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

[Christian Ehrhardt ]

Trying to connect using
novnc   latest/stable:    1.2.0      2020-07-31 (6) 18MB -

as-is failing to connect
Keeping VNC up and refreshing qemu.


Updating to the new qemu from focal proposed (by now resolved the archive 
publishing issues we had before this morning).
Get:67 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 qemu-utils 
amd64 1:4.2-3ubuntu6.7 [975 kB]                                                 
                                 
Get:68 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 
qemu-system-common amd64 1:4.2-3ubuntu6.7 [1056 kB]                             
                                            
Get:69 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 
qemu-block-extra amd64 1:4.2-3ubuntu6.7 [53.8 kB]                               
                                            
Get:70 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 
qemu-system-data all 1:4.2-3ubuntu6.7 [563 kB]                                  
                                            
Get:71 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 qemu-kvm 
amd64 1:4.2-3ubuntu6.7 [13.1 kB]                                                
                                   
Get:72 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 
qemu-system-x86 amd64 1:4.2-3ubuntu6.7 [6720 kB]                                
                                            
Get:73 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 
qemu-system-gui amd64 1:4.2-3ubuntu6.7 [40.8 kB]                                
                                            
Get:74 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 
qemu-system-mips amd64 1:4.2-3ubuntu6.7 [12.9 MB]


Now the same novnc1.2 can connect to it \o/
Setting verified

** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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

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

Status in QEMU:
  Fix Released
Status in qemu package in Ubuntu:
  Fix Released
Status in qemu source package in Focal:
  Fix Committed

Bug description:
  [Impact]

   * The exact details of the protocol/subprotocal was slightly unclear
     between the projects. So qemu ended up insisting on "binary" being
     used but newer noVNC clients no more used it.

   * Qemu got fixed in 5.0 to be more tolerant and accept an empty sub-
     protocol as well. This SRU backports that fix to Focal.

  [Test Case]

   * Without the fix the following will "Failed to connect", but with
  the fix it will work.

  $ sudo apt install qemu-system-x86
  # will only boot into a failing bootloader, but that is enough
  $ qemu-system-x86_64 -vnc :0,websocket
  # We need version 1.2 or later, so use the snap
  $ snap install novnc
  $ novnc --vnc localhost:5700
  Connect browser to http://<IP>:6080/vnc.html
  Click "Connect"

   * Cross check with an older noVNC (e.g. the one in Focal) if the 
     connectivity still works on those as well

     - Reminders when switching between the noVNC implementations
       - always refresh the browser with all clear ctrl+alt+f5
       - start/stop the snapped one via snap.novnc.novncsvc.service

  [Regression Potential]

   * This is exclusive to the functionality of noVNC, so regressions would 
     have to be expected in there. The tests try to exercise the basics, but
     e.g. Openstack would be a major product using 

  [Other Info]
   
   * The noVNC in Focal itself does not yet have the offending change, but
     we want the qemu in focal to be connecteable from ~any type of client


  ---


  
  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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