implement connection limiter to replace manual limiting code

include/TConnectionLimiter.h

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <mutex>
+#include <optional>
+#include <string>
+#include <unordered_map>
+#include <utility>
+
+class TConnectionLimiter {
+public:
+    class TGuard {
+    public:
+        TGuard() = default;
+        TGuard(TConnectionLimiter* owner, std::string ip);
+
+        TGuard(const TGuard&) = delete;
+        TGuard& operator=(const TGuard&) = delete;
+
+        ~TGuard() { Release(); }
+
+        // not threadsafe
+        TGuard(TGuard&& other) noexcept { *this = std::move(other); }
+        // not threadsafe
+        TGuard& operator=(TGuard&& other) noexcept;
+
+    private:
+        friend class TConnectionLimiter;
+
+        // not threadsafe
+        void Release();
+
+        TConnectionLimiter* mOwner { nullptr };
+        std::string mIp;
+    };
+
+    TConnectionLimiter(size_t maxPerIp, size_t maxGlobal);
+
+    [[nodiscard]] std::optional<TGuard> TryAcquire(const std::string& ip);
+
+private:
+    void Release(const std::string& ip) {
+        std::unique_lock Lock { mMutex };
+        auto It = mPerIp.find(ip);
+        if (It != mPerIp.end()) {
+            // this guard exists to avoid underflow in case something goes wrong and this gets called too many times
+            if (It->second > 0)
+                --It->second;
+            if (It->second == 0)
+                mPerIp.erase(It);
+        }
+        // this guard exists to avoid underflow in case something goes wrong and this gets called too many times
+        if (mGlobal > 0)
+            --mGlobal;
+    }
+
+    const size_t mMaxPerIp;
+    const size_t mMaxGlobal;
+
+    std::mutex mMutex { };
+    std::unordered_map<std::string, size_t> mPerIp { };
+    size_t mGlobal = 0;
+};

include/TNetwork.h

@@ -20,6 +20,7 @@
 
 #include "BoostAliases.h"
 #include "Compat.h"
+#include "TConnectionLimiter.h"
 #include "TResourceManager.h"
 #include "TServer.h"
 #include <boost/asio/io_context.hpp>
@@ -40,7 +41,7 @@ public:
     void DisconnectClient(const std::weak_ptr<TClient>& c, const std::string& R);
     void DisconnectClient(TClient& c, const std::string& R);
     [[nodiscard]] bool SyncClient(const std::weak_ptr<TClient>& c);
-    void Identify(TConnection&& client);
+    void Identify(TConnection&& client, TConnectionLimiter::TGuard&&);
     std::shared_ptr<TClient> Authentication(TConnection&& ClientConnection);
     void SyncResources(TClient& c);
     [[nodiscard]] bool UDPSend(TClient& Client, std::vector<uint8_t> Data);
@@ -61,8 +62,7 @@ private:
     std::thread mUDPThread;
     std::thread mTCPThread;
     std::mutex mOpenIDMutex;
-    std::map<std::string, uint16_t> mClientMap;
-    std::mutex mClientMapMutex;
+    TConnectionLimiter mConnectionLimiter;
 
     std::vector<uint8_t> UDPRcvFromClient(boost::asio::ip::udp::endpoint& ClientEndpoint);
     void OnConnect(const std::weak_ptr<TClient>& c);