[Twisted-Python] SSHSessionProcessProtocol.inConnectionLost() behavior and Git over Conch

James Y Knight foom at fuhm.net
Fri Mar 5 12:07:18 EST 2010

On Mar 4, 2010, at 11:51 PM, Michael Hudson-Doyle wrote:

> Maybe
> it's a simple logic error and it method should be
> 'outConnectionClosed' instead?

I'd agree with that. Clearly it should not be sending EOF there for  
the server process closing its stdin. One more detail though: you  
actually need to wait for both stdout and stderr to close, not just  

There *is* no standard SSH protocol message for closing your stdin.
But if openssh 5.1 or later connects to an openssh 5.1 or later  
server, it will use the nonstandard eow at openssh.org command to  
indicate a closed stdin.

Thus, on standard ssh servers/clients, the command:
   ssh hostname yes | true
will hang forever. True closed its stdin by virtue of exiting, but  
that can't get propagated across the ssh link. So, yes never gets a  
SIGPIPE, and thus never closes its stdout and the command keeps  
running forever.

But on openssh 5.1 or greater on both ends, it will "work properly".

BTW, you can't reasonably implement this extension in conch even if  
you wanted to, because openssh client will only send it to servers  
which identify themselves as openssh servers.



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