Prevent undefined behaviour if too many players joined battle or soccer

src/network/protocols/server_lobby.cpp

@@ -2456,7 +2456,7 @@ void ServerLobby::startSelection(const Event *event)
     if (!has_peer_plays_game)
     {
         for (STKPeer* peer : always_spectate_peers)
-            peer->setAlwaysSpectate(false);
+            peer->setAlwaysSpectate(ASM_NONE);
         always_spectate_peers.clear();
     }
     else
@@ -2469,6 +2469,40 @@ void ServerLobby::startSelection(const Event *event)
             peer->setWaitingForGame(true);
     }
 
+    unsigned max_player = 0;
+    STKHost::get()->updatePlayers(&max_player);
+
+    if (max_player > 10 && (RaceManager::get()->isBattleMode() ||
+        RaceManager::get()->isSoccerMode()))
+    {
+        // Set late coming player to spectate if too many players in battle or
+        // soccer
+        std::sort(peers.begin(), peers.end(),
+            [](const std::shared_ptr<STKPeer>& a,
+            const std::shared_ptr<STKPeer>& b)
+            { return a->getHostId() > b->getHostId(); });
+        int remove_player = max_player - 10;
+        for (unsigned i = 0; i < peers.size(); i++)
+        {
+            auto& peer = peers[i];
+            if (!peer->isValidated() || peer->isWaitingForGame())
+                continue;
+            peer->setAlwaysSpectate(ASM_FULL);
+            peer->setWaitingForGame(true);
+            always_spectate_peers.insert(peer.get());
+            remove_player -= (int)peer->getPlayerProfiles().size();
+            if (remove_player <= 0)
+                break;
+            // In case something goes wrong (all players need spectate)
+            if (i == peers.size() - 1)
+            {
+                Log::error("ServerLobby", "Too many players and cannot set "
+                    "spectate for late coming players!");
+                return;
+            }
+        }
+    }
+
     for (const std::string& kart_erase : karts_erase)
     {
         m_available_kts.first.erase(kart_erase);
@@ -2478,7 +2512,7 @@ void ServerLobby::startSelection(const Event *event)
         m_available_kts.second.erase(track_erase);
     }
 
-    unsigned max_player = 0;
+    max_player = 0;
     STKHost::get()->updatePlayers(&max_player);
     if (auto ai = m_ai_peer.lock())
     {
@@ -4684,6 +4718,7 @@ void ServerLobby::addWaitingPlayersToGame()
         if (!peer || !peer->isValidated())
             continue;
 
+        peer->resetAlwaysSpectateFull();
         peer->setWaitingForGame(false);
         peer->setSpectator(false);
         if (m_peers_ready.find(peer) == m_peers_ready.end())
@@ -5522,10 +5557,10 @@ void ServerLobby::handleServerCommand(Event* event,
                 delete chat;
                 return;
             }
-            peer->setAlwaysSpectate(true);
+            peer->setAlwaysSpectate(ASM_COMMAND);
         }
         else
-            peer->setAlwaysSpectate(false);
+            peer->setAlwaysSpectate(ASM_NONE);
         updatePlayerList();
     }
     else if (argv[0] == "listserveraddon")

src/network/stk_peer.cpp

@@ -44,7 +44,7 @@ STKPeer::STKPeer(ENetPeer *enet_peer, STKHost* host, uint32_t host_id)
     m_host_id             = host_id;
     m_connected_time      = StkTime::getMonoTimeMs();
     m_validated.store(false);
-    m_always_spectate.store(false);
+    m_always_spectate.store(ASM_NONE);
     m_average_ping.store(0);
     m_packet_loss.store(0);
     m_waiting_for_game.store(true);

src/network/stk_peer.hpp

@@ -61,6 +61,13 @@ enum AddonScore : int
     AS_TOTAL = 4,
 };   // AddonScore
 
+enum AlwaysSpectateMode : uint8_t
+{
+    ASM_NONE = 0, //!< Default, not spectating at all
+    ASM_COMMAND = 1, //!< Set by player through command
+    ASM_FULL = 2, //!< Set by server because too many players joined
+};   // AlwaysSpectateMode
+
 /*! \class STKPeer
  *  \brief Represents a peer.
  *  This class is used to interface the ENetPeer structure.
@@ -85,7 +92,7 @@ protected:
 
     std::atomic_bool m_warned_for_high_ping;
 
-    std::atomic_bool m_always_spectate;
+    std::atomic<uint8_t> m_always_spectate;
 
     /** Host id of this peer. */
     uint32_t m_host_id;
@@ -292,10 +299,17 @@ public:
     // ------------------------------------------------------------------------
     const SocketAddress& getAddress() const { return *m_socket_address.get(); }
     // ------------------------------------------------------------------------
-    void setAlwaysSpectate(bool val)          { m_always_spectate.store(val); }
+    void setAlwaysSpectate(AlwaysSpectateMode mode)
+                                             { m_always_spectate.store(mode); }
     // ------------------------------------------------------------------------
-    bool alwaysSpectate() const            { return m_always_spectate.load(); }
-
+    bool alwaysSpectate() const
+                               { return m_always_spectate.load() != ASM_NONE; }
+    // ------------------------------------------------------------------------
+    void resetAlwaysSpectateFull()
+    {
+        if (m_always_spectate.load() == ASM_FULL)
+            m_always_spectate.store(ASM_NONE);
+    }
 };   // STKPeer
 
 #endif // STK_PEER_HPP