JMAP over WebSocket: A JSON Meta Application Protocol (JMAP) Subprotocol for WebSocket

Internet Engineering Task Force (IETF)                      K. Murchison
Request for Comments: 8887                                      Fastmail
Category: Standards Track                                    August 2020
ISSN: 2070-1721


   A JSON Meta Application Protocol (JMAP) Subprotocol for WebSocket

Abstract

   This document defines a binding for the JSON Meta Application
   Protocol (JMAP) over a WebSocket transport layer.  The WebSocket
   binding for JMAP provides higher performance than the current HTTP
   binding for JMAP.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8887.

Copyright Notice

   Copyright (c) 2020 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  Discovering Support for JMAP over WebSocket
   4.  JMAP Subprotocol
     4.1.  Authentication
     4.2.  Handshake
     4.3.  WebSocket Messages
       4.3.1.  Handling Invalid Data
       4.3.2.  JMAP Requests
       4.3.3.  JMAP Responses
       4.3.4.  JMAP Request-Level Errors
       4.3.5.  JMAP Push Notifications
     4.4.  Examples
   5.  Security Considerations
     5.1.  Connection Confidentiality and Integrity
     5.2.  Non-browser Clients
   6.  IANA Considerations
     6.1.  Registration of the WebSocket JMAP Subprotocol
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgments
   Author's Address

1.  Introduction

   JMAP [RFC8620] over HTTP [RFC7235] requires that every JMAP API
   request be authenticated.  Depending on the type of authentication
   used by the JMAP client and the configuration of the JMAP server,
   authentication could be an expensive operation both in time and
   resources.  In such circumstances, reauthenticating for every JMAP
   API request may harm performance.

   The WebSocket [RFC6455] binding for JMAP eliminates this performance
   hit by authenticating just the WebSocket handshake request and having
   those credentials remain in effect for the duration of the WebSocket
   connection.  This binding supports JMAP API requests and responses,
   with optional support for push notifications.

   Furthermore, the WebSocket binding for JMAP can optionally compress
   [RFC7692] both JMAP API requests and responses.  Although compression
   of HTTP responses is ubiquitous, compression of HTTP requests has
   very low, if any, deployment and therefore isn't a viable option for
   JMAP API requests over HTTP.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document uses the terminology defined in the core JMAP
   specification [RFC8620].

3.  Discovering Support for JMAP over WebSocket

   The JMAP capabilities object is returned as part of the standard JMAP
   Session object (see Section 2 of [RFC8620]).  Servers supporting this
   specification MUST add a property named
   "urn:ietf:params:jmap:websocket" to the capabilities object.  The
   value of this property is an object that MUST contain the following
   information on server capabilities:

   *  url: "String"

      The wss-URI (see Section 3 of [RFC6455]) to use for initiating a
      JMAP-over-WebSocket handshake (the "WebSocket URL endpoint"
      colloquially).

   *  supportsPush: "Boolean"

      This is true if the server supports push notifications over the
      WebSocket, as described in Section 4.3.5.

   Example:

   "urn:ietf:params:jmap:websocket": {
     "url": "wss://server.example.com/jmap/ws/",
     "supportsPush": true
   }

4.  JMAP Subprotocol

   The term WebSocket subprotocol refers to an application-level
   protocol layered on top of a WebSocket connection.  This document
   specifies the WebSocket JMAP subprotocol for carrying JMAP API
   requests, responses, and optional push notifications through a
   WebSocket connection.  Binary data is handled per Section 6 of
   [RFC8620] (via a separate HTTP connection or stream) or per a future
   extension to JMAP or this specification.

4.1.  Authentication

   A JMAP WebSocket connection is authenticated by presenting a user's
   credentials in the HTTP request [RFC7235] that initiates the
   WebSocket handshake.  See Section 8.2 of [RFC8620] for
   recommendations regarding the selection of HTTP authentication
   schemes.

4.2.  Handshake

   The JMAP WebSocket client and JMAP WebSocket server negotiate the use
   of the WebSocket JMAP subprotocol during the WebSocket handshake,
   either via an HTTP/1.1 Upgrade request (see Section 4 of [RFC6455])
   or an HTTP/2 Extended CONNECT request (see Section 5 of [RFC8441]).
   The WebSocket JMAP subprotocol is also intended to run over future
   bindings of HTTP (e.g., HTTP/3) provided that there is a defined
   mechanism for performing a WebSocket handshake over that binding.

   Regardless of the method used for the WebSocket handshake, the client
   MUST first perform a TLS handshake on a JMAP WebSocket URL endpoint
   (Section 3) having the "wss://" scheme (WebSocket over TLS) in
   accordance with the requirements of running the particular binding of
   HTTP over TLS (see [RFC2818] and Section 4.1 of [RFC6455] for
   HTTP/1.1 and Section 9.2 of [RFC7540] for HTTP/2).  If the TLS
   handshake fails, the client MUST close the connection.  Otherwise,
   the client MUST make an authenticated HTTP request [RFC7235] on the
   encrypted connection and MUST include the value "jmap" in the list of
   protocols for the "Sec-WebSocket-Protocol" header field.

   The reply from the server MUST also contain a corresponding "Sec-
   WebSocket-Protocol" header field with a value of "jmap" in order for
   a JMAP subprotocol connection to be established.

   Once the handshake has successfully completed, the WebSocket
   connection is established and can be used for JMAP API requests,
   responses, and optional push notifications.  Other message types MUST
   NOT be transmitted over this connection.

   The credentials used for authenticating the HTTP request to initiate
   the handshake remain in effect for the duration of the WebSocket
   connection.  If the authentication credentials for the user expire,
   the server can either treat subsequent requests as if they are
   unauthenticated or close the WebSocket connection.  In the latter
   case, the server MAY send a Close frame with a status code of 1008
   (Policy Violation), as defined in Section 7.4.1 of [RFC6455].

4.3.  WebSocket Messages

   Data frame messages in the JMAP subprotocol MUST be text frames and
   contain UTF-8 encoded data.  The messages MUST be in the form of a
   single JMAP Request object (see Section 3.3 of [RFC8620]), JMAP
   WebSocketPushEnable object (see Section 4.3.5.2), or JMAP
   WebSocketPushDisable object (see Section 4.3.5.3) when sent from the
   client to the server, and MUST be in the form of a single JMAP
   Response object, JSON Problem Details object, or JMAP StateChange
   object (see Sections 3.4, 3.6.1, and 7.1 of [RFC8620], respectively)
   when sent from the server to the client.

   Note that fragmented WebSocket messages (split over multiple text
   frames) MUST be coalesced prior to parsing them as JSON objects.

4.3.1.  Handling Invalid Data

   If a client or server receives a binary frame, the endpoint can
   either ignore the frame or close the WebSocket connection.  In the
   latter case, the endpoint MAY send a Close frame with a status code
   of 1003 (Unsupported Data), as defined in Section 7.4.1 of [RFC6455].

   If a client receives a message that is not in the form of a JSON
   Problem Details object, a JMAP Response object, or a JMAP StateChange
   object, the client can either ignore the message or close the
   WebSocket connection.  In the latter case, the endpoint MAY send a
   Close frame with a status code of 1007 (Invalid frame payload data),
   as defined in Section 7.4.1 of [RFC6455].

   A server MUST return an appropriate JSON Problem Details object
   (Section 4.3.4) for any request-level errors (e.g., an invalid JMAP
   object, an unsupported capability or method call, or exceeding a
   server request limit).

4.3.2.  JMAP Requests

   The specification extends the Request object with two additional
   arguments when used over a WebSocket:

   *  @type: "String"

      This MUST be the string "Request".

   *  id: "String" (optional)

      A client-specified identifier for the request to be echoed back in
      the response to this request.

   JMAP over WebSocket allows the server to process requests out of
   order.  The client-specified identifier is used as a mechanism for
   the client to correlate requests and responses.

   Additionally, the "maxConcurrentRequests" limit in the "capabilities"
   object (see Section 2 of [RFC8620]) also applies to requests made on
   the WebSocket connection.  When using the WebSocket JMAP subprotocol
   over a binding of HTTP that allows multiplexing of requests (e.g.,
   HTTP/2), this limit applies to the sum of requests made on both the
   JMAP API endpoint and the WebSocket connection.

4.3.3.  JMAP Responses

   The specification extends the Response object with two additional
   arguments when used over a WebSocket:

   *  @type: "String"

      This MUST be the string "Response".

   *  requestId: "String" (optional; MUST be returned if an identifier
      is included in the request)

      The client-specified identifier in the corresponding request.

4.3.4.  JMAP Request-Level Errors

   The specification extends the Problem Details object for request-
   level errors (see Section 3.6.1 of [RFC8620]) with two additional
   arguments when used over a WebSocket:

   *  @type: "String"

      This MUST be the string "RequestError".

   *  requestId: "String" (optional; MUST be returned if given in the
      request)

      The client-specified identifier in the corresponding request.

4.3.5.  JMAP Push Notifications

   JMAP-over-WebSocket servers that support push notifications on the
   WebSocket will advertise a "supportsPush" property with a value of
   true in the "urn:ietf:params:jmap:websocket" server capabilities
   object.

4.3.5.1.  Notification Format

   All push notifications take the form of a standard StateChange object
   (see Section 7.1 of [RFC8620]).

   The specification extends the StateChange object with one additional
   argument when used over a WebSocket:

   *  pushState: "String" (optional)

      A (preferably short) string that encodes the entire server state
      visible to the user (not just the objects returned in this call).

      The purpose of the "pushState" token is to allow a client to
      immediately get any changes that occurred while it was
      disconnected (see Section 4.3.5.2).  If the server does not
      support "pushState" tokens, the client will have to issue a series
      of "/changes" requests (see Section 5.2 of [RFC8620]) upon
      reconnection to update its state to match that of the server.

4.3.5.2.  Enabling Notifications

   A client enables push notifications from the server for the current
   connection by sending a WebSocketPushEnable object to the server.  A
   WebSocketPushEnable object has the following properties:

   *  @type: "String"

      This MUST be the string "WebSocketPushEnable".

   *  dataTypes: "String[]|null"

      A list of data type names (e.g., "Mailbox" or "Email") that the
      client is interested in.  A StateChange notification will only be
      sent if the data for one of these types changes.  Other types are
      omitted from the TypeState object.  If null, changes will be
      pushed for all supported data types.

   *  pushState: "String" (optional)

      The last "pushState" token that the client received from the
      server.  Upon receipt of a "pushState" token, the server SHOULD
      immediately send all changes since that state token.

4.3.5.3.  Disabling Notifications

   A client disables push notifications from the server for the current
   connection by sending a WebSocketPushDisable object to the server.  A
   WebSocketPushDisable object has the following property:

   *  @type: "String"

      This MUST be the string "WebSocketPushDisable".

4.4.  Examples

   The following examples show WebSocket JMAP opening handshakes, a JMAP
   Core/echo request and response, and a subsequent closing handshake.
   The examples assume that the JMAP WebSocket URL endpoint has been
   advertised in the JMAP Session object as having a path of "/jmap/ws/"
   and that TLS negotiation has already succeeded.  Note that folding of
   header fields is for editorial purposes only.

   WebSocket JMAP connection via HTTP/1.1 with push notifications for
   mail [RFC8621] is enabled.  This example assumes that the client has
   cached pushState "aaa" from a previous connection.

   [[ From Client ]]                [[ From Server ]]

   GET /jmap/ws/ HTTP/1.1
   Host: server.example.com
   Upgrade: websocket
   Connection: Upgrade
   Authorization: Basic Zm9vOmJhcg==
   Sec-WebSocket-Key:
     dGhlIHNhbXBsZSBub25jZQ==
   Sec-WebSocket-Protocol: jmap
   Sec-WebSocket-Version: 13
   Origin: https://www.example.com

                                    HTTP/1.1 101 Switching Protocols
                                    Upgrade: websocket
                                    Connection: Upgrade
                                    Sec-WebSocket-Accept:
                                      s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
                                    Sec-WebSocket-Protocol: jmap

   [WebSocket connection established]

   WS_DATA
   {
     "@type": "WebSocketPushEnable",
     "dataTypes": [ "Mailbox", "Email" ],
     "pushState": "aaa"
   }

                                    WS_DATA
                                    {
                                      "@type": "StateChange",
                                      "changed": {
                                        "a456": {
                                          "Mailbox": "d35ecb040aab"
                                        }
                                      },
                                      "pushState": "bbb"
                                    }

   WS_DATA
   {
     "@type": "Request",
     "id": "R1",
     "using": [ "urn:ietf:params:jmap:core" ],
     "methodCalls": [
       [
         "Core/echo", {
           "hello": true,
           "high": 5
         },
         "b3ff"
       ]
     ]
   }

                                    WS_DATA
                                    {
                                      "@type": "Response",
                                      "requestId": "R1",
                                      "methodResponses": [
                                        [
                                          "Core/echo", {
                                            "hello": true,
                                            "high": 5
                                          },
                                          "b3ff"
                                        ]
                                      ]
                                    }

   WS_DATA
   The quick brown fox jumps
    over the lazy dog.

                                    WS_DATA
                                    {
                                      "@type": "RequestError",
                                      "requestId": null,
                                      "type":
                                "urn:ietf:params:jmap:error:notJSON",
                                      "status": 400,
                                      "detail":
                                "The request did not parse as I-JSON."
                                    }

   [A new email is received]

                                    WS_DATA
                                    {
                                      "@type": "StateChange",
                                      "changed": {
                                        "a123": {
                                          "Email": "0af7a512ce70"
                                        }
                                      }
                                      "pushState": "ccc"
                                    }

   WS_CLOSE

                                    WS_CLOSE

   [WebSocket connection closed]

   WebSocket JMAP connection on an HTTP/2 stream that also negotiates
   compression [RFC7692]:

   [[ From Client ]]                [[ From Server ]]

                                    SETTINGS
                                    SETTINGS_ENABLE_CONNECT_PROTOCOL = 1

   HEADERS + END_HEADERS
   :method = CONNECT
   :protocol = websocket
   :scheme = https
   :path = /jmap/ws/
   :authority = server.example.com
   origin: https://example.com
   authorization = Basic Zm9vOmJhcg==
   sec-websocket-protocol = jmap
   sec-websocket-version = 13
   sec-websocket-extensions =
     permessage-deflate
   origin = https://www.example.com

                                    HEADERS + END_HEADERS
                                    :status = 200
                                    sec-websocket-protocol = jmap
                                    sec-websocket-extensions =
                                      permessage-deflate

   [WebSocket connection established]

   DATA
   WS_DATA
   [compressed text]

                                    DATA
                                    WS_DATA
                                    [compressed text]

   ...

   DATA + END_STREAM
   WS_CLOSE

                                    DATA + END_STREAM
                                    WS_CLOSE

   [WebSocket connection closed]
   [HTTP/2 stream closed]

5.  Security Considerations

   The security considerations for both WebSocket (see Section 10 of
   [RFC6455]) and JMAP (see Section 8 of [RFC8620]) apply to the
   WebSocket JMAP subprotocol.  Specific security considerations are
   described below.

5.1.  Connection Confidentiality and Integrity

   To ensure the confidentiality and integrity of data sent and received
   via JMAP over WebSocket, the WebSocket connection MUST use TLS 1.2
   [RFC5246] or later, following the recommendations in BCP 195
   [RFC7525].  Servers SHOULD support TLS 1.3 [RFC8446] or later.

5.2.  Non-browser Clients

   JMAP over WebSocket can be used by clients both running inside and
   outside of a web browser.  As such, the security considerations in
   Sections 10.2 and 10.1 of [RFC6455] apply to those respective
   environments.

6.  IANA Considerations

6.1.  Registration of the WebSocket JMAP Subprotocol

   Per this specification, IANA has registered the following in the
   "WebSocket Subprotocol Name Registry" within the "WebSocket Protocol
   Registries".

   Subprotocol Identifier:  jmap

   Subprotocol Common Name:  WebSocket Transport for JMAP (JSON Meta
      Application Protocol)

   Subprotocol Definition:  RFC 8887

7.  References

7.1.  Normative References

   [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>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [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>.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, DOI 10.17487/RFC6455, December 2011,
              <https://www.rfc-editor.org/info/rfc6455>.

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,
              <https://www.rfc-editor.org/info/rfc7235>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [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>.

   [RFC7692]  Yoshino, T., "Compression Extensions for WebSocket",
              RFC 7692, DOI 10.17487/RFC7692, December 2015,
              <https://www.rfc-editor.org/info/rfc7692>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8441]  McManus, P., "Bootstrapping WebSockets with HTTP/2",
              RFC 8441, DOI 10.17487/RFC8441, September 2018,
              <https://www.rfc-editor.org/info/rfc8441>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8620]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July
              2019, <https://www.rfc-editor.org/info/rfc8620>.

7.2.  Informative References

   [RFC8621]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621,
              August 2019, <https://www.rfc-editor.org/info/rfc8621>.

Acknowledgments

   The author would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Neil Jenkins, Robert Mueller, and Chris Newman.

Author's Address

   Kenneth Murchison
   Fastmail US LLC
   1429 Walnut Street, Suite 1201
   Philadelphia, PA 19102
   United States of America

   Email: murch@fastmailteam.com
   URI:   http://www.fastmail.com/