Websocket: [question] why are 'Sec-WebSocket-Extensions' headers not supported by upgrader.

[IngCr3at1on]

I misunderstood your original question @marti1125, now that I understand you were asking a related but still slightly separate question I've created a new issue for this using the 'reference in new issue' function.

Original comment is as follows:

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I am trying to understand subprotocols using client/server example

I just modify https://github.com/gorilla/websocket/blob/master/examples/echo/server.go#L23

c, err := upgrader.Upgrade(w, r, r.Header)

in the terminal show upgrade:websocket: application specific 'Sec-WebSocket-Extensions' headers are unsupported

_Originally posted by @marti1125 in https://github.com/gorilla/websocket/issues/404#issuecomment-531591181_

[IngCr3at1on]

As noted in the OP I moved this over from the original issue to keep that issue on task. To answer the question itself; I believe (after a bit of reading) that this is really just related to the included (experimental) implementation of RFC7692.

To that end have a look at https://godoc.org/github.com/gorilla/websocket#hdr-Compression_EXPERIMENTAL
You should be able to enable compression via boolean there, rather than attaching the header yourself.

[nhooyr]

@elithrar This issue has been resolved and can be closed.

[9tech7]

@nhooyr may I know in which version has been solved?
I'm using v1.4.2 and when I pass the r.Header I get the same error as @IngCr3at1on mentioned

conn, err := upgrader.Upgrade(w, r, r.Header)

websocket: application specific 'Sec-WebSocket-Extensions' headers are unsupported

[nhooyr]

websocket: application specific 'Sec-WebSocket-Extensions' headers are unsupported

So this header error means you're setting Sec-WebSocket-Extensions before calling Upgrade. You just need to stop doing that as you cannot use a custom extension (one that isn't RFC 7692 compression).

[9tech7]

You just need to stop doing that

stop passing r.Header in the Upgrade() do you mean?

thanks for the reference link. I can see

1. Extension Negotiation
   To offer use of a PMCE, a client MUST include the extension name of
   the PMCE in the "Sec-WebSocket-Extensions" header field of its
   opening handshake of the WebSocket connection.

so not sure when you said

you cannot use a custom extension

This is what I get as a response and the request on the browser. if I pass r.Header to the Upgrade().

---

btw, I'm using the gorilla chat example for the client-side exactly and no changes on its js code. on the other hand on the server, I'm not sending any custom or manual header as a response to the client's request.

So to avoid this error in order to just get the result I can validate the origin manually which I don't this this is the production level / proper solution!

var Upgrader = websocket.Upgrader{
    ReadBufferSize:  1024,
    WriteBufferSize: 1024,

    CheckOrigin: func(r *http.Request) bool {
        if r.Header.Get("Origin") == "http://localhost:9090" {  // <=====
            return true
        }
        return false
    },
}                                                             

May I ask what is proper / production level the solution?

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Also, in the example, I can see they pass nil as the responseHeader. so if we need to pass nil, why the function has the responseHeader parameter?

func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header) (*Conn, error)

[nhooyr]

I think you're confused on what responseHeader is for. Please see the docs on Upgrade and inspect its source code.