twisted.conch.ssh.filetransfer.FileTransferClient._sendRequest will wait forever for server to respond

	@adiroiban reported
Trac ID	trac#9569
Type	defect
Created	2019-01-05 08:31:16Z

When a SFTP client request is done, Twisted will make the request and naively wait forever for the server to respond.

The code is here https://github.com/twisted/twisted/blob/eb2aaeb5d8e95ad1c4ec1889855d9cd151f696e2/src/twisted/conch/ssh/filetransfer.py#L530

With bogus servers or under very low networks it might takes a long to respond... and I expect that most users of Twisted SFTP client will not want to wait for that long.

I am suggesting to use a 60 seconds timeout deferred, instead of the normal deferred here

    _scheduler = reactor

    def _sendRequest(self, msg, data):
        data = struct.pack('!L', self.counter) + data
        d = defer.Deferred()
        d.addTimeout(60, self._scheduler)
        self.openRequests[self.counter] = d
        self.counter += 1
        self.sendPacket(msg, data)
        return d

What do you think?

trac-id__9569 9569
type__defect defect
reporter__adiroiban adiroiban
priority__normal normal
milestone__None None
branch__ 
branch_author__ 
status__new new
resolution__None None
component__conch conch
keywords__None None
time__1546677076927112 1546677076927112
changetime__1546896431314958 1546896431314958
version__None None
owner__None None

Start in src/twisted/conch/ssh/filetransfer.py at FileTransferClient._sendRequest, the entry point identified in the issue. Review how openRequests and Deferred responses are handled, then verify that an unresponsive SFTP server no longer leaves the request waiting forever and that normal responses still complete.