Release S7NetPlus 0.17.0

Release highlights:
- Add Read-/WriteBytes overloads for Span<byte> and Memory<byte>

.github/workflows/test.yml

@@ -14,14 +14,14 @@ jobs:
       DOTNET_NOLOGO : 1
     strategy:
       matrix:
-        os: [windows-latest, ubuntu-latest, macos-latest]
+        os: [windows-latest, ubuntu-20.04, macos-latest]
         test-framework: [netcoreapp3.1, net5.0]
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             test-framework: netcoreapp3.1
             installSnap7: true
             dotnet-sdk: '3.1.x'
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             test-framework: net5.0
             installSnap7: true
             dotnet-sdk: '5.0.x'
@@ -48,7 +48,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - name: Install Snap7 Linux
-        if: ${{ matrix.installSnap7 && matrix.os == 'ubuntu-latest' }}
+        if: ${{ matrix.installSnap7 && matrix.os == 'ubuntu-20.04' }}
         run: |
           sudo add-apt-repository ppa:gijzelaar/snap7
           sudo apt-get update

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/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>
@@ -950,6 +1026,47 @@ namespace S7.Net.UnitTest
             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>
@@ -982,6 +1099,7 @@ namespace S7.Net.UnitTest
             };
             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/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/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 () =>
@@ -44,11 +44,16 @@ namespace S7.Net
             }
         }
 
-        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();
         }
 
@@ -117,6 +122,34 @@ namespace S7.Net
             return resultBytes;
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <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 (buffer.Length > 0)
+            {
+                //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
+                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;
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Read and decode a certain number of bytes of the "VarType" provided.
         /// This can be used to read multiple consecutive variables of the same type (Word, DWord, Int, etc).
@@ -315,6 +348,33 @@ namespace S7.Net
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <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 async Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, ReadOnlyMemory<byte> value, CancellationToken cancellationToken = default)
+        {
+            int localIndex = 0;
+            while (value.Length > 0)
+            {
+                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;
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Write a single bit from a DB with the specified index.
         /// </summary>
@@ -446,6 +506,20 @@ namespace S7.Net
             Array.Copy(s7data, 18, buffer, offset, count);
         }
 
+#if NET5_0_OR_GREATER
+
+        private async Task ReadBytesWithSingleRequestAsync(DataType dataType, int db, int startByteAdr, Memory<byte> buffer, CancellationToken cancellationToken)
+        {
+            var dataToSend = BuildReadRequestPackage(new[] { new DataItemAddress(dataType, db, startByteAdr, buffer.Length) });
+
+            var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
+            AssertReadResponse(s7data, buffer.Length);
+
+            s7data.AsSpan(18, buffer.Length).CopyTo(buffer.Span);
+        }
+
+#endif
+
         /// <summary>
         /// Write DataItem(s) to the PLC. Throws an exception if the response is invalid
         /// or when the PLC reports errors for item(s) written.
@@ -491,6 +565,37 @@ namespace S7.Net
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Writes up to 200 bytes to the PLC. You must specify the memory area type, memory are address, byte start address and bytes count.
+        /// </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 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, ReadOnlyMemory<byte> value, CancellationToken cancellationToken)
+        {
+            try
+            {
+                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value.Span);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken).ConfigureAwait(false);
+
+                ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
+            }
+            catch (OperationCanceledException)
+            {
+                throw;
+            }
+            catch (Exception exc)
+            {
+                throw new PlcException(ErrorCode.WriteData, exc);
+            }
+        }
+
+#endif
+
         private async Task WriteBitWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue, CancellationToken cancellationToken)
         {
             try

S7.Net/PlcSynchronous.cs

@@ -51,6 +51,32 @@ namespace S7.Net
             return result;
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <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 (buffer.Length > 0)
+            {
+                //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
+                var maxToRead = Math.Min(buffer.Length, MaxPDUSize - 18);
+                ReadBytesWithSingleRequest(dataType, db, startByteAdr + index, buffer.Slice(0, maxToRead));
+                buffer = buffer.Slice(maxToRead);
+                index += maxToRead;
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Read and decode a certain number of bytes of the "VarType" provided.
         /// This can be used to read multiple consecutive variables of the same type (Word, DWord, Int, etc).
@@ -193,6 +219,33 @@ namespace S7.Net
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <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;
+            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(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;
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Write a single bit from a DB with the specified index.
         /// </summary>
@@ -317,6 +370,33 @@ namespace S7.Net
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        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);
+                BuildHeaderPackage(package);
+                // package.Add(0x02);  // datenart
+                BuildReadDataRequestPackage(package, dataType, db, startByteAdr, buffer.Length);
+
+                var dataToSend = package.ToArray();
+                var s7data = RequestTsdu(dataToSend);
+                AssertReadResponse(s7data, buffer.Length);
+
+                s7data.AsSpan(18, buffer.Length).CopyTo(buffer);
+            }
+            catch (Exception exc)
+            {
+                throw new PlcException(ErrorCode.ReadData, exc);
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Write DataItem(s) to the PLC. Throws an exception if the response is invalid
         /// or when the PLC reports errors for item(s) written.
@@ -349,6 +429,25 @@ namespace S7.Net
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        private void WriteBytesWithASingleRequest(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
+        {
+            try
+            {
+                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value);
+                var s7data = RequestTsdu(dataToSend);
+
+                ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
+            }
+            catch (Exception exc)
+            {
+                throw new PlcException(ErrorCode.WriteData, exc);
+            }
+        }
+
+#endif
+
         private byte[] BuildWriteBytesPackage(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count)
         {
             int varCount = count;
@@ -380,6 +479,41 @@ namespace S7.Net
             return package.ToArray();
         }
 
+#if NET5_0_OR_GREATER
+
+        private byte[] BuildWriteBytesPackage(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
+        {
+            int varCount = value.Length;
+            // first create the header
+            int packageSize = 35 + varCount;
+            var package = new MemoryStream(new byte[packageSize]);
+
+            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.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)));
+
+            // now join the header and the data
+            package.Write(value);
+
+            return package.ToArray();
+        }
+
+#endif
+
         private byte[] BuildWriteBitPackage(DataType dataType, int db, int startByteAdr, bool bitValue, int bitAdr)
         {
             var value = new[] { bitValue ? (byte)1 : (byte)0 };

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>

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;

appveyor.yml

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