Re: [Libguestfs] Provide NBD via Browser over Websockets

["Richard W.M. Jones" <rjones@redhat.com>]

On Fri, May 29, 2020 at 08:58:06AM -0500, Eric Blake wrote:
> 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

I guess the idea is to have a zero-install solution for the browser.
As I said in the email earlier this is very common for IPMI-type
remote access to blade servers and in my experience is implemented
using a Java applet and a proprietary protocol terminated at the BMC
(which then emulates a virtual CDROM to the server).  There are some
HP blade servers on Red Hat's internal Beaker instance where you can
play with this.  For qemu we wouldn't need to invent a new protocol
when NBD is available and already implemented (albeit not yet on top
of WebSockets).

The NBD server must run inside the browser and therefore be either
written from scratch in Javascript, or an existing server
cross-compiled to WASM (if that is possible - I don't really know).

> 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).

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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