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joffrey-bion / krossbow

A Kotlin multiplatform coroutine-based STOMP client over websockets, with built-in conversions.
MIT License
205 stars 16 forks source link

Support selecting web socket subprotocols (`Sec-WebSocket-Protocol` header) #493

Closed joffrey-bion closed 6 months ago

joffrey-bion commented 6 months ago

Unlike general custom headers, which are not supported in browsers and SockJS, the Sec-WebSocket-Protocol header is supported in every client implementation. This header allows to send a list of web socket subprotocols that the client wants to speak over the web socket. This is useful, but also sometimes necessary in some servers (see issue https://github.com/joffrey-bion/krossbow/issues/497 for more details).

Currently, though, Krossbow forbids any header in the browser and SockJS clients, even though the subprotocols list is technically supported in both.

Also, the subprotocol cannot be set via its header name in the JDK11 client implementation, it has to use a particular API, so we should treat it as a special case.

The Ktor and OkHttp clients do not have a special API for it, but it would still be worth providing protocols separately in the WebSocketClient.connect() function.

The Spring client has a special syntax sugar to set this specific header.

joffrey-bion commented 6 months ago

Labeled "breaking" because usages of connect() with custom headers and without named parameters will break at compile time in the new version.