JMAP K. Murchison
Internet-Draft FastMail
Intended status: Standards Track March 10, 2019
Expires: September 11, 2019

A JSON Meta Application Protocol (JMAP) Subprotocol for WebSocket
draft-ietf-jmap-websocket-01

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.

Open Issues

Status of This Memo

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This Internet-Draft will expire on September 11, 2019.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Introduction

JMAP over HTTP 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, authenticating every JMAP API request may harm performance.

The WebSocket 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 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.

The same terminology is used in this document as in the core JMAP specification.

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 [I-D.ietf-jmap-core]). 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 which MUST contain the following information on server capabilities:

wsUrl:
"String" The URL to use for initiating a JMAP over WebSocket handshake.

Server support for push notifications over the WebSocket is OPTIONAL. A server advertises that it supports push notifications by returning the "wsURL" property in URI Template (level 3) format containing the variable "{?types}". The use of this variable is described in Section 4.2.4.

Example:

"urn:ietf:params:jmap:websocket": {
  "wsUrl": "/jmap/ws/{?types}"
}

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 MUST NOT be uploaded or downloaded through a WebSocket JMAP connection. Binary data is handled per Section 6 of [I-D.ietf-jmap-core]) via a separate HTTP connection or stream.

4.1. Handshake

The JMAP WebSocket client and JMAP WebSocket server negotiate the use of the WebSocket JMAP subprotocol during the WebSocket handshake, either via a HTTP/1.1 Upgrade request (see Section 1.3 of [RFC6455]) or a HTTP/2 Extended CONNECT request (see Section 5 of [RFC8441]).

Regardless of the method used for the WebSocket handshake, the client MUST make an authenticated HTTP request on the JMAP "wsURL", and the client 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 'jmap' in its corresponding 'Sec-WebSocket-Protocol' header field in order for a JMAP subprotocol connection to be established.

If a client receives a handshake response that does not include 'jmap' in the 'Sec-WebSocket-Protocol' header, then a JMAP subprotocol WebSocket connection was not established and the client MUST close the WebSocket connection.

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.

4.2. WebSocket Messages

Data frame messages in the JMAP subprotocol MUST be of the text type and contain UTF-8 encoded data. The messages MUST be in the form of a single JMAP Request object (see Section 3.2 of [I-D.ietf-jmap-core]) when sent from the client to the server, and in the form of a single JMAP Response object, JSON Problem Details object, or JMAP StateChange object (see Sections 3.3, 3.5.1, and 7.1 respectively of [I-D.ietf-jmap-core]) when sent from the server to the client.

4.2.1. JMAP Requests

JMAP over WebSocket allows out of order processing of requests, thereby requiring a mechanism for the client to correlate requests and responses. To this end, this specification adds one extra argument to the request object:

id:
"String" (default: ) A client-specified identifier for the request.

Additionally, the "maxConcurrentRequests" field in the "capabilities" object (see Section 2 of [I-D.ietf-jmap-core]) limits the number of inflight requests over the WebSocket.

4.2.2. JMAP Responses

This specification adds two extra arguments to the Response object:

@type:
"String" This MUST be the string "Response".
requestId:
"String|null" The client-specified identifier in the corresponding request. If "null", no identifier was provided in the request.

4.2.3. JMAP Request-level Errors

This specification adds two extra arguments to the Problem Details object:

@type:
"String" This MUST be the string "RequestError".
requestId:
"String|null" The client-specified identifier in the corresponding request. If "null", no identifier was provided in the request.

4.2.4. JMAP Push Notifications

JMAP over WebSocket servers that support push notifications on the WebSocket will advertise a "wsURL" property in URI Template (level 3) format containing the variable "{?types}".

A client enables push notifications on the server as part of the authenticated HTTP request that initiates the WebSocket handshake by substituting the appropriate variables:

types:
This MUST be either:

All push notifications take the form of a standard StateChange object (see Section 7.1 of [I-D.ietf-jmap-core]).

4.3. 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 "wsURL" has been advertised in the JMAP Session object as "/jmap/ws/{?types}". Note that folding of header fields is for editorial purposes only.

WebSocket JMAP connection via HTTP/1.1 with push notifications enabled:

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

GET /jmap/ws/?types=Email,Mailbox 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: http://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
{
  "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."
                                   }

                                   WS_DATA
                                   {
                                     "@type": "StateChange",
                                     "changed": {
                                       "a123": {
                                         "Mailbox": "0af7a512ce70",
                                       }
                                     }
                                   }

WS_CLOSE

                                   WS_CLOSE

[WebSocket connection closed]

WebSocket JMAP connection on a HTTP/2 stream which also negotiates compression:

[[ 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
authorization = Basic Zm9vOmJhcg==
sec-websocket-protocol = jmap
sec-websocket-version = 13
sec-websocket-extensions =
  permessage-deflate
origin = http://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 [I-D.ietf-jmap-core]) apply to the WebSocket JMAP subprotocol.

6. IANA Considerations

6.1. Registration of the WebSocket JMAP Subprotocol

This specification requests IANA to register the WebSocket JMAP subprotocol under the "WebSocket Subprotocol Name" Registry with the following data:

Subprotocol Identifier:
JMAP
Subprotocol Common Name:
WebSocket Transport for JMAP (JSON Meta Application Protocol)
Subprotocol Definition:
RFCXXXX (this document)

7. 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.

8. References

8.1. Normative References

[I-D.ietf-jmap-core] Jenkins, N. and C. Newman, "JSON Meta Application Protocol", Internet-Draft draft-ietf-jmap-core-14, January 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC 6455, DOI 10.17487/RFC6455, December 2011.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M. and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/RFC6570, March 2012.
[RFC7235] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, DOI 10.17487/RFC7235, June 2014.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2", RFC 8441, DOI 10.17487/RFC8441, September 2018.

8.2. Informative References

[I-D.ietf-jmap-mail] Jenkins, N. and C. Newman, "JMAP for Mail", Internet-Draft draft-ietf-jmap-mail-15, February 2019.
[RFC7692] Yoshino, T., "Compression Extensions for WebSocket", RFC 7692, DOI 10.17487/RFC7692, December 2015.

Appendix A. Change History (To be removed by RFC Editor before publication)

Changes since ietf-00:

Changes since murchison-02:

Changes since murchison-01:

Changes since murchison-00:

Author's Address

Kenneth Murchison FastMail US LLC 1429 Walnut Street - Suite 1201 Philadelphia, PA 19102 USA EMail: murch@fastmailteam.com URI: http://www.fastmail.com/