Comment 1 by ledangster:

If your handler uses *websocket.Conn directly then you directly change PayloadType
(since it's publicly modifiable) to websocket.BinaryFrame before writing out the
frame(s):
 conn.PayloadType = websocket.BinaryFrame
 ...
 conn.Write(...)

Comment 2 by errordeveloper:

That worked, pardon for newbie bug report. Perhaps I could suggest it needs
to be a little more clear in the docs.

Comment 3:

Labels changed: added repo-net.

PayloadType is an exported field. It should be documented.

Also, Write should probably mention that it uses the value of PayloadType. Its documentation currently says nothing about that.

We no longer maintain x/net/websocket. @dmitshur and @ledangster, there was a suggestion for that documentation update but we instead recommend alternatives:

• https://godoc.org/github.com/gorilla/websocket
• https://godoc.org/nhooyr.io/websocket
  So I am not sure if we can do much here. I am going to close this issue, but please feel free to reopen. Thank you.

We no longer maintain x/net/websocket.

Do you have a reference for that? I'm asking because I don't know.

This is not to suggest that this package is maintained actively or in an exemplary manner, but as far as I can see, #18152 is still in open state with NeedsDecision state, which suggests to me it's still under maintenance.

I don't see a benefit in closing this issue (and not the 12 other open issues with "x/net/websocket:" prefix) until there's some sort of resolution to #18152, given that this issue properly titled/labeled and it is tracking a valid problem in the golang.org/x/net/websocket package that hasn't been resolved yet.

Do you have a reference for that? I'm asking because I don't know.

Basically #18152 (comment).

It may not be worded explicitly, but it effectively means that.

Also: golang/net@97edce0

// This package currently lacks some features found in an alternative
// and more actively maintained WebSocket package:
//
// https://godoc.org/github.com/gorilla/websocket
//

Stress on "more actively maintained". Which indirectly means, this is not well-maintained.

AFAIU, #18152 is about doing something about the fact that it's unmaintained, by merging with gorilla/websocket or something else. But it is clear that the repo in its current state is unmaintained, and users are encouraged to look somewhere else.

Thank you for digging up the references @agnivade, and for helping me answer Dmitri’s question.