear + at the start or end of a stream. An endpoint that receives a second + HEADERS frame without the END_STREAM flag set MUST treat the + corresponding request or response as malformed (Section 8.1.2.6). Trailing header fields are carried in a header block that also terminates the stream. That is, a sequence starting with a HEADERS frame, followed by zero or more CONTINUATION frames, where the HEADERS frame bears an END_STREAM flag. Header blocks after the first that do not terminate the stream are not part of an HTTP request or response. An HTTP request/response exchange fully consumes a single stream. A request starts with the HEADERS frame that puts the stream into an - "open" state and ends with a frame bearing END_STREAM, which causes - the stream to become "half closed" for the client. A response starts - with a HEADERS frame and ends with a frame bearing END_STREAM, - optionally followed by CONTINUATION frames, which places the stream - in the "closed" state. - -8.1.1. Informational Responses - - The 1xx series of HTTP response status codes ([RFC7231], Section 6.2) - are not supported in HTTP/2. - - The most common use case for 1xx is using an Expect header field with - a "100-continue" token (colloquially, "Expect/continue") to indicate - that the client expects a 100 (Continue) non-final response status - code, receipt of which indicates that the client should continue - sending the request body if it has not already done so. - - Typically, Expect/continue is used by clients wishing to avoid - sending a large amount of data in a request body, only to have the - request rejected by the origin server, thereby leaving the connection - potentially unusable. - - HTTP/2 does not enable the Expect/continue mechanism; if the server - sends a final status code to reject the request, it can do so without - making the underlying connection unusable. - - Note that this means HTTP/2 clients sending requests with bodies may - waste at least one round trip of sent data when the request is - rejected. This can be mitigated by restricting the amount of data - sent for the first round trip by bandwidth-constrained clients, in - anticipation of a final status code. - - Other defined 1xx status codes are not applicable to HTTP/2. For - example, the semantics of 101 (Switching Protocols) aren't suitable - to a multiplexed protocol. Likewise, 102 (Processing) [RFC2518] is - no longer necessary to ensure connection liveness, because HTTP/2 has - a separate means of keeping the connection alive. The use of the 102 - (Processing) status code for progress reporting has since been - deprecated and is not retained. - - This difference between protocol versions necessitates special - handling by intermediaries that translate between them: + "open" state. The request ends with a frame bearing END_STREAM, + which causes the stream to become "half closed (local)" for the + client and "half closed (remote)" for the server. A response starts + with a HEADERS frame and ends with a frame bearing END_STREAM, which + places the stream in the "closed" state. - o An intermediary that translates HTTP/1.1 requests to HTTP/2 MUST - generate a 100 (Continue) response if a received request includes - and Expect header field with a "100-continue" token ([RFC7231], - Section 5.1.1), unless it can immediately generate a final status - code. It MUST NOT forward the "100-continue" expectation in the - request header fields. +8.1.1. Upgrading From HTTP/2 - o An intermediary that translates HTTP/2 to HTTP/1.1 MAY add an - Expect header field with a "100-continue" expectation when - forwarding a request that has a body; see [RFC7231], Section 5.1.1 - for specific requirements. + HTTP/2 removes support for the 101 (Switching Protocols) + informational status code ([RFC7231], Section 6.2.2). - o An intermediary that gateways HTTP/2 to HTTP/1.1 MUST discard all - other 1xx informational responses. + The semantics of 101 (Switching Protocols) aren't applicable to a + multiplexed protocol. Alternative protocols are able to use the same + mechanisms that HTTP/2 uses to negotiate their use (see Section 3). 8.1.2. HTTP Header Fields HTTP header fields carry information as a series of key-value pairs. For a listing of registered HTTP headers, see the Message Header Field Registry maintained at [4]. +8.1.2.1. Pseudo-Header Fields + While HTTP/1.x used the message start-line (see [RFC7230], Section 3.1) to convey the target URI and method of the request, and - the status code for the response, HTTP/2 uses special pseudo-headers - beginning with ':' character (ASCII 0x3a) for this purpose. + the status code for the response, HTTP/2 uses special pseudo-header + fields beginning with ':' character (ASCII 0x3a) for this purpose. + + Pseudo-header fields are only valid in the HTTP/2 context. These are + not HTTP header fields. Endpoints MUST NOT generate pseudo-header + fields other than those defined in this document. + + Pseudo-header fields are only valid in the context in which they are + defined. Pseudo-header fields defined for requests MUST NOT appear + in responses; pseudo-header fields defined for responses MUST NOT + appear in requests. Pseudo-header fields MUST NOT appear in + trailers. Endpoints MUST treat a request or response that contains + undefined or invalid pseudo-header fields as malformed + (Section 8.1.2.6). Just as in HTTP/1.x, header field names are strings of ASCII characters that are compared in a case-insensitive fashion. However, header field names MUST be converted to lowercase prior to their encoding in HTTP/2. A request or response containing uppercase - header field names MUST be treated as malformed (Section 8.1.2.5). + header field names MUST be treated as malformed (Section 8.1.2.6). + + All pseudo-header fields MUST appear in the header block before + regular header fields. Any request or response that contains a + pseudo-header field that appears in a header block after a regular + header field MUST be treated as malformed (Section 8.1.2.6). + +8.1.2.2. Hop-by-Hop Header Fields HTTP/2 does not use the Connection header field to indicate "hop-by- hop" header fields; in this protocol, connection-specific metadata is conveyed by other means. As such, a HTTP/2 message containing - Connection MUST be treated as malformed (Section 8.1.2.5). + Connection MUST be treated as malformed (Section 8.1.2.6). This means that an intermediary transforming an HTTP/1.x message to HTTP/2 will need to remove any header fields nominated by the Connection header field, along with the Connection header field itself. Such intermediaries SHOULD also remove other connection- specific header fields, such as Keep-Alive, Proxy-Connection, Transfer-Encoding and Upgrade, even if they are not nominated by Connection. One exception to this is the TE header field, which MAY be present in an HTTP/2 request, but when it is MUST NOT contain any value other than "trailers". Note: HTTP/2 purposefully does not support upgrade to another protocol. The handshake methods described in Section 3 are believed sufficient to negotiate the use of alternative protocols. -8.1.2.1. Request Header Fields +8.1.2.3. Request Header Fields HTTP/2 defines a number of pseudo header fields starting with a colon ':' character that carry information about the request target: o The ":method" header field includes the HTTP method ([RFC7231], Section 4). o The ":scheme" header field includes the scheme portion of the target URI ([RFC3986], Section 3.1). @@ -2451,156 +2466,104 @@ asterisk form (see [RFC7230], Section 5.3). Clients that generate HTTP/2 requests directly SHOULD instead omit the "Host" header field. An intermediary that converts an HTTP/2 request to HTTP/1.1 MUST create a "Host" header field if one is not present in a request by copying the value of the ":authority" header field. o The ":path" header field includes the path and query parts of the target URI (the "path-absolute" production from [RFC3986] and optionally a '?' character followed by the "query" production, see - [RFC3986], Section 3.3 and [RFC3986], Section 3.4). This field - MUST NOT be empty; URIs that do not contain a path component MUST - include a value of '/', unless the request is an OPTIONS request - in asterisk form, in which case the ":path" header field MUST - include '*'. + [RFC3986], Section 3.3 and [RFC3986], Section 3.4). A request in + asterisk form includes the value '*' for the ":path" header field. + + This field MUST NOT be empty for "http" or "https" URIs; "http" or + "https" URIs that do not contain a path component MUST include a + value of '/'. The exception to this rule is an OPTIONS request + for an "http" or "https" URI that does not include a path + component; these MUST include a ":path" header field with a value + of '*' (see [RFC7230], Section 5.3.4). All HTTP/2 requests MUST include exactly one valid value for the ":method", ":scheme", and ":path" header fields, unless this is a CONNECT request (Section 8.3). An HTTP request that omits mandatory - header fields is malformed (Section 8.1.2.5). - - Header field names that start with a colon are only valid in the - HTTP/2 context. These are not HTTP header fields. Implementations - MUST NOT generate header fields that start with a colon, and they - MUST ignore and discard any header field that starts with a colon. - In particular, header fields with names starting with a colon MUST - NOT be exposed as HTTP header fields. + header fields is malformed (Section 8.1.2.6). HTTP/2 does not define a way to carry the version identifier that is included in the HTTP/1.1 request line. -8.1.2.2. Response Header Fields +8.1.2.4. Response Header Fields A single ":status" header field is defined that carries the HTTP status code field (see [RFC7231], Section 6). This header field MUST be included in all responses, otherwise the response is malformed - (Section 8.1.2.5). + (Section 8.1.2.6). HTTP/2 does not define a way to carry the version or reason phrase that is included in an HTTP/1.1 status line. -8.1.2.3. Header Field Ordering - - HTTP Header Compression [COMPRESSION] does not preserve the order of - header fields, because the relative order of header fields with - different names is not important. However, the same header field can - be repeated to form a list (see [RFC7230], Section 3.2.2), where the - relative order of header field values is significant. This - repetition can occur either as a single header field with a comma- - separated list of values, or as several header fields with a single - value, or any combination thereof. Therefore, in the latter case, - ordering needs to be preserved before compression takes place. - - To preserve the order of multiple occurrences of a header field with - the same name, its ordered values are concatenated into a single - value using a zero-valued octet (0x0) to delimit them. - - After decompression, header fields that have values containing zero - octets (0x0) MUST be split into multiple header fields before being - processed. - - For example, the following HTTP/1.x header block: - - Content-Type: text/html - Cache-Control: max-age=60, private - Cache-Control: must-revalidate - - contains three Cache-Control directives; two directives in the first - Cache-Control header field, and the third directive in the second - Cache-Control field. Before compression, they would need to be - converted to a form similar to this (with 0x0 represented as '\0'): - - cache-control = max-age=60, private\0must-revalidate - content-type = text/html - - Note here that the ordering between Content-Type and Cache-Control is - not preserved, but the relative ordering of the Cache-Control - directives - as well as the fact that the first two were comma- - separated, while the last was on a different line - is. - - Header fields containing multiple values MUST be concatenated into a - single value unless the ordering of that header field is known to be - not significant. - - The special case of "set-cookie" - which does not form a comma- - separated list, but can have multiple values - does not depend on - ordering. The "set-cookie" header field MAY be encoded as multiple - header field values, or as a single concatenated value. - -8.1.2.4. Compressing the Cookie Header Field +8.1.2.5. Compressing the Cookie Header Field The Cookie header field [COOKIE] can carry a significant amount of redundant data. The Cookie header field uses a semi-colon (";") to delimit cookie- pairs (or "crumbs"). This header field doesn't follow the list construction rules in HTTP (see [RFC7230], Section 3.2.2), which prevents cookie-pairs from being separated into different name-value pairs. This can significantly reduce compression efficiency as individual cookie-pairs are updated. To allow for better compression efficiency, the Cookie header field MAY be split into separate header fields, each with one or more cookie-pairs. If there are multiple Cookie header fields after decompression, these MUST be concatenated into a single octet string - using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; "). - - The Cookie header field MAY be split using a zero octet (0x0), as - defined in Section 8.1.2.3. When decoding, zero octets MUST be - replaced with the cookie delimiter ("; "). + using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; ") + before being passed into a non-HTTP/2 context, such as an HTTP/1.1 + connection, or a generic HTTP server application. - Therefore, the following sets of Cookie header fields are - semantically equivalent, though the final form might appear in a - different order after compression and decompression. + Therefore, the following two lists of Cookie header fields are + semantically equivalent. cookie: a=b; c=d; e=f - cookie: a=b\0c=d; e=f - cookie: a=b cookie: c=d cookie: e=f -8.1.2.5. Malformed Messages +8.1.2.6. Malformed Requests and Responses - A malformed request or response is one that uses a valid sequence of - HTTP/2 frames, but is otherwise invalid due to the presence of - prohibited header fields, the absence of mandatory header fields, or - the inclusion of uppercase header field names. + A malformed request or response is one that is an otherwise valid + sequence of HTTP/2 frames, but is otherwise invalid due to the + presence of extraneous frames, prohibited header fields, the absence + of mandatory header fields, or the inclusion of uppercase header + field names. A request or response that includes an entity body can include a "content-length" header field. A request or response is also malformed if the value of a "content-length" header field does not - equal the sum of the DATA frame payload lengths that form the body. + equal the sum of the DATA frame payload lengths that form the body, + with the exception of responses to HEAD requests, which always + contain no DATA frames. Intermediaries that process HTTP requests or responses (i.e., any intermediary not acting as a tunnel) MUST NOT forward a malformed - request or response. + request or response. Malformed requests or responses that are + detected MUST be treated as a stream error (Section 5.4.2) of type + PROTOCOL_ERROR. - Implementations that detect malformed requests or responses need to - ensure that the stream ends. For malformed requests, a server MAY - send an HTTP response prior to closing or resetting the stream. - Clients MUST NOT accept a malformed response. Note that these - requirements are intended to protect against several types of common - attacks against HTTP; they are deliberately strict, because being - permissive can expose implementations to these vulnerabilities. + For malformed requests, a server MAY send an HTTP response prior to + closing or resetting the stream. Clients MUST NOT accept a malformed + response. Note that these requirements are intended to protect + against several types of common attacks against HTTP; they are + deliberately strict, because being permissive can expose + implementations to these vulnerabilities. 8.1.3. Examples This section shows HTTP/1.1 requests and responses, with illustrations of equivalent HTTP/2 requests and responses. An HTTP GET request includes request header fields and no body and is therefore transmitted as a single HEADERS frame, followed by zero or more CONTINUATION frames containing the serialized block of request header fields. The HEADERS frame in the following has both the @@ -2687,20 +2650,30 @@ 0 Foo: bar DATA - END_STREAM {binary data} HEADERS + END_STREAM + END_HEADERS foo = bar + An informational response using a 1xx status code other than 101 is + transmitted as a HEADERS frame, followed by zero or more CONTINUATION + frames: + + HTTP/1.1 103 BAR HEADERS + Extension-Field: bar ==> - END_STREAM + + END_HEADERS + :status = 103 + extension-field = bar + 8.1.4. Request Reliability Mechanisms in HTTP/2 In HTTP/1.1, an HTTP client is unable to retry a non-idempotent request when an error occurs, because there is no means to determine the nature of the error. It is possible that some server processing occurred prior to the error, which could result in undesirable effects if the request were reattempted. HTTP/2 provides two mechanisms for providing a guarantee to a client that a request has not been processed: @@ -2772,21 +2745,21 @@ includes a request body. Pushed responses are always associated with an explicit request from the client. The PUSH_PROMISE frames sent by the server are sent on that explicit request's stream. The PUSH_PROMISE frame also includes a promised stream identifier, chosen from the stream identifiers available to the server (see Section 5.1.1). The header fields in PUSH_PROMISE and any subsequent CONTINUATION frames MUST be a valid and complete set of request header fields - (Section 8.1.2.1). The server MUST include a method in the ":method" + (Section 8.1.2.3). The server MUST include a method in the ":method" header field that is safe and cacheable. If a client receives a PUSH_PROMISE that does not include a complete and valid set of header fields, or the ":method" header field identifies a method that is not safe, it MUST respond with a stream error (Section 5.4.2) of type PROTOCOL_ERROR. The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to sending any frames that reference the promised responses. This avoids a race where clients issue requests prior to receiving any PUSH_PROMISE frames. @@ -2794,32 +2767,37 @@ For example, if the server receives a request for a document containing embedded links to multiple image files, and the server chooses to push those additional images to the client, sending push promises before the DATA frames that contain the image links ensures that the client is able to see the promises before discovering embedded links. Similarly, if the server pushes responses referenced by the header block (for instance, in Link header fields), sending the push promises before sending the header block ensures that clients do not request them. - PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE - frames can be sent by the server on any stream that was opened by the - client. They MUST be sent on a stream that is in either the "open" - or "half closed (remote)" state to the server. PUSH_PROMISE frames - are interspersed with the frames that comprise a response, though - they cannot be interspersed with HEADERS and CONTINUATION frames that - comprise a single header block. + PUSH_PROMISE frames MUST NOT be sent by the client. + + PUSH_PROMISE frames can be sent by the server in response to any + client-initiated stream, but the stream MUST be in either the "open" + or "half closed (remote)" state with respect to the server. + PUSH_PROMISE frames are interspersed with the frames that comprise a + response, though they cannot be interspersed with HEADERS and + CONTINUATION frames that comprise a single header block. + + Sending a PUSH_PROMISE frame creates a new stream and puts the stream + into the "reserved (local)" state for the server and the "reserved + (remote)" state for the client. 8.2.2. Push Responses After sending the PUSH_PROMISE frame, the server can begin delivering - the pushed response as a response (Section 8.1.2.2) on a server- + the pushed response as a response (Section 8.1.2.4) on a server- initiated stream that uses the promised stream identifier. The server uses this stream to transmit an HTTP response, using the same sequence of frames as defined in Section 8.1. This stream becomes "half closed" to the client (Section 5.1) after the initial HEADERS frame is sent. Once a client receives a PUSH_PROMISE frame and chooses to accept the pushed response, the client SHOULD NOT issue any requests for the promised response until after the promised stream has closed. @@ -2836,32 +2814,41 @@ streams. This does not prohibit a server from sending PUSH_PROMISE frames; clients need to reset any promised streams that are not wanted. Clients receiving a pushed response MUST validate that the server is authorized to provide the response, see Section 10.1. For example, a server that offers a certificate for only the "example.com" DNS-ID or Common Name is not permitted to push a response for "https://www.example.org/doc". + The response for a PUSH_PROMISE stream begins with a HEADERS frame, + which immediately puts the stream into the "half closed (remote)" + state for the server and "half closed (local)" state for the client, + and ends with a frame bearing END_STREAM, which places the stream in + the "closed" state. + + Note: The client never sends a frame with the END_STREAM flag for a + server push. + 8.3. The CONNECT Method In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is used to convert an HTTP connection into a tunnel to a remote host. CONNECT is primarily used with HTTP proxies to establish a TLS session with an origin server for the purposes of interacting with "https" resources. In HTTP/2, the CONNECT method is used to establish a tunnel over a single HTTP/2 stream to a remote host, for similar purposes. The HTTP header field mapping works as mostly as defined in Request - Header Fields (Section 8.1.2.1), with a few differences. + Header Fields (Section 8.1.2.3), with a few differences. Specifically: o The ":method" header field is set to "CONNECT". o The ":scheme" and ":path" header fields MUST be omitted. o The ":authority" header field contains the host and port to connect to (equivalent to the authority-form of the request-target of CONNECT requests, see [RFC7230], Section 5.3). @@ -2952,21 +2939,21 @@ result in requests being directed to the wrong origin server. For example, TLS termination might be performed by a middlebox that uses the TLS Server Name Indication (SNI) [TLS-EXT] extension to select the an origin server. This means that it is possible for clients to send confidential information to servers that might not be the intended target for the request, even though the server has valid authentication credentials. A server that does not wish clients to reuse connections can indicate that it is not authoritative for a request by sending a 421 (Not - Authoritative) status code in response to request (see + Authoritative) status code in response to the request (see Section 9.1.2). 9.1.2. The 421 (Not Authoritative) Status Code The 421 (Not Authoritative) status code indicates that the current origin server is not authoritative for the requested resource, in the sense of [RFC7230], Section 9.1 (see also Section 10.1). Clients receiving a 421 (Not Authoritative) response from a server MAY retry the request - whether the request method is idempotent or @@ -2980,20 +2967,27 @@ indicated by the method definition or explicit cache controls (see Section 4.2.2 of [RFC7234]). 9.2. Use of TLS Features Implementations of HTTP/2 MUST support TLS 1.2 [TLS12] for HTTP/2 over TLS. The general TLS usage guidance in [TLSBCP] SHOULD be followed, with some additional restrictions that are specific to HTTP/2. + An implementation of HTTP/2 over TLS MUST use TLS 1.2 or higher with + the restrictions on feature set and cipher suite described in this + section. Due to implementation limitations, it might not be possible + to fail TLS negotiation. An endpoint MUST immediately terminate an + HTTP/2 connection that does not meet these minimum requirements with + a connection error (Section 5.4.1) of type INADEQUATE_SECURITY. + 9.2.1. TLS Features The TLS implementation MUST support the Server Name Indication (SNI) [TLS-EXT] extension to TLS. HTTP/2 clients MUST indicate the target domain name when negotiating TLS. The TLS implementation MUST disable compression. TLS compression can lead to the exposure of information that would not otherwise be revealed [RFC3749]. Generic compression is unnecessary since HTTP/2 provides compression features that are more aware of context and @@ -3022,32 +3016,32 @@ restricted. HTTP/2 MUST only be used with cipher suites that have ephemeral key exchange, such as the ephemeral Diffie-Hellman (DHE) [TLS12] or the elliptic curve variant (ECDHE) [RFC4492]. Ephemeral key exchange MUST have a minimum size of 2048 bits for DHE or security level of 128 bits for ECDHE. Clients MUST accept DHE sizes of up to 4096 bits. HTTP MUST NOT be used with cipher suites that use stream or block ciphers. Authenticated Encryption with Additional Data (AEAD) modes, such as the Galois Counter Model (GCM) mode for AES [RFC5288] are acceptable. - Clients MAY advertise support of other cipher suites in order to - allow for connection to servers that do not support HTTP/2 to - complete without the additional latency imposed by using a separate - connection for fallback. + The effect of these restrictions is that TLS 1.2 implementations + could have non-intersecting sets of available cipher suites, since + these prevent the use of the cipher suite that TLS 1.2 makes + mandatory. To avoid this problem, implementations of HTTP/2 that use + TLS 1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 + [TLS-ECDHE] with P256 [FIPS186]. - An implementation SHOULD NOT negotiate a TLS connection for HTTP/2 - without also negotiating a cipher suite that meets these - requirements. Due to implementation limitations, it might not be - possible to fail TLS negotiation. An endpoint MUST immediately - terminate an HTTP/2 connection that does not meet these minimum - requirements with a connection error (Section 5.4.1) of type - INADEQUATE_SECURITY. + Clients MAY advertise support of cipher suites that are prohibited by + the above restrictions in order to allow for connection to servers + that do not support HTTP/2. This enables a fallback to protocols + without these constraints without the additional latency imposed by + using a separate connection for fallback. 10. Security Considerations 10.1. Server Authority A client is only able to accept HTTP/2 responses from servers that are authoritative for those resources. This is particularly important for server push (Section 8.2), where the client validates the PUSH_PROMISE before accepting the response. @@ -3185,20 +3179,30 @@ header fields that are critical to routing, such as ":authority", ":path", and ":scheme" are not guaranteed to be present early in the header block. In particular, values that are in the reference set cannot be emitted until the header block ends. This can prevent streaming of the header fields to their ultimate destination, and forces the endpoint to buffer the entire header block. Since there is no hard limit to the size of a header block, an endpoint could be forced to exhaust available memory. + An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to avise peers + of limits that might apply on the size of header blocks. This + setting is only advisory, so endpoints MAY choose to send header + blocks that exceed this limit and risk having the request or response + being treated as malformed. This setting is advertised hop-by-hop, + so any request or response could encounter a hop with a lower, + unknown limit. An intermediary can attempt to avoid this problem by + passing on values presented by different peers, but they are not + obligated to do so. + A server that receives a larger header block than it is willing to handle can send an HTTP 431 (Request Header Fields Too Large) status code [RFC6585]. A client can discard responses that it cannot process. The header block MUST be processed to ensure a consistent connection state, unless the connection is closed. 10.6. Use of Compression HTTP/2 enables greater use of compression for both header fields (Section 4.3) and entity bodies. Compression can allow an attacker @@ -3260,45 +3264,45 @@ features. As far as this creates observable differences in behavior, they could be used as a basis for fingerprinting a specific client, as defined in Section 1.8 of [HTML5]. 11. IANA Considerations A string for identifying HTTP/2 is entered into the "Application Layer Protocol Negotiation (ALPN) Protocol IDs" registry established - in [TLSALPN]. + in [TLS-ALPN]. This document establishes a registry for frame types, settings, and error codes. These new registries are entered into a new "Hypertext Transfer Protocol (HTTP) 2 Parameters" section. This document registers the "HTTP2-Settings" header field for use in HTTP; and the 421 (Not Authoritative) status code. This document registers the "PRI" method for use in HTTP, to avoid collisions with the connection preface (Section 3.5). 11.1. Registration of HTTP/2 Identification Strings This document creates two registrations for the identification of HTTP/2 in the "Application Layer Protocol Negotiation (ALPN) Protocol - IDs" registry established in [TLSALPN]. + IDs" registry established in [TLS-ALPN]. The "h2" string identifies HTTP/2 when used over TLS: Protocol: HTTP/2 over TLS - Identification Sequence: 0x68 0x32 ("h2") Specification: This document + The "h2c" string identifies HTTP/2 when used over cleartext TCP: Protocol: HTTP/2 over TCP Identification Sequence: 0x68 0x32 0x63 ("h2c") Specification: This document 11.2. Frame Type Registry @@ -3360,20 +3364,22 @@ An initial set of setting registrations can be found in Section 6.5.2. +------------------------+------+---------------+---------------+ | Name | Code | Initial Value | Specification | +------------------------+------+---------------+---------------+ | HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 | | ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 | | MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 | | INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 | + | MAX_FRAME_SIZE | 0x5 | 65536 | Section 6.5.2 | + | MAX_HEADER_LIST_SIZE | 0x6 | (infinite) | Section 6.5.2 | +------------------------+------+---------------+---------------+ 11.4. Error Code Registry This document establishes a registry for HTTP/2 error codes. The "HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2 Error Code" registry operates under the "Expert Review" policy [RFC5226]. Registrations for error codes are required to include a description @@ -3482,37 +3488,42 @@ o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism). o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro, Jitu Padhye, Roberto Peon, Rob Trace (Flow control). o Mike Bishop (Extensibility). o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike Bishop, Herve Ruellan (Substantial editorial contributions). + o Kari Hurtta, Tatsuhiro Tsujikawa, Greg Wilkins, Poul-Henning Kamp. + o Alexey Melnikov was an editor of this document during 2013. o A substantial proportion of Martin's contribution was supported by Microsoft during his employment there. 13. References 13.1. Normative References [COMPRESSION] Ruellan, H. and R. Peon, "HPACK - Header Compression for - HTTP/2", draft-ietf-httpbis-header-compression-08 (work in - progress), June 2014. + HTTP/2", draft-ietf-httpbis-header-compression-09 (work in + progress), July 2014. [COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265, April 2011. + [FIPS186] NIST, "Digital Signature Standard (DSS)", FIPS PUB 186-4, + July 2013. + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data @@ -3544,60 +3555,61 @@ [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June 2014. [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014. [TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. + [TLS-ALPN] + Friedl, S., Popov, A., Langley, A., and E. Stephan, + "Transport Layer Security (TLS) Application-Layer Protocol + Negotiation Extension", RFC 7301, July 2014. + + [TLS-ECDHE] + Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA- + 256/384 and AES Galois Counter Mode (GCM)", RFC 5289, + August 2008. + [TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, January 2011. [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. - [TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, - "Transport Layer Security (TLS) Application Layer Protocol - Negotiation Extension", draft-ietf-tls-applayerprotoneg-05 - (work in progress), March 2014. - 13.2. Informative References [ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP Alternative Services", draft-ietf-httpbis-alt-svc-01 (work in progress), April 2014. [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, September 2004. [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the - CRIME Attack", July 2013, . [HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", W3C Candidate Recommendation CR-html5-20140204, Febuary 2014, . Latest version available at [5]. [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions for High Performance", RFC 1323, May 1992. - [RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D. - Jensen, "HTTP Extensions for Distributed Authoring -- - WEBDAV", RFC 2518, February 1999. - [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol Compression Methods", RFC 3749, May 2004. [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B. Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS)", RFC 4492, May 2006. [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, August 2008. @@ -3616,68 +3628,86 @@ 13.3. URIs [1] https://www.iana.org/assignments/message-headers [2] https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/ cfUef2gL3iU [3] https://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc- principles-01 -Appendix A. Change Log (to be removed by RFC Editor before publication) +Appendix A. Change Log -A.1. Since draft-ietf-httpbis-http2-12 + This section is to be removed by RFC Editor before publication. + +A.1. Since draft-ietf-httpbis-http2-13 + + Pseudo-header fields are now required to appear strictly before + regular ones. + + Restored 1xx series status codes, except 101. + + Changed frame length field 24-bits. Expanded frame header to 9 + octets. Added a setting to limit the damage. + + Added a setting to advise peers of header set size limits. + + Removed segments. + + Made non-semantic-bearing HEADERS frames illegal in the HTTP mapping. + +A.2. Since draft-ietf-httpbis-http2-12 Restored extensibility options. Restricting TLS cipher suites to AEAD only. Removing Content-Encoding requirements. Permitting the use of PRIORITY after stream close. Removed ALTSVC frame. Removed BLOCKED frame. Reducing the maximum padding size to 256 octets; removing padding from CONTINUATION frames. Removed per-frame GZIP compression. -A.2. Since draft-ietf-httpbis-http2-11 +A.3. Since draft-ietf-httpbis-http2-11 Added BLOCKED frame (at risk). Simplified priority scheme. Added DATA per-frame GZIP compression. -A.3. Since draft-ietf-httpbis-http2-10 +A.4. Since draft-ietf-httpbis-http2-10 Changed "connection header" to "connection preface" to avoid confusion. Added dependency-based stream prioritization. Added "h2c" identifier to distinguish between cleartext and secured HTTP/2. Adding missing padding to PUSH_PROMISE. Integrate ALTSVC frame and supporting text. Dropping requirement on "deflate" Content-Encoding. Improving security considerations around use of compression. -A.4. Since draft-ietf-httpbis-http2-09 +A.5. Since draft-ietf-httpbis-http2-09 Adding padding for data frames. Renumbering frame types, error codes, and settings. Adding INADEQUATE_SECURITY error code. Updating TLS usage requirements to 1.2; forbidding TLS compression. Removing extensibility for frames and settings. @@ -3688,57 +3718,57 @@ Changing the protocol identification token to "h2". Changing the use of :authority to make it optional and to allow userinfo in non-HTTP cases. Allowing split on 0x0 for Cookie. Reserved PRI method in HTTP/1.1 to avoid possible future collisions. -A.5. Since draft-ietf-httpbis-http2-08 +A.6. Since draft-ietf-httpbis-http2-08 Added cookie crumbling for more efficient header compression. Added header field ordering with the value-concatenation mechanism. -A.6. Since draft-ietf-httpbis-http2-07 +A.7. Since draft-ietf-httpbis-http2-07 Marked draft for implementation. -A.7. Since draft-ietf-httpbis-http2-06 +A.8. Since draft-ietf-httpbis-http2-06 Adding definition for CONNECT method. Constraining the use of push to safe, cacheable methods with no request body. Changing from :host to :authority to remove any potential confusion. Adding setting for header compression table size. Adding settings acknowledgement. Removing unnecessary and potentially problematic flags from CONTINUATION. Added denial of service considerations. -A.8. Since draft-ietf-httpbis-http2-05 +A.9. Since draft-ietf-httpbis-http2-05 Marking the draft ready for implementation. Renumbering END_PUSH_PROMISE flag. Editorial clarifications and changes. -A.9. Since draft-ietf-httpbis-http2-04 +A.10. Since draft-ietf-httpbis-http2-04 Added CONTINUATION frame for HEADERS and PUSH_PROMISE. PUSH_PROMISE is no longer implicitly prohibited if SETTINGS_MAX_CONCURRENT_STREAMS is zero. Push expanded to allow all safe methods without a request body. Clarified the use of HTTP header fields in requests and responses. Prohibited HTTP/1.1 hop-by-hop header fields. @@ -3749,48 +3779,48 @@ Clarified requirements around handling different frames after stream close, stream reset and GOAWAY. Added more specific prohibitions for sending of different frame types in various stream states. Making the last received setting value the effective value. Clarified requirements on TLS version, extension and ciphers. -A.10. Since draft-ietf-httpbis-http2-03 +A.11. Since draft-ietf-httpbis-http2-03 Committed major restructuring atrocities. Added reference to first header compression draft. Added more formal description of frame lifecycle. Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA. Removed HEADERS+PRIORITY, added optional priority to HEADERS frame. Added PRIORITY frame. -A.11. Since draft-ietf-httpbis-http2-02 +A.12. Since draft-ietf-httpbis-http2-02 Added continuations to frames carrying header blocks. Replaced use of "session" with "connection" to avoid confusion with other HTTP stateful concepts, like cookies. Removed "message". Switched to TLS ALPN from NPN. Editorial changes. -A.12. Since draft-ietf-httpbis-http2-01 +A.13. Since draft-ietf-httpbis-http2-01 Added IANA considerations section for frame types, error codes and settings. Removed data frame compression. Added PUSH_PROMISE. Added globally applicable flags to framing. @@ -3809,37 +3839,37 @@ Restructured frame header. Removed distinction between data and control frames. Altered flow control properties to include session-level limits. Added note on cacheability of pushed resources and multiple tenant servers. Changed protocol label form based on discussions. -A.13. Since draft-ietf-httpbis-http2-00 +A.14. Since draft-ietf-httpbis-http2-00 Changed title throughout. Removed section on Incompatibilities with SPDY draft#2. Changed INTERNAL_ERROR on GOAWAY to have a value of 2 [6]. Replaced abstract and introduction. Added section on starting HTTP/2.0, including upgrade mechanism. Removed unused references. Added flow control principles (Section 5.2.1) based on [7]. -A.14. Since draft-mbelshe-httpbis-spdy-00 +A.15. Since draft-mbelshe-httpbis-spdy-00 Adopted as base for draft-ietf-httpbis-http2. Updated authors/editors list. Added status note. Authors' Addresses Mike Belshe