Server: option to maximize send/receive buffers to OS limit

Author: vis2k

kcp2k/Assets/kcp2k/highlevel/KcpServer.cs

@@ -18,6 +18,9 @@ public class KcpServer
         // DualMode uses both IPv6 and IPv4. not all platforms support it.
         // (Nintendo Switch, etc.)
         public bool DualMode;
+        // too small send/receive buffers might cause connection drops under
+        // heavy load. using the OS max size can make a difference already.
+        public bool MaximizeSendReceiveBuffersToOSLimit = true;
 
         // kcp configuration
         // NoDelay is recommended to reduce latency. This also scales better
@@ -94,6 +97,43 @@ public KcpServer(Action<int> OnConnected,
 
         public bool IsActive() => socket != null;
 
+        // if connections drop under heavy load, increase to OS limit.
+        // if still not enough, increase the OS limit.
+        void ConfigureSocketBufferSizes()
+        {
+            if (MaximizeSendReceiveBuffersToOSLimit)
+            {
+                // log initial size for comparison.
+                // remember initial size for log comparison
+                int initialReceive = socket.ReceiveBufferSize;
+                int initialSend = socket.SendBufferSize;
+
+                // 100k attempts of 1 KB increases = default + 100 MB max
+                const int attempts = 100_000;
+                const int increase = 1024;
+
+                // setting a too large size throws a socket exception.
+                // so let's keep increasing until we encounter it.
+                for (int i = 0; i < attempts; ++i)
+                {
+                    // increase in 1 KB steps
+                    try { socket.ReceiveBufferSize += increase; }
+                    catch (SocketException) { break; }
+                }
+
+                for (int i = 0; i < attempts; ++i)
+                {
+                    // increase in 1 KB steps
+                    try { socket.SendBufferSize += increase; }
+                    catch (SocketException) { break; }
+                }
+
+                Log.Info($"KcpServer: RecvBuf = {initialReceive}=>{socket.ReceiveBufferSize} ({socket.ReceiveBufferSize/initialReceive}x) SendBuf = {initialSend}=>{socket.SendBufferSize} ({socket.SendBufferSize/initialSend}x) increased to OS limits!");
+            }
+            // otherwise still log the defaults for info.
+            else Log.Info($"KcpServer: RecvBuf = {socket.ReceiveBufferSize} SendBuf = {socket.SendBufferSize}. If connections drop under heavy load, enable {nameof(MaximizeSendReceiveBuffersToOSLimit)} to increase it to OS limit. If they still drop, increase the OS limit.");
+        }
+
         public void Start(ushort port)
         {
             // only start once
@@ -117,10 +157,8 @@ public void Start(ushort port)
                 socket.Bind(new IPEndPoint(IPAddress.Any, port));
             }
 
-            // show socket buffer size.
-            // if connections drop under heavy load, increase to OS limit.
-            // if still not enough, increase the OS limit.
-            Log.Info($"KcpServer: RecvBuf = {socket.ReceiveBufferSize} SendBuf = {socket.SendBufferSize}. If connections drop under heavy load, increase to OS limit. If they still drop, increase the OS limit.");
+            // configure socket buffer size.
+            ConfigureSocketBufferSizes();
         }
 
         public void Send(int connectionId, ArraySegment<byte> segment, KcpChannel channel)