StreamProducer defer patch

[KyleJ]

If a callback occurs after self.deferred is set to None in _doWrite (for instance: while the producer is paused) and returns a deferred None, StreamProducder halts early.

Patch (for trunk/twisted/web2/stream.py):

--- stream.py   2007-07-17 21:08:26.000000000 -0700
+++ stream2.py  2007-07-17 21:09:12.000000000 -0700
@@ -729,7 +729,7 @@
     
     def resumeProducing(self):
         self.paused = False
-        if self.deferred is not None:
+        if self.deferred is not None and self.deferred.result is not None:
             return
 
         try:

[exarkun]

Got a unit test?

[exarkun]

Not going to fix this in web2 (see #4821). Also I still don't quite understand how to trigger this behavior either. There are no streams in Twisted Web, so no parallel misbehavior, so not retargeting this at the web component.