[Libguestfs] Provide NBD via Browser over Websockets

[Eric Blake]

On 5/29/20 8:50 AM, Daniel P. Berrangé wrote:

>>> (2) You need to persuade qemu's NBD client to read from a WebSocket.
>>> I didn't really know anything about WebSockets until today but it
>>> seems as if they are a full-duplex protocol layered on top of HTTP [a].
>>> Is there a WebSocket proxy that turns WS into plain TCP (a bit like
>>> stunnel)?  Google suggests [b].
>>>
>>> [a] https://en.wikipedia.org/wiki/WebSocket#Protocol_handshake
>>> [b] https://github.com/novnc/websockify
>>
>> qemu already knows how to connect as a client to websockets; Dan Berrange
>> knows more about that setup.  I suspect it would not be too difficult to
>> teach the qemu NBD client code to use a WebSocket instead of a Unix or TCP
>> socket as its data source.
> 
> Actually the inverse. The QIOChannelWebsocket impl is only the server
> side of the problem, as used by QEMU's VNC server. We've never implemented
> the client side. There is nothing especially stopping us doing that - just
> needs someone motivated with time to work on it.

In the meantime, you may still be able to set up something like:

local machine:
iso -> NBD server -> Unix socket -> websockify -> WebSocket

remote machine:
WebSocket -> websockify -> Unix socket -> qemu NBD client

Adding websocket client support into qemu would reduce the length of the 
chain slightly (for less data copying) by getting rid of a websockify 
proxy middleman, but would not necessarily improve performance (it's 
hard to say where the latency bottlenecks will be in the chain).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org