Move Account Validity callbacks to a dedicated file

Spreading module callback registration across the codebase is both a bit
messy and makes it unclear where a user should register callbacks if
they want to define a new class of callbacks.

Consolidating these under the synapse.module_api module cleans things up
a bit, puts related code in the same place and makes it much more
obvious how to extend it.

6 files changed, 153 insertions, 103 deletions

diff --git a/synapse/handlers/account_validity.py b/synapse/handlers/account_validity.py
index 33e45e3a11..4aa4ebf7e4 100644
--- a/synapse/handlers/account_validity.py
+++ b/synapse/handlers/account_validity.py
@@ -15,9 +15,7 @@
 import email.mime.multipart
 import email.utils
 import logging
-from typing import TYPE_CHECKING, Awaitable, Callable, List, Optional, Tuple
-
-from twisted.web.http import Request
+from typing import TYPE_CHECKING, List, Optional, Tuple
 
 from synapse.api.errors import AuthError, StoreError, SynapseError
 from synapse.metrics.background_process_metrics import wrap_as_background_process
@@ -30,25 +28,17 @@ if TYPE_CHECKING:
 
 logger = logging.getLogger(__name__)
 
-# Types for callbacks to be registered via the module api
-IS_USER_EXPIRED_CALLBACK = Callable[[str], Awaitable[Optional[bool]]]
-ON_USER_REGISTRATION_CALLBACK = Callable[[str], Awaitable]
-# Temporary hooks to allow for a transition from `/_matrix/client` endpoints
-# to `/_synapse/client/account_validity`. See `register_account_validity_callbacks`.
-ON_LEGACY_SEND_MAIL_CALLBACK = Callable[[str], Awaitable]
-ON_LEGACY_RENEW_CALLBACK = Callable[[str], Awaitable[Tuple[bool, bool, int]]]
-ON_LEGACY_ADMIN_REQUEST = Callable[[Request], Awaitable]
-
 
 class AccountValidityHandler:
     def __init__(self, hs: "HomeServer"):
         self.hs = hs
         self.config = hs.config
-        self.store = self.hs.get_datastores().main
-        self.send_email_handler = self.hs.get_send_email_handler()
-        self.clock = self.hs.get_clock()
+        self.store = hs.get_datastores().main
+        self.send_email_handler = hs.get_send_email_handler()
+        self.clock = hs.get_clock()
 
-        self._app_name = self.hs.config.email.email_app_name
+        self._app_name = hs.config.email.email_app_name
+        self._module_api_callbacks = hs.get_module_api_callbacks().account_validity
 
         self._account_validity_enabled = (
             hs.config.account_validity.account_validity_enabled
@@ -78,69 +68,6 @@ class AccountValidityHandler:
             if hs.config.worker.run_background_tasks:
                 self.clock.looping_call(self._send_renewal_emails, 30 * 60 * 1000)
 
-        self._is_user_expired_callbacks: List[IS_USER_EXPIRED_CALLBACK] = []
-        self._on_user_registration_callbacks: List[ON_USER_REGISTRATION_CALLBACK] = []
-        self._on_legacy_send_mail_callback: Optional[
-            ON_LEGACY_SEND_MAIL_CALLBACK
-        ] = None
-        self._on_legacy_renew_callback: Optional[ON_LEGACY_RENEW_CALLBACK] = None
-
-        # The legacy admin requests callback isn't a protected attribute because we need
-        # to access it from the admin servlet, which is outside of this handler.
-        self.on_legacy_admin_request_callback: Optional[ON_LEGACY_ADMIN_REQUEST] = None
-
-    def register_account_validity_callbacks(
-        self,
-        is_user_expired: Optional[IS_USER_EXPIRED_CALLBACK] = None,
-        on_user_registration: Optional[ON_USER_REGISTRATION_CALLBACK] = None,
-        on_legacy_send_mail: Optional[ON_LEGACY_SEND_MAIL_CALLBACK] = None,
-        on_legacy_renew: Optional[ON_LEGACY_RENEW_CALLBACK] = None,
-        on_legacy_admin_request: Optional[ON_LEGACY_ADMIN_REQUEST] = None,
-    ) -> None:
-        """Register callbacks from module for each hook."""
-        if is_user_expired is not None:
-            self._is_user_expired_callbacks.append(is_user_expired)
-
-        if on_user_registration is not None:
-            self._on_user_registration_callbacks.append(on_user_registration)
-
-        # The builtin account validity feature exposes 3 endpoints (send_mail, renew, and
-        # an admin one). As part of moving the feature into a module, we need to change
-        # the path from /_matrix/client/unstable/account_validity/... to
-        # /_synapse/client/account_validity, because:
-        #
-        #   * the feature isn't part of the Matrix spec thus shouldn't live under /_matrix
-        #   * the way we register servlets means that modules can't register resources
-        #     under /_matrix/client
-        #
-        # We need to allow for a transition period between the old and new endpoints
-        # in order to allow for clients to update (and for emails to be processed).
-        #
-        # Once the email-account-validity module is loaded, it will take control of account
-        # validity by moving the rows from our `account_validity` table into its own table.
-        #
-        # Therefore, we need to allow modules (in practice just the one implementing the
-        # email-based account validity) to temporarily hook into the legacy endpoints so we
-        # can route the traffic coming into the old endpoints into the module, which is
-        # why we have the following three temporary hooks.
-        if on_legacy_send_mail is not None:
-            if self._on_legacy_send_mail_callback is not None:
-                raise RuntimeError("Tried to register on_legacy_send_mail twice")
-
-            self._on_legacy_send_mail_callback = on_legacy_send_mail
-
-        if on_legacy_renew is not None:
-            if self._on_legacy_renew_callback is not None:
-                raise RuntimeError("Tried to register on_legacy_renew twice")
-
-            self._on_legacy_renew_callback = on_legacy_renew
-
-        if on_legacy_admin_request is not None:
-            if self.on_legacy_admin_request_callback is not None:
-                raise RuntimeError("Tried to register on_legacy_admin_request twice")
-
-            self.on_legacy_admin_request_callback = on_legacy_admin_request
-
     async def is_user_expired(self, user_id: str) -> bool:
         """Checks if a user has expired against third-party modules.
 
@@ -150,7 +77,7 @@ class AccountValidityHandler:
         Returns:
             Whether the user has expired.
         """
-        for callback in self._is_user_expired_callbacks:
+        for callback in self._module_api_callbacks.is_user_expired_callbacks:
             expired = await delay_cancellation(callback(user_id))
             if expired is not None:
                 return expired
@@ -168,7 +95,7 @@ class AccountValidityHandler:
         Args:
             user_id: The ID of the newly registered user.
         """
-        for callback in self._on_user_registration_callbacks:
+        for callback in self._module_api_callbacks.on_user_registration_callbacks:
             await callback(user_id)
 
     @wrap_as_background_process("send_renewals")
@@ -198,8 +125,8 @@ class AccountValidityHandler:
         """
         # If a module supports sending a renewal email from here, do that, otherwise do
         # the legacy dance.
-        if self._on_legacy_send_mail_callback is not None:
-            await self._on_legacy_send_mail_callback(user_id)
+        if self._module_api_callbacks.on_legacy_send_mail_callback is not None:
+            await self._module_api_callbacks.on_legacy_send_mail_callback(user_id)
             return
 
         if not self._account_validity_renew_by_email_enabled:
@@ -336,8 +263,10 @@ class AccountValidityHandler:
         """
         # If a module supports triggering a renew from here, do that, otherwise do the
         # legacy dance.
-        if self._on_legacy_renew_callback is not None:
-            return await self._on_legacy_renew_callback(renewal_token)
+        if self._module_api_callbacks.on_legacy_renew_callback is not None:
+            return await self._module_api_callbacks.on_legacy_renew_callback(
+                renewal_token
+            )
 
         try:
             (
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 424239e3df..595c23e78d 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -73,13 +73,6 @@ from synapse.events.third_party_rules import (
     ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK,
 )
 from synapse.handlers.account_data import ON_ACCOUNT_DATA_UPDATED_CALLBACK
-from synapse.handlers.account_validity import (
-    IS_USER_EXPIRED_CALLBACK,
-    ON_LEGACY_ADMIN_REQUEST,
-    ON_LEGACY_RENEW_CALLBACK,
-    ON_LEGACY_SEND_MAIL_CALLBACK,
-    ON_USER_REGISTRATION_CALLBACK,
-)
 from synapse.handlers.auth import (
     CHECK_3PID_AUTH_CALLBACK,
     CHECK_AUTH_CALLBACK,
@@ -105,6 +98,13 @@ from synapse.logging.context import (
     run_in_background,
 )
 from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.module_api.callbacks.account_validity_callbacks import (
+    IS_USER_EXPIRED_CALLBACK,
+    ON_LEGACY_ADMIN_REQUEST,
+    ON_LEGACY_RENEW_CALLBACK,
+    ON_LEGACY_SEND_MAIL_CALLBACK,
+    ON_USER_REGISTRATION_CALLBACK,
+)
 from synapse.rest.client.login import LoginResponse
 from synapse.storage import DataStore
 from synapse.storage.background_updates import (
@@ -250,6 +250,7 @@ class ModuleApi:
         self._push_rules_handler = hs.get_push_rules_handler()
         self._device_handler = hs.get_device_handler()
         self.custom_template_dir = hs.config.server.custom_template_directory
+        self._callbacks = hs.get_module_api_callbacks()
 
         try:
             app_name = self._hs.config.email.email_app_name
@@ -271,7 +272,6 @@ class ModuleApi:
         self._account_data_manager = AccountDataManager(hs)
 
         self._spam_checker = hs.get_spam_checker()
-        self._account_validity_handler = hs.get_account_validity_handler()
         self._third_party_event_rules = hs.get_third_party_event_rules()
         self._password_auth_provider = hs.get_password_auth_provider()
         self._presence_router = hs.get_presence_router()
@@ -332,7 +332,7 @@ class ModuleApi:
 
         Added in Synapse v1.39.0.
         """
-        return self._account_validity_handler.register_account_validity_callbacks(
+        return self._callbacks.account_validity.register_callbacks(
             is_user_expired=is_user_expired,
             on_user_registration=on_user_registration,
             on_legacy_send_mail=on_legacy_send_mail,
diff --git a/synapse/module_api/callbacks/__init__.py b/synapse/module_api/callbacks/__init__.py
new file mode 100644
index 0000000000..884c6413cc
--- /dev/null
+++ b/synapse/module_api/callbacks/__init__.py
@@ -0,0 +1,24 @@
+# Copyright 2023 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from .account_validity_callbacks import AccountValidityModuleApiCallbacks
+
+__all__ = [
+    "ModuleApiCallbacks",
+]
+
+
+class ModuleApiCallbacks:
+    def __init__(self) -> None:
+        self.account_validity = AccountValidityModuleApiCallbacks()
diff --git a/synapse/module_api/callbacks/account_validity_callbacks.py b/synapse/module_api/callbacks/account_validity_callbacks.py
new file mode 100644
index 0000000000..661e1146f2
--- /dev/null
+++ b/synapse/module_api/callbacks/account_validity_callbacks.py
@@ -0,0 +1,93 @@
+# Copyright 2023 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+from typing import Awaitable, Callable, List, Optional, Tuple
+
+from twisted.web.http import Request
+
+logger = logging.getLogger(__name__)
+
+# Types for callbacks to be registered via the module api
+IS_USER_EXPIRED_CALLBACK = Callable[[str], Awaitable[Optional[bool]]]
+ON_USER_REGISTRATION_CALLBACK = Callable[[str], Awaitable]
+# Temporary hooks to allow for a transition from `/_matrix/client` endpoints
+# to `/_synapse/client/account_validity`. See `register_account_validity_callbacks`.
+ON_LEGACY_SEND_MAIL_CALLBACK = Callable[[str], Awaitable]
+ON_LEGACY_RENEW_CALLBACK = Callable[[str], Awaitable[Tuple[bool, bool, int]]]
+ON_LEGACY_ADMIN_REQUEST = Callable[[Request], Awaitable]
+
+
+class AccountValidityModuleApiCallbacks:
+    def __init__(self) -> None:
+        self.is_user_expired_callbacks: List[IS_USER_EXPIRED_CALLBACK] = []
+        self.on_user_registration_callbacks: List[ON_USER_REGISTRATION_CALLBACK] = []
+        self.on_legacy_send_mail_callback: Optional[ON_LEGACY_SEND_MAIL_CALLBACK] = None
+        self.on_legacy_renew_callback: Optional[ON_LEGACY_RENEW_CALLBACK] = None
+
+        # The legacy admin requests callback isn't a protected attribute because we need
+        # to access it from the admin servlet, which is outside of this handler.
+        self.on_legacy_admin_request_callback: Optional[ON_LEGACY_ADMIN_REQUEST] = None
+
+    def register_callbacks(
+        self,
+        is_user_expired: Optional[IS_USER_EXPIRED_CALLBACK] = None,
+        on_user_registration: Optional[ON_USER_REGISTRATION_CALLBACK] = None,
+        on_legacy_send_mail: Optional[ON_LEGACY_SEND_MAIL_CALLBACK] = None,
+        on_legacy_renew: Optional[ON_LEGACY_RENEW_CALLBACK] = None,
+        on_legacy_admin_request: Optional[ON_LEGACY_ADMIN_REQUEST] = None,
+    ) -> None:
+        """Register callbacks from module for each hook."""
+        if is_user_expired is not None:
+            self.is_user_expired_callbacks.append(is_user_expired)
+
+        if on_user_registration is not None:
+            self.on_user_registration_callbacks.append(on_user_registration)
+
+        # The builtin account validity feature exposes 3 endpoints (send_mail, renew, and
+        # an admin one). As part of moving the feature into a module, we need to change
+        # the path from /_matrix/client/unstable/account_validity/... to
+        # /_synapse/client/account_validity, because:
+        #
+        #   * the feature isn't part of the Matrix spec thus shouldn't live under /_matrix
+        #   * the way we register servlets means that modules can't register resources
+        #     under /_matrix/client
+        #
+        # We need to allow for a transition period between the old and new endpoints
+        # in order to allow for clients to update (and for emails to be processed).
+        #
+        # Once the email-account-validity module is loaded, it will take control of account
+        # validity by moving the rows from our `account_validity` table into its own table.
+        #
+        # Therefore, we need to allow modules (in practice just the one implementing the
+        # email-based account validity) to temporarily hook into the legacy endpoints so we
+        # can route the traffic coming into the old endpoints into the module, which is
+        # why we have the following three temporary hooks.
+        if on_legacy_send_mail is not None:
+            if self.on_legacy_send_mail_callback is not None:
+                raise RuntimeError("Tried to register on_legacy_send_mail twice")
+
+            self.on_legacy_send_mail_callback = on_legacy_send_mail
+
+        if on_legacy_renew is not None:
+            if self.on_legacy_renew_callback is not None:
+                raise RuntimeError("Tried to register on_legacy_renew twice")
+
+            self.on_legacy_renew_callback = on_legacy_renew
+
+        if on_legacy_admin_request is not None:
+            if self.on_legacy_admin_request_callback is not None:
+                raise RuntimeError("Tried to register on_legacy_admin_request twice")
+
+            self.on_legacy_admin_request_callback = on_legacy_admin_request
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index 357e9a574d..281e8fd0ad 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -683,19 +683,18 @@ class AccountValidityRenewServlet(RestServlet):
     PATTERNS = admin_patterns("/account_validity/validity$")
 
     def __init__(self, hs: "HomeServer"):
-        self.account_activity_handler = hs.get_account_validity_handler()
+        self.account_validity_handler = hs.get_account_validity_handler()
+        self.account_validity_module_callbacks = (
+            hs.get_module_api_callbacks().account_validity
+        )
         self.auth = hs.get_auth()
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         await assert_requester_is_admin(self.auth, request)
 
-        if self.account_activity_handler.on_legacy_admin_request_callback:
-            expiration_ts = (
-                await (
-                    self.account_activity_handler.on_legacy_admin_request_callback(
-                        request
-                    )
-                )
+        if self.account_validity_module_callbacks.on_legacy_admin_request_callback:
+            expiration_ts = await self.account_validity_module_callbacks.on_legacy_admin_request_callback(
+                request
             )
         else:
             body = parse_json_object_from_request(request)
@@ -706,7 +705,7 @@ class AccountValidityRenewServlet(RestServlet):
                     "Missing property 'user_id' in the request body",
                 )
 
-            expiration_ts = await self.account_activity_handler.renew_account_for_user(
+            expiration_ts = await self.account_validity_handler.renew_account_for_user(
                 body["user_id"],
                 body.get("expiration_ts"),
                 not body.get("enable_renewal_emails", True),
diff --git a/synapse/server.py b/synapse/server.py
index df80fc1beb..9bd374ceae 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -108,6 +108,7 @@ from synapse.http.matrixfederationclient import MatrixFederationHttpClient
 from synapse.media.media_repository import MediaRepository
 from synapse.metrics.common_usage_metrics import CommonUsageMetricsManager
 from synapse.module_api import ModuleApi
+from synapse.module_api.callbacks import ModuleApiCallbacks
 from synapse.notifier import Notifier, ReplicationNotifier
 from synapse.push.bulk_push_rule_evaluator import BulkPushRuleEvaluator
 from synapse.push.pusherpool import PusherPool
@@ -778,6 +779,10 @@ class HomeServer(metaclass=abc.ABCMeta):
         return ModuleApi(self, self.get_auth_handler())
 
     @cache_in_self
+    def get_module_api_callbacks(self) -> ModuleApiCallbacks:
+        return ModuleApiCallbacks()
+
+    @cache_in_self
     def get_account_data_handler(self) -> AccountDataHandler:
         return AccountDataHandler(self)