x/net/websocket: Read/Copy fail with long frames

[gopherbot]

by nroos@webware-experts.de:

When using io.Copy() with a websocket as source, this fails if incoming websocket frames
are too large.

The reason is because io.Copy() uses a buffer with a default size for the Read().
websocket.Read() in turn uses bufio.ReadSlice() to read the current frame up to the
final 0xff. But if the incoming websocket frame size exceeds the buffer size of
io.Copy(), a ErrBufferFull ("bufio: buffer full") is generated.

The websocket specification does not limit the size of a frame, so this behaviour is
somewhat undesirable, as the success of a io.Copy() depends on the size of internal
buffers and the undeterminable websocket frame size.

What steps will reproduce the problem?

1. One process needs to open a websocket connection to a Go websocket server (pseudo
code, obviously):

   ws := websocket.Dial("127.0.0.1:80")
   buf := make([]byte, 100000)
   ws.Write(buf)

2. Websocket server:

   ws := accepted websocket.Conn
   writer := io.Writer
   err := io.Copy(writer, ws)

What is the expected output?

   err == nil

What do you see instead?

   err == bufio.ErrBufferFull

Which revision are you using?  (hg identify)

   1b38d90eebcd+ (release-branch.r58) tip

   (patches applied at other locations)

[gopherbot]

Comment 1 by nroos@webware-experts.de:

The websocket.Read() does not work either (with long websocket frames). This means i
can't even do a "manual" copy with a sufficient large buffer.

[rsc]

Comment 2:

we're still discussing what the right websocket api is.

Owner changed to @rsc.

Status changed to Accepted.

[rsc]

Comment 3:

Labels changed: added priority-later.

[rsc]

Comment 5:

[The time for maybe has passed.]

[rsc]

Comment 7:

Labels changed: added go1.3maybe.

[rsc]

Comment 8:

Labels changed: added release-none, removed go1.3maybe.

[rsc]

Comment 9:

Labels changed: added repo-net.

[odeke-em]

So we retired x/net/websocket with an advisory https://pkg.go.dev/golang.org/x/net/websocket?tab=doc to instead use

• https://godoc.org/github.com/gorilla/websocket
• https://godoc.org/nhooyr.io/websocket

And thus I shall close this issue.