Merge ~cjwatson/turnip:loseWriteConnection-test-failure into turnip:master

[Colin Watson]

Check if transport is connected before closing it

We've seen occasional test failures in `loseWriteConnection` calls for
some time because the socket had already been closed, and they've become
much more frequent of late. Checking whether the transport is still
connected before telling it to lose its write connection should help.

LP: #1641100

[Tom Wardill (twom)]

review: Approve

[Otto Co-Pilot (otto-copilot)]

Voting criteria not met
https://jenkins.ols.canonical.com/online-services/job/turnip/40/

[Colin Watson (cjwatson)]

review: Approve

diff --git a/turnip/pack/git.py b/turnip/pack/git.py
index c18742f..d45e1db 100644
--- a/turnip/pack/git.py
+++ b/turnip/pack/git.py
@@ -381,7 +381,7 @@ class PackProxyServerProtocol(PackServerProtocol):
 
     def readConnectionLost(self):
         # Forward the closed stdin down the stack.
-        if self.peer is not None:
+        if self.peer is not None and self.peer.transport.connected:
             self.peer.transport.loseWriteConnection()
 
 
diff --git a/turnip/pack/ssh.py b/turnip/pack/ssh.py
index b753220..3526bb9 100644
--- a/turnip/pack/ssh.py
+++ b/turnip/pack/ssh.py
@@ -176,7 +176,8 @@ class SmartSSHSession(DoNothingSession):
             self.pack_protocol.transport.loseConnection()
 
     def eofReceived(self):
-        if self.pack_protocol is not None:
+        if (self.pack_protocol is not None and
+                self.pack_protocol.transport.connected):
             self.pack_protocol.transport.loseWriteConnection()