A JSON Meta Application Protocol (JMAP) Subprotocol for WebSocket
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ART
JMAP
jmap
websocket
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.
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, reauthenticating for 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.
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
when, and only when, they appear in all capitals, as shown here.
This document uses the terminology defined in the core JMAP
specification .
Discovering Support for JMAP over WebSocket
The JMAP capabilities object is returned as part of the
standard JMAP Session object (see
).
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 ) 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 .
Example:
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 (via a separate HTTP connection or stream)
or per a future extension to JMAP or this specification.
Authentication
A JMAP WebSocket connection is authenticated by presenting
a user's credentials in the
HTTP request that initiates the WebSocket handshake.
See for
recommendations regarding the selection of HTTP authentication
schemes.
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 )
or an HTTP/2 Extended CONNECT request (see
).
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
having the "wss://" scheme (WebSocket over TLS) in
accordance with the requirements of running the particular
binding of HTTP over TLS (see
and for HTTP/1.1
and for HTTP/2).
If the TLS handshake fails, the client MUST close the
connection. Otherwise, the client MUST make an
authenticated HTTP request
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
.
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
),
JMAP WebSocketPushEnable object (see ),
or JMAP WebSocketPushDisable object (see )
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 , , and of ,
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.
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
.
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 .
A server MUST return an appropriate
JSON Problem Details object
for any request-level errors
(e.g., an invalid JMAP object, an unsupported capability or
method call, or exceeding a server request limit).
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 ) 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.
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.
JMAP Request-Level Errors
The specification extends the Problem Details object
for request-level errors (see ) 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.
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.
Notification Format
All push notifications take the form of a standard
StateChange object (see ).
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 ). If the server does not support
"pushState" tokens, the client will have to issue a series of
"/changes" requests (see ) upon reconnection to
update its state to match that of the server.
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.
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".
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
is enabled. This example assumes that the client has cached
pushState "aaa" from a previous connection.
WebSocket JMAP connection on an HTTP/2 stream that also
negotiates compression:
Security Considerations
The security considerations for both WebSocket (see ) and JMAP (see ) apply to the
WebSocket JMAP subprotocol. Specific security considerations are
described below.
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
or later, following the recommendations in BCP 195.
Servers SHOULD support TLS 1.3 or
later.
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 and of
apply to those respective environments.
IANA Considerations
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
References
Normative References
Informative References
Acknowledgments
The author would like to thank the following individuals for
contributing their ideas and support for writing this
specification: , , and .