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proposals/3896-appservice-media.md

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+# MSC3896: Appservice media
+
+Appservices often need to bridge media, and do so by reuploading files to the homeserver. This
+can cause a lot of storage usage. This MSC proposes a way for appservices to register media
+(`mxc://`) namespaces.
+
+## Proposal
+
+This proposal adds a new key (`media`) to the namespaces block of appservice registration.
+
+Whenever the homeserver gets a request that matches the regex, it should make a http GET request
+to `/_matrix/app/v1/media/{mediaId}`.
+
+For example:
+
+```yaml
+namespaces:
+  media:
+    - exclusive: true
+      regex: "foobar-.*"
+```
+
+In this case, fetching `mxc://server.tld/foobar-bazqux` leads to a request to
+`/_matrix/app/v1/media/foobar-bazqux`.
+
+Appservices may set `Cache-Control` on their response. Homeservers should cache the response, though
+they may remove cached remote media to save space.
+
+## Potential issues
+
+Media may not be able to load if the appservice is unable to reach wherever remote media is stored.
+
+## Alternatives
+
+*none*
+
+## Security considerations
+
+*none*
+
+## Unstable prefix
+
+`org.eu.celery.msc3896.media` should be used instead of `media`
+
+## Dependencies
+
+*none*