Merge pull request #485 from dylandrush/484_Public_PLCExceptions

Made all exceptions public

.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-20.04, macos-latest]
+        test-framework: [netcoreapp3.1, net5.0]
+        include:
+          - os: ubuntu-20.04
+            test-framework: netcoreapp3.1
+            installSnap7: true
+            dotnet-sdk: '3.1.x'
+          - os: ubuntu-20.04
+            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-20.04' }}
+        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 }}

GitVersion.yml

@@ -1,21 +0,0 @@
-assembly-informational-format: '{NuGetVersion}'
-mode: ContinuousDeployment
-branches:
-  master:
-    tag: rc
-    increment: Minor
-  feature:
-    regex: features?[/-]
-    tag: rc-{BranchName}
-    increment: Minor
-  pull-request:
-    regex: (pull|pull\-requests|pr)[/-]
-    tag: rc-pr-{BranchName}
-    increment: Minor
-  hotfix:
-    regex: hotfix(es)?[/-]
-    tag: rc
-    increment: Patch
-  develop:
-    regex: dev(elop)?(ment)?$
-    tag: b

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)

S7.Net.UnitTest/Helpers/TestClass.cs

@@ -1,4 +1,6 @@
 
+using S7.Net.Types;
+
 namespace S7.Net.UnitTest.Helpers
 {
     class TestClass
@@ -51,5 +53,16 @@ namespace S7.Net.UnitTest.Helpers
         /// DB1.DBD16
         /// </summary>
         public ushort DWordVariable { get; set; }
+
+        /// <summary>
+        /// DB1.DBX20.0
+        /// </summary>
+        [S7String(S7StringType.S7WString, 10)]
+        public string WStringVariable { get; set; }
+        /// <summary>
+        /// DB1.DBX44.0
+        /// </summary>
+        [S7String(S7StringType.S7String, 10)]
+        public string StringVariable { get; set; }
     }
 }

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

@@ -7,6 +7,12 @@ using S7.Net.Types;
 using S7.UnitTest.Helpers;
 using System.Threading.Tasks;
 using System.Threading;
+using System.Security.Cryptography;
+
+
+#if NET5_0_OR_GREATER
+using System.Buffers;
+#endif
 
 #endregion
 
@@ -138,6 +144,33 @@ namespace S7.Net.UnitTest
             CollectionAssert.AreEqual(data, readData);
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Write/Read a large amount of data to test PDU max
+        /// </summary>
+        [TestMethod]
+        public async Task Test_Async_WriteLargeByteArrayWithMemory()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var randomEngine = new Random();
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(8192);
+            var data = dataOwner.Memory.Slice(0, 8192);
+            var db = 2;
+            randomEngine.NextBytes(data.Span);
+
+            await plc.WriteBytesAsync(DataType.DataBlock, db, 0, data);
+
+            using var readDataOwner = MemoryPool<byte>.Shared.Rent(data.Length);
+            var readData = readDataOwner.Memory.Slice(0, data.Length);
+            await plc.ReadBytesAsync(readData, DataType.DataBlock, db, 0);
+
+            CollectionAssert.AreEqual(data.ToArray(), readData.ToArray());
+        }
+
+#endif
+
         /// <summary>
         /// Read/Write a class that has the same properties of a DB with the same field in the same order
         /// </summary>
@@ -154,7 +187,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -168,6 +203,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(tc.LRealVariable, tc2.LRealVariable);
             Assert.AreEqual(tc.RealVariable, tc2.RealVariable);
             Assert.AreEqual(tc.DWordVariable, tc2.DWordVariable);
+            Assert.AreEqual(tc.WStringVariable, tc2.WStringVariable);
+            Assert.AreEqual(tc.StringVariable, tc2.StringVariable);
         }
 
         [TestMethod]
@@ -580,7 +617,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -628,7 +667,10 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
+
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -646,6 +688,9 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2.LRealVariable, 3), Math.Round(tc2Generic.LRealVariable, 3));
             Assert.AreEqual(tc2.RealVariable, tc2Generic.RealVariable);
             Assert.AreEqual(tc2.DWordVariable, tc2Generic.DWordVariable);
+            Assert.AreEqual(tc2.WStringVariable, tc2Generic.WStringVariable);
+            Assert.AreEqual(tc2.StringVariable, tc2Generic.StringVariable);
+
         }
 
         [TestMethod]
@@ -671,7 +716,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -686,6 +733,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2Generic.LRealVariable, 3), Math.Round(tc2GenericWithClassFactory.LRealVariable, 3));
             Assert.AreEqual(tc2Generic.RealVariable, tc2GenericWithClassFactory.RealVariable);
             Assert.AreEqual(tc2Generic.DWordVariable, tc2GenericWithClassFactory.DWordVariable);
+            Assert.AreEqual(tc2Generic.WStringVariable, tc2GenericWithClassFactory.WStringVariable);
+            Assert.AreEqual(tc2Generic.StringVariable, tc2GenericWithClassFactory.StringVariable);
         }
 
         [TestMethod]
@@ -792,7 +841,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
             plc.WriteClass(tc, DB2);
 
@@ -914,6 +965,31 @@ namespace S7.Net.UnitTest
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        [TestMethod]
+        public async Task Test_Async_ReadWriteBytesManyWithMemory()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            using var data = MemoryPool<byte>.Shared.Rent(2000);
+            for (int i = 0; i < data.Memory.Length; i++)
+                data.Memory.Span[i] = (byte)(i % 256);
+
+            await plc.WriteBytesAsync(DataType.DataBlock, 2, 0, data.Memory);
+
+            using var readData = MemoryPool<byte>.Shared.Rent(data.Memory.Length);
+
+            await plc.ReadBytesAsync(readData.Memory.Slice(0, data.Memory.Length), DataType.DataBlock, 2, 0);
+
+            for (int x = 0; x < data.Memory.Length; x++)
+            {
+                Assert.AreEqual(x % 256, readData.Memory.Span[x], string.Format("Bit {0} failed", x));
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Write a large amount of data and test cancellation
         /// </summary>
@@ -935,20 +1011,95 @@ 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.");
         }
+
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Write a large amount of data and test cancellation
+        /// </summary>
+        [TestMethod]
+        public async Task Test_Async_WriteLargeByteArrayWithCancellationWithMemory()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var cancellationSource = new CancellationTokenSource();
+            var cancellationToken = cancellationSource.Token;
+
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(8192);
+            var data = dataOwner.Memory.Slice(0, 8192);
+            var randomEngine = new Random();
+            var db = 2;
+            randomEngine.NextBytes(data.Span);
+
+            cancellationSource.CancelAfter(TimeSpan.FromMilliseconds(5));
+            try
+            {
+                await plc.WriteBytesAsync(DataType.DataBlock, db, 0, data, cancellationToken);
+            }
+            catch (OperationCanceledException)
+            {
+                // everything is good, that is the exception we expect
+                Console.WriteLine("Operation was cancelled as expected.");
+                return;
+            }
+            catch (Exception e)
+            {
+                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.");
+        }
+
+#endif
+
+        /// <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/S7NetTestsSync.cs

@@ -5,6 +5,11 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using S7.Net.UnitTest.Helpers;
 using S7.Net.Types;
 using S7.UnitTest.Helpers;
+using System.Security.Cryptography;
+
+#if NET5_0_OR_GREATER
+using System.Buffers;
+#endif
 
 #endregion
 
@@ -183,6 +188,9 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
+
             plc.WriteClass(tc, DB2);
             TestClass tc2 = new TestClass();
             // Values that are read from a class are stored inside the class itself, that is passed by reference
@@ -194,6 +202,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(tc.LRealVariable, tc2.LRealVariable);
             Assert.AreEqual(tc.RealVariable, tc2.RealVariable);
             Assert.AreEqual(tc.DWordVariable, tc2.DWordVariable);
+            Assert.AreEqual(tc.WStringVariable, tc2.WStringVariable);
+            Assert.AreEqual(tc.StringVariable, tc2.StringVariable);
         }
 
         /// <summary>
@@ -577,6 +587,8 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
 
             plc.WriteClass(tc, DB2);
 
@@ -622,6 +634,8 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
 
             plc.WriteClass(tc, DB2);
 
@@ -637,6 +651,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2.LRealVariable, 3), Math.Round(tc2Generic.LRealVariable, 3));
             Assert.AreEqual(tc2.RealVariable, tc2Generic.RealVariable);
             Assert.AreEqual(tc2.DWordVariable, tc2Generic.DWordVariable);
+            Assert.AreEqual(tc2.WStringVariable, tc2Generic.WStringVariable);
+            Assert.AreEqual(tc2.StringVariable, tc2Generic.StringVariable);
         }
 
         [TestMethod, ExpectedException(typeof(PlcException))]
@@ -665,6 +681,8 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
 
             plc.WriteClass(tc, DB2);
 
@@ -679,6 +697,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2Generic.LRealVariable, 3), Math.Round(tc2GenericWithClassFactory.LRealVariable, 3));
             Assert.AreEqual(tc2Generic.RealVariable, tc2GenericWithClassFactory.RealVariable);
             Assert.AreEqual(tc2Generic.DWordVariable, tc2GenericWithClassFactory.DWordVariable);
+            Assert.AreEqual(tc2Generic.WStringVariable, tc2GenericWithClassFactory.WStringVariable);
+            Assert.AreEqual(tc2Generic.StringVariable, tc2GenericWithClassFactory.StringVariable);
         }
 
         [TestMethod, ExpectedException(typeof(PlcException))]
@@ -762,6 +782,33 @@ namespace S7.Net.UnitTest
             CollectionAssert.AreEqual(data, readData);
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Write/Read a large amount of data to test PDU max
+        /// </summary>
+        [TestMethod]
+        public void T33_WriteLargeByteArrayWithSpan()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var randomEngine = new Random();
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(8192);
+            var data = dataOwner.Memory.Span.Slice(0, 8192);
+            var db = 2;
+            randomEngine.NextBytes(data);
+
+            plc.WriteBytes(DataType.DataBlock, db, 0, data);
+
+            using var readDataOwner = MemoryPool<byte>.Shared.Rent(data.Length);
+            var readData = readDataOwner.Memory.Span.Slice(0, data.Length);
+            plc.ReadBytes(readData, DataType.DataBlock, db, 0);
+
+            CollectionAssert.AreEqual(data.ToArray(), readData.ToArray());
+        }
+
+#endif
+
         [TestMethod, ExpectedException(typeof(PlcException))]
         public void T18_ReadStructThrowsIfPlcIsNotConnected()
         {
@@ -837,6 +884,9 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
+
             plc.WriteClass(tc, DB2);
 
             int expectedReadBytes = (int)Types.Class.GetClassSize(tc);
@@ -987,6 +1037,32 @@ namespace S7.Net.UnitTest
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        [TestMethod]
+        public void T27_ReadWriteBytesManyWithSpan()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(2000);
+            var data = dataOwner.Memory.Span;
+            for (int i = 0; i < data.Length; i++)
+                data[i] = (byte)(i % 256);
+
+            plc.WriteBytes(DataType.DataBlock, 2, 0, data);
+
+            using var readDataOwner = MemoryPool<byte>.Shared.Rent(data.Length);
+            var readData = readDataOwner.Memory.Span.Slice(0, data.Length);
+            plc.ReadBytes(readData, DataType.DataBlock, 2, 0);
+
+            for (int x = 0; x < data.Length; x++)
+            {
+                Assert.AreEqual(x % 256, readData[x], $"Mismatch at offset {x}, expected {x % 256}, actual {readData[x]}.");
+            }
+        }
+
+#endif
+
         [TestMethod]
         public void T28_ReadClass_DoesntCrash_When_ReadingLessThan1Byte()
         {
@@ -1041,7 +1117,7 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(test_value, test_value2, "Compare DateTimeLong Write/Read");
         }
 
-        #endregion
+#endregion
 
         #region Private methods
 

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/ClassTests.cs

@@ -17,6 +17,19 @@ namespace S7.Net.UnitTest.TypeTests
             Assert.AreEqual(Class.GetClassSize(new TestClassUnevenSize(3, 17)), 10);
         }
 
+        /// <summary>
+        /// Ensure Uint32 is correctly parsed through ReadClass functions. Adresses issue https://github.com/S7NetPlus/s7netplus/issues/414
+        /// </summary>
+        [TestMethod]
+        public void TestUint32Read()
+        {
+            var result = new TestUint32();
+            var data = new byte[4] { 0, 0, 0, 5 };
+            var bytesRead = Class.FromBytes(result, data);
+            Assert.AreEqual(bytesRead, data.Length);
+            Assert.AreEqual(5u, result.Value1);
+        }
+
         private class TestClassUnevenSize
         {
             public bool Bool { get; set; }
@@ -29,5 +42,10 @@ namespace S7.Net.UnitTest.TypeTests
                 Bools = new bool[bitCount];
             }
         }
+
+        private class TestUint32
+        {
+            public uint Value1 { get; set; }
+        }
     }
 }

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

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/Helper/MemoryStreamExtension.cs

@@ -1,6 +1,10 @@
-
+using System;
+using System.Buffers;
+using System.IO;
+
 namespace S7.Net.Helper
 {
+#if !NET5_0_OR_GREATER
     internal static class MemoryStreamExtension
     {
         /// <summary>
@@ -10,9 +14,25 @@ namespace S7.Net.Helper
         /// </summary>
         /// <param name="stream"></param>
         /// <param name="value"></param>
-        public static void WriteByteArray(this System.IO.MemoryStream stream, byte[] value)
+        public static void Write(this MemoryStream stream, byte[] value)
         {
             stream.Write(value, 0, value.Length);
         }
+
+        /// <summary>
+        /// Helper function to write the whole content of the given byte span to a memory stream.
+        /// </summary>
+        /// <param name="stream"></param>
+        /// <param name="value"></param>
+        public static void Write(this MemoryStream stream, ReadOnlySpan<byte> value)
+        {
+            byte[] buffer = ArrayPool<byte>.Shared.Rent(value.Length);
+
+            value.CopyTo(buffer);
+            stream.Write(buffer, 0, value.Length);
+
+            ArrayPool<byte>.Shared.Return(buffer);
+        }
     }
+#endif
 }

S7.Net/PLC.cs

@@ -15,16 +15,24 @@ namespace S7.Net
     /// </summary>
     public partial class Plc : IDisposable
     {
-        private readonly TaskQueue queue = new TaskQueue();
+        /// <summary>
+        /// The default port for the S7 protocol.
+        /// </summary>
+        public const int DefaultPort = 102;
 
-        private const int CONNECTION_TIMED_OUT_ERROR_CODE = 10060;
+        /// <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
@@ -36,6 +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>
@@ -108,25 +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($"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.", nameof(cpu));
-
-            if (string.IsNullOrEmpty(ip))
-                throw new ArgumentException("IP address must valid.", nameof(ip));
-
-            CPU = cpu;
-            IP = ip;
-            Port = port;
-            Rack = rack;
-            Slot = slot;
-            MaxPDUSize = 240;
         }
+
         /// <summary>
         /// Creates a PLC object with all the parameters needed for connections.
         /// For S7-1200 and S7-1500, the default is rack = 0 and slot = 0.
@@ -135,23 +137,51 @@ namespace S7.Net
         /// </summary>
         /// <param name="cpu">CpuType of the PLC (select from the enum)</param>
         /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="port">Port number used for the connection, default 102.</param>
         /// <param name="rack">rack of the PLC, usually it's 0, but check in the hardware configuration of Step7 or TIA portal</param>
         /// <param name="slot">slot of the CPU of the PLC, usually it's 2 for S7300-S7400, 0 for S7-1200 and S7-1500.
         ///  If you use an external ethernet card, this must be set accordingly.</param>
-        public Plc(CpuType cpu, string ip, Int16 rack, Int16 slot)
+        public Plc(CpuType cpu, string ip, int port, Int16 rack, Int16 slot)
+            : this(ip, port, TsapPair.GetDefaultTsapPair(cpu, rack, slot))
         {
             if (!Enum.IsDefined(typeof(CpuType), cpu))
-                throw new ArgumentException($"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>
@@ -162,6 +192,7 @@ namespace S7.Net
             if (tcpClient != null)
             {
                 if (tcpClient.Connected) tcpClient.Close();
+                tcpClient = null; // Can not reuse TcpClient once connection gets closed.
             }
         }
 

S7.Net/PLCExceptions.cs

@@ -6,7 +6,7 @@ using System.Runtime.Serialization;
 
 namespace S7.Net
 {
-    internal class WrongNumberOfBytesException : Exception
+    public class WrongNumberOfBytesException : Exception
     {
         public WrongNumberOfBytesException() : base()
         {
@@ -27,7 +27,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class InvalidAddressException : Exception
+    public class InvalidAddressException : Exception
     {
         public InvalidAddressException() : base ()
         {
@@ -48,7 +48,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class InvalidVariableTypeException : Exception
+    public class InvalidVariableTypeException : Exception
     {
         public InvalidVariableTypeException() : base()
         {
@@ -69,7 +69,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class TPKTInvalidException : Exception
+    public class TPKTInvalidException : Exception
     {
         public TPKTInvalidException() : base()
         {
@@ -90,7 +90,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class TPDUInvalidException : Exception
+    public class TPDUInvalidException : Exception
     {
         public TPDUInvalidException() : base()
         {

S7.Net/PLCHelpers.cs

@@ -1,7 +1,6 @@
 using S7.Net.Helper;
 using S7.Net.Protocol.S7;
 using S7.Net.Types;
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using DateTime = S7.Net.Types.DateTime;
@@ -18,13 +17,13 @@ namespace S7.Net
         private static void BuildHeaderPackage(System.IO.MemoryStream stream, int amount = 1)
         {
             //header size = 19 bytes
-            stream.WriteByteArray(new byte[] { 0x03, 0x00 });
+            stream.Write(new byte[] { 0x03, 0x00 });
             //complete package size
-            stream.WriteByteArray(Types.Int.ToByteArray((short)(19 + (12 * amount))));
-            stream.WriteByteArray(new byte[] { 0x02, 0xf0, 0x80, 0x32, 0x01, 0x00, 0x00, 0x00, 0x00 });
+            stream.Write(Int.ToByteArray((short)(19 + (12 * amount))));
+            stream.Write(new byte[] { 0x02, 0xf0, 0x80, 0x32, 0x01, 0x00, 0x00, 0x00, 0x00 });
             //data part size
-            stream.WriteByteArray(Types.Word.ToByteArray((ushort)(2 + (amount * 12))));
-            stream.WriteByteArray(new byte[] { 0x00, 0x00, 0x04 });
+            stream.Write(Word.ToByteArray((ushort)(2 + (amount * 12))));
+            stream.Write(new byte[] { 0x00, 0x00, 0x04 });
             //amount of requests
             stream.WriteByte((byte)amount);
         }
@@ -41,7 +40,7 @@ namespace S7.Net
         private static void BuildReadDataRequestPackage(System.IO.MemoryStream stream, DataType dataType, int db, int startByteAdr, int count = 1)
         {
             //single data req = 12
-            stream.WriteByteArray(new byte[] { 0x12, 0x0a, 0x10 });
+            stream.Write(new byte[] { 0x12, 0x0a, 0x10 });
             switch (dataType)
             {
                 case DataType.Timer:
@@ -53,8 +52,8 @@ namespace S7.Net
                     break;
             }
 
-            stream.WriteByteArray(Word.ToByteArray((ushort)(count)));
-            stream.WriteByteArray(Word.ToByteArray((ushort)(db)));
+            stream.Write(Word.ToByteArray((ushort)(count)));
+            stream.Write(Word.ToByteArray((ushort)(db)));
             stream.WriteByte((byte)dataType);
             var overflow = (int)(startByteAdr * 8 / 0xffffU); // handles words with address bigger than 8191
             stream.WriteByte((byte)overflow);
@@ -62,10 +61,10 @@ namespace S7.Net
             {
                 case DataType.Timer:
                 case DataType.Counter:
-                    stream.WriteByteArray(Types.Word.ToByteArray((ushort)(startByteAdr)));
+                    stream.Write(Word.ToByteArray((ushort)(startByteAdr)));
                     break;
                 default:
-                    stream.WriteByteArray(Types.Word.ToByteArray((ushort)((startByteAdr) * 8)));
+                    stream.Write(Word.ToByteArray((ushort)((startByteAdr) * 8)));
                     break;
             }
         }
@@ -242,8 +241,8 @@ 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

@@ -25,7 +25,7 @@ namespace S7.Net
         /// <returns>A task that represents the asynchronous open operation.</returns>
         public async Task OpenAsync(CancellationToken cancellationToken = default)
         {
-            var stream = await ConnectAsync().ConfigureAwait(false);
+            var stream = await ConnectAsync(cancellationToken).ConfigureAwait(false);
             try
             {
                 await queue.Enqueue(async () =>
@@ -37,18 +37,23 @@ namespace S7.Net
                     return default(object);
                 }).ConfigureAwait(false);
             }
-            catch(Exception)
+            catch (Exception)
             {
                 stream.Dispose();
                 throw;
             }
         }
 
-        private async Task<NetworkStream> ConnectAsync()
+        private async Task<NetworkStream> ConnectAsync(CancellationToken cancellationToken)
         {
             tcpClient = new TcpClient();
             ConfigureConnection();
+
+#if NET5_0_OR_GREATER
+            await tcpClient.ConnectAsync(IP, Port, cancellationToken).ConfigureAwait(false);
+#else
             await tcpClient.ConnectAsync(IP, Port).ConfigureAwait(false);
+#endif
             return tcpClient.GetStream();
         }
 
@@ -60,7 +65,7 @@ namespace S7.Net
 
         private async Task RequestConnection(Stream stream, CancellationToken cancellationToken)
         {
-            var requestData = ConnectionRequest.GetCOTPConnectionRequest(CPU, Rack, Slot);
+            var requestData = ConnectionRequest.GetCOTPConnectionRequest(TsapPair);
             var response = await NoLockRequestTpduAsync(stream, requestData, cancellationToken).ConfigureAwait(false);
 
             if (response.PDUType != COTP.PduType.ConnectionConfirmed)
@@ -90,7 +95,6 @@ namespace S7.Net
             MaxPDUSize = s7data[18] * 256 + s7data[19];
         }
 
-
         /// <summary>
         /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
         /// If the read was not successful, check LastErrorCode or LastErrorString.
@@ -105,16 +109,34 @@ namespace S7.Net
         public async Task<byte[]> ReadBytesAsync(DataType dataType, int db, int startByteAdr, int count, CancellationToken cancellationToken = default)
         {
             var resultBytes = new byte[count];
+
+            await ReadBytesAsync(resultBytes, dataType, db, startByteAdr, cancellationToken).ConfigureAwait(false);
+
+            return resultBytes;
+        }
+
+        /// <summary>
+        /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the read was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="buffer">Buffer to receive the read bytes. The <see cref="Memory{T}.Length"/> determines the number of bytes to read.</param>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</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.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>Returns the bytes in an array</returns>
+        public async Task ReadBytesAsync(Memory<byte> buffer, DataType dataType, int db, int startByteAdr, CancellationToken cancellationToken = default)
+        {
             int index = 0;
-            while (count > 0)
+            while (buffer.Length > 0)
             {
                 //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).ConfigureAwait(false);
-                count -= maxToRead;
+                var maxToRead = Math.Min(buffer.Length, MaxPDUSize - 18);
+                await ReadBytesWithSingleRequestAsync(dataType, db, startByteAdr + index, buffer.Slice(0, maxToRead), cancellationToken).ConfigureAwait(false);
+                buffer = buffer.Slice(maxToRead);
                 index += maxToRead;
             }
-            return resultBytes;
         }
 
         /// <summary>
@@ -290,6 +312,21 @@ namespace S7.Net
             return dataItems;
         }
 
+        /// <summary>
+        /// Write a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the write was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to write DB1.DBW200, this is 200.</param>
+        /// <param name="value">Bytes to write. If more than 200, multiple requests will be made.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>A task that represents the asynchronous write operation.</returns>
+        public Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, byte[] value, CancellationToken cancellationToken = default)
+        {
+            return WriteBytesAsync(dataType, db, startByteAdr, value.AsMemory(), cancellationToken);
+        }
 
         /// <summary>
         /// Write a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
@@ -302,15 +339,14 @@ namespace S7.Net
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
         /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
         /// <returns>A task that represents the asynchronous write operation.</returns>
-        public async Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, byte[] value, CancellationToken cancellationToken = default)
+        public async Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, ReadOnlyMemory<byte> value, CancellationToken cancellationToken = default)
         {
             int localIndex = 0;
-            int count = value.Length;
-            while (count > 0)
+            while (value.Length > 0)
             {
-                var maxToWrite = (int)Math.Min(count, MaxPDUSize - 35);
-                await WriteBytesWithASingleRequestAsync(dataType, db, startByteAdr + localIndex, value, localIndex, maxToWrite, cancellationToken).ConfigureAwait(false);
-                count -= maxToWrite;
+                var maxToWrite = (int)Math.Min(value.Length, MaxPDUSize - 35);
+                await WriteBytesWithASingleRequestAsync(dataType, db, startByteAdr + localIndex, value.Slice(0, maxToWrite), cancellationToken).ConfigureAwait(false);
+                value = value.Slice(maxToWrite);
                 localIndex += maxToWrite;
             }
         }
@@ -436,14 +472,14 @@ namespace S7.Net
             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)
+        private async Task ReadBytesWithSingleRequestAsync(DataType dataType, int db, int startByteAdr, Memory<byte> buffer, CancellationToken cancellationToken)
         {
-            var dataToSend = BuildReadRequestPackage(new [] { new DataItemAddress(dataType, db, startByteAdr, count)});
+            var dataToSend = BuildReadRequestPackage(new[] { new DataItemAddress(dataType, db, startByteAdr, buffer.Length) });
 
             var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
-            AssertReadResponse(s7data, count);
+            AssertReadResponse(s7data, buffer.Length);
 
-            Array.Copy(s7data, 18, buffer, offset, count);
+            s7data.AsSpan(18, buffer.Length).CopyTo(buffer.Span);
         }
 
         /// <summary>
@@ -472,11 +508,11 @@ namespace S7.Net
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <param name="value">Bytes to write. The lenght of this parameter can't be higher than 200. If you need more, use recursion.</param>
         /// <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)
+        private async Task WriteBytesWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, ReadOnlyMemory<byte> value, CancellationToken cancellationToken)
         {
             try
             {
-                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value, dataOffset, count);
+                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value.Span);
                 var s7data = await RequestTsduAsync(dataToSend, cancellationToken).ConfigureAwait(false);
 
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
@@ -521,22 +557,46 @@ namespace S7.Net
                 NoLockRequestTsduAsync(stream, requestData, offset, length, cancellationToken));
         }
 
-        private static async Task<COTP.TPDU> NoLockRequestTpduAsync(Stream stream, byte[] requestData,
+        private 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);
+            cancellationToken.ThrowIfCancellationRequested();
+            try
+            {
+                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();
+                }
 
-            return response;
+                throw;
+            }
         }
 
-        private static async Task<byte[]> NoLockRequestTsduAsync(Stream stream, byte[] requestData, int offset, int length,
+        private 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);
+            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();
+                }
 
-            return response;
+                throw;
+            }
         }
     }
 }

S7.Net/PlcSynchronous.cs

@@ -39,16 +39,32 @@ namespace S7.Net
         public byte[] ReadBytes(DataType dataType, int db, int startByteAdr, int count)
         {
             var result = new byte[count];
+
+            ReadBytes(result, dataType, db, startByteAdr);
+
+            return result;
+        }
+
+        /// <summary>
+        /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the read was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="buffer">Buffer to receive the read bytes. The <see cref="Span{T}.Length"/> determines the number of bytes to read.</param>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
+        /// <returns>Returns the bytes in an array</returns>
+        public void ReadBytes(Span<byte> buffer, DataType dataType, int db, int startByteAdr)
+        {
             int index = 0;
-            while (count > 0)
+            while (buffer.Length > 0)
             {
                 //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
-                var maxToRead = Math.Min(count, MaxPDUSize - 18);
-                ReadBytesWithSingleRequest(dataType, db, startByteAdr + index, result, index, maxToRead);
-                count -= maxToRead;
+                var maxToRead = Math.Min(buffer.Length, MaxPDUSize - 18);
+                ReadBytesWithSingleRequest(dataType, db, startByteAdr + index, buffer.Slice(0, maxToRead));
+                buffer = buffer.Slice(maxToRead);
                 index += maxToRead;
             }
-            return result;
         }
 
         /// <summary>
@@ -111,7 +127,6 @@ namespace S7.Net
             return ReadStruct(typeof(T), db, startByteAdr) 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.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
@@ -178,17 +193,29 @@ namespace S7.Net
         /// <param name="startByteAdr">Start byte address. If you want to write DB1.DBW200, this is 200.</param>
         /// <param name="value">Bytes to write. If more than 200, multiple requests will be made.</param>
         public void WriteBytes(DataType dataType, int db, int startByteAdr, byte[] value)
+        {
+            WriteBytes(dataType, db, startByteAdr, value.AsSpan());
+        }
+
+        /// <summary>
+        /// Write a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the write was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to write DB1.DBW200, this is 200.</param>
+        /// <param name="value">Bytes to write. If more than 200, multiple requests will be made.</param>
+        public void WriteBytes(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
         {
             int localIndex = 0;
-            int count = value.Length;
-            while (count > 0)
+            while (value.Length > 0)
             {
                 //TODO: Figure out how to use MaxPDUSize here
                 //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);
-                count -= maxToWrite;
+                var maxToWrite = Math.Min(value.Length, MaxPDUSize - 28);//TODO tested only when the MaxPDUSize is 480
+                WriteBytesWithASingleRequest(dataType, db, startByteAdr + localIndex, value.Slice(0, maxToWrite));
+                value = value.Slice(maxToWrite);
                 localIndex += maxToWrite;
             }
         }
@@ -294,22 +321,22 @@ namespace S7.Net
             WriteClassAsync(classValue, db, startByteAdr).GetAwaiter().GetResult();
         }
 
-        private void ReadBytesWithSingleRequest(DataType dataType, int db, int startByteAdr, byte[] buffer, int offset, int count)
+        private void ReadBytesWithSingleRequest(DataType dataType, int db, int startByteAdr, Span<byte> buffer)
         {
             try
             {
                 // first create the header
-                int packageSize = 19 + 12; // 19 header + 12 for 1 request
-                var package = new System.IO.MemoryStream(packageSize);
+                const int packageSize = 19 + 12; // 19 header + 12 for 1 request
+                var dataToSend = new byte[packageSize];
+                var package = new MemoryStream(dataToSend);
                 BuildHeaderPackage(package);
                 // package.Add(0x02);  // datenart
-                BuildReadDataRequestPackage(package, dataType, db, startByteAdr, count);
+                BuildReadDataRequestPackage(package, dataType, db, startByteAdr, buffer.Length);
 
-                var dataToSend = package.ToArray();
                 var s7data = RequestTsdu(dataToSend);
-                AssertReadResponse(s7data, count);
+                AssertReadResponse(s7data, buffer.Length);
 
-                Array.Copy(s7data, 18, buffer, offset, count);
+                s7data.AsSpan(18, buffer.Length).CopyTo(buffer);
             }
             catch (Exception exc)
             {
@@ -326,7 +353,6 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
-
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
             var response = RequestTsdu(message.Array, 0, length);
@@ -334,11 +360,11 @@ namespace S7.Net
             S7WriteMultiple.ParseResponse(response, response.Length, dataItems);
         }
 
-        private void WriteBytesWithASingleRequest(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count)
+        private void WriteBytesWithASingleRequest(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
         {
             try
             {
-                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value, dataOffset, count);
+                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value);
                 var s7data = RequestTsdu(dataToSend);
 
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
@@ -349,35 +375,37 @@ namespace S7.Net
             }
         }
 
-        private byte[] BuildWriteBytesPackage(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count)
+        private byte[] BuildWriteBytesPackage(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
         {
-            int varCount = count;
+            int varCount = value.Length;
             // first create the header
             int packageSize = 35 + varCount;
-            var package = new MemoryStream(new byte[packageSize]);
+            var packageData = new byte[packageSize];
+            var package = new MemoryStream(packageData);
 
             package.WriteByte(3);
             package.WriteByte(0);
             //complete package size
-            package.WriteByteArray(Int.ToByteArray((short)packageSize));
-            package.WriteByteArray(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount - 1)));
-            package.WriteByteArray(new byte[] { 0, 0x0e });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount + 4)));
-            package.WriteByteArray(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x02 });
-            package.WriteByteArray(Word.ToByteArray((ushort)varCount));
-            package.WriteByteArray(Word.ToByteArray((ushort)(db)));
+            package.Write(Int.ToByteArray((short)packageSize));
+            // This overload doesn't allocate the byte array, it refers to assembly's static data segment
+            package.Write(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
+            package.Write(Word.ToByteArray((ushort)(varCount - 1)));
+            package.Write(new byte[] { 0, 0x0e });
+            package.Write(Word.ToByteArray((ushort)(varCount + 4)));
+            package.Write(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x02 });
+            package.Write(Word.ToByteArray((ushort)varCount));
+            package.Write(Word.ToByteArray((ushort)(db)));
             package.WriteByte((byte)dataType);
             var overflow = (int)(startByteAdr * 8 / 0xffffU); // handles words with address bigger than 8191
             package.WriteByte((byte)overflow);
-            package.WriteByteArray(Word.ToByteArray((ushort)(startByteAdr * 8)));
-            package.WriteByteArray(new byte[] { 0, 4 });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount * 8)));
+            package.Write(Word.ToByteArray((ushort)(startByteAdr * 8)));
+            package.Write(new byte[] { 0, 4 });
+            package.Write(Word.ToByteArray((ushort)(varCount * 8)));
 
             // now join the header and the data
-            package.Write(value, dataOffset, count);
+            package.Write(value);
 
-            return package.ToArray();
+            return packageData;
         }
 
         private byte[] BuildWriteBitPackage(DataType dataType, int db, int startByteAdr, bool bitValue, int bitAdr)
@@ -386,33 +414,33 @@ namespace S7.Net
             int varCount = 1;
             // first create the header
             int packageSize = 35 + varCount;
-            var package = new MemoryStream(new byte[packageSize]);
+            var packageData = new byte[packageSize];
+            var package = new MemoryStream(packageData);
 
             package.WriteByte(3);
             package.WriteByte(0);
             //complete package size
-            package.WriteByteArray(Int.ToByteArray((short)packageSize));
-            package.WriteByteArray(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount - 1)));
-            package.WriteByteArray(new byte[] { 0, 0x0e });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount + 4)));
-            package.WriteByteArray(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x01 }); //ending 0x01 is used for writing a sinlge bit
-            package.WriteByteArray(Word.ToByteArray((ushort)varCount));
-            package.WriteByteArray(Word.ToByteArray((ushort)(db)));
+            package.Write(Int.ToByteArray((short)packageSize));
+            package.Write(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
+            package.Write(Word.ToByteArray((ushort)(varCount - 1)));
+            package.Write(new byte[] { 0, 0x0e });
+            package.Write(Word.ToByteArray((ushort)(varCount + 4)));
+            package.Write(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x01 }); //ending 0x01 is used for writing a sinlge bit
+            package.Write(Word.ToByteArray((ushort)varCount));
+            package.Write(Word.ToByteArray((ushort)(db)));
             package.WriteByte((byte)dataType);
             var overflow = (int)(startByteAdr * 8 / 0xffffU); // handles words with address bigger than 8191
             package.WriteByte((byte)overflow);
-            package.WriteByteArray(Word.ToByteArray((ushort)(startByteAdr * 8 + bitAdr)));
-            package.WriteByteArray(new byte[] { 0, 0x03 }); //ending 0x03 is used for writing a sinlge bit
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount)));
+            package.Write(Word.ToByteArray((ushort)(startByteAdr * 8 + bitAdr)));
+            package.Write(new byte[] { 0, 0x03 }); //ending 0x03 is used for writing a sinlge bit
+            package.Write(Word.ToByteArray((ushort)(varCount)));
 
             // now join the header and the data
-            package.WriteByteArray(value);
+            package.Write(value);
 
-            return package.ToArray();
+            return packageData;
         }
 
-
         private void WriteBitWithASingleRequest(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue)
         {
             try
@@ -444,7 +472,8 @@ namespace S7.Net
             {
                 // first create the header
                 int packageSize = 19 + (dataItems.Count * 12);
-                var package = new System.IO.MemoryStream(packageSize);
+                var dataToSend = new byte[packageSize];
+                var package = new MemoryStream(dataToSend);
                 BuildHeaderPackage(package, dataItems.Count);
                 // package.Add(0x02);  // datenart
                 foreach (var dataItem in dataItems)
@@ -452,8 +481,7 @@ namespace S7.Net
                     BuildReadDataRequestPackage(package, dataItem.DataType, dataItem.DB, dataItem.StartByteAdr, VarTypeToByteLength(dataItem.VarType, dataItem.Count));
                 }
 
-                var dataToSend = package.ToArray();
-                var s7data = RequestTsdu(dataToSend);
+                byte[] s7data = RequestTsdu(dataToSend);
 
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
 

S7.Net/Protocol/ConnectionRequest.cs

@@ -1,10 +1,8 @@
-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
@@ -15,54 +13,15 @@ namespace S7.Net.Protocol
                     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/S7.Net.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFrameworks>net452;netstandard2.0;netstandard1.3</TargetFrameworks>
+    <TargetFrameworks>net452;netstandard2.0;netstandard1.3;net5.0</TargetFrameworks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>
     <InternalsVisibleTo>S7.Net.UnitTest</InternalsVisibleTo>
@@ -27,6 +27,10 @@
     <DefineConstants>NET_FULL</DefineConstants>
   </PropertyGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)' != 'net5.0'">
+    <PackageReference Include="System.Memory" Version="4.5.5" />
+  </ItemGroup>
+  
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
   </ItemGroup>

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/Class.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
+using System.Runtime.InteropServices;
 
 namespace S7.Net.Types
 {
@@ -25,7 +26,7 @@ namespace S7.Net.Types
 
         }
 
-        private static double GetIncreasedNumberOfBytes(double numBytes, Type type)
+        private static double GetIncreasedNumberOfBytes(double numBytes, Type type, PropertyInfo? propertyInfo)
         {
             switch (type.Name)
             {
@@ -38,30 +39,30 @@ namespace S7.Net.Types
                     break;
                 case "Int16":
                 case "UInt16":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 2;
                     break;
                 case "Int32":
                 case "UInt32":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 4;
                     break;
                 case "Single":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 4;
                     break;
                 case "Double":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 8;
                     break;
+                case "String":
+                    S7StringAttribute? attribute = propertyInfo?.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
+                    if (attribute == default(S7StringAttribute))
+                        throw new ArgumentException("Please add S7StringAttribute to the string field");
+
+                    IncrementToEven(ref numBytes);
+                    numBytes += attribute.ReservedLengthInBytes;
+                    break;
                 default:
                     var propertyClass = Activator.CreateInstance(type);
                     numBytes = GetClassSize(propertyClass, numBytes, true);
@@ -93,12 +94,12 @@ namespace S7.Net.Types
                     IncrementToEven(ref numBytes);
                     for (int i = 0; i < array.Length; i++)
                     {
-                        numBytes = GetIncreasedNumberOfBytes(numBytes, elementType);
+                        numBytes = GetIncreasedNumberOfBytes(numBytes, elementType, property);
                     }
                 }
                 else
                 {
-                    numBytes = GetIncreasedNumberOfBytes(numBytes, property.PropertyType);
+                    numBytes = GetIncreasedNumberOfBytes(numBytes, property.PropertyType, property);
                 }
             }
             if (false == isInnerProperty)
@@ -111,7 +112,7 @@ namespace S7.Net.Types
             return numBytes;
         }
 
-        private static object? GetPropertyValue(Type propertyType, byte[] bytes, ref double numBytes)
+        private static object? GetPropertyValue(Type propertyType, PropertyInfo? propertyInfo, byte[] bytes, ref double numBytes)
         {
             object? value = null;
 
@@ -133,50 +134,35 @@ namespace S7.Net.Types
                     numBytes++;
                     break;
                 case "Int16":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     // hier auswerten
                     ushort source = Word.FromBytes(bytes[(int)numBytes + 1], bytes[(int)numBytes]);
                     value = source.ConvertToShort();
                     numBytes += 2;
                     break;
                 case "UInt16":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     // hier auswerten
                     value = Word.FromBytes(bytes[(int)numBytes + 1], bytes[(int)numBytes]);
                     numBytes += 2;
                     break;
                 case "Int32":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
-                    // hier auswerten
-                    uint sourceUInt = DWord.FromBytes(bytes[(int)numBytes + 3],
-                                                                       bytes[(int)numBytes + 2],
-                                                                       bytes[(int)numBytes + 1],
-                                                                       bytes[(int)numBytes + 0]);
+                    IncrementToEven(ref numBytes);
+                    var wordBuffer = new byte[4];
+                    Array.Copy(bytes, (int)numBytes, wordBuffer, 0, wordBuffer.Length);
+                    uint sourceUInt = DWord.FromByteArray(wordBuffer);
                     value = sourceUInt.ConvertToInt();
                     numBytes += 4;
                     break;
                 case "UInt32":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
-                    // hier auswerten
-                    value = DWord.FromBytes(
-                        bytes[(int)numBytes],
-                        bytes[(int)numBytes + 1],
-                        bytes[(int)numBytes + 2],
-                        bytes[(int)numBytes + 3]);
+                    IncrementToEven(ref numBytes);
+                    var wordBuffer2 = new byte[4];
+                    Array.Copy(bytes, (int)numBytes, wordBuffer2, 0, wordBuffer2.Length);
+                    value = DWord.FromByteArray(wordBuffer2);
                     numBytes += 4;
                     break;
                 case "Single":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     // hier auswerten
                     value = Real.FromByteArray(
                         new byte[] {
@@ -187,15 +173,31 @@ namespace S7.Net.Types
                     numBytes += 4;
                     break;
                 case "Double":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     var buffer = new byte[8];
                     Array.Copy(bytes, (int)numBytes, buffer, 0, 8);
                     // hier auswerten
                     value = LReal.FromByteArray(buffer);
                     numBytes += 8;
                     break;
+                case "String":
+                    S7StringAttribute? attribute = propertyInfo?.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
+                    if (attribute == default(S7StringAttribute))
+                        throw new ArgumentException("Please add S7StringAttribute to the string field");
+
+                    IncrementToEven(ref numBytes);
+
+                    // get the value
+                    var sData = new byte[attribute.ReservedLengthInBytes];
+                    Array.Copy(bytes, (int)numBytes, sData, 0, sData.Length);
+                    value = attribute.Type switch
+                    {
+                        S7StringType.S7String => S7String.FromByteArray(sData),
+                        S7StringType.S7WString => S7WString.FromByteArray(sData),
+                        _ => throw new ArgumentException("Please use a valid string type for the S7StringAttribute")
+                    };
+                    numBytes += sData.Length;
+                    break;
                 default:
                     var propClass = Activator.CreateInstance(propertyType);
                     numBytes = FromBytes(propClass, bytes, numBytes);
@@ -227,7 +229,7 @@ namespace S7.Net.Types
                     for (int i = 0; i < array.Length && numBytes < bytes.Length; i++)
                     {
                         array.SetValue(
-                            GetPropertyValue(elementType, bytes, ref numBytes),
+                            GetPropertyValue(elementType, property, bytes, ref numBytes),
                             i);
                     }
                 }
@@ -235,7 +237,7 @@ namespace S7.Net.Types
                 {
                     property.SetValue(
                         sourceClass,
-                        GetPropertyValue(property.PropertyType, bytes, ref numBytes),
+                        GetPropertyValue(property.PropertyType, property, bytes, ref numBytes),
                         null);
                 }
             }
@@ -243,7 +245,7 @@ namespace S7.Net.Types
             return numBytes;
         }
 
-        private static double SetBytesFromProperty(object propertyValue, byte[] bytes, double numBytes)
+        private static double SetBytesFromProperty(object propertyValue, PropertyInfo? propertyInfo, byte[] bytes, double numBytes)
         {
             int bytePos = 0;
             int bitPos = 0;
@@ -285,6 +287,18 @@ namespace S7.Net.Types
                 case "Double":
                     bytes2 = LReal.ToByteArray((double)propertyValue);
                     break;
+                case "String":
+                    S7StringAttribute? attribute = propertyInfo?.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
+                    if (attribute == default(S7StringAttribute))
+                        throw new ArgumentException("Please add S7StringAttribute to the string field");
+
+                    bytes2 = attribute.Type switch
+                    {
+                        S7StringType.S7String => S7String.ToByteArray((string)propertyValue, attribute.ReservedLength),
+                        S7StringType.S7WString => S7WString.ToByteArray((string)propertyValue, attribute.ReservedLength),
+                        _ => throw new ArgumentException("Please use a valid string type for the S7StringAttribute")
+                    };
+                    break;
                 default:
                     numBytes = ToBytes(propertyValue, bytes, numBytes);
                     break;
@@ -320,12 +334,12 @@ namespace S7.Net.Types
                     Type elementType = property.PropertyType.GetElementType();
                     for (int i = 0; i < array.Length && numBytes < bytes.Length; i++)
                     {
-                        numBytes = SetBytesFromProperty(array.GetValue(i), bytes, numBytes);
+                        numBytes = SetBytesFromProperty(array.GetValue(i), property, bytes, numBytes);
                     }
                 }
                 else
                 {
-                    numBytes = SetBytesFromProperty(property.GetValue(sourceClass, null), bytes, numBytes);
+                    numBytes = SetBytesFromProperty(property.GetValue(sourceClass, null), property, bytes, numBytes);
                 }
             }
             return numBytes;

S7.Net/Types/S7String.cs

@@ -9,6 +9,18 @@ namespace S7.Net.Types
     /// </summary>
     public static class S7String
     {
+        private static Encoding stringEncoding = Encoding.ASCII;
+
+        /// <summary>
+        /// The Encoding used when serializing and deserializing S7String (Encoding.ASCII by default)
+        /// </summary>
+        /// <exception cref="ArgumentNullException">StringEncoding must not be null</exception>
+        public static Encoding StringEncoding
+        {
+            get => stringEncoding;
+            set => stringEncoding = value ?? throw new ArgumentNullException(nameof(StringEncoding));
+        }
+
         /// <summary>
         /// Converts S7 bytes to a string
         /// </summary>
@@ -30,7 +42,7 @@ namespace S7.Net.Types
 
             try
             {
-                return Encoding.ASCII.GetString(bytes, 2, length);
+                return StringEncoding.GetString(bytes, 2, length);
             }
             catch (Exception e)
             {
@@ -38,7 +50,6 @@ namespace S7.Net.Types
                     $"Failed to parse {VarType.S7String} from data. Following fields were read: size: '{size}', actual length: '{length}', total number of bytes (including header): '{bytes.Length}'.",
                     e);
             }
-            
         }
 
         /// <summary>
@@ -56,7 +67,7 @@ namespace S7.Net.Types
 
             if (reservedLength > 254) throw new ArgumentException($"The maximum string length supported is 254.");
 
-            var bytes = Encoding.ASCII.GetBytes(value);
+            var bytes = StringEncoding.GetBytes(value);
             if (bytes.Length > reservedLength) throw new ArgumentException($"The provided string length ({bytes.Length} is larger than the specified reserved length ({reservedLength}).");
 
             var buffer = new byte[2 + reservedLength];

S7.Net/Types/S7StringAttribute.cs

@@ -2,7 +2,7 @@
 
 namespace S7.Net.Types
 {
-    [AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
     public sealed class S7StringAttribute : Attribute
     {
         private readonly S7StringType type;

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}"

appveyor.yml

@@ -1,4 +1,4 @@
-image: Visual Studio 2019
+image: Visual Studio 2022
 configuration: Release
 install:
   - choco install gitversion.portable -y