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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 © 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must 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.  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/