Add server announcement room configuration by anoadragon453 · Pull Request #20353 · element-hq/synapse

anoadragon453 · 2026-10-13T17:03:39Z

WIP

Pull Request Checklist

Pull request is based on the develop branch
Pull request includes a changelog file. The entry should:
- Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
- Use markdown where necessary, mostly for code blocks.
- End with either a period (.) or an exclamation mark (!).
- Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
Code style is correct (run the linters)

github-actions · 2026-10-13T17:06:37Z

Schema Diff

Please check that this looks as expected!

common (sqlite)

Unchanged

common (postgres)

Unchanged

main (sqlite)

--- /tmp/schema_diff_tgjuazit/before/main/full_schemas/9999/full.sql.sqlite	2026-10-15 20:58:05.209617672 +0000
+++ /tmp/schema_diff_tgjuazit/after/main/full_schemas/9999/full.sql.sqlite	2026-10-15 20:57:51.511489320 +0000
@@ -1219,20 +1219,27 @@
     -- all subsequent sticky events for the same room with higher
     -- `stream_id`s are also unsent.
     --
     -- Not a foreign key because we must still support expiration of sticky events.
     sticky_events_stream_position INTEGER NOT NULL,
 
     -- It's enough to track one position per (destination, room_id) pair.
     PRIMARY KEY (destination, room_id)
 );
 CREATE INDEX destination_rooms_sticky_events_backlog_room_id ON destination_rooms_sticky_events_backlog (room_id);
+CREATE TABLE server_announcement_rooms (
+    id TEXT PRIMARY KEY NOT NULL,
+    room_id TEXT UNIQUE NOT NULL,
+    avatar_path TEXT,
+    avatar_sha256 TEXT,
+    avatar_mxc TEXT
+);
 CREATE UNIQUE INDEX receipts_graph_unique_index ON receipts_graph (room_id, receipt_type, user_id) WHERE thread_id IS NULL;
 CREATE UNIQUE INDEX receipts_linearized_unique_index ON receipts_linearized (room_id, receipt_type, user_id) WHERE thread_id IS NULL;
 CREATE INDEX device_lists_changes_in_room_by_room_idx ON device_lists_changes_in_room (room_id, stream_id) ;
 CREATE INDEX events_jump_to_date_idx ON events (room_id, origin_server_ts) WHERE NOT outlier;
 CREATE INDEX room_membership_user_room_idx ON room_memberships (user_id, room_id) ;
 CREATE UNIQUE INDEX profiles_full_user_id_key ON profiles (full_user_id) ;
 CREATE UNIQUE INDEX full_users_unique_idx ON user_filters (full_user_id, filter_id) ;
 CREATE INDEX event_push_actions_stream_highlight_index ON event_push_actions (highlight, stream_ordering) WHERE highlight=0;
 CREATE INDEX current_state_events_stream_ordering_idx ON current_state_events (event_stream_ordering) ;
 CREATE INDEX local_current_membership_stream_ordering_idx ON local_current_membership (event_stream_ordering) ;

main (postgres)

--- /tmp/schema_diff_tgjuazit/before/main/full_schemas/9999/full.sql.postgres	2026-10-15 20:58:05.905624351 +0000
+++ /tmp/schema_diff_tgjuazit/after/main/full_schemas/9999/full.sql.postgres	2026-10-15 20:57:52.284496693 +0000
@@ -1022,20 +1022,27 @@
 CREATE TABLE scheduled_tasks (
     id text NOT NULL,
     action text NOT NULL,
     status text NOT NULL,
     "timestamp" bigint NOT NULL,
     resource_id text,
     params text,
     result text,
     error text
 );
+CREATE TABLE server_announcement_rooms (
+    id text NOT NULL,
+    room_id text NOT NULL,
+    avatar_path text,
+    avatar_sha256 text,
+    avatar_mxc text
+);
 CREATE TABLE server_keys_json (
     server_name text NOT NULL,
     key_id text NOT NULL,
     from_server text NOT NULL,
     ts_added_ms bigint NOT NULL,
     ts_valid_until_ms bigint NOT NULL,
     key_json bytea NOT NULL
 );
 CREATE TABLE server_signature_keys (
     server_name text,
@@ -1572,20 +1579,24 @@
 ALTER TABLE ONLY room_stats_current
     ADD CONSTRAINT room_stats_current_pkey PRIMARY KEY (room_id);
 ALTER TABLE ONLY room_tags_revisions
     ADD CONSTRAINT room_tag_revisions_uniqueness UNIQUE (user_id, room_id);
 ALTER TABLE ONLY room_tags
     ADD CONSTRAINT room_tag_uniqueness UNIQUE (user_id, room_id, tag);
 ALTER TABLE ONLY rooms
     ADD CONSTRAINT rooms_pkey PRIMARY KEY (room_id);
 ALTER TABLE ONLY scheduled_tasks
     ADD CONSTRAINT scheduled_tasks_pkey PRIMARY KEY (id);
+ALTER TABLE ONLY server_announcement_rooms
+    ADD CONSTRAINT server_announcement_rooms_pkey PRIMARY KEY (id);
+ALTER TABLE ONLY server_announcement_rooms
+    ADD CONSTRAINT server_announcement_rooms_room_id_key UNIQUE (room_id);
 ALTER TABLE ONLY server_keys_json
     ADD CONSTRAINT server_keys_json_uniqueness UNIQUE (server_name, key_id, from_server);
 ALTER TABLE ONLY server_signature_keys
     ADD CONSTRAINT server_signature_keys_server_name_key_id_key UNIQUE (server_name, key_id);
 ALTER TABLE ONLY sessions
     ADD CONSTRAINT sessions_session_type_session_id_key UNIQUE (session_type, session_id);
 ALTER TABLE ONLY sliding_sync_connection_positions
     ADD CONSTRAINT sliding_sync_connection_positions_pkey PRIMARY KEY (connection_position);
 ALTER TABLE ONLY sliding_sync_connection_required_state
     ADD CONSTRAINT sliding_sync_connection_required_state_pkey PRIMARY KEY (required_state_id);

state (sqlite)

Unchanged

state (postgres)

Unchanged

anoadragon453 · 2026-10-13T17:26:35Z

schema/synapse-config.schema.yaml should have been updated instead, and then ./scripts-dev/gen_config_documentation.py schema/synapse-config.schema.yaml > docs/usage/configuration/config_documentation.md run to generate the md documentation.

anoadragon453 · 2026-10-13T17:27:49Z

+* `id` (string, required): A unique, nonempty configuration identifier. This is not
+  a Matrix room ID. Keep it stable: it maps the configuration entry to its existing
+  room, so changing the name, topic, avatar, or allowed users does not create a new
+  room. Changing `id` creates a new mapping rather than renaming the existing one.


Suggested change

* `id` (string, required): A unique, nonempty configuration identifier. This is not

a Matrix room ID. Keep it stable: it maps the configuration entry to its existing

room, so changing the name, topic, avatar, or allowed users does not create a new

room. Changing `id` creates a new mapping rather than renaming the existing one.

* `id` (string, required): A unique, nonempty configuration identifier. This is not

a Matrix room ID. It should not be changed after the associated room has been created.

It maps the configuration entry to its existing

room, so changing the name, topic, avatar, or allowed users does not create a new

room. Changing `id` creates a new mapping rather than renaming the existing one.

anoadragon453 · 2026-10-13T17:28:25Z

+
+Each entry is an object with the following options:
+
+* `id` (string, required): A unique, nonempty configuration identifier. This is not


I guess when an announcement room is purged, the mapping should also be deleted.

anoadragon453 · 2026-10-13T17:29:10Z

+* `room_topic` (string|null): An optional topic for the room. Defaults to `null`.
+* `room_avatar_url` (string|null): A valid `mxc://` URI for the **room** avatar.
+  Mutually exclusive with `room_avatar_path`. Defaults to `null`.
+* `room_avatar_path` (string|null): A path to a local file to upload as the **room**


Suggested change

* `room_avatar_path` (string|null): A path to a local file to upload as the **room**

* `room_avatar_path` (string|null): A path to a local file to upload as the room

anoadragon453 · 2026-10-13T17:35:07Z

+  paths are resolved against the process's working directory. Files must be
+  readable by the **main process**, where uploads take place; they do not need to
+  be available on workers. Using this option requires


TODO: This is a concern. There's only ever one media worker. Why can't that worker upload the file?

anoadragon453 · 2026-10-15T17:30:39Z

+
+    async def check_events(
+        self, requester: Requester, events_and_context: Sequence[EventPersistencePair]
+    ) -> None:


Suggested change

) -> None:

) -> None:

"""Check that one or more events may be sent in a local

server announcement room.

Prevent users other than those configured from sending events

in the room. Also prevent any state events, as the rooms are managed by

configuration.

"""

anoadragon453 · 2026-10-15T17:33:18Z

+                    # In particular, allow removed users to leave during cleanup.
+                    # Matrix auth still checks whether the transition is valid.


Suggested change

# In particular, allow removed users to leave during cleanup.

# Matrix auth still checks whether the transition is valid.

anoadragon453 · 2026-10-15T17:35:33Z

+                if (
+                    event.sender != creator
+                    and event.state_key == event.sender
+                    and event.membership in (Membership.JOIN, Membership.LEAVE)
+                ):


Suggested change

if (

event.sender != creator

and event.state_key == event.sender

and event.membership in (Membership.JOIN, Membership.LEAVE)

):

# We need to allow users to join themselves so that we can generate

# join events for allowed users.

#

# We need to allow users to leave themselves so that we can generate

# leave events for users when purging an announcement room.

#

# In both cases, the homeserver is sending membership events on

# behalf of users.

if (

event.sender != creator

and event.state_key == event.sender

and event.membership in (Membership.JOIN, Membership.LEAVE)

):

anoadragon453 · 2026-10-15T17:39:16Z

+        """Cache an uploaded avatar for an existing announcement room mapping.
+
+        The caller supplies the file path, SHA-256 hex digest and uploaded MXC URI.


Suggested change

"""Cache an uploaded avatar for an existing announcement room mapping.

The caller supplies the file path, SHA-256 hex digest and uploaded MXC URI.

"""Cache an uploaded avatar for an existing announcement room mapping.

The sha256 hash allows one to check whether the file has changed on

disk.

anoadragon453 · 2026-10-15T17:49:36Z

+-- Mappings are retained even when announcements are removed from configuration.
+-- There is deliberately no foreign key to rooms: these mappings must not block
+-- normal room purges or disappear as a side effect of a purge.


Actually, I think we should purge mappings when a room is purged. What if someone messes up an announcement room and wants to start over but keep the same nice ID. They wouldn't have any way to do so other than editing the database by hand.

A better lifecycle would be:

An administrator purges the announcement room.

Purging also deletes its announcement mapping.

On the next startup/reconciliation, an entry with that same id creates a new Matrix room and stores the new mapping.

If the administrator wants it gone permanently, they remove the configuration entry as well. If they want to start over, they keep it. That makes the config id identify the logical announcement room, rather than permanently binding it to one Matrix room ID.

anoadragon453 · 2026-10-19T11:20:02Z

Superseded by #20372 and a future PR. This PR ended up needing to be broken into smaller chunks.

anoadragon453 commented Oct 15, 2026

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MadLittleMods added A-Server-Announcements Message all users on a homeserver at once (separate from "Server Notices") A-Config labels Oct 15, 2026

anoadragon453 added 7 commits October 15, 2026 21:54

Add server announcement room configuration

275b603

Persist server announcement room mappings and avatar metadata

3a7860e

Reconcile configured announcement rooms on startup

6a6d41c

Protect server announcement room state and membership

8e8b922

Support announcement reconciliation with separate event writers

da55b1e

Upload and cache configured server announcement avatars

4bcf614

Add changelog for experimental server announcement rooms

59a39c5

anoadragon453 force-pushed the anoa/server_announcements_config_create_rooms branch from e939ae4 to 59a39c5 Compare October 15, 2026 20:55

anoadragon453 closed this Oct 19, 2026


		Each entry is an object with the following options:

		* `id` (string, required): A unique, nonempty configuration identifier. This is not

	* `room_avatar_path` (string\|null): A path to a local file to upload as the room
	* `room_avatar_path` (string\|null): A path to a local file to upload as the room

-    ) -> None:
+    ) -> None:
+    """Check that one or more events may be sent in a local
+    server announcement room.
+    Prevent users other than those configured from sending events
+    in the room. Also prevent any state events, as the rooms are managed by
+    configuration.
+    """

		# In particular, allow removed users to leave during cleanup.
		# Matrix auth still checks whether the transition is valid.

		"""Cache an uploaded avatar for an existing announcement room mapping.

		The caller supplies the file path, SHA-256 hex digest and uploaded MXC URI.

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anoadragon453 commented Oct 13, 2026

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Schema Diff

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