[Twisted-Python] Tunneling using conch (with application.service)

[Sean Hollingsworth]

Your advice helped considerably. Thank  you.

Sean M Hollingsworth

On Sat, Aug 8, 2009 at 4:49 PM, <exarkun at twistedmatrix.com> wrote:

> On 6 Aug, 03:47 pm, smhollingsworth at gmail.com wrote:
> >I 19ve got an app written that runs as a service using
> >twisted.application.service that I need to tunnel through SSH. Right
> >now, I
> >use a script that makes use of Paramiko (and runs separate from my app)
> >to
> >set up a tunnel. That more or less works, but I 19ve had some problems
> >with
> >the tunnel just going away and would like to integrate the tunneling
> >into
> >the app, using conch. I 19ve found an example of tunneling via conch, at
> >http://twistedmatrix.com/pipermail/twisted-
> >python/2009-February/019196.html,
> >that I think I can use as a base to add the code to my app.
> >
> >Right now my app is basically:
> >
> >class DataPuller(service.Service):
> >    ...Code for my app...
> >    ... The app pulls data from a database and I can only connect to the
> >server via SSH...
> >
> >application = service.Application( 18Data_puller 19)
> >dpService = DataPuller()
> >dpService.setServiceParent(application)
> >
> >My main problems are that I 19m not sure whether or not the example
> >linked to
> >above is a good one for tunneling with conch and, if it is, how do I
> >merge
> >the example tunneling code with my app code. From the example, where
> >the
> >code is:
>
> The example you linked to sets up the traditional port forwarding
> behavior.
> A local port is opened and connections to it are tunneled over the SSH
> connection, where data is then delivered to some address accessible from
> the server on the other end of the SSH connection.
>
> This is fine and should work, and probably very closely mirrors what
> you're
> doing with Paramiko, so if you're happy with that, you should go for it.
>
> However, it's also possible for you to do this tunneling without opening
> the extra local port.  Since your application and the SSH client code
> are
> all in the same process, you don't need the TCP connection to a local
> port
> to do this IPC to interact wiht the tunnel.  You can set up the tunnel
> part
> of things, but instead of binding a local port to accept connections on,
> you can just open a connection over the tunnel and write bytes into it
> with
> API calls.
>
> I *don't* have an example of doing things this way, and I don't even
> know
> exactly what it involves. ;)  However, the example you linked to gives a
> clue about where to start on this approach: when it binds the local
> port,
> it uses the forwarding.SSHListenForwardingFactory factory, so I'd start
> by looking at that class and see what it does.  The rest is just
> mimicking
> its behavior without actually using reactor.listenTCP.
> >class Connection(connection.SSHConnection):
> >        .
> >        .
> >        .
> >        def serviceStarted(self):
> >
> >Do I instantiate my DataPuller class there, in serviceStarted (and not
> >subclass from service.Service)? If so, how do I wrap the tunneling code
> >so
> >that I can make it a service? If not, do I need put the tunneling code
> >inside my DataPuller class? What would that look like?
>
> If you want things to happen when your program starts or when it is
> about
> to stop, then using service.Service is still a good idea.  That's the
> easy
> way to hook into startup and shutdown events.  However, you may not want
> to do anything other than set up (or tear down) the SSH connection in
> your
> service.Service subclass.  Creating your new non-Service DataPuller in
> the
> Connection's serviceStarted (or maybe even a little later - after you
> actually set up the connection over the tunnel over the connection) then
> makes sense.
>
> Jean-Paul
>
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