ppy/osu · error · InvalidOperationException

Cannot join an inactive room.

Error message

Cannot join an inactive room.

What it means

Thrown by MultiplayerClient.JoinRoom when the passed Room has no RoomID. A room must exist server-side (have been created) to be joinable; a locally constructed Room with null RoomID cannot be joined.

Source

Thrown at osu.Game/Online/Multiplayer/MultiplayerClient.cs:264

                await runOnUpdateThreadAsync(() => pendingRequests.Clear(), cancellationSource.Token).ConfigureAwait(false);
                var multiplayerRoom = await CreateRoomInternal(new MultiplayerRoom(room)).ConfigureAwait(false);
                await setupJoinedRoom(room, multiplayerRoom, cancellationSource.Token).ConfigureAwait(false);
            }, cancellationSource.Token).ConfigureAwait(false);
        }

        /// <summary>
        /// Joins the <see cref="MultiplayerRoom"/> for a given API <see cref="Room"/>.
        /// </summary>
        /// <param name="room">The API <see cref="Room"/>.</param>
        /// <param name="password">An optional password to use for the join operation.</param>
        /// <exception cref="InvalidOperationException">If the current user is already in another room, or <paramref name="room"/> does not represent an active room.</exception>
        public async Task JoinRoom(Room room, string? password = null)
        {
            if (Room != null)
                throw new InvalidOperationException("Cannot join a multiplayer room while already in one.");

            if (room.RoomID == null)
                throw new InvalidOperationException("Cannot join an inactive room.");

            var cancellationSource = joinCancellationSource = new CancellationTokenSource();

            await joinOrLeaveTaskChain.Add(async () =>
            {
                await runOnUpdateThreadAsync(() => pendingRequests.Clear(), cancellationSource.Token).ConfigureAwait(false);
                var multiplayerRoom = await JoinRoomInternal(room.RoomID.Value, password ?? room.Password).ConfigureAwait(false);
                await setupJoinedRoom(room, multiplayerRoom, cancellationSource.Token).ConfigureAwait(false);
            }, cancellationSource.Token).ConfigureAwait(false);
        }

        /// <summary>
        /// Performs post-join setup of a <see cref="MultiplayerRoom"/>.
        /// </summary>
        /// <param name="apiRoom">The incoming API <see cref="Room"/> that was requested to be joined.</param>
        /// <param name="joinedRoom">The resuling <see cref="MultiplayerRoom"/> that was joined.</param>
        /// <param name="cancellationToken">A token to cancel the process.</param>
        private async Task setupJoinedRoom(Room apiRoom, MultiplayerRoom joinedRoom, CancellationToken cancellationToken)

View on GitHub (pinned to d9c73e12ad)

Solutions

1. Only join rooms obtained from the API listing (CreateRoom result or a fetched Room) so RoomID is populated.
2. Guard: if (room.RoomID == null) reject the join in the UI.
3. Verify the API response deserialized RoomID correctly (check JSON property mapping).

Example fix

// before
await client.JoinRoom(new Room { Name = "test" });

// after
if (room.RoomID == null) throw new InvalidOperationException("room not created server-side");
await client.JoinRoom(room);

if (room.RoomID == null)
    throw new InvalidOperationException("Cannot join: room has no RoomID.");
await client.JoinRoom(room, password);

bool IsJoinable(Room room) => room.RoomID.HasValue;

try { await client.JoinRoom(room, password); }
catch (InvalidOperationException ex) { /* inactive room: require a created/listed Room */ }

When it happens

Trigger: Calling JoinRoom(room) where room.RoomID == null, i.e. using a Room instance that was never created via CreateRoom or fetched from the API room listings.

Common situations: Passing a freshly `new Room { Name = ... }` to JoinRoom instead of a Room object returned from the API listing endpoint; deserialization dropping the RoomID field.

Related errors

• Cannot create a multiplayer room while already in one.
• Cannot join a multiplayer room while already in one.
• Must be joined to a match to change settings.
• Cannot toggle ready when in {localUser.State}
• Cannot toggle spectate when in {localUser.State}

AI-assisted analysis of ppy/osu@d9c73e12ad (2026-08-13). Data as JSON: /api/errors/f3504286406357ea. Report an issue: GitHub.