For the content repo, don't just use homeserver.hostname as that might not include the port due to SRV.

synapse/app/homeserver.py

@@ -37,6 +37,7 @@ import logging
 import logging.config
 import sqlite3
 import os
+import re
 
 logger = logging.getLogger(__name__)
 
@@ -255,8 +256,14 @@ def setup():
 
     logger.info("Server hostname: %s", args.host)
 
+    if re.search(":[0-9]+$", args.host):
+        domain_with_port = args.host
+    else:
+        domain_with_port = "%s:%s" % (args.host, args.port)
+
     hs = SynapseHomeServer(
         args.host,
+        domain_with_port=domain_with_port,
         upload_dir=os.path.abspath("uploads"),
         db_name=db_name,
     )

synapse/http/server.py

@@ -325,7 +325,9 @@ class ContentRepoResource(resource.Resource):
 
             # FIXME (erikj): These should use constants.
             file_name = os.path.basename(fname)
-            url = "http://%s/matrix/content/%s" % (self.hs.hostname, file_name)
+            url = "http://%s/matrix/content/%s" % (
+                self.hs.domain_with_port, file_name
+            )
 
             respond_with_json_bytes(request, 200,
                                     json.dumps({"content_token": url}),