Port the ThirdPartyEventRules module interface to the new generic interface (#10386)

Port the third-party event rules interface to the generic module interface introduced in v1.37.0

Author: babolivier

changelog.d/10386.removal

@@ -0,0 +1 @@
+The third-party event rules module interface is deprecated in favour of the generic module interface introduced in Synapse v1.37.0. See the [upgrade notes](https://matrix-org.github.io/synapse/latest/upgrade.html#upgrading-to-v1390) for more information.

docs/modules.md

@@ -186,7 +186,7 @@ The arguments passed to this callback are:
 ```python
 async def check_media_file_for_spam(
     file_wrapper: "synapse.rest.media.v1.media_storage.ReadableFileWrapper",
-    file_info: "synapse.rest.media.v1._base.FileInfo"
+    file_info: "synapse.rest.media.v1._base.FileInfo",
 ) -> bool
 ```
 
@@ -223,6 +223,66 @@ Called after successfully registering a user, in case the module needs to perfor
 operations to keep track of them. (e.g. add them to a database table). The user is
 represented by their Matrix user ID.
 
+#### Third party rules callbacks
+
+Third party rules callbacks allow module developers to add extra checks to verify the
+validity of incoming events. Third party event rules callbacks can be registered using
+the module API's `register_third_party_rules_callbacks` method.
+
+The available third party rules callbacks are:
+
+```python
+async def check_event_allowed(
+    event: "synapse.events.EventBase",
+    state_events: "synapse.types.StateMap",
+) -> Tuple[bool, Optional[dict]]
+```
+
+**<span style="color:red">
+This callback is very experimental and can and will break without notice. Module developers
+are encouraged to implement `check_event_for_spam` from the spam checker category instead.
+</span>**
+
+Called when processing any incoming event, with the event and a `StateMap`
+representing the current state of the room the event is being sent into. A `StateMap` is
+a dictionary that maps tuples containing an event type and a state key to the
+corresponding state event. For example retrieving the room's `m.room.create` event from
+the `state_events` argument would look like this: `state_events.get(("m.room.create", ""))`.
+The module must return a boolean indicating whether the event can be allowed.
+
+Note that this callback function processes incoming events coming via federation
+traffic (on top of client traffic). This means denying an event might cause the local
+copy of the room's history to diverge from that of remote servers. This may cause
+federation issues in the room. It is strongly recommended to only deny events using this
+callback function if the sender is a local user, or in a private federation in which all
+servers are using the same module, with the same configuration.
+
+If the boolean returned by the module is `True`, it may also tell Synapse to replace the
+event with new data by returning the new event's data as a dictionary. In order to do
+that, it is recommended the module calls `event.get_dict()` to get the current event as a
+dictionary, and modify the returned dictionary accordingly.
+
+Note that replacing the event only works for events sent by local users, not for events
+received over federation.
+
+```python
+async def on_create_room(
+    requester: "synapse.types.Requester",
+    request_content: dict,
+    is_requester_admin: bool,
+) -> None
+```
+
+Called when processing a room creation request, with the `Requester` object for the user
+performing the request, a dictionary representing the room creation request's JSON body
+(see [the spec](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-createroom)
+for a list of possible parameters), and a boolean indicating whether the user performing
+the request is a server admin.
+
+Modules can modify the `request_content` (by e.g. adding events to its `initial_state`),
+or deny the room's creation by raising a `module_api.errors.SynapseError`.
+
+
 ### Porting an existing module that uses the old interface
 
 In order to port a module that uses Synapse's old module interface, its author needs to:

docs/sample_config.yaml

@@ -2654,19 +2654,6 @@ stats:
 #    action: allow
 
 
-# Server admins can define a Python module that implements extra rules for
-# allowing or denying incoming events. In order to work, this module needs to
-# override the methods defined in synapse/events/third_party_rules.py.
-#
-# This feature is designed to be used in closed federations only, where each
-# participating server enforces the same rules.
-#
-#third_party_event_rules:
-#  module: "my_custom_project.SuperRulesSet"
-#  config:
-#    example_option: 'things'
-
-
 ## Opentracing ##
 
 # These settings enable opentracing, which implements distributed tracing.

docs/upgrade.md

@@ -86,6 +86,19 @@ process, for example:
     ```
 
 
+# Upgrading to v1.39.0
+
+## Deprecation of the current third-party rules module interface
+
+The current third-party rules module interface is deprecated in favour of the new generic
+modules system introduced in Synapse v1.37.0. Authors of third-party rules modules can refer
+to [this documentation](modules.md#porting-an-existing-module-that-uses-the-old-interface)
+to update their modules. Synapse administrators can refer to [this documentation](modules.md#using-modules)
+to update their configuration once the modules they are using have been updated.
+
+We plan to remove support for the current third-party rules interface in September 2021.
+
+
 # Upgrading to v1.38.0
 
 ## Re-indexing of `events` table on Postgres databases

synapse/app/_base.py

@@ -38,6 +38,7 @@
 from synapse.config.homeserver import HomeServerConfig
 from synapse.crypto import context_factory
 from synapse.events.spamcheck import load_legacy_spam_checkers
+from synapse.events.third_party_rules import load_legacy_third_party_event_rules
 from synapse.logging.context import PreserveLoggingContext
 from synapse.metrics.background_process_metrics import wrap_as_background_process
 from synapse.metrics.jemalloc import setup_jemalloc_stats
@@ -368,6 +369,7 @@ def run_sighup(*args, **kwargs):
         module(config=config, api=module_api)
 
     load_legacy_spam_checkers(hs)
+    load_legacy_third_party_event_rules(hs)
 
     # If we've configured an expiry time for caches, start the background job now.
     setup_expire_lru_cache_entries(hs)

synapse/config/third_party_event_rules.py

@@ -28,18 +28,3 @@ def read_config(self, config, **kwargs):
             self.third_party_event_rules = load_module(
                 provider, ("third_party_event_rules",)
             )
-
-    def generate_config_section(self, **kwargs):
-        return """\
-        # Server admins can define a Python module that implements extra rules for
-        # allowing or denying incoming events. In order to work, this module needs to
-        # override the methods defined in synapse/events/third_party_rules.py.
-        #
-        # This feature is designed to be used in closed federations only, where each
-        # participating server enforces the same rules.
-        #
-        #third_party_event_rules:
-        #  module: "my_custom_project.SuperRulesSet"
-        #  config:
-        #    example_option: 'things'
-        """