Release S7NetPlus 0.13.0

Release highlights:
- Change default TSAP for S7 200
- Add S7 200 Smart support
- Add support for custom TSAP's
- Align data to even bytes when parsing responses from class and struct
  reads
- Close connection on IOException
- Add cancellation for Read/Write
- Set default Read-/WriteTimeout to 10 seconds
- Cleanup of sync helper methods

.github/workflows/test.yml

@@ -0,0 +1,80 @@
+name: Test
+
+on:
+  [pull_request, push]
+  
+jobs:
+
+  build_test:
+    name: test-${{ matrix.os }}-${{ matrix.test-framework }}
+    runs-on: ${{ matrix.os }}
+    env:
+      configuration: Release
+      artifacts: ${{ github.workspace }}/artifacts
+      DOTNET_NOLOGO : 1
+    strategy:
+      matrix:
+        os: [windows-latest, ubuntu-latest, macos-latest]
+        test-framework: [netcoreapp3.1, net5.0]
+        include:
+          - os: ubuntu-latest
+            test-framework: netcoreapp3.1
+            installSnap7: true
+            dotnet-sdk: '3.1.x'
+          - os: ubuntu-latest
+            test-framework: net5.0
+            installSnap7: true
+            dotnet-sdk: '5.0.x'
+          - os: macos-latest
+            test-framework: netcoreapp3.1
+            installSnap7: true
+            dotnet-sdk: '3.1.x'
+          - os: macos-latest
+            test-framework: net5.0
+            installSnap7: true
+            dotnet-sdk: '5.0.x'
+          - os: windows-latest
+            test-framework: netcoreapp3.1
+            dotnet-sdk: '3.1.x'
+          - os: windows-latest
+            test-framework: net5.0
+            dotnet-sdk: '5.0.x'
+          - os: windows-latest
+            test-framework: net452
+            dotnet-sdk: '5.0.x'
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install Snap7 Linux
+        if: ${{ matrix.installSnap7 && matrix.os == 'ubuntu-latest' }}
+        run: |
+          sudo add-apt-repository ppa:gijzelaar/snap7
+          sudo apt-get update
+          sudo apt-get install libsnap7-1 libsnap7-dev
+          
+      - name: Install Snap7 MacOs
+        if: ${{ matrix.installSnap7 && matrix.os == 'macos-latest' }}
+        run: |
+          brew install snap7
+
+      - name: Setup Dotnet
+        uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: ${{ matrix.dotnet-sdk }}
+          
+      - name: Nuget Cache
+        uses: actions/cache@v2
+        with:
+          path: ~/.nuget/packages
+          # Look to see if there is a cache hit for the corresponding requirements file
+          key: ${{ runner.os }}-${{ matrix.test-framework }}-nuget-${{ hashFiles('**/packages.lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ matrix.test-framework }}-nuget
+
+      - name: Restore
+        run: dotnet restore S7.Net.UnitTest
+        
+      - name: Test
+        run: dotnet test --no-restore --nologo --verbosity normal --logger GitHubActions --framework ${{ matrix.test-framework }}

S7.Net.UnitTest/ConnectionCloseTest.cs

@@ -0,0 +1,181 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.IO;
+using System.Linq;
+using System.Net.Sockets;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace S7.Net.UnitTest
+{
+    /// <summary>
+    /// Test stream which only gives 1 byte per read.
+    /// </summary>
+    class TestStreamConnectionClose : Stream
+    {
+        private readonly CancellationTokenSource _cancellationTokenSource;
+
+        public TestStreamConnectionClose(CancellationTokenSource cancellationTokenSource)
+        {
+            _cancellationTokenSource = cancellationTokenSource;
+        }
+        public override bool CanRead => false;
+
+        public override bool CanSeek => throw new NotImplementedException();
+
+        public override bool CanWrite => true;
+
+        public override long Length => throw new NotImplementedException();
+
+        public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+
+        public override void Flush()
+        {
+            throw new NotImplementedException();
+        }
+        
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void SetLength(long value)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            _cancellationTokenSource.Cancel();
+        }
+    }
+
+    /// <summary>
+    /// These tests are intended to test <see cref="StreamExtensions"/> functions and other stream-related special cases.
+    /// </summary>
+    [TestClass]
+    public class ConnectionCloseTest
+    {
+        const short TestServerPort = 31122;
+        const string TestServerIp = "127.0.0.1";
+
+        [TestMethod]
+        public async Task Test_CancellationDuringTransmission()
+        {
+            var plc = new Plc(CpuType.S7300, TestServerIp, TestServerPort, 0, 2);
+
+            // Set up a shared cancellation source so we can let the stream
+            // initiate cancel after some data has been written to it.
+            var cancellationSource = new CancellationTokenSource();
+            var cancellationToken = cancellationSource.Token;
+
+            var stream = new TestStreamConnectionClose(cancellationSource);
+            var requestData = new byte[100]; // empty data, it does not matter what is in there
+
+            // Set up access to private method and field
+            var dynMethod = plc.GetType().GetMethod("NoLockRequestTpduAsync",
+                BindingFlags.NonPublic | BindingFlags.Instance);
+            if (dynMethod == null)
+            {
+                throw new NullReferenceException("Could not find method 'NoLockRequestTpduAsync' on Plc object.");
+            }
+            var tcpClientField = plc.GetType().GetField("tcpClient", BindingFlags.NonPublic | BindingFlags.Instance);
+            if (tcpClientField == null)
+            {
+                throw new NullReferenceException("Could not find field 'tcpClient' on Plc object.");
+            }
+
+            // Set a value to tcpClient field so we can later ensure that it has been closed.
+            tcpClientField.SetValue(plc, new TcpClient());
+            var tcpClientValue = tcpClientField.GetValue(plc);
+            Assert.IsNotNull(tcpClientValue);
+            
+            try
+            {
+                var result = (Task<COTP.TPDU>) dynMethod.Invoke(plc, new object[] { stream, requestData, cancellationToken });
+                await result;
+            }
+            catch (OperationCanceledException)
+            {
+                Console.WriteLine("Task was cancelled as expected.");
+
+                // Ensure that the plc connection was closed since the task was cancelled
+                // after data has been sent through the network. We expect that the tcpClient
+                // object was set to NULL
+                var tcpClientValueAfter = tcpClientField.GetValue(plc);
+                Assert.IsNull(tcpClientValueAfter);
+                return;
+            }
+            catch (Exception e)
+            {
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
+            }
+
+            // Ensure test fails if cancellation did not occur.
+            Assert.Fail("Task was not cancelled as expected.");
+        }
+
+        [TestMethod]
+        public async Task Test_CancellationBeforeTransmission()
+        {
+            var plc = new Plc(CpuType.S7300, TestServerIp, TestServerPort, 0, 2);
+
+            // Set up a cancellation source
+            var cancellationSource = new CancellationTokenSource();
+            var cancellationToken = cancellationSource.Token;
+
+            var stream = new TestStreamConnectionClose(cancellationSource);
+            var requestData = new byte[100]; // empty data, it does not matter what is in there
+
+            // Set up access to private method and field
+            var dynMethod = plc.GetType().GetMethod("NoLockRequestTpduAsync",
+                BindingFlags.NonPublic | BindingFlags.Instance);
+            if (dynMethod == null)
+            {
+                throw new NullReferenceException("Could not find method 'NoLockRequestTpduAsync' on Plc object.");
+            }
+            var tcpClientField = plc.GetType().GetField("tcpClient", BindingFlags.NonPublic | BindingFlags.Instance);
+            if (tcpClientField == null)
+            {
+                throw new NullReferenceException("Could not find field 'tcpClient' on Plc object.");
+            }
+
+            // Set a value to tcpClient field so we can later ensure that it has been closed.
+            tcpClientField.SetValue(plc, new TcpClient());
+            var tcpClientValue = tcpClientField.GetValue(plc);
+            Assert.IsNotNull(tcpClientValue);
+
+            try
+            {
+                // cancel the task before we start transmitting data
+                cancellationSource.Cancel();
+                var result = (Task<COTP.TPDU>)dynMethod.Invoke(plc, new object[] { stream, requestData, cancellationToken });
+                await result;
+            }
+            catch (OperationCanceledException)
+            {
+                Console.WriteLine("Task was cancelled as expected.");
+
+                // Ensure that the plc connection was not closed, since we cancelled the task before
+                // sending data through the network. We expect that the tcpClient
+                // object was NOT set to NULL
+                var tcpClientValueAfter = tcpClientField.GetValue(plc);
+                Assert.IsNotNull(tcpClientValueAfter);
+                return;
+            }
+            catch (Exception e)
+            {
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
+            }
+
+            // Ensure test fails if cancellation did not occur.
+            Assert.Fail("Task was not cancelled as expected.");
+        }
+    }
+}

S7.Net.UnitTest/ConnectionRequestTest.cs

@@ -9,52 +9,52 @@ namespace S7.Net.UnitTest
         [TestMethod]
         public void Test_ConnectionRequest_S7_200()
         {
-            CollectionAssert.AreEqual(MakeConnectionRequest(16, 0, 16, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7200, 0, 0));
+            CollectionAssert.AreEqual(MakeConnectionRequest(16, 0, 16, 1),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7200, 0, 0)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_300()
         {
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7300, 0, 0));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7300, 0, 0)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7300, 0, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7300, 0, 1)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7300, 1, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7300, 1, 1)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_400()
         {
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7400, 0, 0));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7400, 0, 0)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7400, 0, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7400, 0, 1)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7400, 1, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7400, 1, 1)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_1200()
         {
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71200, 0, 0));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71200, 0, 0)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71200, 0, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71200, 0, 1)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71200, 1, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71200, 1, 1)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_1500()
         {
-            CollectionAssert.AreEqual(MakeConnectionRequest(0x10, 0x2, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71500, 0, 0));
-            CollectionAssert.AreEqual(MakeConnectionRequest(0x10, 0x2, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71500, 0, 1));
-            CollectionAssert.AreEqual(MakeConnectionRequest(0x10, 0x2, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71500, 1, 1));
+            CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71500, 0, 0)));
+            CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71500, 0, 1)));
+            CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71500, 1, 1)));
         }
 
         private static byte[] MakeConnectionRequest(byte sourceTsap1, byte sourceTsap2, byte destTsap1, byte destTsap2)
@@ -63,7 +63,7 @@ namespace S7.Net.UnitTest
             {
                 3, 0, 0, 22, //TPKT
                 17, //COTP Header Length
-                224, //Connect Request 
+                224, //Connect Request
                 0, 0, //Destination Reference
                 0, 46, //Source Reference
                 0, //Flags

S7.Net.UnitTest/ProtocolTests.cs

@@ -1,14 +1,10 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using S7.Net;
-
 using System.IO;
+using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using S7.Net.Protocol;
-using System.Collections;
 
 namespace S7.Net.UnitTest
 {
@@ -21,21 +17,17 @@ namespace S7.Net.UnitTest
         public async Task TPKT_Read()
         {
             var m = new MemoryStream(StringToByteArray("0300002902f0803203000000010002001400000401ff0400807710000100000103000000033f8ccccd"));
-            var t = TPKT.Read(m);
-            Assert.AreEqual(0x03, t.Version);
-            Assert.AreEqual(0x29, t.Length);
-            m.Position = 0;
-            t = await TPKT.ReadAsync(m, TestContext.CancellationTokenSource.Token);
+            var t = await TPKT.ReadAsync(m, TestContext.CancellationTokenSource.Token);
             Assert.AreEqual(0x03, t.Version);
             Assert.AreEqual(0x29, t.Length);
         }
 
         [TestMethod]
         [ExpectedException(typeof(TPKTInvalidException))]
-        public void TPKT_ReadShort()
+        public async Task TPKT_ReadShort()
         {
             var m = new MemoryStream(StringToByteArray("0300002902f0803203000000010002001400000401ff040080"));
-            var t = TPKT.Read(m);
+            var t = await TPKT.ReadAsync(m, CancellationToken.None);
         }
 
 
@@ -48,14 +40,11 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        public void COTP_ReadTSDU()
+        public async Task COTP_ReadTSDU()
         {
             var expected = StringToByteArray("320700000400000800080001120411440100ff09000400000000");
             var m = new MemoryStream(StringToByteArray("0300000702f0000300000702f0000300002102f080320700000400000800080001120411440100ff09000400000000"));
-            var t = COTP.TSDU.Read(m);
-            Assert.IsTrue(expected.SequenceEqual(t));
-            m.Position = 0;
-            t = COTP.TSDU.ReadAsync(m, TestContext.CancellationTokenSource.Token).Result;
+            var t = await COTP.TSDU.ReadAsync(m, TestContext.CancellationTokenSource.Token);
             Assert.IsTrue(expected.SequenceEqual(t));
         }
 
@@ -69,14 +58,13 @@ namespace S7.Net.UnitTest
 
 
         [TestMethod]
-        public void TestResponseCode()
+        public async Task TestResponseCode()
         {
             var expected = StringToByteArray("320700000400000800080001120411440100ff09000400000000");
             var m = new MemoryStream(StringToByteArray("0300000702f0000300000702f0000300002102f080320700000400000800080001120411440100ff09000400000000"));
-            var t = COTP.TSDU.Read(m);
+            var t = await COTP.TSDU.ReadAsync(m, CancellationToken.None);
             Assert.IsTrue(expected.SequenceEqual(t));
 
-
             // Test all possible byte values. Everything except 0xff should throw an exception.
             var testData = Enumerable.Range(0, 256).Select(i => new { StatusCode = (ReadWriteErrorCode)i, ThrowsException = i != (byte)ReadWriteErrorCode.Success });
 

S7.Net.UnitTest/S7.Net.UnitTest.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net452;netcoreapp3.1;net5.0</TargetFrameworks>
 
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>

S7.Net.UnitTest/S7NetTestsAsync.cs

@@ -935,20 +935,53 @@ namespace S7.Net.UnitTest
             {
                 await plc.WriteBytesAsync(DataType.DataBlock, db, 0, data, cancellationToken);
             }
-            catch(TaskCanceledException)
+            catch(OperationCanceledException)
             {
                 // everything is good, that is the exception we expect
-                Console.WriteLine("Task was cancelled as expected.");
+                Console.WriteLine("Operation was cancelled as expected.");
                 return;
             }
             catch(Exception e)
             {
-                Assert.Fail($"Wrong exception type received. Expected {typeof(TaskCanceledException)}, received {e.GetType()}.");
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
             }
 
             // Depending on how tests run, this can also just succeed without getting cancelled at all. Do nothing in this case.
             Console.WriteLine("Task was not cancelled as expected.");
         }
+
+        /// <summary>
+        /// Write a large amount of data and test cancellation
+        /// </summary>
+        [TestMethod]
+        public async Task Test_Async_ParseDataIntoDataItemsAlignment()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var db = 2;
+            // First write a sensible S7 string capacity
+            await plc.WriteBytesAsync(DataType.DataBlock, db, 0, new byte[] {5, 0});
+
+            // Read two data items, with the first having odd number of bytes (7),
+            // and the second has to be aligned on a even address
+            var dataItems = new List<DataItem>
+            {
+                new DataItem
+                {
+                    DataType = DataType.DataBlock,
+                    DB = db,
+                    VarType = VarType.S7String,
+                    Count = 5
+                },
+                new DataItem
+                {
+                    DataType = DataType.DataBlock,
+                    DB = db,
+                    VarType = VarType.Word,
+                }
+            };
+            await plc.ReadMultipleVarsAsync(dataItems, CancellationToken.None);
+        }
         #endregion
     }
 }

S7.Net.UnitTest/StreamTests.cs

@@ -2,6 +2,7 @@
 using System;
 using System.IO;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace S7.Net.UnitTest
@@ -15,6 +16,7 @@ namespace S7.Net.UnitTest
         {
             Data = data;
         }
+
         public override bool CanRead => _position < Data.Length;
 
         public override bool CanSeek => throw new NotImplementedException();
@@ -26,21 +28,31 @@ namespace S7.Net.UnitTest
         public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
         public byte[] Data { get; }
 
+        int _position = 0;
+
         public override void Flush()
         {
             throw new NotImplementedException();
         }
 
-        int _position = 0;
         public override int Read(byte[] buffer, int offset, int count)
         {
+            throw new NotImplementedException();
+        }
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
             if (_position >= Data.Length)
             {
-                return 0;
+                return Task.FromResult(0);
             }
+
             buffer[offset] = Data[_position];
             ++_position;
-            return 1;
+
+            return Task.FromResult(1);
         }
 
         public override long Seek(long offset, SeekOrigin origin)
@@ -78,21 +90,21 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        public void TPKT_ReadRestrictedStream()
+        public async Task TPKT_ReadRestrictedStream()
         {
             var fullMessage = ProtocolUnitTest.StringToByteArray("0300002902f0803203000000010002001400000401ff0400807710000100000103000000033f8ccccd");
             var m = new TestStream1BytePerRead(fullMessage);
-            var t = TPKT.Read(m);
+            var t = await TPKT.ReadAsync(m, CancellationToken.None);
             Assert.AreEqual(fullMessage.Length, t.Length);
             Assert.AreEqual(fullMessage.Last(), t.Data.Last());
         }
 
         [TestMethod]
-        public void TPKT_ReadStreamTooShort()
+        public async Task TPKT_ReadStreamTooShort()
         {
             var fullMessage = ProtocolUnitTest.StringToByteArray("0300002902f0803203000000010002001400");
             var m = new TestStream1BytePerRead(fullMessage);
-            Assert.ThrowsException<TPKTInvalidException>(() => TPKT.Read(m));
+            await Assert.ThrowsExceptionAsync<TPKTInvalidException>(() => TPKT.ReadAsync(m, CancellationToken.None));
         }
     }
 }

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/COTP.cs

@@ -50,22 +50,6 @@ namespace S7.Net
                 Data = new byte[0];
             }
 
-            /// <summary>
-            /// Reads COTP TPDU (Transport protocol data unit) from the network stream
-            /// See: https://tools.ietf.org/html/rfc905
-            /// </summary>
-            /// <param name="stream">The socket to read from</param>
-            /// <returns>COTP DPDU instance</returns>
-            public static TPDU Read(Stream stream)
-            {
-                var tpkt = TPKT.Read(stream);
-                if (tpkt.Length == 0)
-                {
-                    throw new TPDUInvalidException("No protocol data received");
-                }
-                return new TPDU(tpkt);
-            }
-
             /// <summary>
             /// Reads COTP TPDU (Transport protocol data unit) from the network stream
             /// See: https://tools.ietf.org/html/rfc905
@@ -100,36 +84,6 @@ namespace S7.Net
         /// </summary>
         public class TSDU
         {
-            /// <summary>
-            /// Reads the full COTP TSDU (Transport service data unit)
-            /// See: https://tools.ietf.org/html/rfc905
-            /// </summary>
-            /// <param name="stream">The stream to read from</param>
-            /// <returns>Data in TSDU</returns>
-            public static byte[] Read(Stream stream)
-            {
-                var segment = TPDU.Read(stream);
-
-                if (segment.LastDataUnit)
-                {
-                    return segment.Data;
-                }
-
-                // More segments are expected, prepare a buffer to store all data
-                var buffer = new byte[segment.Data.Length];
-                Array.Copy(segment.Data, buffer, segment.Data.Length);
-
-                while (!segment.LastDataUnit)
-                {
-                    segment = TPDU.Read(stream);
-                    var previousLength = buffer.Length;
-                    Array.Resize(ref buffer, buffer.Length + segment.Data.Length);
-                    Array.Copy(segment.Data, 0, buffer, previousLength, segment.Data.Length);
-                }
-
-                return buffer;
-            }
-
             /// <summary>
             /// Reads the full COTP TSDU (Transport service data unit)
             /// See: https://tools.ietf.org/html/rfc905
@@ -137,7 +91,7 @@ namespace S7.Net
             /// <param name="stream">The stream to read from</param>
             /// <returns>Data in TSDU</returns>
             public static async Task<byte[]> ReadAsync(Stream stream, CancellationToken cancellationToken)
-            {                
+            {
                 var segment = await TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
 
                 if (segment.LastDataUnit)

S7.Net/Enums.cs

@@ -15,6 +15,11 @@
         /// </summary>
         Logo0BA8 = 1,
 
+        /// <summary>
+        /// S7 200 Smart
+        /// </summary>
+        S7200Smart = 2,
+
         /// <summary>
         /// S7 300 cpu type
         /// </summary>

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;
 
@@ -13,14 +15,24 @@ namespace S7.Net
     /// </summary>
     public partial class Plc : IDisposable
     {
-        private const int CONNECTION_TIMED_OUT_ERROR_CODE = 10060;
-        
+        /// <summary>
+        /// The default port for the S7 protocol.
+        /// </summary>
+        public const int DefaultPort = 102;
+
+        /// <summary>
+        /// The default timeout (in milliseconds) used for <see cref="P:ReadTimeout"/> and <see cref="P:WriteTimeout"/>.
+        /// </summary>
+        public const int DefaultTimeout = 10_000;
+
+        private readonly TaskQueue queue = new TaskQueue();
+
         //TCP connection to device
         private TcpClient? tcpClient;
         private NetworkStream? _stream;
 
-        private int readTimeout = 0; // default no timeout
-        private int writeTimeout = 0; // default no timeout
+        private int readTimeout = DefaultTimeout; // default no timeout
+        private int writeTimeout = DefaultTimeout; // default no timeout
 
         /// <summary>
         /// IP address of the PLC
@@ -32,6 +44,11 @@ namespace S7.Net
         /// </summary>
         public int Port { get; }
 
+        /// <summary>
+        /// The TSAP addresses used during the connection request.
+        /// </summary>
+        public TsapPair TsapPair { get; set; }
+
         /// <summary>
         /// CPU type of the PLC
         /// </summary>
@@ -104,25 +121,14 @@ namespace S7.Net
         /// </summary>
         /// <param name="cpu">CpuType of the PLC (select from the enum)</param>
         /// <param name="ip">Ip address of the PLC</param>
-        /// <param name="port">Port address of the PLC, default 102</param>
         /// <param name="rack">rack of the PLC, usually it's 0, but check in the hardware configuration of Step7 or TIA portal</param>
         /// <param name="slot">slot of the CPU of the PLC, usually it's 2 for S7300-S7400, 0 for S7-1200 and S7-1500.
         ///  If you use an external ethernet card, this must be set accordingly.</param>
-        public Plc(CpuType cpu, string ip, int port, Int16 rack, Int16 slot)
+        public Plc(CpuType cpu, string ip, Int16 rack, Int16 slot)
+            : this(cpu, ip, DefaultPort, rack, slot)
         {
-            if (!Enum.IsDefined(typeof(CpuType), cpu))
-                throw new ArgumentException($"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.", nameof(cpu));
-
-            if (string.IsNullOrEmpty(ip))
-                throw new ArgumentException("IP address must valid.", nameof(ip));
-
-            CPU = cpu;
-            IP = ip;
-            Port = port;
-            Rack = rack;
-            Slot = slot;
-            MaxPDUSize = 240;
         }
+
         /// <summary>
         /// Creates a PLC object with all the parameters needed for connections.
         /// For S7-1200 and S7-1500, the default is rack = 0 and slot = 0.
@@ -131,23 +137,51 @@ namespace S7.Net
         /// </summary>
         /// <param name="cpu">CpuType of the PLC (select from the enum)</param>
         /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="port">Port number used for the connection, default 102.</param>
         /// <param name="rack">rack of the PLC, usually it's 0, but check in the hardware configuration of Step7 or TIA portal</param>
         /// <param name="slot">slot of the CPU of the PLC, usually it's 2 for S7300-S7400, 0 for S7-1200 and S7-1500.
         ///  If you use an external ethernet card, this must be set accordingly.</param>
-        public Plc(CpuType cpu, string ip, Int16 rack, Int16 slot)
+        public Plc(CpuType cpu, string ip, int port, Int16 rack, Int16 slot)
+            : this(ip, port, TsapPair.GetDefaultTsapPair(cpu, rack, slot))
         {
             if (!Enum.IsDefined(typeof(CpuType), cpu))
-                throw new ArgumentException($"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.", nameof(cpu));
+                throw new ArgumentException(
+                    $"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.",
+                    nameof(cpu));
 
+            CPU = cpu;
+            Rack = rack;
+            Slot = slot;
+        }
+
+        /// <summary>
+        /// Creates a PLC object with all the parameters needed for connections.
+        /// For S7-1200 and S7-1500, the default is rack = 0 and slot = 0.
+        /// You need slot > 0 if you are connecting to external ethernet card (CP).
+        /// For S7-300 and S7-400 the default is rack = 0 and slot = 2.
+        /// </summary>
+        /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="tsapPair">The TSAP addresses used for the connection request.</param>
+        public Plc(string ip, TsapPair tsapPair) : this(ip, DefaultPort, tsapPair)
+        {
+        }
+
+        /// <summary>
+        /// Creates a PLC object with all the parameters needed for connections. Use this constructor
+        /// if you want to manually override the TSAP addresses used during the connection request.
+        /// </summary>
+        /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="port">Port number used for the connection, default 102.</param>
+        /// <param name="tsapPair">The TSAP addresses used for the connection request.</param>
+        public Plc(string ip, int port, TsapPair tsapPair)
+        {
             if (string.IsNullOrEmpty(ip))
                 throw new ArgumentException("IP address must valid.", nameof(ip));
 
-            CPU = cpu;
             IP = ip;
-            Port = 102;
-            Rack = rack;
-            Slot = slot;
+            Port = port;
             MaxPDUSize = 240;
+            TsapPair = tsapPair;
         }
 
         /// <summary>
@@ -158,6 +192,7 @@ namespace S7.Net
             if (tcpClient != null)
             {
                 if (tcpClient.Connected) tcpClient.Close();
+                tcpClient = null; // Can not reuse TcpClient once connection gets closed.
             }
         }
 
@@ -242,6 +277,16 @@ 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), 
-        /// the address of the memory, the address of the byte and the bytes count. 
+        /// 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.
         /// </summary>
         /// <param name="dataType">MemoryType (DB, Timer, Counter, etc.)</param>
         /// <param name="db">Address of the memory to be read</param>
@@ -184,7 +184,7 @@ 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:
@@ -242,8 +242,8 @@ namespace S7.Net
                 // next Item
                 offset += byteCnt;
 
-                // Fill byte in response when bytecount is odd
-                if (dataItem.Count % 2 != 0 && (dataItem.VarType == VarType.Byte || dataItem.VarType == VarType.Bit))
+                // Always align to even offset
+                if (offset % 2 != 0)
                     offset++;
             }
         }

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;
 
@@ -28,11 +28,16 @@ namespace S7.Net
             var stream = await ConnectAsync().ConfigureAwait(false);
             try
             {
-                cancellationToken.ThrowIfCancellationRequested();
-                await EstablishConnection(stream, cancellationToken).ConfigureAwait(false);
-                _stream = stream;
+                await queue.Enqueue(async () =>
+                {
+                    cancellationToken.ThrowIfCancellationRequested();
+                    await EstablishConnection(stream, cancellationToken).ConfigureAwait(false);
+                    _stream = stream;
+
+                    return default(object);
+                }).ConfigureAwait(false);
             }
-            catch(Exception)
+            catch (Exception)
             {
                 stream.Dispose();
                 throw;
@@ -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 COTP.TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            var requestData = ConnectionRequest.GetCOTPConnectionRequest(TsapPair);
+            var response = await NoLockRequestTpduAsync(stream, requestData, 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");
 
@@ -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>
@@ -179,10 +185,10 @@ 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>
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
@@ -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>
@@ -221,7 +227,7 @@ 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>
@@ -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).ConfigureAwait(false);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
 
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
 
                 ParseDataIntoDataItems(s7data, dataItems);
@@ -435,12 +438,9 @@ namespace S7.Net
 
         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) });
 
-            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).ConfigureAwait(false);
+            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).ConfigureAwait(false);
-
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
                 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).ConfigureAwait(false);
-
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (OperationCanceledException)
@@ -520,13 +510,57 @@ 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();
+
+            return queue.Enqueue(() =>
+                NoLockRequestTsduAsync(stream, requestData, offset, length, cancellationToken));
+        }
+
+        private async Task<COTP.TPDU> NoLockRequestTpduAsync(Stream stream, byte[] requestData,
+            CancellationToken cancellationToken = default)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            try
             {
-                throw new PlcException(ErrorCode.ConnectionError, "Plc is not connected");
+                using var closeOnCancellation = cancellationToken.Register(Close);
+                await stream.WriteAsync(requestData, 0, requestData.Length, cancellationToken).ConfigureAwait(false);
+                return await COTP.TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception exc)
+            {
+                if (exc is TPDUInvalidException || exc is TPKTInvalidException)
+                {
+                    Close();
+                }
+
+                throw;
+            }
+        }
+
+        private async Task<byte[]> NoLockRequestTsduAsync(Stream stream, byte[] requestData, int offset, int length,
+            CancellationToken cancellationToken = default)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            try
+            {
+                using var closeOnCancellation = cancellationToken.Register(Close);
+                await stream.WriteAsync(requestData, offset, length, cancellationToken).ConfigureAwait(false);
+                return await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception exc)
+            {
+                if (exc is TPDUInvalidException || exc is TPKTInvalidException)
+                {
+                    Close();
+                }
+
+                throw;
             }
-            return _stream;
         }
     }
 }

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 = COTP.TSDU.Read(stream);
+                var s7data = RequestTsdu(dataToSend);
                 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 = COTP.TSDU.Read(stream); //TODO use Async
+                var s7data = RequestTsdu(dataToSend);
 
                 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/Protocol/ConnectionRequest.cs

@@ -1,68 +1,27 @@
-using System;
-
-namespace S7.Net.Protocol
+namespace S7.Net.Protocol
 {
     internal static class ConnectionRequest
     {
-        public static byte[] GetCOTPConnectionRequest(CpuType cpu, Int16 rack, Int16 slot)
+        public static byte[] GetCOTPConnectionRequest(TsapPair tsapPair)
         {
             byte[] bSend1 = {
                     3, 0, 0, 22, //TPKT
                     17,     //COTP Header Length
-                    224,    //Connect Request 
+                    224,    //Connect Request
                     0, 0,   //Destination Reference
                     0, 46,  //Source Reference
                     0,      //Flags
                     193,    //Parameter Code (src-tasp)
                     2,      //Parameter Length
-                    1, 0,   //Source TASP
+                    tsapPair.Local.FirstByte, tsapPair.Local.SecondByte,   //Source TASP
                     194,    //Parameter Code (dst-tasp)
                     2,      //Parameter Length
-                    3, 0,   //Destination TASP
+                    tsapPair.Remote.FirstByte, tsapPair.Remote.SecondByte,   //Destination TASP
                     192,    //Parameter Code (tpdu-size)
                     1,      //Parameter Length
                     10      //TPDU Size (2^10 = 1024)
                 };
 
-            switch (cpu)
-            {
-                case CpuType.S7200:
-                    //S7200: Chr(193) & Chr(2) & Chr(16) & Chr(0) 'Eigener Tsap
-                    bSend1[13] = 0x10;
-                    bSend1[14] = 0x00;
-                    //S7200: Chr(194) & Chr(2) & Chr(16) & Chr(0) 'Fremder Tsap
-                    bSend1[17] = 0x10;
-                    bSend1[18] = 0x00;
-                    break;
-                case CpuType.Logo0BA8:
-                    // These values are taken from NodeS7, it's not verified if these are
-                    // exact requirements to connect to the Logo0BA8.
-                    bSend1[13] = 0x01;
-                    bSend1[14] = 0x00;
-                    bSend1[17] = 0x01;
-                    bSend1[18] = 0x02;
-                    break;
-                case CpuType.S71200:
-                case CpuType.S7300:
-                case CpuType.S7400:
-                    //S7300: Chr(193) & Chr(2) & Chr(1) & Chr(0)  'Eigener Tsap
-                    bSend1[13] = 0x01;
-                    bSend1[14] = 0x00;
-                    //S7300: Chr(194) & Chr(2) & Chr(3) & Chr(2)  'Fremder Tsap
-                    bSend1[17] = 0x03;
-                    bSend1[18] = (byte) ((rack << 5) | (int) slot);
-                    break;
-                case CpuType.S71500:
-                    // Eigener Tsap
-                    bSend1[13] = 0x10;
-                    bSend1[14] = 0x02;
-                    // Fredmer Tsap
-                    bSend1[17] = 0x03;
-                    bSend1[18] = (byte) ((rack << 5) | (int) slot);
-                    break;
-                default:
-                    throw new Exception("Wrong CPU Type Secified");
-            }
             return bSend1;
         }
     }

S7.Net/Protocol/Tsap.cs

@@ -0,0 +1,31 @@
+namespace S7.Net.Protocol
+{
+    /// <summary>
+    /// Provides a representation of the Transport Service Access Point, or TSAP in short. TSAP's are used
+    /// to specify a client and server address. For most PLC types a default TSAP is available that allows
+    /// connection from any IP and can be calculated using the rack and slot numbers.
+    /// </summary>
+    public struct Tsap
+    {
+        /// <summary>
+        /// First byte of the TSAP.
+        /// </summary>
+        public byte FirstByte { get; set; }
+
+        /// <summary>
+        /// Second byte of the TSAP.
+        /// </summary>
+        public byte SecondByte { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Tsap" /> class using the specified values.
+        /// </summary>
+        /// <param name="firstByte">The first byte of the TSAP.</param>
+        /// <param name="secondByte">The second byte of the TSAP.</param>
+        public Tsap(byte firstByte, byte secondByte)
+        {
+            FirstByte = firstByte;
+            SecondByte = secondByte;
+        }
+    }
+}

S7.Net/Protocol/TsapPair.cs

@@ -0,0 +1,96 @@
+using System;
+
+namespace S7.Net.Protocol
+{
+    /// <summary>
+    /// Implements a pair of TSAP addresses used to connect to a PLC.
+    /// </summary>
+    public class TsapPair
+    {
+        /// <summary>
+        /// The local <see cref="Tsap" />.
+        /// </summary>
+        public Tsap Local { get; set; }
+
+        /// <summary>
+        /// The remote <see cref="Tsap" />
+        /// </summary>
+        public Tsap Remote { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="TsapPair" /> class using the specified local and
+        /// remote TSAP.
+        /// </summary>
+        /// <param name="local">The local TSAP.</param>
+        /// <param name="remote">The remote TSAP.</param>
+        public TsapPair(Tsap local, Tsap remote)
+        {
+            Local = local;
+            Remote = remote;
+        }
+
+        /// <summary>
+        /// Builds a <see cref="TsapPair" /> that can be used to connect to a PLC using the default connection
+        /// addresses.
+        /// </summary>
+        /// <remarks>
+        /// The remote TSAP is constructed using <code>new Tsap(0x03, (byte) ((rack &lt;&lt; 5) | slot))</code>.
+        /// </remarks>
+        /// <param name="cpuType">The CPU type of the PLC.</param>
+        /// <param name="rack">The rack of the PLC's network card.</param>
+        /// <param name="slot">The slot of the PLC's network card.</param>
+        /// <returns>A TSAP pair that matches the given parameters.</returns>
+        /// <exception cref="ArgumentOutOfRangeException">The <paramref name="cpuType"/> is invalid.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="rack"/> parameter is less than 0.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="rack"/> parameter is greater than 15.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="slot"/> parameter is less than 0.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="slot"/> parameter is greater than 15.</exception>
+        public static TsapPair GetDefaultTsapPair(CpuType cpuType, int rack, int slot)
+        {
+            if (rack < 0) throw InvalidRackOrSlot(rack, nameof(rack), "minimum", 0);
+            if (rack > 0x0F) throw InvalidRackOrSlot(rack, nameof(rack), "maximum", 0x0F);
+
+            if (slot < 0) throw InvalidRackOrSlot(slot, nameof(slot), "minimum", 0);
+            if (slot > 0x0F) throw InvalidRackOrSlot(slot, nameof(slot), "maximum", 0x0F);
+
+            switch (cpuType)
+            {
+                case CpuType.S7200:
+                    return new TsapPair(new Tsap(0x10, 0x00), new Tsap(0x10, 0x01));
+                case CpuType.Logo0BA8:
+                    // The actual values are probably on a per-project basis
+                    return new TsapPair(new Tsap(0x01, 0x00), new Tsap(0x01, 0x02));
+                case CpuType.S7200Smart:
+                case CpuType.S71200:
+                case CpuType.S71500:
+                case CpuType.S7300:
+                case CpuType.S7400:
+                    // Testing with S7 1500 shows only the remote TSAP needs to match. This might differ for other
+                    // PLC types.
+                    return new TsapPair(new Tsap(0x01, 0x00), new Tsap(0x03, (byte) ((rack << 5) | slot)));
+                default:
+                    throw new ArgumentOutOfRangeException(nameof(cpuType), "Invalid CPU Type specified");
+            }
+        }
+
+        private static ArgumentOutOfRangeException InvalidRackOrSlot(int value, string name, string extrema,
+            int extremaValue)
+        {
+            return new ArgumentOutOfRangeException(name,
+                $"Invalid {name} value specified (decimal: {value}, hexadecimal: {value:X}), {extrema} value " +
+                $"is {extremaValue} (decimal) or {extremaValue:X} (hexadecimal).");
+        }
+    }
+}

S7.Net/TPKT.cs

@@ -25,34 +25,6 @@ namespace S7.Net
             Data = data;
         }
 
-        /// <summary>
-        /// Reads a TPKT from the socket
-        /// </summary>
-        /// <param name="stream">The stream to read from</param>
-        /// <returns>TPKT Instance</returns>
-        public static TPKT Read(Stream stream)
-        {
-            var buf = new byte[4];
-            int len = stream.ReadExact(buf, 0, 4);
-            if (len < 4) throw new TPKTInvalidException($"TPKT header is incomplete / invalid. Received Bytes: {len} expected: {buf.Length}");
-            var version = buf[0];
-            var reserved1 = buf[1];
-            var length = buf[2] * 256 + buf[3]; //BigEndian
-
-            var data = new byte[length - 4];
-            len = stream.ReadExact(data, 0, data.Length);
-            if (len < data.Length)
-                throw new TPKTInvalidException($"TPKT payload is incomplete / invalid. Received Bytes: {len} expected: {data.Length}");
-
-            return new TPKT
-            (
-                version: version,
-                reserved1: reserved1,
-                length: length,
-                data: data
-            );
-        }
-
         /// <summary>
         /// Reads a TPKT from the socket Async
         /// </summary>

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);
         }
-
     }
 }

S7.sln

@@ -9,6 +9,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 	ProjectSection(SolutionItems) = preProject
 		appveyor.yml = appveyor.yml
 		README.md = README.md
+		.github\workflows\test.yml = .github\workflows\test.yml
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "S7.Net.UnitTest", "S7.Net.UnitTest\S7.Net.UnitTest.csproj", "{303CCED6-9ABC-4899-A509-743341AAA804}"