Fix a case in which chunked responses could be closed prematurely.

bdarnell · bdarnell · commit 4b346bdde80c · 2011-09-22T10:38:35.000-07:00
The bug manifests with certain patterns of fast-path/slow-path writes on the IOStream, so it's difficult to test (it was more likely to occur in 2.0 than in 2.1). http://groups.google.com/group/python-tornado/browse_thread/thread/7228881f7af38070
diff --git a/tornado/httpserver.py b/tornado/httpserver.py
@@ -190,7 +190,14 @@ def _on_write_complete(self):
             callback = self._write_callback
             self._write_callback = None
             callback()            
-        if self._request_finished:
+        # _on_write_complete is enqueued on the IOLoop whenever the
+        # IOStream's write buffer becomes empty, but it's possible for
+        # another callback that runs on the IOLoop before it to
+        # simultaneously write more data and finish the request.  If
+        # there is still data in the IOStream, a future
+        # _on_write_complete will be responsible for calling
+        # _finish_request.
+        if self._request_finished and not self.stream.writing():
             self._finish_request()
 
     def _finish_request(self):
