Start handlers for new media endpoints when media resource configured (#17483)

This is in response to issue #17473. 
Not all the necessary handlers to deal with media requests are started
now when configuring synapse to use a media worker as per the [example
config](https://element-hq.github.io/synapse/latest/workers.html#synapseappmedia_repository).
The new media endpoints introduced with authenticated media fall under
the `client` & `federation` handlers in synapse.
This PR starts up handlers for the new media endpoints if a worker has
been configured with only the `media` resource type.

### Pull Request Checklist

<!-- Please read
https://element-hq.github.io/synapse/latest/development/contributing_guide.html
before submitting your pull request -->

* [X] Pull request is based on the develop branch
* [x] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
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- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [X] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct
(run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

---------

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

2 files changed, 29 insertions, 0 deletions

diff --git a/synapse/app/generic_worker.py b/synapse/app/generic_worker.py
index 248622fa92..53f1859256 100644
--- a/synapse/app/generic_worker.py
+++ b/synapse/app/generic_worker.py
@@ -206,6 +206,21 @@ class GenericWorkerServer(HomeServer):
                                 "/_synapse/admin": admin_resource,
                             }
                         )
+
+                        if "federation" not in res.names:
+                            # Only load the federation media resource separately if federation
+                            # resource is not specified since federation resource includes media
+                            # resource.
+                            resources[FEDERATION_PREFIX] = TransportLayerServer(
+                                self, servlet_groups=["media"]
+                            )
+                        if "client" not in res.names:
+                            # Only load the client media resource separately if client
+                            # resource is not specified since client resource includes media
+                            # resource.
+                            resources[CLIENT_API_PREFIX] = ClientRestResource(
+                                self, servlet_groups=["media"]
+                            )
                     else:
                         logger.warning(
                             "A 'media' listener is configured but the media"
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index e114ab7ec4..2a824e8457 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -101,6 +101,12 @@ class SynapseHomeServer(HomeServer):
                     # Skip loading openid resource if federation is defined
                     # since federation resource will include openid
                     continue
+                if name == "media" and (
+                    "federation" in res.names or "client" in res.names
+                ):
+                    # Skip loading media resource if federation or client are defined
+                    # since federation & client resources will include media
+                    continue
                 if name == "health":
                     # Skip loading, health resource is always included
                     continue
@@ -231,6 +237,14 @@ class SynapseHomeServer(HomeServer):
                     "'media' resource conflicts with enable_media_repo=False"
                 )
 
+        if name == "media":
+            resources[FEDERATION_PREFIX] = TransportLayerServer(
+                self, servlet_groups=["media"]
+            )
+            resources[CLIENT_API_PREFIX] = ClientRestResource(
+                self, servlet_groups=["media"]
+            )
+
         if name in ["keys", "federation"]:
             resources[SERVER_KEY_PREFIX] = KeyResource(self)