Try to set canonical room alias on room creation.

The spec does not require servers to apply a room canonical alias event upon room creation (yet).
Still, synapse does that, since users can set their desired alias in Elements room creation dialog.
With this commit, conduit also sets that alias if it is a valid one.

This closes https://gitlab.com/famedly/conduit/-/issues/123

src/client_server/room.rs

@@ -43,24 +43,24 @@ pub async fn create_room_route(
     );
     let state_lock = mutex_state.lock().await;
 
-    let alias = body
-        .room_alias_name
-        .as_ref()
-        .map_or(Ok(None), |localpart| {
-            // TODO: Check for invalid characters and maximum length
-            let alias =
-                RoomAliasId::try_from(format!("#{}:{}", localpart, db.globals.server_name()))
-                    .map_err(|_| Error::BadRequest(ErrorKind::InvalidParam, "Invalid alias."))?;
+    let alias: Option<RoomAliasId> =
+        body.room_alias_name
+            .as_ref()
+            .map_or(Ok(None), |localpart| {
+                // TODO: Check for invalid characters and maximum length
+                let alias =
+                    RoomAliasId::try_from(format!("#{}:{}", localpart, db.globals.server_name()))
+                        .map_err(|_| Error::BadRequest(ErrorKind::InvalidParam, "Invalid alias."))?;
 
-            if db.rooms.id_from_alias(&alias)?.is_some() {
-                Err(Error::BadRequest(
-                    ErrorKind::RoomInUse,
-                    "Room alias already exists.",
-                ))
-            } else {
-                Ok(Some(alias))
-            }
-        })?;
+                if db.rooms.id_from_alias(&alias)?.is_some() {
+                    Err(Error::BadRequest(
+                        ErrorKind::RoomInUse,
+                        "Room alias already exists.",
+                    ))
+                } else {
+                    Ok(Some(alias))
+                }
+            })?;
 
     let mut content = ruma::events::room::create::CreateEventContent::new(sender_user.clone());
     content.federate = body.creation_content.federate;
@@ -172,9 +172,33 @@ pub async fn create_room_route(
         &state_lock,
     )?;
 
-    // 4. Events set by preset
+    // 4. Canonical room alias
 
-    // 4.1 Join Rules
+    if let Some(room_alias_id) = &alias {
+        db.rooms.build_and_append_pdu(
+            PduBuilder {
+                event_type: EventType::RoomCanonicalAlias,
+                content: serde_json::to_value(
+                    ruma::events::room::canonical_alias::CanonicalAliasEventContent {
+                        alias: Some(room_alias_id.clone()),
+                        alt_aliases: vec![],
+                    },
+                )
+                .expect("We checked that alias earlier, it must be fine"),
+                unsigned: None,
+                state_key: Some("".to_owned()),
+                redacts: None,
+            },
+            &sender_user,
+            &room_id,
+            &db,
+            &state_lock,
+        );
+    }
+
+    // 5. Events set by preset
+
+    // 5.1 Join Rules
     db.rooms.build_and_append_pdu(
         PduBuilder {
             event_type: EventType::RoomJoinRules,
@@ -199,7 +223,7 @@ pub async fn create_room_route(
         &state_lock,
     )?;
 
-    // 4.2 History Visibility
+    // 5.2 History Visibility
     db.rooms.build_and_append_pdu(
         PduBuilder {
             event_type: EventType::RoomHistoryVisibility,
@@ -217,7 +241,7 @@ pub async fn create_room_route(
         &state_lock,
     )?;
 
-    // 4.3 Guest Access
+    // 5.3 Guest Access
     db.rooms.build_and_append_pdu(
         PduBuilder {
             event_type: EventType::RoomGuestAccess,
@@ -243,7 +267,7 @@ pub async fn create_room_route(
         &state_lock,
     )?;
 
-    // 5. Events listed in initial_state
+    // 6. Events listed in initial_state
     for event in &body.initial_state {
         let pdu_builder = PduBuilder::from(event.deserialize().map_err(|e| {
             warn!("Invalid initial state event: {:?}", e);
@@ -259,7 +283,7 @@ pub async fn create_room_route(
             .build_and_append_pdu(pdu_builder, &sender_user, &room_id, &db, &state_lock)?;
     }
 
-    // 6. Events implied by name and topic
+    // 7. Events implied by name and topic
     if let Some(name) = &body.name {
         db.rooms.build_and_append_pdu(
             PduBuilder {
@@ -296,7 +320,7 @@ pub async fn create_room_route(
         )?;
     }
 
-    // 7. Events implied by invite (and TODO: invite_3pid)
+    // 8. Events implied by invite (and TODO: invite_3pid)
     drop(state_lock);
     for user_id in &body.invite {
         let _ = invite_helper(sender_user, user_id, &room_id, &db, body.is_direct).await;