Add time ping handling (#503)

client -> server `t[8 bytes]`
server -> client `t[client's 8 bytes][server time 8 bytes]`

---

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generated or otherwise automatically generated may be rejected without
further discussion.
I declare that I fully understand all code I pushed into this PR, and
wrote all this code myself and own the rights to this code.

include/TServer.h

@@ -53,7 +53,10 @@ public:
 
     io_context& IoCtx() { return mIoCtxPoller.IoCtx(); }
 
+    uint64_t GetServerTimeMS() const { return std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - TimeSyncStart).count();}
+    double GetServerTime() const { return std::chrono::duration<double>(std::chrono::steady_clock::now() - TimeSyncStart).count(); }
 private:
+    std::chrono::time_point<std::chrono::steady_clock> TimeSyncStart;
     TIoPollThread mIoCtxPoller;
     TClientSet mClients;
     mutable RWMutex mClientsMutex;

src/TLuaEngine.cpp

@@ -1012,6 +1012,14 @@ TLuaEngine::StateThreadData::StateThreadData(const std::string& Name, TLuaStateI
     }
     MPTable.set_function("Get", &LuaAPI::MP::Get);
 
+    MPTable.set_function("GetServerTimeMS", [this](const sol::this_state ts) {
+        return make_object(sol::state_view(ts), this->mEngine->Server().GetServerTimeMS());
+    });
+
+    MPTable.set_function("GetServerTime", [this](const sol::this_state ts) {
+        return make_object(sol::state_view(ts), this->mEngine->Server().GetServerTime());
+    });
+
     auto UtilTable = StateView.create_named_table("Util");
     UtilTable.set_function("LogDebug", [this](sol::variadic_args args) {
         std::string ToPrint = "";

src/TServer.cpp

@@ -123,6 +123,12 @@ TEST_CASE("GetPidVid") {
 TServer::TServer(const std::vector<std::string_view>& Arguments) {
     beammp_info("BeamMP Server v" + Application::ServerVersionString());
     Application::SetSubsystemStatus("Server", Application::Status::Starting);
+    std::mt19937_64 TimeSyncRandomDevice(std::random_device{}());
+
+    TimeSyncStart = std::chrono::steady_clock::now()
+        - std::chrono::duration_cast<std::chrono::steady_clock::duration>(
+            std::chrono::duration<double>(std::uniform_real_distribution<double>(0.0, 2592000.0)(TimeSyncRandomDevice))
+        );
     Application::SetSubsystemStatus("Server", Application::Status::Good);
 }
 
@@ -210,6 +216,24 @@ void TServer::GlobalParser(const std::weak_ptr<TClient>& Client, std::vector<uin
         return;
     }
     switch (Code) {
+    case 't':
+        if (!udp && Packet.size() == 9) {
+            auto Time = GetServerTimeMS();
+
+            std::vector<uint8_t> ServerTime(sizeof(uint64_t));
+            std::memcpy(ServerTime.data(), &Time, sizeof(uint64_t));
+
+            auto Data = Packet;
+
+            beammp_debugf("Sending server time {} to client  '{}' ({}), client time: {}", Time, LockedClient->GetName(), LockedClient->GetID(), reinterpret_cast<uint64_t>(Data.data()));
+
+            Data.insert(Data.end(), ServerTime.begin(), ServerTime.end());
+
+            if (!Network.Respond(*LockedClient, Data, true)) {
+                Network.DisconnectClient(*LockedClient, "Failed to send time");
+            }
+        }
+        return;
     case 'H': // initial connection
         if (udp) {
             beammp_debugf("Received 'H' packet over UDP from client '{}' ({}), ignoring it", LockedClient->GetName(), LockedClient->GetID());