Multiplayer: Send an error message when connecting to a full room

src/network/room.cpp

@@ -68,6 +68,11 @@ public:
      */
     bool IsValidMacAddress(const MacAddress& address) const;
 
+    /**
+     * Sends a ID_ROOM_IS_FULL message telling the client that the room is full.
+     */
+    void SendRoomIsFull(ENetPeer* client);
+
     /**
      * Sends a ID_ROOM_NAME_COLLISION message telling the client that the name is invalid.
      */
@@ -193,6 +198,13 @@ void Room::RoomImpl::StartLoop() {
 }
 
 void Room::RoomImpl::HandleJoinRequest(const ENetEvent* event) {
+    {
+        std::lock_guard<std::mutex> lock(member_mutex);
+        if (members.size() >= room_information.member_slots) {
+            SendRoomIsFull(event->peer);
+            return;
+        }
+    }
     Packet packet;
     packet.Append(event->packet->data, event->packet->dataLength);
     packet.IgnoreBytes(sizeof(u8)); // Ignore the message type
@@ -295,6 +307,16 @@ void Room::RoomImpl::SendWrongPassword(ENetPeer* client) {
     enet_host_flush(server);
 }
 
+void Room::RoomImpl::SendRoomIsFull(ENetPeer* client) {
+    Packet packet;
+    packet << static_cast<u8>(IdRoomIsFull);
+
+    ENetPacket* enet_packet =
+        enet_packet_create(packet.GetData(), packet.GetDataSize(), ENET_PACKET_FLAG_RELIABLE);
+    enet_peer_send(client, 0, enet_packet);
+    enet_host_flush(server);
+}
+
 void Room::RoomImpl::SendVersionMismatch(ENetPeer* client) {
     Packet packet;
     packet << static_cast<u8>(IdVersionMismatch);
@@ -527,7 +549,9 @@ bool Room::Create(const std::string& name, const std::string& server_address, u1
     }
     address.port = server_port;
 
-    room_impl->server = enet_host_create(&address, max_connections, NumChannels, 0, 0);
+    // In order to send the room is full message to the connecting client, we need to leave one slot
+    // open so enet won't reject the incoming connection without telling us
+    room_impl->server = enet_host_create(&address, max_connections + 1, NumChannels, 0, 0);
     if (!room_impl->server) {
         return false;
     }

src/network/room.h

@@ -57,7 +57,8 @@ enum RoomMessageTypes : u8 {
     IdMacCollision,
     IdVersionMismatch,
     IdWrongPassword,
-    IdCloseRoom
+    IdCloseRoom,
+    IdRoomIsFull,
 };
 
 /// This is what a server [person creating a server] would use.

src/network/room_member.cpp

@@ -154,6 +154,9 @@ void RoomMember::RoomMemberImpl::MemberLoop() {
                     HandleJoinPacket(&event); // Get the MAC Address for the client
                     SetState(State::Joined);
                     break;
+                case IdRoomIsFull:
+                    SetState(State::RoomIsFull);
+                    break;
                 case IdNameCollision:
                     SetState(State::NameCollision);
                     break;

src/network/room_member.h

@@ -54,11 +54,12 @@ public:
         LostConnection, ///< Connection closed
 
         // Reasons why connection was rejected
-        NameCollision,  ///< Somebody is already using this name
-        MacCollision,   ///< Somebody is already using that mac-address
-        WrongVersion,   ///< The room version is not the same as for this RoomMember
-        WrongPassword,  ///< The password doesn't match the one from the Room
-        CouldNotConnect ///< The room is not responding to a connection attempt
+        NameCollision,   ///< Somebody is already using this name
+        MacCollision,    ///< Somebody is already using that mac-address
+        WrongVersion,    ///< The room version is not the same as for this RoomMember
+        WrongPassword,   ///< The password doesn't match the one from the Room
+        CouldNotConnect, ///< The room is not responding to a connection attempt
+        RoomIsFull       ///< Room is already at the maximum number of players
     };
 
     struct MemberInformation {