Add support for compression to federation responses (#13537)

Closes #13415.

Signed-off-by: Ayush Anand <iamayushanand@gmail.com>

changelog.d/13537.bugfix

@@ -0,0 +1 @@
+Add support for compression to federation responses.

docs/usage/configuration/config_documentation.md

@@ -444,7 +444,7 @@ Sub-options for each listener include:
    * `names`: a list of names of HTTP resources. See below for a list of valid resource names.
 
    * `compress`: set to true to enable gzip compression on HTTP bodies for this resource. This is currently only supported with the
-     `client`, `consent` and `metrics` resources.
+     `client`, `consent`, `metrics` and `federation` resources.
 
 * `additional_resources`: Only valid for an 'http' listener. A map of
    additional endpoints which should be loaded via dynamic modules.

synapse/app/homeserver.py

@@ -220,7 +220,10 @@ class SynapseHomeServer(HomeServer):
             resources.update({"/_matrix/consent": consent_resource})
 
         if name == "federation":
-            resources.update({FEDERATION_PREFIX: TransportLayerServer(self)})
+            federation_resource: Resource = TransportLayerServer(self)
+            if compress:
+                federation_resource = gz_wrap(federation_resource)
+            resources.update({FEDERATION_PREFIX: federation_resource})
 
         if name == "openid":
             resources.update(