Re: [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