Catch the exceptions thrown by twisted when you write to a closed connection

synapse/http/server.py

@@ -367,10 +367,29 @@ def respond_with_json_bytes(request, code, json_bytes, send_cors=False,
                           "Origin, X-Requested-With, Content-Type, Accept")
 
     request.write(json_bytes)
-    request.finish()
+    finish_request(request)
     return NOT_DONE_YET
 
 
+def finish_request(request):
+    """ Finish writing the response to the request.
+
+    Twisted throws a RuntimeException if the connection closed before the
+    response was written but doesn't provide a convenient or reliable way to
+    determine if the connection was closed. So we catch and log the RuntimeException
+
+    You might think that ``request.notifyFinish`` could be used to tell if the
+    request was finished. However the deferred it returns won't fire if the
+    connection was already closed, meaning we'd have to have called the method
+    right at the start of the request. By the time we want to write the response
+    it will already be too late.
+    """
+    try:
+        request.finish()
+    except RuntimeError as e:
+        logger.info("Connection disconnected before response was written: %r", e)
+
+
 def _request_user_agent_is_curl(request):
     user_agents = request.requestHeaders.getRawHeaders(
         "User-Agent", default=[]

synapse/rest/client/v1/login.py

@@ -17,6 +17,8 @@ from twisted.internet import defer
 
 from synapse.api.errors import SynapseError, LoginError, Codes
 from synapse.types import UserID
+from synapse.http.server import finish_request
+
 from base import ClientV1RestServlet, client_path_patterns
 
 import simplejson as json
@@ -263,7 +265,7 @@ class SAML2RestServlet(ClientV1RestServlet):
                                  '?status=authenticated&access_token=' +
                                  token + '&user_id=' + user_id + '&ava=' +
                                  urllib.quote(json.dumps(saml2_auth.ava)))
-                request.finish()
+                finish_request(request)
                 defer.returnValue(None)
             defer.returnValue((200, {"status": "authenticated",
                                      "user_id": user_id, "token": token,
@@ -272,7 +274,7 @@ class SAML2RestServlet(ClientV1RestServlet):
             request.redirect(urllib.unquote(
                              request.args['RelayState'][0]) +
                              '?status=not_authenticated')
-            request.finish()
+            finish_request(request)
             defer.returnValue(None)
         defer.returnValue((200, {"status": "not_authenticated"}))
 
@@ -309,7 +311,7 @@ class CasRedirectServlet(ClientV1RestServlet):
             "service": "%s?%s" % (hs_redirect_url, client_redirect_url_param)
         })
         request.redirect("%s?%s" % (self.cas_server_url, service_param))
-        request.finish()
+        finish_request(request)
 
 
 class CasTicketServlet(ClientV1RestServlet):
@@ -362,7 +364,7 @@ class CasTicketServlet(ClientV1RestServlet):
         redirect_url = self.add_login_token_to_redirect_url(client_redirect_url,
                                                             login_token)
         request.redirect(redirect_url)
-        request.finish()
+        finish_request(request)
 
     def add_login_token_to_redirect_url(self, url, token):
         url_parts = list(urlparse.urlparse(url))

synapse/rest/client/v2_alpha/auth.py

@@ -18,6 +18,7 @@ from twisted.internet import defer
 from synapse.api.constants import LoginType
 from synapse.api.errors import SynapseError
 from synapse.api.urls import CLIENT_V2_ALPHA_PREFIX
+from synapse.http.server import finish_request
 from synapse.http.servlet import RestServlet
 
 from ._base import client_v2_patterns
@@ -130,7 +131,7 @@ class AuthRestServlet(RestServlet):
             request.setHeader(b"Content-Length", b"%d" % (len(html_bytes),))
 
             request.write(html_bytes)
-            request.finish()
+            finish_request(request)
             defer.returnValue(None)
         else:
             raise SynapseError(404, "Unknown auth stage type")
@@ -176,7 +177,7 @@ class AuthRestServlet(RestServlet):
             request.setHeader(b"Content-Length", b"%d" % (len(html_bytes),))
 
             request.write(html_bytes)
-            request.finish()
+            finish_request(request)
 
             defer.returnValue(None)
         else:

synapse/rest/media/v0/content_repository.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from synapse.http.server import respond_with_json_bytes
+from synapse.http.server import respond_with_json_bytes, finish_request
 
 from synapse.util.stringutils import random_string
 from synapse.api.errors import (
@@ -144,7 +144,7 @@ class ContentRepoResource(resource.Resource):
             # after the file has been sent, clean up and finish the request
             def cbFinished(ignored):
                 f.close()
-                request.finish()
+                finish_request(request)
             d.addCallback(cbFinished)
         else:
             respond_with_json_bytes(

synapse/rest/media/v1/base_resource.py

@@ -16,7 +16,7 @@
 from .thumbnailer import Thumbnailer
 
 from synapse.http.matrixfederationclient import MatrixFederationHttpClient
-from synapse.http.server import respond_with_json
+from synapse.http.server import respond_with_json, finish_request
 from synapse.util.stringutils import random_string
 from synapse.api.errors import (
     cs_error, Codes, SynapseError
@@ -238,7 +238,7 @@ class BaseMediaResource(Resource):
             with open(file_path, "rb") as f:
                 yield FileSender().beginFileTransfer(f, request)
 
-            request.finish()
+            finish_request(request)
         else:
             self._respond_404(request)