Use a producer to stream back responses

The problem with dumping all of the json response into the Request object at once is that doing so starts the timeout for the next request to be received: so if it takes longer than 60s to stream back the response to the client, the client never gets it. The correct solution is to use Producer; then the timeout is only started once all of the content is sent over the TCP connection. However, we then need to hook the completion logging in via notifyFinish (which is a much better way of doing things anyway), in order to correctly read the response length.
matrix-org · Aug 15, 2018 · 6f3bf1b · 6f3bf1b
1 parent 614e6d5
commit 6f3bf1b
Showing 1 changed file with 13 additions and 4 deletions.
diff --git a/synapse/http/server.py b/synapse/http/server.py
@@ -27,6 +27,7 @@
 from twisted.python import failure
 from twisted.web import resource, server
 from twisted.web.server import NOT_DONE_YET
+from twisted.web.static import NoRangeStaticProducer
 from twisted.web.util import redirectTo
 
 import synapse.events
@@ -42,6 +43,11 @@
 from synapse.util.logcontext import LoggingContext, PreserveLoggingContext
 from synapse.util.metrics import Measure
 
+if PY3:
+    from io import BytesIO
+else:
+    from cStringIO import StringIO as BytesIO
+
 logger = logging.getLogger(__name__)
 
 HTML_ERROR_TEMPLATE = """<!DOCTYPE html>
@@ -413,8 +419,7 @@ def respond_with_json(request, code, json_object, send_cors=False,
         return
 
     if pretty_print:
-        json_bytes = (encode_pretty_printed_json(json_object) + "\n"
-                      ).encode("utf-8")
+        json_bytes = encode_pretty_printed_json(json_object) + b"\n"
     else:
         if canonical_json or synapse.events.USE_FROZEN_DICTS:
             # canonicaljson already encodes to bytes
@@ -450,8 +455,12 @@ def respond_with_json_bytes(request, code, json_bytes, send_cors=False,
     if send_cors:
         set_cors_headers(request)
 
-    request.write(json_bytes)
-    finish_request(request)
+    # todo: we can almost certainly avoid this copy and encode the json straight into
+    # the bytesIO, but it would involve faffing around with string->bytes wrappers.
+    bytes_io = BytesIO(json_bytes)
+
+    producer = NoRangeStaticProducer(request, bytes_io)
+    producer.start()
     return NOT_DONE_YET