NETCONF                                                          E. Voit
Internet-Draft                                               A. Tripathy                                         E. Nilsen-Nygaard
Intended status: Standards Track                       E. Nilsen-Nygaard
Expires: August 4, 2018                           Cisco Systems
Expires: November 19, 2018                                      A. Clemm
                                                                  Huawei
                                                              A. Gonzalez Prieto
                                                                  VMWare
                                                              A. Bierman
                                                               YumaWorks
                                                        January 31,
                                                            May 18, 2018

          RESTCONF and HTTP Transport for Event Notifications
                  draft-ietf-netconf-restconf-notif-04
                  draft-ietf-netconf-restconf-notif-05

Abstract

   This document defines RESTCONF, HTTP2, and HTTP1.1 bindings for the
   transport of subscription requests and corresponding push updates.
   Being subscribed may be either publisher defined event streams or
   nodes/subtrees of YANG Datastores.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   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 https://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 August 4, November 19, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution  Dynamic Subscription  . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Transport Connectivity  . . . . . .   3
     3.1.  Dynamic YANG Subscription with RESTCONF control . . . . .   3
   4.  Mandatory JSON . . . . . .   4
     3.2.  Discovery . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  RESTCONF RPCs and datastore support HTTP Status Codes . . . . . . . . . . .   4
     3.4.  Call Flow for HTTP2 . . . . . . . . . . . . . . . . . . .   6
   5.  Notification Messages
     3.5.  Call flow for HTTP1.1 . . . . . . . . . . . . . . . . . .   8
   4.  Configured Subscription . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . .  10
     4.1.  Transport Connectivity  . .   7
   7.  Acknowledgments . . . . . . . . . . . . . . .  10
     4.2.  Call Flow . . . . . . . .   7
   8.  References . . . . . . . . . . . . . . . .  11
   5.  QoS Treatment . . . . . . . . .   7
     8.1.  Normative References . . . . . . . . . . . . . . .  12
   6.  Mandatory JSON and datastore support  . . .   7
     8.2.  Informative References . . . . . . . . .  12
   7.  Notification Messages . . . . . . . .   8
   Appendix A.  End-to-End Deployment Guidance . . . . . . . . . . .   9
     A.1.  Call Home .  12
   8.  YANG Tree . . . . . . . . . . . . . . . . . . . . . . .   9
     A.2.  TLS Heartbeat . . .  12
   9.  YANG module . . . . . . . . . . . . . . . . . . .   9
   Appendix B.  RESTCONF over GRPC . . . . . .  13
   10. IANA Considerations . . . . . . . . . . .   9
   Appendix C.  Encoded Subscription and Notification Message
                Examples . . . . . . . . . .  15
   11. Security Considerations . . . . . . . . . . . .  10
     C.1.  RESTCONF Subscription and Events over HTTP1.1 . . . . . .  10
     C.2.  Event Notification over HTTP2 .  16
   12. Acknowledgments . . . . . . . . . . . . .  14
   Appendix D.  Changes between revisions . . . . . . . . . .  17
   13. References  . . .  14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  17
     13.1.  Normative References .  15

1.  Introduction

   Mechanisms to support event subscription and push are defined in
   [I-D.draft-ietf-netconf-subscribed-notifications].  Enhancements to
   [I-D.draft-ietf-netconf-subscribed-notifications] which enable YANG
   Datastore subscription and push are defined in
   [I-D.ietf-netconf-yang-push].  This document provides a transport
   specification for these protocols over RESTCONF and HTTP.  Driving
   these requirements is [RFC7923].

   The streaming of notifications encapsulating the resulting
   information push can be done with either HTTP1.1 and HTTP2.  When
   using HTTP2 [RFC7540] benefits which can be realized include:

   o  Elimination . . . . . . . . . . . . . . . . .  17
     13.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  RESTCONF over GRPC . . . . . . . . . . . . . . . . .  19
   Appendix B.  Examples . . . . . . . . . . . . . . . . . . . . . .  19
     B.1.  Dynamic Subscriptions . . . . . . . . . . . . . . . . . .  20
       B.1.1.  Establishing Dynamic Subscriptions  . . . . . . . . .  20
       B.1.2.  Modifying Dynamic Subscriptions . . . . . . . . . . .  22
       B.1.3.  Deleting Dynamic Subscriptions  . . . . . . . . . . .  24
     B.2.  Configured Subscriptions  . . . . . . . . . . . . . . . .  25
       B.2.1.  Creating Configured Subscriptions . . . . . . . . . .  25
       B.2.2.  Modifying Configured Subscriptions  . . . . . . . . .  28
       B.2.3.  Deleting Configured Subscriptions . . . . . . . . . .  30
     B.3.  Subscription State Notifications  . . . . . . . . . . . .  31
       B.3.1.  subscription-started and subscription-modified  . . .  31
       B.3.2.  subscription-completed, subscription-resumed, and
               replay-complete . . . . . . . . . . . . . . . . . . .  32
       B.3.3.  subscription-terminated and subscription-suspended  .  32
   Appendix C.  Changes between revisions  . . . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   Mechanisms to support event subscription and push are defined in
   [I-D.draft-ietf-netconf-subscribed-notifications].  Enhancements to
   [I-D.draft-ietf-netconf-subscribed-notifications] which enable YANG
   datastore subscription and push are defined in
   [I-D.ietf-netconf-yang-push].  This document provides a transport
   specification for these protocols over RESTCONF [RFC8040] and HTTP.
   Driving these requirements is [RFC7923].

   The streaming of notifications encapsulating the resulting
   information push can be done with either HTTP1.1 [RFC7231] or HTTP2
   [RFC7540].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The following terms use the definitions from
   [I-D.draft-ietf-netconf-subscribed-notifications]: configured
   subscription, dynamic subscription, event stream, notification
   message, publisher, receiver, subscriber, and subscription.

   Other terms reused include datastore, which is defined in [RFC8342],
   and HTTP2 stream which maps to the definition of "stream" within
   [RFC7540], Section 2.

   [ note to the RFC Editor - please replace XXXX within this document
   with the number of this document ]

3.  Dynamic Subscription

   This section provides specifics on how to establish and maintain
   dynamic subscriptions over HTTP 1.1 and HTTP2 via signaling messages
   transported over RESTCONF [RFC8040].  Subscribing to event streams is
   accomplished in this way via a RESTCONF POST into RPCs defined within
   [I-D.draft-ietf-netconf-subscribed-notifications] Section 2.4.  YANG
   datastore subscription is accomplished via augmentations to
   [I-D.draft-ietf-netconf-subscribed-notifications] as described within
   [I-D.ietf-netconf-yang-push] Section 4.4.

   Common across all HTTP based dynamic subscriptions is that a POST
   needs to be made against a specific URI on the Publisher.
   Subscribers cannot pre-determine the URI against which a subscription
   might exist on a publisher, as the URI will only exist after the
   "establish-subscription" has been accepted.  There subscription URI
   will be determined and sent as part of the response to the
   "establish-subscription", and a subsequent POST to this URI will be
   done in order to start the flow of notification messages back to the
   subscriber.  A subscription does not become ACTIVE as per
   Section 2.4.1. of [I-D.draft-ietf-netconf-subscribed-notifications]
   until the POST is received.

3.1.  Transport Connectivity

   For a dynamic subscription, where an HTTP client session doesn't
   already exist, a new client session is initiated from the subscriber.
   If the subscriber is unsure if HTTP2 is supported by the publisher,
   HTTP1.1 will be used for initial messages, and these messages will
   include an HTTP version upgrade request as per [RFC7230],
   Section 6.7.  If a publisher response indicates that HTTP2 is
   supported, HTTP2 will be used between subscriber and publisher for
   future HTTP interactions as per [RFC7540].

   A subscriber SHOULD establish the HTTP session over TLS [RFC5246] in
   order to secure the content in transit.

   Without the involvement of additional protocols, neither HTTP1.1 nor
   HTTP2 sessions by themselves allow for a quick recognition of when
   the communication path has been lost with the publisher.  Where quick
   recognition of the loss of a publisher is required, a subscriber
   SHOULD connect over TLS [RFC5246], and use a TLS heartbeat [RFC6520]
   to track HTTP session continuity.  In the case where a TLS heartbeat
   is included, it should be sent just from receiver to publisher.  Loss
   of the heartbeat MUST result in any subscription related TCP sessions
   between those endpoints being torn down.  A subscriber can then
   attempt to re-establish.

3.2.  Discovery

   Subscribers can learn what event streams a RESTCONF server supports
   by querying the "streams" container of ietf-subscribed-
   notification.yang.  Subscribers can learn what datastores a RESTCONF
   server supports by following [I-D.draft-ietf-netconf-nmda-restconf].

3.3.  RESTCONF RPCs and HTTP Status Codes

   Specific HTTP responses codes as defined in [RFC7231] section 6 will
   indicate the result of RESTCONF RPC requests with publisher.  An HTTP
   status code of 200 is the proper response to any successful RPC
   defined within [I-D.draft-ietf-netconf-subscribed-notifications] or
   [I-D.ietf-netconf-yang-push].

   If a publisher fails to serve the RPC request for one of the reasons
   indicated in [I-D.draft-ietf-netconf-subscribed-notifications]
   Section 2.4.6 or [I-D.ietf-netconf-yang-push] Appendix A, this will
   be indicated by "406" status code transported in the HTTP response.

   When a "406" status code is returned, the RPC reply MUST include an
   "rpc-error" element per [RFC8040] Section 7.1 with the following
   parameter values:

   o  an "error-type" node of "application".

   o  an "error-tag" node of "operation-failed".

   o  an "error-app-tag" node with the value being a string that
      corresponds to an identity associated with the error, as defined
      in [I-D.draft-ietf-netconf-subscribed-notifications] section 2.4.6
      for general subscriptions, and [I-D.ietf-netconf-yang-push]
      Appendix A.1, for datastore subscriptions.  The tag to use depends
      on the RPC for which the error occurred.  Viable errors for
      different RPCs are as follows:

            RPC                     select an identity with a base
            ----------------------  ------------------------------
            establish-subscription  establish-subscription-error
            modify-subscription     modify-subscription-error
            delete-subscription     delete-subscription-error
            kill-subscription       kill-subscription-error
            resynch-subscription    resynch-subscription-error

   Each error identity will be inserted as the "error-app-tag" using
   JSON encoding following the form <modulename>:<identityname>.  An
   example of such as valid encoding would be "ietf-subscribed-
   notifications:no-such-subscription".

   o  In case of error responses to an "establish-subscription" or
      "modify-subscription" request there is the option of including an
      "error-info" node.  This node may contain hints for parameter
      settings that might lead to successful RPC requests in the future.
      Following are the yang-data structures which may be returned:

      establish-subscription returns hints in yang-data structure
      ---------------------- ------------------------------------
      target: event stream   establish-subscription-stream-error-info
      target: datastore      establish-subscription-datastore-error-info

      modify-subscription    returns hints in yang-data structure
      ---------------------- ------------------------------------
      target: event stream   modify-subscription-stream-error-info
      target: datastore      modify-subscription-datastore-error-info

      The yang-data included within "error-info" SHOULD NOT include the
      optional leaf "error-reason", as such a leaf would be redundant
      with information that is already placed within the
      "error-app-tag".

      In case of an rpc error as a result of a "delete-subscription", a
      "kill-subscription", or a "resynch-subscription" request, no
      "error-info" needs to be included, as the "subscription-id" is
      the only RPC input parameter and no hints regarding this RPC input
      parameters need to be provided.

   Note that "error-path" does not need to be included with the "rpc-
   error" element, as subscription errors are generally not associated
   with nodes in the datastore but with the choice of RPC input
   parameters.

3.4.  Call Flow for HTTP2

   Requests to [I-D.draft-ietf-netconf-subscribed-notifications] or
   [I-D.ietf-netconf-yang-push] augmented RPCs are sent on one or more
   HTTP2 streams indicated by (a) in Figure 1.  A successful "establish-
   subscription" will result in an RPC response returned with both a
   subscription identifier which uniquely identifies a subscription, as
   well as a URI which uniquely identifies the location of subscription
   on the publisher.  This URI is defined via the "uri" leaf the Data
   Model in Section 9.

   An HTTP POST is then sent on a logically separate HTTP2 stream (b) to
   the URI on the publisher.  This initiates to initiate the flow of
   notification messages which are sent in HTTP Data frames as a
   response to the POST.  In the case below, a newly established
   subscription has its associated notification messages pushed over
   HTTP2 stream (7).  These notification messages are placed into a
   HTTP2 Data frame (see [RFC7540] Section 6.1).

   +------------+                                 +------------+
   | Subscriber |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       | RESTCONF POST (RPC:establish-subscription)   |
       |--------------------------------------------->|
       |                          HTTP 200 OK (ID,URI)|
       |<---------------------------------------------|
       |   (7)HTTP POST (URI)                             (7)
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                     HTTP Data (notif-message)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |             HTTP Data (subscription-modified)|
       |    |<------------------------------------------(c)|
       |    |                     HTTP Data (notif-message)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                  HTTP Headers (end of head-of-line blocking stream)|
       |   (/7)<-----------------------------------------(/7)
       |

                       Figure 1: Dynamic with HTTP2

   Additional requirements for dynamic subscriptions over HTTP2 include:

   o  Weighting and proportional dequeuing of Events from different  A unique HTTP2 stream MAY be used for each subscription.

   o  A single HTTP2 stream MUST NOT be used for subscriptions with
      different DSCP values.

   o  All subscription state notifications from a publisher MUST be
      returned in a separate HTTP Data frame within the HTTP2 stream
      used by the subscription to which the state change refers.

   o  In addition to an RPC response for a "modify-subscription" RPC
      traveling over (a), a "subscription-modified" state change
      notification must be sent within HTTP2 stream (b).  This allows
      the receiver to know exactly when the new terms of the
      subscription have been applied to the notification messages.  See
      arrow (c).

   o  Additional RPCs for a particular subscription MUST NOT use the
      HTTP2 stream currently providing notification messages
      subscriptions.

   o  Explicit precedence  An HTTP end of stream message MUST not be sent until all
      subscriptions using that HTTP2 stream have completed.

3.5.  Call flow for HTTP1.1

   The call flow is defined in Figure 2.  Requests to
   [I-D.draft-ietf-netconf-subscribed-notifications] or
   [I-D.ietf-netconf-yang-push] augmented RPCs are sent on a TCP
   connection indicated by (a).  A successful "establish-subscription"
   will result in subscriptions so that events from one an RPC response returned with both a subscription must be sent before another dequeues

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
   identifier which uniquely identifies a subscription, as well as a URI
   which uniquely identifies the location of subscription on the
   publisher (b).  This URI is defined via the "uri" leaf the Data Model
   in this
   document Section 9.

   An HTTP POST is then sent on a logically separate TCP connection (b)
   to the URI on the publisher.  This initiates to initiate the flow of
   notification messages which are sent in SSE [W3C-20150203] as a
   response to the POST.

   +--------------+                             +--------------+
   |  Subscriber  |                             |   Publisher  |
   |TCP connection|                             |TCP connection|
   |  (a)  (b)    |                             |    (a)  (b)  |
   +--------------+                             +--------------+
       | RESTCONF POST (RPC:establish-subscription)   |
       |--------------------------------------------->|
       |                          HTTP 200 OK (ID,URI)|
       |<---------------------------------------------|
       |    |HTTP GET (URI)                                |
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                           SSE (notif-message)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                   SSE (subscription-modified)|
       |    |<------------------------------------------(c)|
       |    |                           SSE (notif-message)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                                              |
       |    |

                      Figure 2: Dynamic with HTTP1.1

   Additional requirements for dynamic subscriptions over HTTP1.1
   include:

   o  All subscription state notifications from a publisher MUST be interpreted as described
      returned in RFC 2119 [RFC2119].

   The following terms a separate SSE message used by the subscription to
      which the state change refers.

   o  Subscription RPCs MUST NOT use the definitions from
   [I-D.draft-ietf-netconf-subscribed-notifications]: configured
   subscription, dynamic subscription, TCP connection currently
      providing notification message, publisher,
   receiver, subscriber, and messages for that subscription.

3.  Solution

   Subscribing to event streams is defined in
   [I-D.draft-ietf-netconf-subscribed-notifications], YANG Datastore
   subscription is defined in [I-D.ietf-netconf-yang-push].  This
   section specifies transport mechanisms applicable

   o  In addition to both.

3.1.  Dynamic YANG Subscription with RESTCONF control

   Dynamic subscriptions an RPC response for both
   [I-D.draft-ietf-netconf-subscribed-notifications] and its
   [I-D.ietf-netconf-yang-push] augmentations are configured and managed
   via signaling messages transported a "modify-subscription" RPC
      traveling over [RFC8040].  These
   interactions will be accomplished via (a), a RESTCONF POST into RPCs
   located on "subscription-modified" state change
      notification must be sent within stream (b).  This allows the publisher.  HTTP responses codes will indicate
      receiver to know exactly when the
   results new terms of the interaction with subscription
      have been applied to the publisher.  An HTTP status code notification messages.  See arrow (c).

   Open question, should we just eliminate this possibility of 200 is HTTP1.1
   for subscriptions?  It would make the proper response to design simpler.

4.  Configured Subscription

   With a successful <establish-
   subscription> RPC call.  The successful <establish-subscription> will
   result in configured subscription, all information needed to establish a HTTP message
   secure relationship with returned subscription URI that receiver is available on the publisher.
   With this information, the publisher will establish a
   logically separate mechanism than was used for secure
   transport connection with the original receiver and then begin pushing
   notification messages to the receiver.  Since RESTCONF
   POST.  This mechanism might not
   exist on the receiver, it is not desirable to require that subscribed
   content be pushed with any dependency on RESTCONF.  Therefore in
   place of RESTCONF, an HTTP2 Client connection must be established
   with an HTTP2 Server located on the receiver.  Notification messages
   will then be sent as part of an extended HTTP POST to the receiver.

4.1.  Transport Connectivity

   Configured subscriptions MUST only be connected over HTTP2 via a parallel TCP
   client session initiated from the publisher.  Following are the
   conditions which MUST be met before estabishing a new HTTP2
   connection with a receiver:

   o  a configured subscription has a receiver in the case of
   HTTP 1.x, or CONNECTING state
      as described in [I-D.draft-ietf-netconf-subscribed-notifications],
      section 2.5.1.,

   o  the case of transport configured for that subscription is HTTP2,

   o  there are state change notifications or notification messages
      pending for that receiver, and

   o  no HTTP2 via transport session exists to that receiver,

   If the above conditions are met, then the publisher MUST initiate a separate HTTP stream within
   transport session via RESTCONF call home [RFC8071], section 4.1 to
   that receiver.  HTTP2 only communications must be used as per
   [RFC7540], Section 3.3 when the HTTP connection.  When session over TLS [RFC5246]. and
   [RFC7540], Section 3.4 when transporting cleartext over TCP.  Note
   that a being returned by subscriber SHOULD establish over TLS in order to secure the publisher, failure
   will be indicated by 4xx range status codes transported
   content in payload.
   Anytime hints transit.

   If the RESTCONF call home fails because the publisher receives
   receiver credentials which are returned from subsequently declined per [RFC8071],
   Section 4.1, step S5 authentication, then that receiver MUST be
   placed into the TIMEOUT state.

   If the call home fails to establish for any other reason, the
   publisher status code 412 is used
   with MUST NOT progress the error-tag "operation-failed".

   Once established, receiver to the resulting stream ACTIVE state.
   Additionally, the publisher SHOULD place the receiver into the
   TIMEOUT state after a predetermined number of notification messages are
   then delivered via SSE for HTTP1.1 and via an HTTP2 DATA frame for
   HTTP2.

3.1.1. either failed call home
   attempts or remote transport session termination by the receiver.

4.2.  Call Flow for

   With HTTP2

   Requests connectivity established, a POST of each new
   "subscription-started" state change notification messages will be
   addressed to [I-D.draft-ietf-netconf-subscribed-notifications] or
   [I-D.ietf-netconf-yang-push] augmented RPCs are sent HTTP augmentation code on one or more
   HTTP2 streams indicated by (a) in Figure 2.  Notification messages
   related the receiver capable of
   accepting and acknowleding to a single subscription are pushed on state change
   notifications.  Until the "HTTP 200 OK" at point (c) of Figure 3 for
   each the "subscription-started" state change notification, a unique logical
   channel (b).
   publisher MUST NOT progress the receiver to the ACTIVE state.  In
   other words, is at point (c) which indicates that the case below, receiver is
   ready for the delivery of subscribed content.  At this point a newly established subscription has
   its associated messages pushed over
   notification-messages including subscribed content may be placed onto
   an HTTP2 stream (7). for that subscription.

   +------------+                                 +------------+
   | Subscriber  Receiver  |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       | RESTCONF POST (RPC:establish-subscription)   |
       |--------------------------------------------->|
       |                             HTTP 200 OK (URI)|
       |HTTP Post Headers, Data (subscription-started)|
       |<---------------------------------------------|
       |   (7)HTTP POST (URI)                             (7)
       |    |--------------------------------------------->|
       |    | HTTP 200 OK| OK                                  |    |<---------------------------------------------|
       |-------------------------------------------->(c)
       |    |       HTTP Post Headers, Data (event-notif)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK| (notif-message)|
       |    |<---------------------------------------------|
       |    |    |                     HTTP Data (subscription-modified)| (notif-message)|
       |    |<---------------------------------------------|
       |    |                    HTTP Data (event-notif)| (sub-terminated)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:delete-subscription)    |HTTP 200 OK                                   |
       |    |--------------------------------------------->|    |
       |    |

                      Figure 3: Configured over HTTP2

   Additional requirements for configured subscriptions over HTTP2
   include:

   o  A unique HTTP2 stream MAY be used for each subscription.

   o  A single HTTP2 stream MUST NOT be used for subscriptions with
      different DSCP values.

   o  All subscription state notifications from a publisher MUST be
      returned in a separate HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    | Data frame within the HTTP2 stream
      used by the subscription to which the state change refers.

   o  An HTTP Headers (end end of stream)|
       |   (/7)<-----------------------------------------(/7)
       |

                       Figure 1: Dynamic with stream message MUST not be sent until all
      subscriptions using that HTTP2 stream have completed.

5.  QoS Treatment

   To meet subscription quality of service promises, the publisher MUST
   take any existing subscription "dscp" and apply it to the DSCP
   marking in the IP header.

   In addition, where HTTP2 transport is available to a notification
   message queued for transport to a receiver, the publisher MUST:

   o  take any existing subscription "priority" and copy it into the
      HTTP2 stream priority, and

   o  take any existing subscription "dependency" and map the HTTP2
      stream for the parent subscription into the HTTP2

3.1.2.  Call flow for HTTP1.1

   Requests to stream
      dependency.

6.  Mandatory JSON and datastore support

   A publisher supporting [I-D.ietf-netconf-yang-push] RPCs are sent on MUST support the TCP
   connection indicated
   "operational" datastore as defined by (a).  Notification messages are pushed on a
   separate connection (b). [RFC8342].

   The "encode-json" feature of
   [I-D.draft-ietf-netconf-subscribed-notifications] is mandatory to
   support.  This connection (b) will be used indicates that JSON is a valid encoding for all
   notification RPCs,
   state change notifications, and subscribed content.

7.  Notification Messages

   Notification messages across all subscriptions.

   +--------------+                             +--------------+
   |  Subscriber  |                             |   Publisher  |
   |TCP connection|                             |TCP connection|
   |  (a)  (b)    |                             |    (a)  (b)  |
   +--------------+                             +--------------+
       | RESTCONF POST (RPC:establish-subscription)   |
       |--------------------------------------------->|
       |                             HTTP 200 OK (URI)|
       |<---------------------------------------------|
       |    |HTTP GET (URI)                                |
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                             SSE (event-notif)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    | transported over HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                   SSE (subscription-modified)|
       |    |<---------------------------------------------|
       |    |                             SSE (event-notif)|
       |    |<---------------------------------------------|
       | RESTCONF POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    | will be encoded using
   one-way operation schema defined within [RFC5277], section 4.

8.  YANG Tree

   The YANG model defined in Section 9 has one leaf augmented into four
   places of [I-D.draft-ietf-netconf-subscribed-notifications], plus two
   identities.  As the resulting full tree is large, it will only be
   inserted at later stages of this document.

9.  YANG module

   This module references
   [I-D.draft-ietf-netconf-subscribed-notifications].

 <CODE BEGINS> file "ietf-http-subscribed-notifications@2018-05-01.yang"
 module ietf-http-subscribed-notifications {
   yang-version 1.1;
   namespace
     "urn:ietf:params:xml:ns:yang:ietf-http-subscribed-notifications";

   prefix hsn;

   import ietf-subscribed-notifications {
     prefix sn;
   }
   import ietf-yang-types {
     prefix yang;
   }

   organization "IETF NETCONF (Network Configuration) Working Group";
   contact
     "WG Web:   <http:/tools.ietf.org/wg/netconf/>
      WG List:  <mailto:netconf@ietf.org>

      Editor:   Eric Voit
                <mailto:evoit@cisco.com>

      Editor:   Alexander Clemm
                <mailto:ludwig@clemm.org>

      Editor:   Einar Nilsen-Nygaard
                <mailto:einarnn@cisco.com>";

   description
     "Defines HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                                              |
       |    |

                      Figure 2: Dynamic with HTTP1.1

3.1.3.  Configured Subscription over HTTP2

   With a configured subscription, all information needed to establish variants as a
   secure relationship supported transports for subscribed
     event notifications.

     Copyright (c) 2018 IETF Trust and the persons identified as authors
     of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with that receiver or without
     modification, is available on permitted pursuant to, and subject to the publisher.
   With license
     terms contained in, the Simplified BSD License set forth in Section
     4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this information, YANG module is part of RFC XXXX; see the publisher will establish RFC
     itself for full legal notices.";

   revision 2018-05-01 {
     description
       "Initial version";
     reference
     "RFC XXXX: RESTCONF and HTTP Transport for Event Notifications";
   }

   identity http2 {
     base sn:transport;
     base sn:inline-address;
     base sn:configurable-encoding;
     description
       "HTTP2 is used a secure transport connection with the receiver for notification messages and then begin pushing state
        change notifications.";
   }

   identity http1.1 {
     base sn:transport;
     base sn:inline-address;
     base sn:configurable-encoding;
     description
       "HTTP1.1 is used a transport for notification messages to the receiver.  Since RESTCONF might not
   exist and state
        change notifications.";
   }

   grouping uri {
     description
       "Provides a reusable description of a URI.";
     leaf uri {
       config false;
       type yang:uri;
       description
         "Location of a subscription specific URI on the receiver, it is not desirable publisher.";
     }
   }

   augment "/sn:establish-subscription/sn:output" {
     description
       "This augmentation allows HTTP specific parameters for a
       response to require that subscribed
   content be pushed with any dependency on RESTCONF.  Therefore in
   place of RESTCONF, a TLS secured HTTP2 Client connection must publisher's subscription request.";
     uses uri;
   }

   augment "/sn:subscriptions/sn:subscription/sn:target" {
     description
       "This augmentation allows HTTP specific parameters to be
   established with an HTTP2 Server located on the receiver.
   Notification messages will then
        exposed for a subscription.";
     uses uri;
   }

   augment "/sn:subscription-started/sn:target" {
     description
       "This augmentation allows HTTP specific parameters to be sent as included
       part of an extended the notification that a subscription has started.";
     uses uri;
   }

   augment "/sn:subscription-modified/sn:target" {
     description
       "This augmentation allows HTTP
   POST specific parameters to the receiver.

   POST messages will be addressed to HTTP augmentation code on the
   receiver capable included
       part of accepting and responding to state change
   notifications and subscribed content the notification messages.  The
   first POST message must be that a subscription-started notification.
   Notifications which include any subscribed content must subscription has been modified.";
     uses uri;
   }

 /* need to add a constraint that HTTP1.1 not be sent
   until allowed for
 configured subscriptions - needs the receipt of an HTTP 200 OK right syntax below...

   augment "sn:subscriptions/sn:subscription/sn:protocol" {
     when '../sn:configured-subscription-state'
     must ' protocol <> "http1.1"' {
       error-message "HTTP1.1 not used for this initial notification. configured subscriptions";
     }
   }

 */

 }
 <CODE ENDS>

10.  IANA Considerations

   This document registers the following namespace URI in the "IETF XML
   Registry" [RFC3688]:

   URI: urn:ietf:params:xml:ns:yang:ietf-http-subscribed-notifications
   Registrant Contact: The 200 OK will indicate that IESG.
   XML: N/A; the receiver requested URI is ready for an XML namespace.

   This document registers the delivery
   of subscribed content.  At following YANG module in the "YANG Module
   Names" registry [RFC6020]:

   Name: ietf-http-subscribed-notifications
   Namespace: urn:ietf:params:xml:ns:yang:ietf-http-subscribed-
   notifications
   Prefix: hsn
   Reference: RFC XXXX: RESTCONF and HTTP Transport for Event
   Notifications

11.  Security Considerations

   The YANG module specified in this point document defines a subscription must be
   allocated its own HTTP2 stream.  Figure 4 depicts this message flow.

   +------------+                                 +------------+
   |  Receiver  |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       |    HTTP Post Headers, Data (sub-start, SubID)|
       |<---------------------------------------------|
       | HTTP 200 OK                                  |
       |--------------------------------------------->|
       |    |         HTTP Post Headers, Data (event-notif)|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       |    |                     HTTP Data (sub-terminate)|
       |    |<---------------------------------------------|
       |    |HTTP 200 OK                                   |
       |    |--------------------------------------------->|

                      Figure 3: Configured over HTTP2

   As the HTTP2 transport schema for data
   that is available designed to be accessed via network management transports
   such as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF
   layer is the receiver, the publisher
   should:

   o  take any subscription-priority secure transport layer, and copy it into the HTTP2 stream
      priority, and

   o  take a subscription-dependency if it has been provided mandatory-to-implement
   secure transport is Secure Shell (SSH) [RFC6242].  The lowest
   RESTCONF layer is HTTPS, and map the
      HTTP2 stream for the parent subscription into mandatory-to-implement secure
   transport is TLS [RFC5246].

   The one new data node introduced in this YANG module may be
   considered sensitive or vulnerable in some network environments.  It
   is thus important to control read access (e.g., via get, get-config,
   or notification) to this data nodes.  These are the HTTP2 stream
      dependency.

4.  Mandatory JSON subtrees and datastore support

   A publisher MUST support JSON encoding of RPCs data
   nodes and Notifications.

   A publisher supporting [I-D.ietf-netconf-yang-push] MUST support the
   "operational" datastore as defined by
   [I.D.draft-ietf-netmod-revised-datastores].

5.  Notification Messages

   Notification messages transported over NETCONF their sensitivity/vulnerability:

   Container: "/subscriptions"

   o  "uri": leaf will show where subscribed resources might be identical in
   format located
      on a publisher.  Access control must be set so that only someone
      with proper access permissions, and content perhaps even HTTP session has
      the ability to those encoded using one-way operations defined
   within [RFC5277], section 4.

6.  Security Considerations access this resource.

   One or more publishers of configured subscriptions could be used to
   overwhelm a receiver which doesn't even support subscriptions.  There
   are two protections needing support on a publisher.  First,
   notification messages for configured subscriptions MUST only be
   transmittable over encrypted transports.  Clients which do not want
   pushed content need only terminate or refuse any transport sessions
   from the publisher.  Second, the HTTP transport augmentation on the
   receiver must send an HTTP 200 OK to a subscription started
   notification before the publisher starts streaming any subscribed
   content.

   One or more publishers could overwhelm a receiver which is unable to
   control or handle the volume of Event Notifications received.  In
   deployments where this might be a concern, HTTP2 transport such as
   HTTP2) should be selected.

   The NETCONF Authorization Control Model [RFC6536] SHOULD be used to
   control and restrict authorization of subscription configuration.

7.

12.  Acknowledgments

   We wish to acknowledge the helpful contributions, comments, and
   suggestions that were received from: Ambika Prasad Tripathy, Alberto
   Gonzalez Prieto, Susan Hares, Tim Jenkins, Balazs Lengyel, Kent
   Watsen, Michael Scharf, and Guangying Zheng.

8.

13.  References

8.1.

13.1.  Normative References

   [GRPC]     "RPC framework that runs over HTTP2", August 2017,
              <https://grpc.io/>.

   [I-D.draft-ietf-netconf-subscribed-notifications]
              Voit, E., Clemm, A., Gonzalez Prieto, A., Tripathy, A.,
              and E. Nilsen-Nygaard, "Custom Subscription to Event
              Streams", draft-ietf-netconf-subscribed-notifications-06 draft-ietf-netconf-subscribed-notifications-13
              (work in progress), January April 2018.

   [I.D.draft-ietf-netmod-revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,

   [I-D.ietf-netconf-yang-push]
              Clemm, A., Voit, E., Gonzalez Prieto, A., Prasad Tripathy,
              A., Nilsen-Nygaard, E., Bierman, A., and R. Wilton, "Network Management Datastore
              Architecture", draft-ietf-netmod-revised-datastores-04
              (work in progress), August 2017. B. Lengyel,
              "Subscribing to YANG datastore push updates", March 2017,
              <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-yang-push/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
              <https://www.rfc-editor.org/info/rfc5277>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC6520]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS) Heartbeat Extension", RFC 6520,
              DOI 10.17487/RFC6520, February 2012,
              <https://www.rfc-editor.org/info/rfc6520>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

8.2.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [W3C-20150203]
              "Server-Sent Events, World Wide Web Consortium CR CR-
              eventsource-20121211", February 2015,
              <https://www.w3.org/TR/2015/REC-eventsource-20150203/>.

13.2.  Informative References

   [GRPC]     "RPC framework that runs over HTTP2", August 2017,
              <https://grpc.io/>.

   [I-D.ietf-netconf-yang-push]

   [I-D.draft-ietf-netconf-netconf-event-notifications]
              Clemm, A., Alexander., Voit, E., Eric., Gonzalez Prieto, A., Prasad Tripathy,
              A., Alberto.,
              Nilsen-Nygaard, E., Bierman, A., and B. Lengyel,
              "Subscribing A. Tripathy, "NETCONF support for
              event notifications", May 2018,
              <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-netconf-event-notifications/>.

   [I-D.draft-ietf-netconf-nmda-restconf]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "RESTCONF Extensions to YANG datastore push updates", March 2017, Support the Network
              Management Datastore Architecture", April 2018,
              <https://datatracker.ietf.org/doc/
              draft-ietf-netconf-yang-push/>.
              draft-ietf-netconf-nmda-restconf/>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7923]  Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
              for Subscription to YANG Datastores", RFC 7923,
              DOI 10.17487/RFC7923, June 2016,
              <https://www.rfc-editor.org/info/rfc7923>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [RFC8071]  Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
              RFC 8071, DOI 10.17487/RFC8071, February 2017,
              <https://www.rfc-editor.org/info/rfc8071>.

   [W3C-20150203]
              "Server-Sent Events, World Wide Web Consortium CR CR-
              eventsource-20121211", February 2015,
              <https://www.w3.org/TR/2015/REC-eventsource-20150203/>.

Appendix A.  End-to-End Deployment Guidance

   Several technologies  RESTCONF over GRPC

   An initial goal for this document was to support [GRPC] transport
   seamlessly without any mapping or extra layering.  However there is
   an incompatibility of RESTCONF and GRPC.  RESTCONF uses HTTP GET, and
   GRPC uses HTTP2's POST rather than GET.  As GET is used across
   RESTCONF for things like capabilities exchange, a seamless mapping
   depends on specification changes outside the scope of this document.
   If/when GRPC supports GET, or RESTCONF is updated to support POST,
   this should be revisited.  It is hoped that the resulting fix will be
   transparent to this document.

Appendix B.  Examples

   This section is non-normative.  To allow easy comparison, this
   section mirrors the functional examples shown with NETCONF over XML
   within [I-D.draft-ietf-netconf-netconf-event-notifications].  In
   addition, HTTP2 vs HTTP1.1 headers are not shown as the contents of
   the JSON encoded objects are identical within.

B.1.  Dynamic Subscriptions

B.1.1.  Establishing Dynamic Subscriptions

   The following figure shows two successful "establish-subscription"
   RPC requests as per
   [I-D.draft-ietf-netconf-subscribed-notifications].  The first request
   is given a subscription identifier of 22, the second, an identifier
   of 23.

      +------------+                  +-----------+
      | Subscriber |                  | Publisher |
      +------------+                  +-----------+
            |                               |
            |establish-subscription         |
            |------------------------------>|  (a)
            |     HTTP 200 OK, id#22, URI#1 |
            |<------------------------------|  (b)
            |POST (URI#1)                   |
            |------------------------------>|  (c)
            | HTTP 200 OK,notif-mesg (id#22)|
            |<------------------------------|
            |                               |
            |                               |
            |stablish-subscription          |
            |------------------------------>|
            |      HTTP 200 OK, id#23, URI#2|
            |<------------------------------|
            |POST (URI#2)                   |
            |------------------------------>|
            |                               |
            |                               |
            |             notif-mesg (id#22)|
            |<------------------------------|
            | HTTP 200 OK,notif-mesg (id#23)|
            |<------------------------------|
            |                               |

            Figure 4: Multiple subscriptions over RESTCONF/HTTP

   To provide examples of the information being transported, example
   messages for interactions in Figure 4 are expected detailed below:

   POST /restconf/operations/subscriptions:establish-subscription

   {
      "establish-subscription": {
         "stream": {
            "ietf-netconf-subscribed-notifications" : "NETCONF"
         },
         "stream-xpath-filter": "/ex:foo/",
         "dscp": "10"
      }
   }

               Figure 5: establish-subscription request (a)

   As publisher was able to fully satisfy the request, the publisher
   sends the subscription identifier of the accepted subscription, and
   the URI:

   HTTP status code - 200

   {
      "identifier": "22",
      "uri": "/subscriptions/22"
   }

               Figure 6: establish-subscription success (b)

   Upon receipt of the successful response, the subscriber POSTs to be seen within a deployment the
   provided URI to
   achieve security and ease-of-use requirements.  These are start the flow of notification messages.  When the
   publisher receives this, the subscription becomes ACTIVE (c).

   POST /restconf/operations/subscriptions/22

             Figure 7: establish-subscription subsequent POST

   While not
   necessary for shown in Figure 4, if the publisher had not been able to
   fully satisfy the request, or subscriber has no authorization to
   establish the subscription, the publisher would have sent an implementation RPC
   error response.  For instance, if the "dscp" value of 10 asserted by
   the subscriber in Figure 5 proved unacceptable, the publisher may
   have returned:

         HTTP status code - 406

         { "ietf-restconf:errors" : {
             "error" : [
               {
                 "error-type": "application",
                 "error-tag": "operation-failed",
                 "error-severity": "error",
                 "error-app-tag":
                     "ietf-subscribed-notifications:dscp-unavailable"
               }
             ]
           }
         }

             Figure 8: an unsuccessful establish subscription

   The subscriber can use this specification, but will be
   useful information in future attempts to consider when considering
   establish a subscription.

B.1.2.  Modifying Dynamic Subscriptions

   An existing subscription may be modified.  The following exchange
   shows a negotiation of such a modification via several exchanges
   between a subscriber and a publisher.  This negotiation consists of a
   failed RPC modification request/response, followed by a successful
   one.

      +------------+                 +-----------+
      | Subscriber |                 | Publisher |
      +------------+                 +-----------+
            |                              |
            |  notification message (id#23)|
            |<-----------------------------|
            |                              |
            |modify-subscription (id#23)   |
            |----------------------------->|  (d)
            |    HTTP 406 error (with hint)|
            |<-----------------------------|  (e)
            |                              |
            |modify-subscription (id#23)   |
            |----------------------------->|
            |                  HTTP 200 OK |
            |<-----------------------------|
            |                              |
            |            notif-mesg (id#23)|
            |<-----------------------------|
            |                              |

   Figure 9: Interaction model for successful subscription modification

   If the operational context.

A.1.  Call Home

   Implementations should include subscription being modified in Figure 9 is a datastore
   subscription as per [I-D.ietf-netconf-yang-push], the ability to transparently
   incorporate 'call home' [RFC8071] so modification
   request made in (d) may look like that secure TLS connections shown in Figure 10.  As can
   originate from be
   seen, the desired device.

A.2.  TLS Heartbeat

   HTTP sessions might not quickly allow modifications being attempted are the application of a subscriber to recognize when new
   xpath filter as well as the communication path has been lost from setting of a new periodic time interval.

   POST /restconf/operations/subscriptions:modify-subscription

   {
    "modify-subscription": {
       "identifier": "23",
       {
         "ietf-yang-push": "datastore-xpath-filter":
         "/interfaces-state/interface/oper-status"
       },
       {
         "ietf-yang-push": "periodic": "500"
       }
    }
   }

             Figure 10: Subscription modification request (c)

   If the publisher can satisfy both changes, the publisher sends a
   positive result for the RPC.  If the publisher cannot satisfy either
   of the proposed changes, the publisher.  To
   recognize this, it publisher sends an RPC error response
   (e).  The following is possible an example RPC error response for (e) which
   includes a receiver to establish a TLS
   heartbeat [RFC6520].  In the case where a TLS heartbeat hint.  This hint is included,
   it should be sent just from receiver to publisher.  Loss of the
   heartbeat should result an alternative time period value which
   might have resulted in any a successful modification:

         HTTP status code - 406

         { "ietf-restconf:errors" : {
             "error" : [
               "error-type": "application",
               "error-tag": "operation-failed",
               "error-severity": "error",
               "error-app-tag": {
                 "ietf-yang-push": "ietf-yang-push:period-unsupported"
               },
               "error-info": {
                 "ietf-yang-push":
                 "modify-subscription-datastore-error-info": {
                    "period-hint": "3000"
                 }
               }
             ]
           }
         }

           Figure 11: Modify subscription related TCP sessions
   between those endpoints being torn down. failure with Hint (e)

B.1.3.  Deleting Dynamic Subscriptions

   The following demonstrates deleting a subscription.  This
   subscription may have been to either a stream or a datastore.

   POST /restconf/operations/subscriptions:delete-subscription

   {
    "delete-subscription": {
       "identifier": "22"
    }
   }

                      Figure 12: Delete subscription

   If the publisher can then
   attempt satisfy the request, the publisher replies with
   success to re-establish.

Appendix B.  RESTCONF over GRPC

   An initial goal the RPC request.

   If the publisher cannot satisfy the request, the publisher sends an
   error-rpc element indicating the modification didn't work.  Figure 13
   shows a valid response for this document existing valid subscription identifier,
   but that subscription identifier was to support [GRPC] created on a different transport
   seamlessly without any mapping or extra layering.  However there is
   an incompatibility of RESTCONF and GRPC.  RESTCONF uses
   session:

         HTTP GET, status code - 406

         {
           "ietf-restconf:errors" : {
             "error" : [
               "error-type": "application",
               "error-tag": "operation-failed",
               "error-severity": "error",
               "error-app-tag":
                  "ietf-subscribed-notifications:no-such-subscription"
             ]
           }
         }

                Figure 13: Unsuccessful delete subscription

B.2.  Configured Subscriptions

   Configured subscriptions may be established, modified, and
   GRPC uses HTTP2's POST rather than GET.  As GET is used across
   RESTCONF for things like capabilities exchange, a seamless mapping
   depends on specification changes outside deleted
   using configuration operations against the scope top-level subtree of
   [I-D.draft-ietf-netconf-subscribed-notifications] or
   [I-D.ietf-netconf-yang-push].

   In this document.
   If/when GRPC supports GET, or RESTCONF is updated to support POST,
   this should be revisited.  It is hoped that the resulting fix will be
   transparent to this document.

Appendix C.  Encoded Subscription and Notification Message Examples

   (Note: examples in this section need significant updates)

C.1.  RESTCONF Subscription and Events over HTTP1.1

   Subscribers can dynamically learn whether section, we present examples of how to manage the
   configuration subscriptions using a HTTP2 client.

B.2.1.  Creating Configured Subscriptions

   For subscription creation via configuration operations, a RESTCONF server supports
   various types of Event or Yang datastore
   client may send:

   POST /restconf/operations/subscriptions/

   {
      "edit-config": {
         "target": {
            "running": null
         },
         "default-operation": "none",
         "config": {
            "subscriptions": {
               "subscription": {
                  "identifier": "22",
                  "transport": "HTTP2",
                  "stream": "NETCONF",
                  "receivers": {
                     "receiver": {
                        "name": "receiver1",
                        "address": "1.2.3.4"
                     }
                  }
               }
            }
         }
      }
   }

                Figure 14: Create a configured subscription capabilities.
   This is done by issuing an HTTP request OPTIONS, HEAD, or GET on

   If the
   stream.  Some examples building upon request is accepted, the Call flow for HTTP1.1 from
   Section 3.2.2 are:

   GET /restconf/data/ietf-restconf-monitoring:restconf-state/
            streams/stream=yang-push HTTP/1.1
   Host: example.com
   Accept: application/yang.data+xml publisher will indicate this.  If the server supports
   request is not accepted because the publisher cannot serve it, it may respond

   HTTP/1.1 200 OK
   Content-Type: application/yang.api+xml
   <stream xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
               <name>yang-push</name>
               <description>Yang push stream</description>
               <access>
                  <encoding>xml</encoding>
                  <location>https://example.com/streams/yang-push-xml
                  </location>
               </access>
               <access>
                  <encoding>json</encoding>
                  <location>https://example.com/streams/yang-push-json
                  </location>
               </access>
            </stream>

   If no
   configuration is changed.  In this case the server does not support any form of subscription, it publisher may
   respond

   HTTP/1.1 404 Not Found
   Date: Mon, 25 Apr 2012 11:10:30 GMT
   Server: example-server

   Subscribers can determine the URL to receive updates by sending an reply:

   HTTP GET as a request for status code - 406

   {
     "ietf-restconf:errors" : {
       "error" : [
         "error-type": "application",
         "error-tag": "resource-denied",
         "error-severity": "error",
         "error-message": {
            "@lang": "en",
            "#text": "Temporarily the "location" leaf with publisher cannot serve this
            subscription due to the stream list
   entry.  The stream current workload."
         }
       ]
     }
   }

   Figure 15: Response to use for may a failed configured subscription establishment

   After a subscription has been created and been verified as VALID,
   HTTP2 connectivity to each receiver will be selected from established if that
   connectivity does not already exist.

   The following figure shows the Event Stream
   list provided in interaction model for the capabilities exchange.  Note that different
   encodings are supporting successful
   creation of a configured subscription.

    +----------+                 +-----------+     +---------+
    |Config Ops|                 | Publisher |     | 1.2.3.4 |
    +----------+                 +-----------+     +---------+
         |                            |                |
         |    Capability Exchange     |                |
         |<-------------------------->|                |
         |                            |                |
         |                            |                |
         |        Edit-config         |                |
         |--------------------------->|                |
         |       RPC Reply: OK        |                |
         |<---------------------------|                |
         |                            |   Call Home    |
         |                            |<-------------->|
         |                            |                |
         |                            |  subscription- |
         |                            |  started       |
         |                            |--------------->|
         |                            |                |
         |                            |  notification  |
         |                            |  message       |
         |                            |--------------->|

         Figure 16: Interaction model for configured subscription
                               establishment

B.2.2.  Modifying Configured Subscriptions

   Configured subscriptions can be modified using different Event Stream locations. configuration
   operations against the top-level container "/subscriptions".

   For example, the subscriber might send subscription established in the previous section
   could be modified as follows, here a adding a second receiver:

   POST /restconf/operations/subscriptions

   {
      "edit-config": {
         "target": {
            "running": null
         },
         "config": {
            "subscriptions": {
               "subscription": {
                  "identifier": "1922",
                  "receivers": {
                     "receiver": {
                        "name": "receiver2",
                        "address": "1.2.3.5"
                     }
                  }
               }
            }
         }
      }
   }

                 Figure 17: Modify configured subscription

   If the request is accepted, the following request:

   GET /restconf/data/ietf-restconf-monitoring:restconf-state/
            streams/stream=yang-push/access=xml/location HTTP/1.1
   Host: example.com
   Accept: application/yang.data+xml

   The publisher might send will indicate success.  The
   result is that the following response:

   HTTP/1.1 200 interaction model described in Figure 16 may be
   extended as follows.

 +----------+                 +-----------+     +---------+  +---------+
 |Config Ops|                 | Publisher |     | 1.2.3.4 |  | 1.2.3.5 |
 +----------+                 +-----------+     +---------+  +---------+
       |                            |  notification  |            |
       |                            |  message       |            |
       |                            |--------------->|            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK
   Content-Type: application/yang.api+xml
      <location
           xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
           https://example.com/streams/yang-push-xml
      </location>

   To subscribe and start receiving updates, the subscriber can then
   send an HTTP GET request        |                |            |
       |<---------------------------|                |            |
       |                            |  subscription- |            |
       |                            |  started       |            |
       |                            |---------------------------->|
       |                            |                |            |
       |                            |  notification  |            |
       |                            |  message       |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |

   Figure 18: Interaction model for configured subscription modification

   Note in the URL returned by the publisher above that in the
   request above.  The accept header must be "text/event-stream".  The
   publisher uses specific example above, modifying a
   configured subscription actually resulted in "subscription-started"
   notification.  And because of existing HTTP2 connectivity, no
   additional call home was needed.  Also note that if the Server Sent Events [W3C-20150203] transport
   strategy to push filtered events from edit of the event stream.

   The publisher MUST support individual parameters within
   configuration had impacted the POST
   request body filter, a separate modify-subscription
   would have been required for all the parameters of a subscription.  The only
   exception is original receiver.

B.2.3.  Deleting Configured Subscriptions

   Configured subscriptions can be deleted using configuration
   operations against the encoding, which is embedded in top-level container "/subscriptions".
   Deleting the URI.  An example
   of this is:

   // subtree filter = /foo
   // periodic updates, every 5 seconds
   POST /restconf/operations/ietf-subscribed-notifications:
        establish-subscription HTTP/1.1
         Host: example.com
         Content-Type: application/yang-data+json

         {
           "ietf-subscribed-notifications:input" : {
             "stream": "push-data"
             "period" : 5,
             "xpath-filter" : "/ex:foo[starts-with('bar'.'some']"
           }
         }

   Should subscription above would result in the following flow
   impacting all active receivers.

 +----------+                 +-----------+     +---------+  +---------+
 |Config Ops|                 | Publisher |     | 1.2.3.4 |  | 1.2.3.5 |
 +----------+                 +-----------+     +---------+  +---------+
       |                            |                |            |
       |                            |  notification  |            |
       |                            |  message       |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |
       |        Edit-config         |                |            |
       |--------------------------->|                |            |
       |       RPC Reply: OK        |                |            |
       |<---------------------------|                |            |
       |                            |  subscription- |            |
       |                            |  terminated    |            |
       |                            |--------------->|            |
       |                            |---------------------------->|
       |                            |                |            |

     Figure 19: Interaction model for configured subscription deletion

B.3.  Subscription State Notifications

   A publisher not support will send subscription state notifications according to
   the requested subscription, it may
   reply:

   HTTP/1.1 501 Not Implemented
   Date: Mon, 23 Apr 2012 17:11:00 GMT
   Server: example-server
   Content-Type: application/yang.errors+xml
       <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
          <error>
              <error-type>application</error-type>
              <error-tag>operation-not-supported</error-tag>
              <error-severity>error</error-severity>
              <error-message>Xpath filters not supported</error-message>
              <error-info>
                  <supported-subscription xmlns="urn:ietf:params:xml:ns:
                      netconf:datastore-push:1.0">
                      <subtree-filter/>
                  </supported-subscription>
              </error-info>
          </error>
        </errors>

   with an equivalent definitions within
   [I-D.draft-ietf-netconf-subscribed-notifications]).

B.3.1.  subscription-started and subscription-modified

   A "subscription-started" encoded in JSON encoding representation of:

   HTTP/1.1 501 Not Implemented
   Date: Mon, 23 Apr 2012 17:11:00 GMT
   Server: example-server
   Content-Type: application/yang.errors+json
         {
           "ietf-restconf:errors": would look like:

   {
             "error":
     "ietf-restconf:notification" : {
               "error-type": "protocol",
               "error-tag": "operation-not-supported",
               "error-message": "Xpath filters not supported."
               "error-info":
       "eventTime": "2007-09-01T10:00:00Z",
       "ietf-subscribed-notifications:subscription-started": {
                  "datastore-push:supported-subscription":
         "identifier": "39",
         "transport": "HTTP2",
         "stream-xpath-filter": "/ex:foo",
         "stream": {
                        "subtree-filter": [null]
                    }
            "ietf-netconf-subscribed-notifications" : "NETCONF"
         }
       }
     }
   }

      Figure 20: subscription-started subscription state notification

   The following "subscription-modified" is an example of a pushed content for the subscription
   above.  It contains a subtree with root foo that contains a leaf
   called bar:

   XML encoding representation:
     <?xml version="1.0" encoding="UTF-8"?>
     <notification xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
        <subscription-id xmlns="urn:ietf:params:xml:ns:restconf:
            datastore-push:1.0">
              my-sub
        </subscription-id>
        <eventTime>2015-03-09T19:14:56.233Z</eventTime>
        <datastore-contents xmlns="urn:ietf:params:xml:ns:restconf:
           datastore-push:1.0">
           <foo xmlns="http://example.com/yang-push/1.0">
             <bar>some_string</bar>
           </foo>
        </datastore-contents>
     </notification>

   Or identical to Figure 20, with just the equivalent YANG over JSON encoding representation as
   defined in [RFC7951]:
   word "started" being replaced by "modified".

B.3.2.  subscription-completed, subscription-resumed, and replay-
        complete

   A "subscription-completed" would look like:

   {
     "ietf-restconf:notification":
     "ietf-restconf:notification" : {
       "datastore-push:subscription-id": "my-sub",
       "eventTime": "2015-03-09T19:14:56.233Z",
       "datastore-push:datastore-contents": {
         "example-mod:foo": "2007-09-01T10:00:00Z",
       "ietf-subscribed-notifications:subscription-completed": { "bar": "some_string" }
       }
         "identifier": "39",
       }
     }

   To modify a subscription, the subscriber issues another POST request
   on the provided URI using the same subscription-id as in the original
   request.  For example, to modify the update period to 10 seconds, the
   subscriber may send:

   POST /restconf/operations/ietf-subscribed-notifications:
         modify-subscription HTTP/1.1
         Host: example.com
         Content-Type: application/yang-data+json

         {
           "ietf-subscribed-notifications:input" : {
             "subscription-id": 100,
             "period" : 10
           }
   }

   To delete a subscription, the subscriber issues a DELETE request on
   the provided URI using the same subscription-id as

          Figure 21: subscription-completed notification in the original
   request

C.2.  Event Notification over HTTP2 JSON

   The basic encoding will "subscription-resumed" and "replay-complete" are virtually
   identical, with "subscription-completed" simply being replaced by
   "subscription-resumed" and "replay-complete".

B.3.3.  subscription-terminated and subscription-suspended

   A "subscription-terminated" would look as below.  It will consists of a JSON
   representation wrapped in an HTTP2 header.

   HyperText Transfer Protocol 2
         Stream: HEADERS, Stream ID: 5
         Header: :method: POST
         Stream: HEADERS, Stream ID: 5 like:

   {
     "ietf-yangpush:notification":
     "ietf-restconf:notification" : {
       "datastore-push:subscription-id": "my-sub",
       "eventTime": "2015-03-09T19:14:56.233Z",
       "datastore-push:datastore-contents": "2007-09-01T10:00:00Z",
       "ietf-subscribed-notifications:subscription-terminated": {
         "foo": { "bar": "some_string" }
         "identifier": "39",
         "error-id": "suspension-timeout"
       }
     }
   }

    Figure 22: subscription-terminated subscription state notification

   The "subscription-suspended" is virtually identical, with
   "subscription-terminated" simply being replaced by "subscription-
   suspended".

Appendix D. C.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   v04 - v05

   o  Error mechanisms updated to match embedded RESTCONF mechanisms

   o  Restructured format and sections of document.

   o  Added a YANG data model for HTTP specific parameters.

   o  Mirrored the examples from the NETCONF transport draft to allow
      easy comparison.

   v03 - v04

   o  Draft not fully synched to new version of subscribed-notifications
      yet.

   o  References updated

   v02 - v03

   o  Event notification reframed to notification message.

   o  Tweaks to wording/capitalization/format.

   v01 - v02

   o  Removed sections now redundant with
      [I-D.draft-ietf-netconf-subscribed-notifications] and
      [I-D.ietf-netconf-yang-push] such as: mechanisms for subscription
      maintenance, terminology definitions, stream discovery.

   o  3rd party subscriptions are out-of-scope.

   o  SSE only used with RESTCONF and HTTP1.1 dynamic subscriptions

   o  Timeframes for event tagging are self-defined.

   o  Clean-up of wording, references to terminology, section numbers.

   v00 - v01

   o  Removed the ability for more than one subscription to go to a
      single HTTP2 stream.

   o  Updated call flows.  Extensively.

   o  SSE only used with RESTCONF and HTTP1.1 dynamic subscriptions

   o  HTTP is not used to determine that a receiver has gone silent and
      is not Receiving Event Notifications

   o  Many clean-ups of wording and terminology

Authors' Addresses

   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com

   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com

   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com

   Alexander Clemm
   Huawei

   Email: ludwig@clemm.org
   Alberto Gonzalez Prieto
   VMWare

   Email: agonzalezpri@vmware.com

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com