Fastmail US LLC

1429 Walnut Street, Suite 1201 Philadelphia PA 19102 United States of America murch@fastmailteam.com http://www.fastmail.com/

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.

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 .

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 Provisions Relating to IETF Documents () 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

• .  Introduction
• .  Conventions Used in This Document
• .  Discovering Support for JMAP over WebSocket
• .  JMAP Subprotocol
  • .  Authentication
  • .  Handshake
  • .  WebSocket Messages
    • .  Handling Invalid Data
    • .  JMAP Requests
    • .  JMAP Responses
    • .  JMAP Request-Level Errors
    • .  JMAP Push Notifications
  • .  Examples
• .  Security Considerations
  • .  Connection Confidentiality and Integrity
  • .  Non-browser Clients
• .  IANA Considerations
  • .  Registration of the WebSocket JMAP Subprotocol
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgments
• Author's Address

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

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. [[ 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: [[ 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]

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 In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo describes how to use Transport Layer Security (TLS) to secure Hypertext Transfer Protocol (HTTP) connections over the Internet. This memo provides information for the Internet community. This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] The WebSocket Protocol enables two-way communication between a client running untrusted code in a controlled environment to a remote host that has opted-in to communications from that code. The security model used for this is the origin-based security model commonly used by web browsers. The protocol consists of an opening handshake followed by basic message framing, layered over TCP. The goal of this technology is to provide a mechanism for browser-based applications that need two-way communication with servers that does not rely on opening multiple HTTP connections (e.g., using XMLHttpRequest or <iframe>s and long polling). [STANDARDS-TRACK] The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypermedia information systems. This document defines the HTTP Authentication framework. Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are widely used to protect data exchanged over application protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the last few years, several serious attacks on TLS have emerged, including attacks on its most commonly used cipher suites and their modes of operation. This document provides recommendations for improving the security of deployed services that use TLS and DTLS. The recommendations are applicable to the majority of use cases. This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent exchanges on the same connection. It also introduces unsolicited push of representations from servers to clients. This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged. This document defines a framework for creating WebSocket extensions that add compression functionality to the WebSocket Protocol. An extension based on this framework compresses the payload data portion of WebSocket data messages on a per-message basis using parameters negotiated during the opening handshake. This framework provides a general method for applying a compression algorithm to the contents of WebSocket messages. Each compression algorithm has to be defined in a document defining the extension by specifying the parameter negotiation and the payload transformation algorithm in detail. This document also specifies one specific compression extension using the DEFLATE algorithm. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document defines a mechanism for running the WebSocket Protocol (RFC 6455) over a single stream of an HTTP/2 connection. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document specifies a protocol for clients to efficiently query, fetch, and modify JSON-based data objects, with support for push notification of changes and fast resynchronisation and for out-of- band binary data upload/download. Informative References This document specifies a data model for synchronising email data with a server using the JSON Meta Application Protocol (JMAP). Clients can use this to efficiently search, access, organise, and send messages, and to get push notifications for fast resynchronisation when new messages are delivered or a change is made in another client.

Acknowledgments The author would like to thank the following individuals for contributing their ideas and support for writing this specification: , , and .

Author's Address Fastmail US LLC

1429 Walnut Street, Suite 1201 Philadelphia PA 19102 United States of America murch@fastmailteam.com http://www.fastmail.com/