[Bug 1849644] Re: QEMU VNC websocket proxy requires non-standard 'binary' subprotocol

[Daniel Berrange]

It isn't mandatory to use a standardized subprotocol, all that's
required is that the client & server agree

  https://developer.mozilla.org/en-
US/docs/Web/HTTP/Protocol_upgrade_mechanism

  "The subprotocols may be selected from the IANA WebSocket Subprotocol
Name Registry or may be a custom name jointly understood by the client
and the server."

QEMU used/required 'binary' because that is what noVNC used when the
QEMU websockets code was first implemented.

It appears that noVNC was changed though to not send a "binary"
subprotocol in

  commit f8318361b1b62c4d76b091132d4a8ccfdd2957e4
  Author: Pierre Ossman <address@hidden>
  Date:   Sat Oct 14 12:45:56 2017 +0200

    Remove wsProtocols setting
    
    It isn't in use anymore since we deprecated support for Base64 mode.

>From QEMU's POV looks like we'll need to tweak code to treat 'binary'
and no sub-protocol as being equivalent.

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https://bugs.launchpad.net/bugs/1849644

Title:
  QEMU VNC websocket proxy requires non-standard 'binary' subprotocol

Status in QEMU:
  New

Bug description:
  When running a machine using "-vnc" and the "websocket" option QEMU
  seems to require the subprotocol called 'binary'. This subprotocol
  does not exist in the WebSocket specification. In fact it has never
  existed in the spec, in one of the very early drafts of WebSockets it
  was briefly mentioned but it never made it to a final version.

  When the WebSocket server requires a non-standard subprotocol any
  WebSocket client that works correctly won't be able to connect.

  One example of such a client is noVNC, it tells the server that it
  doesn't want to use any subprotocol. QEMU's WebSocket proxy doesn't
  let noVNC connect. If noVNC is modified to ask for 'binary' it will
  work, this is, however, incorrect behavior.

  Looking at the code in "io/channel-websock.c" it seems it's quite
  hard-coded to binary:

  Look at line 58 and 433 here:
  https://git.qemu.org/?p=qemu.git;a=blob;f=io/channel-websock.c

  This code has to be made more dynamic, and shouldn't require binary.

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