Fixed an issue with UDP not recovering after a Communication Loss

- The Socket Receive Buffer is flushed if we receive an incorrect Service ID from the PLC.

Author: ashneilson

RICADO.Omron/Channels/EthernetChannel.cs

@@ -147,6 +147,26 @@ internal async Task<ProcessRequestResult> ProcessRequestAsync(FINSRequest reques
             }
             catch (FINSException e)
             {
+                if(e.Message.Contains("Service ID") && responseMessage.Length >= 9 && responseMessage.Span[9] != request.ServiceID)
+                {
+                    try
+                    {
+                        if (!_semaphore.Wait(0))
+                        {
+                            await _semaphore.WaitAsync(cancellationToken);
+                        }
+
+                        await PurgeReceiveBuffer(timeout, cancellationToken);
+                    }
+                    catch
+                    {
+                    }
+                    finally
+                    {
+                        _semaphore.Release();
+                    }
+                }
+
                 throw new OmronException("Received a FINS Error Response from Omron PLC '" + _remoteHost + ":" + _port + "'", e);
             }
         }
@@ -162,6 +182,8 @@ internal async Task<ProcessRequestResult> ProcessRequestAsync(FINSRequest reques
 
         protected abstract Task<ReceiveMessageResult> ReceiveMessageAsync(int timeout, CancellationToken cancellationToken);
 
+        protected abstract Task PurgeReceiveBuffer(int timeout, CancellationToken cancellationToken);
+
         #endregion
 
 

RICADO.Omron/Channels/EthernetTCPChannel.cs

@@ -135,6 +135,40 @@ protected override Task<ReceiveMessageResult> ReceiveMessageAsync(int timeout, C
             return receiveMessageAsync(enTCPCommandCode.FINSFrame, timeout, cancellationToken);
         }
 
+        protected override async Task PurgeReceiveBuffer(int timeout, CancellationToken cancellationToken)
+        {
+            try
+            {
+                if (_client.Connected == false)
+                {
+                    return;
+                }
+
+                if(_client.Available == 0)
+                {
+                    await Task.Delay(timeout / 4);
+                }
+                
+                DateTime startTimestamp = DateTime.UtcNow;
+                Memory<byte> buffer = new byte[2000];
+
+                while (_client.Connected && _client.Available > 0 && DateTime.UtcNow.Subtract(startTimestamp).TotalMilliseconds < timeout)
+                {
+                    try
+                    {
+                        await _client.ReceiveAsync(buffer, timeout, cancellationToken);
+                    }
+                    catch
+                    {
+                        return;
+                    }
+                }
+            }
+            catch
+            {
+            }
+        }
+
         #endregion
 
 

RICADO.Omron/Channels/EthernetUDPChannel.cs

@@ -190,6 +190,35 @@ protected override async Task<ReceiveMessageResult> ReceiveMessageAsync(int time
             return result;
         }
 
+        protected override async Task PurgeReceiveBuffer(int timeout, CancellationToken cancellationToken)
+        {
+            try
+            {
+                if (_client.Available == 0)
+                {
+                    await Task.Delay(timeout / 4);
+                }
+
+                DateTime startTimestamp = DateTime.UtcNow;
+                Memory<byte> buffer = new byte[2000];
+
+                while (_client.Available > 0 && DateTime.UtcNow.Subtract(startTimestamp).TotalMilliseconds < timeout)
+                {
+                    try
+                    {
+                        await _client.ReceiveAsync(buffer, timeout, cancellationToken);
+                    }
+                    catch
+                    {
+                        return;
+                    }
+                }
+            }
+            catch
+            {
+            }
+        }
+
         #endregion