Merge branch 'develop' into githubActions2

S7.Net.UnitTest/S7NetTestsSync.cs

@@ -933,7 +933,14 @@ namespace S7.Net.UnitTest
             S7TestServer.Stop();
 
             var unreachablePlc = new Plc(CpuType.S7300, "255.255.255.255", 0, 2);
-            Assert.IsFalse(unreachablePlc.IsAvailable);
+            try
+            {
+                unreachablePlc.Open();
+            }
+            catch
+            {
+            }
+            Assert.IsFalse(unreachablePlc.IsConnected);
         }
 
         [TestMethod]
@@ -944,7 +951,8 @@ namespace S7.Net.UnitTest
             S7TestServer.Start(TestServerPort);
 
             var reachablePlc = CreatePlc();
-            Assert.IsTrue(reachablePlc.IsAvailable);
+            reachablePlc.Open();
+            Assert.IsTrue(reachablePlc.IsConnected);
         }
 
         [TestMethod]

S7.Net.UnitTest/TypeTests/BooleanTests.cs

@@ -0,0 +1,38 @@
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Boolean = S7.Net.Types.Boolean;
+
+namespace S7.Net.UnitTest.TypeTests
+{
+    [TestClass]
+    public class BooleanTests
+    {
+        [DataTestMethod]
+        [DataRow(0)]
+        [DataRow(1)]
+        [DataRow(2)]
+        [DataRow(3)]
+        [DataRow(4)]
+        [DataRow(5)]
+        [DataRow(6)]
+        [DataRow(7)]
+        public void TestValidSetBitValues(int index)
+        {
+            Assert.AreEqual(Math.Pow(2, index), Boolean.SetBit(0, index));
+        }
+
+        [DataTestMethod]
+        [DataRow(0)]
+        [DataRow(1)]
+        [DataRow(2)]
+        [DataRow(3)]
+        [DataRow(4)]
+        [DataRow(5)]
+        [DataRow(6)]
+        [DataRow(7)]
+        public void TestValidClearBitValues(int index)
+        {
+            Assert.AreEqual((byte) ((uint) Math.Pow(2, index) ^ uint.MaxValue), Boolean.ClearBit(byte.MaxValue, index));
+        }
+    }
+}

S7.Net.UnitTest/TypeTests/S7StringTests.cs

@@ -117,13 +117,24 @@ namespace S7.Net.UnitTest.TypeTests
             AssertToByteArrayAndBackEquals("Abc", 4, 4, 3, (byte) 'A', (byte) 'b', (byte) 'c', 0);
         }
 
+        [TestMethod]
+        public void OddS7StringByteLength()
+        {
+            AssertVarTypeToByteLength(VarType.S7String, 1, 4);
+        }
+
+        [TestMethod]
+        public void EvenS7StringByteLength()
+        {
+            AssertVarTypeToByteLength(VarType.S7String, 2, 4);
+        }
+
         private static void AssertFromByteArrayEquals(string expected, params byte[] bytes)
         {
             var convertedString = S7String.FromByteArray(bytes);
             Assert.AreEqual(expected, convertedString);
         }
 
-
         private static void AssertToByteArrayAndBackEquals(string value, int reservedLength, params byte[] expected)
         {
             var convertedData = S7String.ToByteArray(value, reservedLength);
@@ -131,5 +142,11 @@ namespace S7.Net.UnitTest.TypeTests
             var convertedBack = S7String.FromByteArray(convertedData);
             Assert.AreEqual(value, convertedBack);
         }
+
+        private void AssertVarTypeToByteLength(VarType varType, int count, int expectedByteLength)
+        {
+            var byteLength = Plc.VarTypeToByteLength(varType, count);
+            Assert.AreEqual(expectedByteLength, byteLength);
+        }
     }
 }

S7.Net.UnitTest/TypeTests/S7WStringTests.cs

@@ -122,6 +122,17 @@ namespace S7.Net.UnitTest.TypeTests
             Assert.AreEqual(expected, convertedString);
         }
 
+        [TestMethod]
+        public void OddS7WStringByteLength()
+        {
+            AssertVarTypeToByteLength(VarType.S7WString, 1, 6);
+        }
+
+        [TestMethod]
+        public void EvenS7WStringByteLength()
+        {
+            AssertVarTypeToByteLength(VarType.S7WString, 2, 8);
+        }
 
         private static void AssertToByteArrayAndBackEquals(string value, int reservedLength, params byte[] expected)
         {
@@ -130,5 +141,11 @@ namespace S7.Net.UnitTest.TypeTests
             var convertedBack = S7WString.FromByteArray(convertedData);
             Assert.AreEqual(value, convertedBack);
         }
+
+        private void AssertVarTypeToByteLength(VarType varType, int count, int expectedByteLength)
+        {
+            var byteLength = Plc.VarTypeToByteLength(varType, count);
+            Assert.AreEqual(expectedByteLength, byteLength);
+        }
     }
 }

S7.Net/Internal/TaskQueue.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace S7.Net.Internal
+{
+    internal class TaskQueue
+    {
+        private static readonly object Sentinel = new object();
+
+        private Task prev = Task.FromResult(Sentinel);
+
+        public async Task<T> Enqueue<T>(Func<Task<T>> action)
+        {
+            var tcs = new TaskCompletionSource<object>();
+            await Interlocked.Exchange(ref prev, tcs.Task).ConfigureAwait(false);
+
+            try
+            {
+                return await action.Invoke().ConfigureAwait(false);
+            }
+            finally
+            {
+                tcs.SetResult(Sentinel);
+            }
+        }
+    }
+}

S7.Net/PLC.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Net.Sockets;
+using S7.Net.Internal;
 using S7.Net.Protocol;
 using S7.Net.Types;
 
@@ -13,8 +15,10 @@ namespace S7.Net
     /// </summary>
     public partial class Plc : IDisposable
     {
+        private readonly TaskQueue queue = new TaskQueue();
+
         private const int CONNECTION_TIMED_OUT_ERROR_CODE = 10060;
-        
+
         //TCP connection to device
         private TcpClient? tcpClient;
         private NetworkStream? _stream;
@@ -75,47 +79,26 @@ namespace S7.Net
                 if (tcpClient != null) tcpClient.SendTimeout = writeTimeout;
             }
         }
-        
-        /// <summary>
-        /// Returns true if a connection to the PLC can be established
-        /// </summary>
-        public bool IsAvailable
-        {
-            //TODO: Fix This
-            get
-            {
-                try
-                {
-                    OpenAsync().GetAwaiter().GetResult();
-                    return true;
-                }
-                catch
-                {
-                    return false;
-                }
-            }
-        }
 
         /// <summary>
-        /// Checks if the socket is connected and polls the other peer (the PLC) to see if it's connected.
+        /// Gets a value indicating whether a connection to the PLC has been established.
-        /// This is the variable that you should continously check to see if the communication is working
-        /// See also: http://stackoverflow.com/questions/2661764/how-to-check-if-a-socket-is-connected-disconnected-in-c
         /// </summary>
-        public bool IsConnected
+        /// <remarks>
-        {
+        /// The <see cref="IsConnected"/> property gets the connection state of the Client socket as
-            get
+        /// of the last I/O operation. When it returns <c>false</c>, the Client socket was either
-            {
+        /// never  connected, or is no longer connected.
-                try
+        ///
-                {
+        /// <para>
-                    if (tcpClient == null)
+        /// Because the <see cref="IsConnected"/> property only reflects the state of the connection
-                        return false;
+        /// as of the most recent operation, you should attempt to send or receive a message to
-
+        /// determine the current state. After the message send fails, this property no longer
-                    //TODO: Actually check communication by sending an empty TPDU
+        /// returns <c>true</c>. Note that this behavior is by design. You cannot reliably test the
-                    return tcpClient.Connected;
+        /// state of the connection because, in the time between the test and a send/receive, the
-                }
+        /// connection could have been lost. Your code should assume the socket is connected, and
-                catch { return false; }
+        /// gracefully handle failed transmissions.
-            }
+        /// </para>
-        }
+        /// </remarks>
+        public bool IsConnected => tcpClient?.Connected ?? false;
 
         /// <summary>
         /// Creates a PLC object with all the parameters needed for connections.
@@ -263,6 +246,16 @@ namespace S7.Net
             }
         }
 
+        private Stream GetStreamIfAvailable()
+        {
+            if (_stream == null)
+            {
+                throw new PlcException(ErrorCode.ConnectionError, "Plc is not connected");
+            }
+
+            return _stream;
+        }
+
         #region IDisposable Support
         private bool disposedValue = false; // To detect redundant calls
 

S7.Net/PLCHelpers.cs

@@ -30,8 +30,8 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Create the bytes-package to request data from the PLC. You have to specify the memory type (dataType), 
+        /// Create the bytes-package to request data from the PLC. You have to specify the memory type (dataType),
-        /// the address of the memory, the address of the byte and the bytes count. 
+        /// the address of the memory, the address of the byte and the bytes count.
         /// </summary>
         /// <param name="dataType">MemoryType (DB, Timer, Counter, etc.)</param>
         /// <param name="db">Address of the memory to be read</param>
@@ -184,13 +184,15 @@ namespace S7.Net
             switch (varType)
             {
                 case VarType.Bit:
-                    return varCount + 7 / 8;
+                    return (varCount + 7) / 8;
                 case VarType.Byte:
                     return (varCount < 1) ? 1 : varCount;
                 case VarType.String:
                     return varCount;
                 case VarType.S7String:
-                    return varCount + 2;
+                    return ((varCount + 2) & 1) == 1 ? (varCount + 3) : (varCount + 2);
+                case VarType.S7WString:
+                    return (varCount * 2) + 4;
                 case VarType.Word:
                 case VarType.Timer:
                 case VarType.Int:

S7.Net/PlcAsynchronous.cs

@@ -1,11 +1,11 @@
 using S7.Net.Types;
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Net.Sockets;
 using System.Threading.Tasks;
 using S7.Net.Protocol;
-using System.IO;
 using System.Threading;
 using S7.Net.Protocol.S7;
 
@@ -28,9 +28,14 @@ namespace S7.Net
             var stream = await ConnectAsync().ConfigureAwait(false);
             try
             {
-                cancellationToken.ThrowIfCancellationRequested();
+                await queue.Enqueue(async () =>
-                await EstablishConnection(stream, cancellationToken).ConfigureAwait(false);
+                {
-                _stream = stream;
+                    cancellationToken.ThrowIfCancellationRequested();
+                    await EstablishConnection(stream, cancellationToken).ConfigureAwait(false);
+                    _stream = stream;
+
+                    return default(object);
+                }).ConfigureAwait(false);
             }
             catch(Exception)
             {
@@ -47,29 +52,30 @@ namespace S7.Net
             return tcpClient.GetStream();
         }
 
-        private async Task EstablishConnection(NetworkStream stream, CancellationToken cancellationToken)
+        private async Task EstablishConnection(Stream stream, CancellationToken cancellationToken)
         {
             await RequestConnection(stream, cancellationToken).ConfigureAwait(false);
             await SetupConnection(stream, cancellationToken).ConfigureAwait(false);
         }
 
-        private async Task RequestConnection(NetworkStream stream, CancellationToken cancellationToken)
+        private async Task RequestConnection(Stream stream, CancellationToken cancellationToken)
         {
             var requestData = ConnectionRequest.GetCOTPConnectionRequest(CPU, Rack, Slot);
-            await stream.WriteAsync(requestData, 0, requestData.Length).ConfigureAwait(false);
+            var response = await NoLockRequestTpduAsync(stream, requestData, cancellationToken).ConfigureAwait(false);
-            var response = await COTP.TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+
             if (response.PDUType != COTP.PduType.ConnectionConfirmed)
             {
                 throw new InvalidDataException("Connection request was denied", response.TPkt.Data, 1, 0x0d);
             }
         }
 
-        private async Task SetupConnection(NetworkStream stream, CancellationToken cancellationToken)
+        private async Task SetupConnection(Stream stream, CancellationToken cancellationToken)
         {
             var setupData = GetS7ConnectionSetup();
-            await stream.WriteAsync(setupData, 0, setupData.Length).ConfigureAwait(false);
 
-            var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            var s7data = await NoLockRequestTsduAsync(stream, setupData, 0, setupData.Length, cancellationToken)
+                .ConfigureAwait(false);
+
             if (s7data.Length < 2)
                 throw new WrongNumberOfBytesException("Not enough data received in response to Communication Setup");
 
@@ -104,7 +110,7 @@ namespace S7.Net
             {
                 //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
                 var maxToRead = Math.Min(count, MaxPDUSize - 18);
-                await ReadBytesWithSingleRequestAsync(dataType, db, startByteAdr + index, resultBytes, index, maxToRead, cancellationToken);
+                await ReadBytesWithSingleRequestAsync(dataType, db, startByteAdr + index, resultBytes, index, maxToRead, cancellationToken).ConfigureAwait(false);
                 count -= maxToRead;
                 index += maxToRead;
             }
@@ -112,7 +118,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Read and decode a certain number of bytes of the "VarType" provided. 
+        /// Read and decode a certain number of bytes of the "VarType" provided.
         /// This can be used to read multiple consecutive variables of the same type (Word, DWord, Int, etc).
         /// If the read was not successful, check LastErrorCode or LastErrorString.
         /// </summary>
@@ -127,7 +133,7 @@ namespace S7.Net
         public async Task<object?> ReadAsync(DataType dataType, int db, int startByteAdr, VarType varType, int varCount, byte bitAdr = 0, CancellationToken cancellationToken = default)
         {
             int cntBytes = VarTypeToByteLength(varType, varCount);
-            byte[] bytes = await ReadBytesAsync(dataType, db, startByteAdr, cntBytes, cancellationToken);
+            byte[] bytes = await ReadBytesAsync(dataType, db, startByteAdr, cntBytes, cancellationToken).ConfigureAwait(false);
             return ParseBytes(varType, bytes, varCount, bitAdr);
         }
 
@@ -142,7 +148,7 @@ namespace S7.Net
         public async Task<object?> ReadAsync(string variable, CancellationToken cancellationToken = default)
         {
             var adr = new PLCAddress(variable);
-            return await ReadAsync(adr.DataType, adr.DbNumber, adr.StartByte, adr.VarType, 1, (byte)adr.BitNumber, cancellationToken);
+            return await ReadAsync(adr.DataType, adr.DbNumber, adr.StartByte, adr.VarType, 1, (byte)adr.BitNumber, cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -158,7 +164,7 @@ namespace S7.Net
         {
             int numBytes = Types.Struct.GetStructSize(structType);
             // now read the package
-            var resultBytes = await ReadBytesAsync(DataType.DataBlock, db, startByteAdr, numBytes, cancellationToken);
+            var resultBytes = await ReadBytesAsync(DataType.DataBlock, db, startByteAdr, numBytes, cancellationToken).ConfigureAwait(false);
 
             // and decode it
             return Types.Struct.FromBytes(structType, resultBytes);
@@ -175,14 +181,14 @@ namespace S7.Net
         /// <returns>Returns a nulable struct. If nothing was read null will be returned.</returns>
         public async Task<T?> ReadStructAsync<T>(int db, int startByteAdr = 0, CancellationToken cancellationToken = default) where T : struct
         {
-            return await ReadStructAsync(typeof(T), db, startByteAdr, cancellationToken) as T?;
+            return await ReadStructAsync(typeof(T), db, startByteAdr, cancellationToken).ConfigureAwait(false) as T?;
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
-        /// <param name="sourceClass">Instance of the class that will store the values</param>       
+        /// <param name="sourceClass">Instance of the class that will store the values</param>
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
@@ -197,7 +203,7 @@ namespace S7.Net
             }
 
             // now read the package
-            var resultBytes = await ReadBytesAsync(DataType.DataBlock, db, startByteAdr, numBytes, cancellationToken);
+            var resultBytes = await ReadBytesAsync(DataType.DataBlock, db, startByteAdr, numBytes, cancellationToken).ConfigureAwait(false);
             // and decode it
             Class.FromBytes(sourceClass, resultBytes);
 
@@ -205,7 +211,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified. To instantiate the class defined by the generic
         /// type, the class needs a default constructor.
         /// </summary>
@@ -217,11 +223,11 @@ namespace S7.Net
         /// <returns>An instance of the class with the values read from the PLC. If no data has been read, null will be returned</returns>
         public async Task<T?> ReadClassAsync<T>(int db, int startByteAdr = 0, CancellationToken cancellationToken = default) where T : class
         {
-            return await ReadClassAsync(() => Activator.CreateInstance<T>(), db, startByteAdr, cancellationToken);
+            return await ReadClassAsync(() => Activator.CreateInstance<T>(), db, startByteAdr, cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
         /// <typeparam name="T">The class that will be instantiated</typeparam>
@@ -234,7 +240,7 @@ namespace S7.Net
         public async Task<T?> ReadClassAsync<T>(Func<T> classFactory, int db, int startByteAdr = 0, CancellationToken cancellationToken = default) where T : class
         {
             var instance = classFactory();
-            var res = await ReadClassAsync(instance, db, startByteAdr, cancellationToken);
+            var res = await ReadClassAsync(instance, db, startByteAdr, cancellationToken).ConfigureAwait(false);
             int readBytes = res.Item1;
             if (readBytes <= 0)
             {
@@ -245,10 +251,10 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads multiple vars in a single request. 
+        /// Reads multiple vars in a single request.
         /// You have to create and pass a list of DataItems and you obtain in response the same list with the values.
         /// Values are stored in the property "Value" of the dataItem and are already converted.
-        /// If you don't want the conversion, just create a dataItem of bytes. 
+        /// If you don't want the conversion, just create a dataItem of bytes.
         /// The number of DataItems as well as the total size of the requested data can not exceed a certain limit (protocol restriction).
         /// </summary>
         /// <param name="dataItems">List of dataitems that contains the list of variables that must be read.</param>
@@ -256,18 +262,15 @@ namespace S7.Net
         /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
         public async Task<List<DataItem>> ReadMultipleVarsAsync(List<DataItem> dataItems, CancellationToken cancellationToken = default)
         {
-            //Snap7 seems to choke on PDU sizes above 256 even if snap7 
+            //Snap7 seems to choke on PDU sizes above 256 even if snap7
             //replies with bigger PDU size in connection setup.
             AssertPduSizeForRead(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             try
             {
                 var dataToSend = BuildReadRequestPackage(dataItems.Select(d => DataItem.GetDataItemAddress(d)).ToList());
-                await stream.WriteAsync(dataToSend, 0, dataToSend.Length);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
 
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
 
                 ParseDataIntoDataItems(s7data, dataItems);
@@ -306,7 +309,7 @@ namespace S7.Net
             while (count > 0)
             {
                 var maxToWrite = (int)Math.Min(count, MaxPDUSize - 35);
-                await WriteBytesWithASingleRequestAsync(dataType, db, startByteAdr + localIndex, value, localIndex, maxToWrite, cancellationToken);
+                await WriteBytesWithASingleRequestAsync(dataType, db, startByteAdr + localIndex, value, localIndex, maxToWrite, cancellationToken).ConfigureAwait(false);
                 count -= maxToWrite;
                 localIndex += maxToWrite;
             }
@@ -328,7 +331,7 @@ namespace S7.Net
             if (bitAdr < 0 || bitAdr > 7)
                 throw new InvalidAddressException(string.Format("Addressing Error: You can only reference bitwise locations 0-7. Address {0} is invalid", bitAdr));
 
-            await WriteBitWithASingleRequestAsync(dataType, db, startByteAdr, bitAdr, value, cancellationToken);
+            await WriteBitWithASingleRequestAsync(dataType, db, startByteAdr, bitAdr, value, cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -347,7 +350,7 @@ namespace S7.Net
             if (value < 0 || value > 1)
                 throw new ArgumentException("Value must be 0 or 1", nameof(value));
 
-            await WriteBitAsync(dataType, db, startByteAdr, bitAdr, value == 1, cancellationToken);
+            await WriteBitAsync(dataType, db, startByteAdr, bitAdr, value == 1, cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -370,7 +373,7 @@ namespace S7.Net
                 //Must be writing a bit value as bitAdr is specified
                 if (value is bool boolean)
                 {
-                    await WriteBitAsync(dataType, db, startByteAdr, bitAdr, boolean, cancellationToken);
+                    await WriteBitAsync(dataType, db, startByteAdr, bitAdr, boolean, cancellationToken).ConfigureAwait(false);
                 }
                 else if (value is int intValue)
                 {
@@ -380,11 +383,11 @@ namespace S7.Net
                                 "Addressing Error: You can only reference bitwise locations 0-7. Address {0} is invalid",
                                 bitAdr), nameof(bitAdr));
 
-                    await WriteBitAsync(dataType, db, startByteAdr, bitAdr, intValue == 1, cancellationToken);
+                    await WriteBitAsync(dataType, db, startByteAdr, bitAdr, intValue == 1, cancellationToken).ConfigureAwait(false);
                 }
                 else throw new ArgumentException("Value must be a bool or an int to write a bit", nameof(value));
             }
-            else await WriteBytesAsync(dataType, db, startByteAdr, Serialization.SerializeValue(value), cancellationToken);
+            else await WriteBytesAsync(dataType, db, startByteAdr, Serialization.SerializeValue(value), cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -399,7 +402,7 @@ namespace S7.Net
         public async Task WriteAsync(string variable, object value, CancellationToken cancellationToken = default)
         {
             var adr = new PLCAddress(variable);
-            await WriteAsync(adr.DataType, adr.DbNumber, adr.StartByte, value, adr.BitNumber, cancellationToken);
+            await WriteAsync(adr.DataType, adr.DbNumber, adr.StartByte, value, adr.BitNumber, cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -414,7 +417,7 @@ namespace S7.Net
         public async Task WriteStructAsync(object structValue, int db, int startByteAdr = 0, CancellationToken cancellationToken = default)
         {
             var bytes = Struct.ToBytes(structValue).ToList();
-            await WriteBytesAsync(DataType.DataBlock, db, startByteAdr, bytes.ToArray(), cancellationToken);
+            await WriteBytesAsync(DataType.DataBlock, db, startByteAdr, bytes.ToArray(), cancellationToken).ConfigureAwait(false);
         }
 
         /// <summary>
@@ -430,17 +433,14 @@ namespace S7.Net
         {
             byte[] bytes = new byte[(int)Class.GetClassSize(classValue)];
             Types.Class.ToBytes(classValue, bytes);
-            await WriteBytesAsync(DataType.DataBlock, db, startByteAdr, bytes, cancellationToken);
+            await WriteBytesAsync(DataType.DataBlock, db, startByteAdr, bytes, cancellationToken).ConfigureAwait(false);
         }
 
         private async Task ReadBytesWithSingleRequestAsync(DataType dataType, int db, int startByteAdr, byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
-            var stream = GetStreamIfAvailable();
-
             var dataToSend = BuildReadRequestPackage(new [] { new DataItemAddress(dataType, db, startByteAdr, count)});
-            await stream.WriteAsync(dataToSend, 0, dataToSend.Length, cancellationToken);
 
-            var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken);
+            var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
             AssertReadResponse(s7data, count);
 
             Array.Copy(s7data, 18, buffer, offset, count);
@@ -456,13 +456,11 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
-            await stream.WriteAsync(message.Array, 0, length).ConfigureAwait(false);
 
-            var response = await COTP.TSDU.ReadAsync(stream, CancellationToken.None).ConfigureAwait(false);
+            var response = await RequestTsduAsync(message.Array, 0, length).ConfigureAwait(false);
+
             S7WriteMultiple.ParseResponse(response, response.Length, dataItems);
         }
 
@@ -476,15 +474,11 @@ namespace S7.Net
         /// <returns>A task that represents the asynchronous write operation.</returns>
         private async Task WriteBytesWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count, CancellationToken cancellationToken)
         {
-
             try
             {
-                var stream = GetStreamIfAvailable();
                 var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value, dataOffset, count);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken).ConfigureAwait(false);
 
-                await stream.WriteAsync(dataToSend, 0, dataToSend.Length, cancellationToken);
-
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (OperationCanceledException)
@@ -499,15 +493,11 @@ namespace S7.Net
 
         private async Task WriteBitWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue, CancellationToken cancellationToken)
         {
-            var stream = GetStreamIfAvailable();
-
             try
             {
                 var dataToSend = BuildWriteBitPackage(dataType, db, startByteAdr, bitValue, bitAdr);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken).ConfigureAwait(false);
 
-                await stream.WriteAsync(dataToSend, 0, dataToSend.Length);
-
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (OperationCanceledException)
@@ -520,13 +510,33 @@ namespace S7.Net
             }
         }
 
-        private Stream GetStreamIfAvailable()
+        private Task<byte[]> RequestTsduAsync(byte[] requestData, CancellationToken cancellationToken = default) =>
+            RequestTsduAsync(requestData, 0, requestData.Length, cancellationToken);
+
+        private Task<byte[]> RequestTsduAsync(byte[] requestData, int offset, int length, CancellationToken cancellationToken = default)
         {
-            if (_stream == null)
+            var stream = GetStreamIfAvailable();
-            {
+
-                throw new PlcException(ErrorCode.ConnectionError, "Plc is not connected");
+            return queue.Enqueue(() =>
-            }
+                NoLockRequestTsduAsync(stream, requestData, offset, length, cancellationToken));
-            return _stream;
+        }
+
+        private static async Task<COTP.TPDU> NoLockRequestTpduAsync(Stream stream, byte[] requestData,
+            CancellationToken cancellationToken = default)
+        {
+            await stream.WriteAsync(requestData, 0, requestData.Length, cancellationToken).ConfigureAwait(false);
+            var response = await COTP.TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+
+            return response;
+        }
+
+        private static async Task<byte[]> NoLockRequestTsduAsync(Stream stream, byte[] requestData, int offset, int length,
+            CancellationToken cancellationToken = default)
+        {
+            await stream.WriteAsync(requestData, offset, length, cancellationToken).ConfigureAwait(false);
+            var response = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+
+            return response;
         }
     }
 }

S7.Net/PlcSynchronous.cs

@@ -2,8 +2,6 @@
 using System;
 using System.IO;
 using System.Collections.Generic;
-using System.Linq;
-using System.Net.Sockets;
 using S7.Net.Protocol;
 using S7.Net.Helper;
 
@@ -54,7 +52,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Read and decode a certain number of bytes of the "VarType" provided. 
+        /// Read and decode a certain number of bytes of the "VarType" provided.
         /// This can be used to read multiple consecutive variables of the same type (Word, DWord, Int, etc).
         /// If the read was not successful, check LastErrorCode or LastErrorString.
         /// </summary>
@@ -115,10 +113,10 @@ namespace S7.Net
 
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
-        /// <param name="sourceClass">Instance of the class that will store the values</param>       
+        /// <param name="sourceClass">Instance of the class that will store the values</param>
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>The number of read bytes</returns>
@@ -138,7 +136,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified. To instantiate the class defined by the generic
         /// type, the class needs a default constructor.
         /// </summary>
@@ -152,7 +150,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
         /// <typeparam name="T">The class that will be instantiated</typeparam>
@@ -186,7 +184,7 @@ namespace S7.Net
             while (count > 0)
             {
                 //TODO: Figure out how to use MaxPDUSize here
-                //Snap7 seems to choke on PDU sizes above 256 even if snap7 
+                //Snap7 seems to choke on PDU sizes above 256 even if snap7
                 //replies with bigger PDU size in connection setup.
                 var maxToWrite = Math.Min(count, MaxPDUSize - 28);//TODO tested only when the MaxPDUSize is 480
                 WriteBytesWithASingleRequest(dataType, db, startByteAdr + localIndex, value, localIndex, maxToWrite);
@@ -298,7 +296,6 @@ namespace S7.Net
 
         private void ReadBytesWithSingleRequest(DataType dataType, int db, int startByteAdr, byte[] buffer, int offset, int count)
         {
-            var stream = GetStreamIfAvailable();
             try
             {
                 // first create the header
@@ -309,9 +306,7 @@ namespace S7.Net
                 BuildReadDataRequestPackage(package, dataType, db, startByteAdr, count);
 
                 var dataToSend = package.ToArray();
-                stream.Write(dataToSend, 0, dataToSend.Length);
+                var s7data = RequestTsdu(dataToSend);
-
-                var s7data = COTP.TSDU.Read(stream);
                 AssertReadResponse(s7data, count);
 
                 Array.Copy(s7data, 18, buffer, offset, count);
@@ -331,13 +326,11 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
-            var stream = GetStreamIfAvailable();
 
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
-            stream.Write(message.Array, 0, length);
+            var response = RequestTsdu(message.Array, 0, length);
 
-            var response = COTP.TSDU.Read(stream);
             S7WriteMultiple.ParseResponse(response, response.Length, dataItems);
         }
 
@@ -345,12 +338,9 @@ namespace S7.Net
         {
             try
             {
-                var stream = GetStreamIfAvailable();
                 var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value, dataOffset, count);
+                var s7data = RequestTsdu(dataToSend);
 
-                stream.Write(dataToSend, 0, dataToSend.Length);
-
-                var s7data = COTP.TSDU.Read(stream);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (Exception exc)
@@ -425,14 +415,11 @@ namespace S7.Net
 
         private void WriteBitWithASingleRequest(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue)
         {
-            var stream = GetStreamIfAvailable();
             try
             {
                 var dataToSend = BuildWriteBitPackage(dataType, db, startByteAdr, bitValue, bitAdr);
+                var s7data = RequestTsdu(dataToSend);
 
-                stream.Write(dataToSend, 0, dataToSend.Length);
-
-                var s7data = COTP.TSDU.Read(stream);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (Exception exc)
@@ -442,10 +429,10 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads multiple vars in a single request. 
+        /// Reads multiple vars in a single request.
         /// You have to create and pass a list of DataItems and you obtain in response the same list with the values.
         /// Values are stored in the property "Value" of the dataItem and are already converted.
-        /// If you don't want the conversion, just create a dataItem of bytes. 
+        /// If you don't want the conversion, just create a dataItem of bytes.
         /// The number of DataItems as well as the total size of the requested data can not exceed a certain limit (protocol restriction).
         /// </summary>
         /// <param name="dataItems">List of dataitems that contains the list of variables that must be read.</param>
@@ -453,8 +440,6 @@ namespace S7.Net
         {
             AssertPduSizeForRead(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             try
             {
                 // first create the header
@@ -468,9 +453,7 @@ namespace S7.Net
                 }
 
                 var dataToSend = package.ToArray();
-                stream.Write(dataToSend, 0, dataToSend.Length);
+                var s7data = RequestTsdu(dataToSend);
-
-                var s7data = COTP.TSDU.Read(stream); //TODO use Async
 
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
 
@@ -481,5 +464,12 @@ namespace S7.Net
                 throw new PlcException(ErrorCode.ReadData, exc);
             }
         }
+
+        private byte[] RequestTsdu(byte[] requestData) => RequestTsdu(requestData, 0, requestData.Length);
+
+        private byte[] RequestTsdu(byte[] requestData, int offset, int length)
+        {
+            return RequestTsduAsync(requestData, offset, length).GetAwaiter().GetResult();
+        }
     }
 }

S7.Net/Types/Boolean.cs

@@ -14,20 +14,51 @@
         }
 
         /// <summary>
-        /// Sets the value of a bit to 1 (true), given the address of the bit
+        /// Sets the value of a bit to 1 (true), given the address of the bit. Returns
+        /// a copy of the value with the bit set.
         /// </summary>
+        /// <param name="value">The input value to modify.</param>
+        /// <param name="bit">The index (zero based) of the bit to set.</param>
+        /// <returns>The modified value with the bit at index set.</returns>
         public static byte SetBit(byte value, int bit)
         {
-            return (byte)((value | (1 << bit)) & 0xFF);
+            SetBit(ref value, bit);
+
+            return value;
+        }
+
+        /// <summary>
+        /// Sets the value of a bit to 1 (true), given the address of the bit.
+        /// </summary>
+        /// <param name="value">The value to modify.</param>
+        /// <param name="bit">The index (zero based) of the bit to set.</param>
+        public static void SetBit(ref byte value, int bit)
+        {
+            value = (byte) ((value | (1 << bit)) & 0xFF);
+        }
+
+        /// <summary>
+        /// Resets the value of a bit to 0 (false), given the address of the bit. Returns
+        /// a copy of the value with the bit cleared.
+        /// </summary>
+        /// <param name="value">The input value to modify.</param>
+        /// <param name="bit">The index (zero based) of the bit to clear.</param>
+        /// <returns>The modified value with the bit at index cleared.</returns>
+        public static byte ClearBit(byte value, int bit)
+        {
+            ClearBit(ref value, bit);
+
+            return value;
         }
 
         /// <summary>
         /// Resets the value of a bit to 0 (false), given the address of the bit
         /// </summary>
-        public static byte ClearBit(byte value, int bit)
+        /// <param name="value">The input value to modify.</param>
+        /// <param name="bit">The index (zero based) of the bit to clear.</param>
+        public static void ClearBit(ref byte value, int bit)
         {
-            return (byte)((value | (~(1 << bit))) & 0xFF);
+            value = (byte) (value & ~(1 << bit) & 0xFF);
         }
-
     }
 }