SETTINGS_ENABLE_WEBSOCKETS settings parameter for HTTP/2 and HTTP/3

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Table of Contents

1. Introduction

The mechanisms for running the WebSocket protocol [RFC6455] over a single stream of an HTTP/2 and HTTP/3 connection is defined in [RFC8441] and [RFC9220]. The extended CONNECT mechanism is used for bootstrapping WebSockets from HTTP/2 and HTTP/3. Support for the extended CONNECT mechanism is advertised using HTTP/2 and HTTP/3 settings parameter SETTINGS_ENABLE_CONNECT_PROTOCOL.¶

However, the support of extended CONNECT does not necessarily indicate support for WebSockets over that HTTP connection. Other protocols such as [WEBTRANSPORT] also use extended CONNECT and send SETTINGS_ENABLE_CONNECT_PROTOCOL settings parameters as well.¶

Suppose the server supports extended CONNECT but not bootstrapping WebSockets over that HTTP connection. In this case, the client sending a WebSocket handshake request will result in a response of 501 (Not Implemented) status code (Section 15.6.2 of [HTTP]), and the client would need to fall back to trying the WebSocket handshake over HTTP/1.¶

This is why a SETTINGS_ENABLE_WEBSOCKETS settings parameter is needed.¶

2. SETTINGS_ENABLE_WEBSOCKETS settigs parameter for H2 and H3

This document adds a new SETTINGS parameter to those defined by [HTTP/3] Section 11.2.2 and [HTTP/2] Section 11.3.¶

The new parameter name is SETTINGS_ENABLE_WEBSOCKETS. The value of the parameter MUST be 0 or 1, with 0 being the default.¶

A sender MUST NOT send a SETTINGS_ENABLE_WEBSOCKETS parameter with the value of 0 after previously sending a value of 1.¶

If the server supports bootstrapping WebSockets over the HTTP connection, it SHOULD include the SETTINGS_ENABLE_WEBSOCKETS parameter in the SETTINGS frame with a value of 1. If the server does not support bootstrapping WebSockets over the HTTP connection it SHOULD send the parameter with a value of 0.¶

A client MUST not send this setting parameter. Receipt of this parameter by a server does not have any impact.¶

The SETTINGS_ENABLE_WEBSOCKETS parameter would allow the client to determine in advance whether the server supports WebSockets over the connection for HTTP/2 or HTTP/3. This allows the client to avoid sending unnecessary WebSocket handshake requests on HTTP connections that do not support WebSockets.¶

This mechanism will improve compatibility with other extended CONNECT-based protocols.¶

For compatibility with past implementations which do not use this parameter, clients MAY initiate a WebSocket request without the receipt of this parameter.¶

3. Security Considerations

This document introduces no new security considerations beyond those discussed in [RFC8441].¶

4. IANA Considerations

Acknowledgments

TODO acknowledge people.¶

Thank you for reading this draft. :)¶

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