[Twisted-Python] SSHSessionProcessProtocol.inConnectionLost() behavior and Git over Conch
micahel at gmail.com
Thu Mar 4 23:51:09 EST 2010
On 4 March 2010 17:46, Bo Shi <bs1984 at gmail.com> wrote:
> Hi All,
> I've been struggling with this issue off and on for the better part of
> a month now. Having implemented a simple git SSH server using some of
> the Conch examples in the official documentation, I encountered an
> issue that would cause a git client to throw an error only part of the
I think it's a bug in conch.
> The little program to reproduce the issue is found at
> (raw version for download)
> and can be executed to start the sample server. Run a command like
> # The /abspath/to/git/repo should be readable by the server user
> $ git clone ssh://user@localhost:2222/abspath/to/git/repo
> (password "user")
> To test the server. On my workstation, I am able to reproduce the
> error at least once every 5 tries. It's definitely not consistent.
> The behavior I see is attached at the end of this email. The client
> fails due to a premature inConnectionLost() call in the
> SSHSessionProcessProtocol that sends an EOF.
> As a workaround, when TraceProcessProtocol.inConnectionLost() is
> overriden to do nothing, the client error goes away. This is somewhat
> foreign territory for me so I'm not sure whether it's a bug in git or
> whether it's a bug in the twisted ProcessProtocol implementation. RFC
> 4254 isn't terribly helpful here:
> 5.3. Closing a Channel
> When a party will no longer send more data to a channel, it SHOULD
> send SSH_MSG_CHANNEL_EOF.
> So on the surface the current behavior of sending an EOF appears fine,
> however, I can't really find any definitive cases of this type of
> problem popping up via, say, default OpenSSH/git combinations.
> Any advice? Is the gitconnbug.py implementation flawed? Should I
> open a ticket? Any git experts know of a case where git-upload-pack
> might close it's stdout pipe?
I think what's actually happening here is that git-upload-pack is
closing its *stdin*. Why conch reacts to that by shutting down the
channel, I don't really know -- it doesn't seem right to me. Maybe
it's a simple logic error and it method should be
At any rate, I think this is a bug -- please file a ticket. And
thanks for the complete example!
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