Add get_media_upload_limits_for_user and on_media_upload_limit_exceeded callbacks to module API (#18848)

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

docs/modules/media_repository_callbacks.md

@@ -64,3 +64,68 @@ If multiple modules implement this callback, they will be considered in order. I
 returns `True`, Synapse falls through to the next one. The value of the first callback that
 returns `False` will be used. If this happens, Synapse will not call any of the subsequent
 implementations of this callback.
+
+### `get_media_upload_limits_for_user`
+
+_First introduced in Synapse v1.139.0_
+
+```python
+async def get_media_upload_limits_for_user(user_id: str, size: int) -> Optional[List[synapse.module_api.MediaUploadLimit]]
+```
+
+**<span style="color:red">
+Caution: This callback is currently experimental. The method signature or behaviour
+may change without notice.
+</span>**
+
+Called when processing a request to store content in the media repository. This can be used to dynamically override
+the [media upload limits configuration](../usage/configuration/config_documentation.html#media_upload_limits).
+
+The arguments passed to this callback are:
+
+* `user_id`: The Matrix user ID of the user (e.g. `@alice:example.com`) making the request.
+
+If the callback returns a list then it will be used as the limits instead of those in the configuration (if any).
+
+If an empty list is returned then no limits are applied (**warning:** users will be able
+to upload as much data as they desire).
+
+If multiple modules implement this callback, they will be considered in order. If a
+callback returns `None`, Synapse falls through to the next one. The value of the first
+callback that does not return `None` will be used. If this happens, Synapse will not call
+any of the subsequent implementations of this callback.
+
+If there are no registered modules, or if all modules return `None`, then
+the default
+[media upload limits configuration](../usage/configuration/config_documentation.html#media_upload_limits)
+will be used.
+
+### `on_media_upload_limit_exceeded`
+
+_First introduced in Synapse v1.139.0_
+
+```python
+async def on_media_upload_limit_exceeded(user_id: str, limit: synapse.module_api.MediaUploadLimit, sent_bytes: int, attempted_bytes: int) -> None
+```
+
+**<span style="color:red">
+Caution: This callback is currently experimental. The method signature or behaviour
+may change without notice.
+</span>**
+
+Called when a user attempts to upload media that would exceed a
+[configured media upload limit](../usage/configuration/config_documentation.html#media_upload_limits).
+
+This callback will only be called on workers which handle
+[POST /_matrix/media/v3/upload](https://spec.matrix.org/v1.15/client-server-api/#post_matrixmediav3upload)
+requests.
+
+This could be used to inform the user that they have reached a media upload limit through
+some external method.
+
+The arguments passed to this callback are:
+
+* `user_id`: The Matrix user ID of the user (e.g. `@alice:example.com`) making the request.
+* `limit`: The `synapse.module_api.MediaUploadLimit` representing the limit that was reached.
+* `sent_bytes`: The number of bytes already sent during the period of the limit.
+* `attempted_bytes`: The number of bytes that the user attempted to send.

docs/usage/configuration/config_documentation.md

@@ -2168,9 +2168,12 @@ max_upload_size: 60M
 ### `media_upload_limits`
 
 *(array)* A list of media upload limits defining how much data a given user can upload in a given time period.
+These limits are applied in addition to the `max_upload_size` limit above (which applies to individual uploads).
 
 An empty list means no limits are applied.
 
+These settings can be overridden using the `get_media_upload_limits_for_user` module API [callback](../../modules/media_repository_callbacks.md#get_media_upload_limits_for_user).
+
 Defaults to `[]`.
 
 Example configuration: