Fix missing CORS headers on OPTION responses (matrix-org#7560)

Broke in matrix-org#7534.

changelog.d/7560.misc

@@ -0,0 +1 @@
+All endpoints now respond with a 200 OK for `OPTIONS` requests.

synapse/http/server.py

@@ -452,7 +452,7 @@ def render_OPTIONS(self, request):
         code, response_json_object = _options_handler(request)
 
         return respond_with_json(
-            request, code, response_json_object, send_cors=False, canonical_json=False,
+            request, code, response_json_object, send_cors=True, canonical_json=False,
         )
 
     def getChildWithDefault(self, path, request):

tests/test_server.py

@@ -203,12 +203,40 @@ def test_unknown_options_request(self):
         self.assertEqual(channel.result["code"], b"200")
         self.assertEqual(channel.result["body"], b"{}")
 
+        # Ensure the correct CORS headers have been added
+        self.assertTrue(
+            channel.headers.hasHeader(b"Access-Control-Allow-Origin"),
+            "has CORS Origin header",
+        )
+        self.assertTrue(
+            channel.headers.hasHeader(b"Access-Control-Allow-Methods"),
+            "has CORS Methods header",
+        )
+        self.assertTrue(
+            channel.headers.hasHeader(b"Access-Control-Allow-Headers"),
+            "has CORS Headers header",
+        )
+
     def test_known_options_request(self):
         """An OPTIONS requests to an known URL still returns 200 OK."""
         channel = self._make_request(b"OPTIONS", b"/res/")
         self.assertEqual(channel.result["code"], b"200")
         self.assertEqual(channel.result["body"], b"{}")
 
+        # Ensure the correct CORS headers have been added
+        self.assertTrue(
+            channel.headers.hasHeader(b"Access-Control-Allow-Origin"),
+            "has CORS Origin header",
+        )
+        self.assertTrue(
+            channel.headers.hasHeader(b"Access-Control-Allow-Methods"),
+            "has CORS Methods header",
+        )
+        self.assertTrue(
+            channel.headers.hasHeader(b"Access-Control-Allow-Headers"),
+            "has CORS Headers header",
+        )
+
     def test_unknown_request(self):
         """A non-OPTIONS request to an unknown URL should 404."""
         channel = self._make_request(b"GET", b"/foo/")