Standardise the module interface (#10062)

This PR adds a common configuration section for all modules (see docs). These modules are then loaded at startup by the homeserver. Modules register their hooks and web resources using the new `register_[...]_callbacks` and `register_web_resource` methods of the module API.

synapse/module_api/__init__.py

@@ -16,6 +16,7 @@ import logging
 from typing import TYPE_CHECKING, Any, Generator, Iterable, List, Optional, Tuple
 
 from twisted.internet import defer
+from twisted.web.resource import IResource
 
 from synapse.events import EventBase
 from synapse.http.client import SimpleHttpClient
@@ -42,7 +43,7 @@ class ModuleApi:
     can register new users etc if necessary.
     """
 
-    def __init__(self, hs, auth_handler):
+    def __init__(self, hs: "HomeServer", auth_handler):
         self._hs = hs
 
         self._store = hs.get_datastore()
@@ -56,6 +57,33 @@ class ModuleApi:
         self._http_client = hs.get_simple_http_client()  # type: SimpleHttpClient
         self._public_room_list_manager = PublicRoomListManager(hs)
 
+        self._spam_checker = hs.get_spam_checker()
+
+    #################################################################################
+    # The following methods should only be called during the module's initialisation.
+
+    @property
+    def register_spam_checker_callbacks(self):
+        """Registers callbacks for spam checking capabilities."""
+        return self._spam_checker.register_callbacks
+
+    def register_web_resource(self, path: str, resource: IResource):
+        """Registers a web resource to be served at the given path.
+
+        This function should be called during initialisation of the module.
+
+        If multiple modules register a resource for the same path, the module that
+        appears the highest in the configuration file takes priority.
+
+        Args:
+            path: The path to register the resource for.
+            resource: The resource to attach to this path.
+        """
+        self._hs.register_module_web_resource(path, resource)
+
+    #########################################################################
+    # The following methods can be called by the module at any point in time.
+
     @property
     def http_client(self):
         """Allows making outbound HTTP requests to remote resources.

synapse/module_api/errors.py

@@ -15,3 +15,4 @@
 """Exception types which are exposed as part of the stable module API"""
 
 from synapse.api.errors import RedirectException, SynapseError  # noqa: F401
+from synapse.config._base import ConfigError  # noqa: F401