breaking: fix: kcp2k V1.16

- fix: SendUnreliable respects ArraySegment.Offset
- fix: potential bug with negative length (see PR #2)
- breaking: removed pause handling because it's not necessary for Mirror anymore

Assets/Mirror/Runtime/Transport/KCP/MirrorTransport/KcpTransport.cs

@@ -162,35 +162,14 @@ public override void ClientSend(ArraySegment<byte> segment, int channelId)
         // process incoming in early update
         public override void ClientEarlyUpdate()
         {
-            // scene change messages disable transports to stop them from
+            // only process messages while transport is enabled.
-            // processing while changing the scene.
+            // scene change messsages disable it to stop processing.
-            // -> we need to check enabled here
-            // -> and in kcp's internal loops, see Awake() OnCheckEnabled setup!
             // (see also: https://github.com/vis2k/Mirror/pull/379)
             if (enabled) client.TickIncoming();
         }
         // process outgoing in late update
         public override void ClientLateUpdate() => client.TickOutgoing();
 
-        // scene change message will disable transports.
-        // kcp processes messages in an internal loop which should be
-        // stopped immediately after scene change (= after disabled)
-        // => kcp has tests to guaranteed that calling .Pause() during the
-        //    receive loop stops the receive loop immediately, not after.
-        void OnEnable()
-        {
-            // unpause when enabled again
-            client?.Unpause();
-            server?.Unpause();
-        }
-
-        void OnDisable()
-        {
-            // pause immediately when not enabled anymore
-            client?.Pause();
-            server?.Pause();
-        }
-
         // server
         public override Uri ServerUri()
         {
@@ -211,10 +190,8 @@ public override void ServerSend(int connectionId, ArraySegment<byte> segment, in
         public override void ServerStop() => server.Stop();
         public override void ServerEarlyUpdate()
         {
-            // scene change messages disable transports to stop them from
+            // only process messages while transport is enabled.
-            // processing while changing the scene.
+            // scene change messsages disable it to stop processing.
-            // -> we need to check enabled here
-            // -> and in kcp's internal loops, see Awake() OnCheckEnabled setup!
             // (see also: https://github.com/vis2k/Mirror/pull/379)
             if (enabled) server.TickIncoming();
         }

Assets/Mirror/Runtime/Transport/KCP/kcp2k/VERSION

@@ -1,3 +1,8 @@
+V1.16 [2022-01-06]
+- fix: SendUnreliable respects ArraySegment.Offset
+- fix: potential bug with negative length (see PR #2)
+- breaking: removed pause handling because it's not necessary for Mirror anymore
+
 V1.15 [2021-12-11]
 - feature: feature: MaxRetransmits aka dead_link now configurable
 - dead_link disconnect message improved to show exact retransmit count

Assets/Mirror/Runtime/Transport/KCP/kcp2k/highlevel/KcpClient.cs

@@ -111,10 +111,5 @@ public void Tick()
             TickIncoming();
             TickOutgoing();
         }
-
-        // pause/unpause to safely support mirror scene handling and to
-        // immediately pause the receive while loop if needed.
-        public void Pause() => connection?.Pause();
-        public void Unpause() => connection?.Unpause();
     }
 }

Assets/Mirror/Runtime/Transport/KCP/kcp2k/highlevel/KcpClientConnection.cs

@@ -17,6 +17,7 @@ public static bool ResolveHostname(string hostname, out IPAddress[] addresses)
         {
             try
             {
+                // NOTE: dns lookup is blocking. this can take a second.
                 addresses = Dns.GetHostAddresses(hostname);
                 return addresses.Length >= 1;
             }

Assets/Mirror/Runtime/Transport/KCP/kcp2k/highlevel/KcpConnection.cs

@@ -20,12 +20,6 @@ public abstract class KcpConnection
         public Action<ArraySegment<byte>, KcpChannel> OnData;
         public Action OnDisconnected;
 
-        // Mirror needs a way to stop the kcp message processing while loop
-        // immediately after a scene change message. Mirror can't process any
-        // other messages during a scene change.
-        // (could be useful for others too)
-        bool paused;
-
         // If we don't receive anything these many milliseconds
         // then consider us disconnected
         public const int DEFAULT_TIMEOUT = 10000;
@@ -315,19 +309,7 @@ void TickIncoming_Authenticated(uint time)
             HandleChoked();
 
             // process all received messages
-            //
+            while (ReceiveNextReliable(out KcpHeader header, out ArraySegment<byte> message))
-            // Mirror scene changing requires transports to immediately stop
-            // processing any more messages after a scene message was
-            // received. and since we are in a while loop here, we need this
-            // extra check.
-            //
-            // note while that this is mainly for Mirror, but might be
-            // useful in other applications too.
-            //
-            // note that we check it BEFORE ever calling ReceiveNext. otherwise
-            // we would silently eat the received message and never process it.
-            while (!paused &&
-                   ReceiveNextReliable(out KcpHeader header, out ArraySegment<byte> message))
             {
                 // message type FSM. no default so we never miss a case.
                 switch (header)
@@ -499,15 +481,8 @@ public void RawInput(byte[] buffer, int msgLength)
                         //    the current state allows it.
                         if (state == KcpState.Authenticated)
                         {
-                            // only process messages while not paused for Mirror
+                            ArraySegment<byte> message = new ArraySegment<byte>(buffer, 1, msgLength - 1);
-                            // scene switching etc.
+                            OnData?.Invoke(message, KcpChannel.Unreliable);
-                            // -> if an unreliable message comes in while
-                            //    paused, simply drop it. it's unreliable!
-                            if (!paused)
-                            {
-                                ArraySegment<byte> message = new ArraySegment<byte>(buffer, 1, msgLength - 1);
-                                OnData?.Invoke(message, KcpChannel.Unreliable);
-                            }
 
                             // set last receive time to avoid timeout.
                             // -> we do this in ANY case even if not enabled.
@@ -578,7 +553,7 @@ void SendUnreliable(ArraySegment<byte> message)
             {
                 // copy channel header, data into raw send buffer, then send
                 rawSendBuffer[0] = (byte)KcpChannel.Unreliable;
-                Buffer.BlockCopy(message.Array, 0, rawSendBuffer, 1, message.Count);
+                Buffer.BlockCopy(message.Array, message.Offset, rawSendBuffer, 1, message.Count);
                 RawSend(rawSendBuffer, message.Count + 1);
             }
             // otherwise content is larger than MaxMessageSize. let user know!
@@ -668,24 +643,5 @@ public void Disconnect()
 
         // get remote endpoint
         public EndPoint GetRemoteEndPoint() => remoteEndPoint;
-
-        // pause/unpause to safely support mirror scene handling and to
-        // immediately pause the receive while loop if needed.
-        public void Pause() => paused = true;
-        public void Unpause()
-        {
-            // unpause
-            paused = false;
-
-            // reset the timeout.
-            // we have likely been paused for > timeout seconds, but that
-            // doesn't mean we should disconnect. for example, Mirror pauses
-            // kcp during scene changes which could easily take > 10s timeout:
-            //   see also: https://github.com/vis2k/kcp2k/issues/8
-            // => Unpause completely resets the timeout instead of restoring the
-            //    time difference when we started pausing. it's more simple and
-            //    it's a good idea to start counting from 0 after we unpaused!
-            lastReceiveTime = (uint)refTime.ElapsedMilliseconds;
-        }
     }
 }

Assets/Mirror/Runtime/Transport/KCP/kcp2k/highlevel/KcpServer.cs

@@ -323,19 +323,5 @@ public void Stop()
             socket?.Close();
             socket = null;
         }
-
-        // pause/unpause to safely support mirror scene handling and to
-        // immediately pause the receive while loop if needed.
-        public void Pause()
-        {
-            foreach (KcpServerConnection connection in connections.Values)
-                connection.Pause();
-        }
-
-        public void Unpause()
-        {
-            foreach (KcpServerConnection connection in connections.Values)
-                connection.Unpause();
-        }
     }
 }

Assets/Mirror/Runtime/Transport/KCP/kcp2k/kcp/Kcp.cs

@@ -27,7 +27,7 @@ public class Kcp
         public const int INTERVAL = 100;
         public const int OVERHEAD = 24;
         public const int FRG_MAX = byte.MaxValue;  // kcp encodes 'frg' as byte. so we can only ever send up to 255 fragments.
-        public const int DEADLINK = 20;            // default maximum amount of 'xmit' retransmissions until a message is considered lost
+        public const int DEADLINK = 20;            // default maximum amount of 'xmit' retransmissions until a segment is considered lost
         public const int THRESH_INIT = 2;
         public const int THRESH_MIN = 2;
         public const int PROBE_INIT = 7000;        // 7 secs to probe window size
@@ -65,7 +65,7 @@ internal struct AckItem
         internal bool updated;
         internal uint ts_probe;      // timestamp probe
         internal uint probe_wait;
-        internal uint dead_link;     // maximum amount of 'xmit' retransmissions until a message is considered lost
+        internal uint dead_link;     // maximum amount of 'xmit' retransmissions until a segment is considered lost
         internal uint incr;
         internal uint current;       // current time (milliseconds). set by Update.
 
@@ -535,7 +535,8 @@ public int Input(byte[] data, int offset, int size)
                 size -= OVERHEAD;
 
                 // enough remaining to read 'len' bytes of the actual payload?
-                if (size < len || len < 0) return -2;
+                // note: original kcp casts uint len to int for <0 check.
+                if (size < len || (int)len < 0) return -2;
 
                 if (cmd != CMD_PUSH && cmd != CMD_ACK &&
                     cmd != CMD_WASK && cmd != CMD_WINS)