Merge pull request #491 from S7NetPlus/plc-status

Plc status

.github/workflows/dotnet.yml

@@ -0,0 +1,134 @@
+# yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json
+
+name: .NET
+
+on:
+  workflow_dispatch: # Allow running the workflow manually from the GitHub UI
+  push:
+    branches:
+      - 'main'       # Run the workflow when pushing to the main branch
+  pull_request:
+    branches:
+      - '*'          # Run the workflow for all pull requests
+  release:
+    types:
+      - published    # Run the workflow when a new GitHub release is published
+  
+env:
+  DOTNET_SKIP_FIRST_TIME_EXPERIENCE: 1
+  DOTNET_NOLOGO: true
+  NuGetDirectory: ${{ github.workspace}}/nuget
+
+defaults:
+  run:
+    shell: pwsh
+
+jobs:
+  create_nuget:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        fetch-depth: 0 # Get all history to allow automatic versioning
+
+    - name: Install GitVersion
+      uses: gittools/actions/gitversion/setup@v0
+      with:
+        versionSpec: '6.x'
+        includePrerelease: true
+        preferLatestVersion: true
+    
+    - name: Determine Version
+      id:   gitversion
+      uses: gittools/actions/gitversion/execute@v0
+
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v3
+
+    - run: >
+        dotnet pack
+        --configuration Release
+        /p:AssemblyVersion=${{ steps.gitversion.outputs.assemblySemVer }}
+        /p:FileVersion=${{ steps.gitversion.outputs.assemblySemFileVer }}
+        /p:InformationalVersion=${{ steps.gitversion.outputs.informationalVersion }}
+        /p:PackageVersion=${{ steps.gitversion.outputs.semVer }}
+        --output ${{ env.NuGetDirectory }}
+
+    - uses: actions/upload-artifact@v3
+      with:
+        name: nuget
+        if-no-files-found: error
+        retention-days: 7
+        path: |
+          ${{ env.NuGetDirectory }}/*.nupkg
+          ${{ env.NuGetDirectory }}/*.snupkg
+
+  run_test:
+    name: test-${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    env:
+      configuration: Release
+      artifacts: ${{ github.workspace }}/artifacts
+    strategy:
+      matrix:
+        os: [windows-latest, ubuntu-20.04, macos-latest]
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install Snap7 Linux
+        if: ${{ 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.os == 'macos-latest' }}
+        run: |
+          brew install snap7
+
+      - name: Setup Dotnet
+        uses: actions/setup-dotnet@v3
+        with:
+          dotnet-version: |
+            6.x
+            7.x
+          
+      - name: Nuget Cache
+        uses: actions/cache@v3
+        with:
+          path: ~/.nuget/packages
+          # Look to see if there is a cache hit for the corresponding requirements file
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/packages.lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget
+        
+      - name: Test
+        run: dotnet test --nologo --verbosity normal --logger GitHubActions
+
+  deploy:
+    # Publish only when creating a GitHub Release
+    # https://docs.github.com/en/repositories/releasing-projects-on-github/managing-releases-in-a-repository
+    # You can update this logic if you want to manage releases differently
+    if: github.event_name == 'release'
+    runs-on: ubuntu-latest
+    needs: [ create_nuget, run_test ]
+    steps:
+      - uses: actions/download-artifact@v3
+        with:
+          name: nuget
+          path: ${{ env.NuGetDirectory }}
+
+      - name: Setup .NET Core
+        uses: actions/setup-dotnet@v3
+
+      # Publish all NuGet packages to NuGet.org
+      # Use --skip-duplicate to prevent errors if a package with the same version already exists.
+      # If you retry a failed workflow, already published packages will be skipped without error.
+      - name: Publish NuGet package
+        run: |
+          foreach($file in (Get-ChildItem "${{ env.NuGetDirectory }}" -Recurse -Include *.nupkg)) {
+              dotnet nuget push $file --api-key "${{ secrets.NUGET_APIKEY }}" --source https://api.nuget.org/v3/index.json --skip-duplicate
+          }

.github/workflows/test.yml

@@ -1,80 +0,0 @@
-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/CommunicationTests/ConnectionOpen.cs

@@ -0,0 +1,28 @@
+using System.Net;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using S7.Net.Protocol;
+
+namespace S7.Net.UnitTest.CommunicationTests;
+
+[TestClass]
+public class ConnectionOpen
+{
+    [TestMethod]
+    public async Task Does_Not_Throw()
+    {
+        var cs = new CommunicationSequence {
+            ConnectionOpenTemplates.ConnectionRequestConfirm,
+            ConnectionOpenTemplates.CommunicationSetup
+        };
+
+        async Task Client(int port)
+        {
+            var conn = new Plc(IPAddress.Loopback.ToString(), port, new TsapPair(new Tsap(1, 2), new Tsap(3, 4)));
+            await conn.OpenAsync();
+            conn.Close();
+        }
+
+        await Task.WhenAll(cs.Serve(out var port), Client(port));
+    }
+}

S7.Net.UnitTest/CommunicationTests/ConnectionOpenTemplates.cs

@@ -0,0 +1,107 @@
+namespace S7.Net.UnitTest.CommunicationTests;
+
+internal static class ConnectionOpenTemplates
+{
+    public static RequestResponsePair ConnectionRequestConfirm { get; } = new RequestResponsePair(
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 16 // Length
+
+            // CR
+            11 // Number of bytes following
+            E0 // CR / Credit
+            00 00 // Destination reference, unused
+            __ __ // Source reference, unused
+            00 // Class / Option
+
+            // Source TSAP
+            C1 // Parameter code
+            02 // Parameter length
+            TSAP_SRC_CHAN // Channel
+            TSAP_SRC_POS // Position
+
+            // Destination TSAP
+            C2 // Parameter code
+            02 // Parameter length
+            TSAP_DEST_CHAN // Channel
+            TSAP_DEST_POS // Position
+
+            // PDU Size parameter
+            C0 // Parameter code
+            01 // Parameter length
+            0A // 1024 byte PDU (2 ^ 10)
+        """,
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 0B // Length
+
+            // CC
+            06 // Length
+            D0 // CC / Credit
+            00 00 // Destination reference
+            00 00 // Source reference
+            00 // Class / Option
+        """
+    );
+
+    public static RequestResponsePair CommunicationSetup { get; } = new RequestResponsePair(
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 19 // Length
+
+            // Data header
+            02 // Length
+            F0 // Data identifier
+            80 // PDU number and end of transmission
+
+            // S7 header
+            32 // Protocol ID
+            01 // Message type job request
+            00 00 // Reserved
+            PDU1 PDU2 // PDU reference
+            00 08 // Parameter length (Communication Setup)
+            00 00 // Data length
+
+            // Communication Setup
+            F0 // Function code
+            00 // Reserved
+            00 03 // Max AMQ caller
+            00 03 // Max AMQ callee
+            03 C0 // PDU size (960)
+        """,
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 1B // Length
+
+            // Data header
+            02 // Length
+            F0 // Data identifier
+            80 // PDU number and end of transmission
+
+            // S7 header
+            32 // Protocol ID
+            03 // Message type ack data
+            00 00 // Reserved
+            PDU1 PDU2 // PDU reference
+            00 08 // Parameter length (Communication Setup)
+            00 00 // Data length
+            00 // Error class
+            00 // Error code
+
+            // Communication Setup
+            F0 // Function code
+            00 // Reserved
+            00 03 // Max AMQ caller
+            00 03 // Max AMQ callee
+            03 C0 // PDU size (960)
+        """
+    );
+}

S7.Net.UnitTest/CommunicationTests/ReadPlcStatus.cs

@@ -0,0 +1,57 @@
+using System.Net;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using S7.Net.Protocol;
+
+namespace S7.Net.UnitTest.CommunicationTests;
+
+[TestClass]
+public class ReadPlcStatus
+{
+    [TestMethod]
+    public async Task Read_Status_Run()
+    {
+        var cs = new CommunicationSequence {
+            ConnectionOpenTemplates.ConnectionRequestConfirm,
+            ConnectionOpenTemplates.CommunicationSetup,
+            {
+                """
+                    // TPKT
+                    03 00 00 21
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 SZL read
+                    32 07 00 00 PDU1 PDU2 00 08 00 08 00 01 12 04 11 44
+                    01 00 ff 09 00 04 04 24 00 00
+                """,
+                """
+                    // TPKT
+                    03 00 00 3d
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 SZL response
+                    32 07 00 00 PDU1 PDU2 00 0c 00 20 00 01 12 08 12 84
+                    01 02 00 00 00 00 ff 09 00 1c 04 24 00 00 00 14
+                    00 01 51 44 ff 08 00 00 00 00 00 00 00 00 14 08
+                    20 12 05 28 34 94
+                """
+            }
+        };
+
+        async Task Client(int port)
+        {
+            var conn = new Plc(IPAddress.Loopback.ToString(), port, new TsapPair(new Tsap(1, 2), new Tsap(3, 4)));
+            await conn.OpenAsync();
+            var status = await conn.ReadStatusAsync();
+
+            Assert.AreEqual(0x08, status);
+            conn.Close();
+        }
+
+        await Task.WhenAll(cs.Serve(out var port), Client(port));
+    }
+}

S7.Net.UnitTest/Framework/IsExternalInit.cs

@@ -0,0 +1,7 @@
+using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    internal record IsExternalInit;
+}

S7.Net.UnitTest/Infrastructure/CommunicationSequence.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Buffers;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading.Tasks;
+
+namespace S7.Net.UnitTest;
+
+internal class CommunicationSequence : IEnumerable<RequestResponsePair>
+{
+    private readonly List<RequestResponsePair> _requestResponsePairs = new List<RequestResponsePair>();
+
+    public void Add(RequestResponsePair requestResponsePair)
+    {
+        _requestResponsePairs.Add(requestResponsePair);
+    }
+
+    public void Add(string requestPattern, string responsePattern)
+    {
+        _requestResponsePairs.Add(new RequestResponsePair(requestPattern, responsePattern));
+    }
+
+    public IEnumerator<RequestResponsePair> GetEnumerator()
+    {
+        return _requestResponsePairs.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+    public Task Serve(out int port)
+    {
+        var socket = CreateBoundListenSocket(out port);
+        socket.Listen(0);
+
+        async Task Impl()
+        {
+            await Task.Yield();
+            var socketIn = socket.Accept();
+
+            var buffer = ArrayPool<byte>.Shared.Rent(1024);
+            try
+            {
+                foreach (var pair in _requestResponsePairs)
+                {
+                    var bytesReceived = socketIn.Receive(buffer, SocketFlags.None);
+
+                    var received = buffer.Take(bytesReceived).ToArray();
+                    Console.WriteLine($"=> {BitConverter.ToString(received)}");
+
+                    var response = Responder.Respond(pair, received);
+
+                    Console.WriteLine($"<= {BitConverter.ToString(response)}");
+                    socketIn.Send(response);
+                }
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return(buffer);
+            }
+
+            socketIn.Close();
+        }
+
+        return Impl();
+    }
+
+    private static Socket CreateBoundListenSocket(out int port)
+    {
+        var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        var endpoint = new IPEndPoint(IPAddress.Loopback, 0);
+
+        socket.Bind(endpoint);
+
+        var localEndpoint = (IPEndPoint)socket.LocalEndPoint!;
+        port = localEndpoint.Port;
+
+        return socket;
+    }
+}

S7.Net.UnitTest/Infrastructure/RequestResponsePair.cs

@@ -0,0 +1,3 @@
+namespace S7.Net.UnitTest;
+
+internal record RequestResponsePair(string RequestPattern, string ResponsePattern);

S7.Net.UnitTest/Infrastructure/Responder.cs

@@ -0,0 +1,80 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+
+namespace S7.Net.UnitTest;
+
+internal static class Responder
+{
+    private const string Comment = "//";
+    private static char[] Space = " ".ToCharArray();
+
+    public static byte[] Respond(RequestResponsePair pair, byte[] request)
+    {
+        var offset = 0;
+        var matches = new Dictionary<string, byte>();
+        var res = new List<byte>();
+        using var requestReader = new StringReader(pair.RequestPattern);
+
+        string line;
+        while ((line = requestReader.ReadLine()) != null)
+        {
+            var tokens = line.Split(Space, StringSplitOptions.RemoveEmptyEntries);
+            foreach (var token in tokens)
+            {
+                if (token.StartsWith(Comment)) break;
+
+                if (offset >= request.Length)
+                {
+                    throw new Exception("Request pattern has more data than request.");
+                }
+
+                var received = request[offset];
+
+                if (token.Length == 2 && byte.TryParse(token, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var value))
+                {
+                    // Number, exact match
+                    if (value != received)
+                    {
+                        throw new Exception($"Incorrect data at offset {offset}. Expected {value:X2}, received {received:X2}.");
+                    }
+                }
+                else
+                {
+                    matches[token] = received;
+                }
+
+                offset++;
+            }
+        }
+
+        if (offset != request.Length) throw new Exception("Request contained more data than request pattern.");
+
+        using var responseReader = new StringReader(pair.ResponsePattern);
+        while ((line = responseReader.ReadLine()) != null)
+        {
+            var tokens = line.Split(Space, StringSplitOptions.RemoveEmptyEntries);
+            foreach (var token in tokens)
+            {
+                if (token.StartsWith(Comment)) break;
+
+                if (token.Length == 2 && byte.TryParse(token, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var value))
+                {
+                    res.Add(value);
+                }
+                else
+                {
+                    if (!matches.TryGetValue(token, out var match))
+                    {
+                        throw new Exception($"Unmatched token '{token}' in response.");
+                    }
+
+                    res.Add(match);
+                }
+            }
+        }
+
+        return res.ToArray();
+    }
+}

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

@@ -1,8 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
-  <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp3.1;net5.0</TargetFrameworks>
+  <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' ">
+    <TargetFrameworks>net6.0;net7.0</TargetFrameworks>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(OS)' == 'Windows_NT' "> 
+    <TargetFrameworks>net462;net6.0;net7.0</TargetFrameworks>
+  </PropertyGroup>
 
+  <PropertyGroup>
+    <LangVersion>latest</LangVersion>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>
     <IsPackable>false</IsPackable>

S7.Net/COTP.cs

@@ -55,6 +55,7 @@ namespace S7.Net
             /// See: https://tools.ietf.org/html/rfc905
             /// </summary>
             /// <param name="stream">The socket to read from</param>
+            /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
             /// <returns>COTP DPDU instance</returns>
             public static async Task<TPDU> ReadAsync(Stream stream, CancellationToken cancellationToken)
             {
@@ -89,6 +90,7 @@ namespace S7.Net
             /// See: https://tools.ietf.org/html/rfc905
             /// </summary>
             /// <param name="stream">The stream to read from</param>
+            /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
             /// <returns>Data in TSDU</returns>
             public static async Task<byte[]> ReadAsync(Stream stream, CancellationToken cancellationToken)
             {

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

@@ -9,29 +9,97 @@ namespace S7.Net
 {
     public partial class Plc
     {
-        /// <summary>
-        /// Creates the header to read bytes from the PLC
-        /// </summary>
-        /// <param name="amount"></param>
-        /// <returns></returns>
-        private static void BuildHeaderPackage(System.IO.MemoryStream stream, int amount = 1)
+        private static void WriteTpktHeader(System.IO.MemoryStream stream, int length)
         {
-            //header size = 19 bytes
             stream.Write(new byte[] { 0x03, 0x00 });
-            //complete package size
-            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.Write(Word.ToByteArray((ushort)(2 + (amount * 12))));
-            stream.Write(new byte[] { 0x00, 0x00, 0x04 });
+            stream.Write(Word.ToByteArray((ushort) length));
+        }
+
+        private static void WriteDataHeader(System.IO.MemoryStream stream)
+        {
+            stream.Write(new byte[] { 0x02, 0xf0, 0x80 });
+        }
+
+        private static void WriteS7Header(System.IO.MemoryStream stream, byte messageType, int parameterLength, int dataLength)
+        {
+            stream.WriteByte(0x32); // S7 protocol ID
+            stream.WriteByte(messageType); // Message type
+            stream.Write(new byte[] { 0x00, 0x00 }); // Reserved
+            stream.Write(new byte[] { 0x00, 0x00 }); // PDU ref
+            stream.Write(Word.ToByteArray((ushort) parameterLength));
+            stream.Write(Word.ToByteArray((ushort) dataLength));
+        }
+
+        /// <summary>
+        /// Creates the header to read bytes from the PLC.
+        /// </summary>
+        /// <param name="stream">The stream to write to.</param>
+        /// <param name="amount">The number of items to read.</param>
+        private static void WriteReadHeader(System.IO.MemoryStream stream, int amount = 1)
+        {
+            // Header size 19, 12 bytes per item
+            WriteTpktHeader(stream, 19 + 12 * amount);
+            WriteDataHeader(stream);
+            WriteS7Header(stream, 0x01, 2 + 12 * amount, 0);
+            // Function code: read request
+            stream.WriteByte(0x04);
             //amount of requests
             stream.WriteByte((byte)amount);
         }
 
+        private static void WriteUserDataHeader(System.IO.MemoryStream stream, int parameterLength, int dataLength)
+        {
+            const byte s7MessageTypeUserData = 0x07;
+
+            WriteTpktHeader(stream, 17 + parameterLength + dataLength);
+            WriteDataHeader(stream);
+            WriteS7Header(stream, s7MessageTypeUserData, parameterLength, dataLength);
+        }
+
+        private static void WriteSzlReadRequest(System.IO.MemoryStream stream, ushort szlId, ushort szlIndex)
+        {
+            WriteUserDataHeader(stream, 8, 8);
+
+            // Parameter
+            const byte szlMethodRequest = 0x11;
+            const byte szlTypeRequest = 0b100;
+            const byte szlFunctionGroupCpuFunctions = 0b100;
+            const byte subFunctionReadSzl = 0x01;
+
+            // Parameter head
+            stream.Write(new byte[] { 0x00, 0x01, 0x12 });
+            // Parameter length
+            stream.WriteByte(0x04);
+            // Method
+            stream.WriteByte(szlMethodRequest);
+            // Type / function group
+            stream.WriteByte(szlTypeRequest << 4 | szlFunctionGroupCpuFunctions);
+            // Subfunction
+            stream.WriteByte(subFunctionReadSzl);
+            // Sequence number
+            stream.WriteByte(0);
+
+            // Data
+            const byte success = 0xff;
+            const byte transportSizeOctetString = 0x09;
+
+            // Return code
+            stream.WriteByte(success);
+            // Transport size
+            stream.WriteByte(transportSizeOctetString);
+            // Length
+            stream.Write(Word.ToByteArray(4));
+            // SZL-ID
+            stream.Write(Word.ToByteArray(szlId));
+            // SZL-Index
+            stream.Write(Word.ToByteArray(szlIndex));
+        }
+
         /// <summary>
         /// Create the bytes-package to request data from the PLC. You have to specify the memory type (dataType),
         /// the address of the memory, the address of the byte and the bytes count.
         /// </summary>
+        /// <param name="stream">The stream to write the read data request to.</param>
         /// <param name="dataType">MemoryType (DB, Timer, Counter, etc.)</param>
         /// <param name="db">Address of the memory to be read</param>
         /// <param name="startByteAdr">Start address of the byte</param>
@@ -252,7 +320,7 @@ namespace S7.Net
             int packageSize = 19 + (dataItems.Count * 12);
             var package = new System.IO.MemoryStream(packageSize);
 
-            BuildHeaderPackage(package, dataItems.Count);
+            WriteReadHeader(package, dataItems.Count);
 
             foreach (var dataItem in dataItems)
             {
@@ -261,5 +329,15 @@ namespace S7.Net
 
             return package.ToArray();
         }
+
+        private static byte[] BuildSzlReadRequestPackage(ushort szlId, ushort szlIndex)
+        {
+            var stream = new System.IO.MemoryStream();
+            
+            WriteSzlReadRequest(stream, szlId, szlIndex);
+            stream.SetLength(stream.Position);
+
+            return stream.ToArray();
+        }
     }
 }

S7.Net/PlcAsynchronous.cs

@@ -312,6 +312,20 @@ namespace S7.Net
             return dataItems;
         }
 
+        /// <summary>
+        /// Read the current status from the PLC. A value of 0x08 indicates the PLC is in run status, regardless of the PLC type.
+        /// </summary>
+        /// <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 operation, with it's result set to the current PLC status on completion.</returns>
+        public async Task<byte> ReadStatusAsync(CancellationToken cancellationToken = default)
+        {
+            var dataToSend = BuildSzlReadRequestPackage(0x0424, 0);
+            var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
+
+            return (byte) (s7data[37] & 0x0f);
+        }
+
         /// <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.
@@ -428,7 +442,6 @@ namespace S7.Net
 
         /// <summary>
         /// Writes a single variable from the PLC, takes in input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.
-        /// If the write was not successful, check <see cref="LastErrorCode"/> or <see cref="LastErrorString"/>.
         /// </summary>
         /// <param name="variable">Input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.</param>
         /// <param name="value">Value to be written to the PLC</param>
@@ -507,6 +520,7 @@ namespace S7.Net
         /// <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>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</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)
         {

S7.Net/PlcSynchronous.cs

@@ -289,7 +289,6 @@ namespace S7.Net
 
         /// <summary>
         /// Writes a single variable from the PLC, takes in input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.
-        /// If the write was not successful, check <see cref="LastErrorCode"/> or <see cref="LastErrorString"/>.
         /// </summary>
         /// <param name="variable">Input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.</param>
         /// <param name="value">Value to be written to the PLC</param>
@@ -329,7 +328,7 @@ namespace S7.Net
                 const int packageSize = 19 + 12; // 19 header + 12 for 1 request
                 var dataToSend = new byte[packageSize];
                 var package = new MemoryStream(dataToSend);
-                BuildHeaderPackage(package);
+                WriteReadHeader(package);
                 // package.Add(0x02);  // datenart
                 BuildReadDataRequestPackage(package, dataType, db, startByteAdr, buffer.Length);
 
@@ -474,7 +473,7 @@ namespace S7.Net
                 int packageSize = 19 + (dataItems.Count * 12);
                 var dataToSend = new byte[packageSize];
                 var package = new MemoryStream(dataToSend);
-                BuildHeaderPackage(package, dataItems.Count);
+                WriteReadHeader(package, dataItems.Count);
                 // package.Add(0x02);  // datenart
                 foreach (var dataItem in dataItems)
                 {
@@ -493,6 +492,18 @@ namespace S7.Net
             }
         }
 
+        /// <summary>
+        /// Read the current status from the PLC. A value of 0x08 indicates the PLC is in run status, regardless of the PLC type.
+        /// </summary>
+        /// <returns>The current PLC status.</returns>
+        public byte ReadStatus()
+        {
+            var dataToSend = BuildSzlReadRequestPackage(0x0424, 0);
+            var s7data = RequestTsdu(dataToSend);
+
+            return (byte) (s7data[37] & 0x0f);
+        }
+
         private byte[] RequestTsdu(byte[] requestData) => RequestTsdu(requestData, 0, requestData.Length);
 
         private byte[] RequestTsdu(byte[] requestData, int offset, int length)

S7.Net/S7.Net.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFrameworks>net452;netstandard2.0;netstandard1.3;net5.0</TargetFrameworks>
+    <TargetFrameworks>net452;net462;netstandard2.0;netstandard1.3;net5.0;net6.0;net7.0</TargetFrameworks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>
     <InternalsVisibleTo>S7.Net.UnitTest</InternalsVisibleTo>
@@ -15,19 +15,20 @@
     <RepositoryType>git</RepositoryType>
     <PackageTags>PLC Siemens Communication S7</PackageTags>
     <Copyright>Derek Heiser 2015</Copyright>
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>latest</LangVersion>
     <Nullable>Enable</Nullable>
     <DebugType>portable</DebugType>
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <NoWarn>$(NoWarn);CS1591;NETSDK1138</NoWarn>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(TargetFramework)' == 'net452' Or '$(TargetFramework)' == 'netstandard2.0' ">
+  <PropertyGroup Condition="'$(TargetFramework)' == 'net452' Or '$(TargetFramework)' == 'net462' Or '$(TargetFramework)' == 'netstandard2.0' ">
     <DefineConstants>NET_FULL</DefineConstants>
   </PropertyGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' != 'net5.0'">
+  <ItemGroup Condition="'$(TargetFramework)' != 'net5.0' And '$(TargetFramework)' != 'net6.0' And '$(TargetFramework)' != 'net7.0'">
     <PackageReference Include="System.Memory" Version="4.5.5" />
   </ItemGroup>
   

S7.Net/StreamExtensions.cs

@@ -39,6 +39,7 @@ namespace S7.Net
         /// <param name="buffer">the buffer to read into</param>
         /// <param name="offset">the offset in the buffer to read into</param>
         /// <param name="count">the amount of bytes to read into the buffer</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
         /// <returns>returns the amount of read bytes</returns>
         public static async Task<int> ReadExactAsync(this Stream stream, byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {

S7.Net/TPKT.cs

@@ -29,6 +29,7 @@ namespace S7.Net
         /// Reads a TPKT from the socket Async
         /// </summary>
         /// <param name="stream">The stream to read from</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
         /// <returns>Task TPKT Instace</returns>
         public static async Task<TPKT> ReadAsync(Stream stream, CancellationToken cancellationToken)
         {

S7.Net/Types/Class.cs

@@ -64,7 +64,8 @@ namespace S7.Net.Types
                     numBytes += attribute.ReservedLengthInBytes;
                     break;
                 default:
-                    var propertyClass = Activator.CreateInstance(type);
+                    var propertyClass = Activator.CreateInstance(type) ??
+                        throw new ArgumentException($"Failed to create instance of type {type}.", nameof(type));
                     numBytes = GetClassSize(propertyClass, numBytes, true);
                     break;
             }
@@ -76,6 +77,8 @@ namespace S7.Net.Types
         /// Gets the size of the class in bytes.
         /// </summary>
         /// <param name="instance">An instance of the class</param>
+        /// <param name="numBytes">The offset of the current field.</param>
+        /// <param name="isInnerProperty"><see langword="true" /> if this property belongs to a class being serialized as member of the class requested for serialization; otherwise, <see langword="false" />.</param>
         /// <returns>the number of bytes</returns>
         public static double GetClassSize(object instance, double numBytes = 0.0, bool isInnerProperty = false)
         {
@@ -84,8 +87,10 @@ namespace S7.Net.Types
             {
                 if (property.PropertyType.IsArray)
                 {
-                    Type elementType = property.PropertyType.GetElementType();
-                    Array array = (Array)property.GetValue(instance, null);
+                    Type elementType = property.PropertyType.GetElementType()!;
+                    Array array = (Array?) property.GetValue(instance, null) ??
+                        throw new ArgumentException($"Property {property.Name} on {instance} must have a non-null value to get it's size.", nameof(instance));
+
                     if (array.Length <= 0)
                     {
                         throw new Exception("Cannot determine size of class, because an array is defined which has no fixed size greater than zero.");
@@ -199,7 +204,9 @@ namespace S7.Net.Types
                     numBytes += sData.Length;
                     break;
                 default:
-                    var propClass = Activator.CreateInstance(propertyType);
+                    var propClass = Activator.CreateInstance(propertyType) ??
+                        throw new ArgumentException($"Failed to create instance of type {propertyType}.", nameof(propertyType));
+
                     numBytes = FromBytes(propClass, bytes, numBytes);
                     value = propClass;
                     break;
@@ -213,6 +220,8 @@ namespace S7.Net.Types
         /// </summary>
         /// <param name="sourceClass">The object to fill in the given array of bytes</param>
         /// <param name="bytes">The array of bytes</param>
+        /// <param name="numBytes">The offset for the current field.</param>
+        /// <param name="isInnerClass"><see langword="true" /> if this class is the type of a member of the class to be serialized; otherwise, <see langword="false" />.</param>
         public static double FromBytes(object sourceClass, byte[] bytes, double numBytes = 0, bool isInnerClass = false)
         {
             if (bytes == null)
@@ -223,9 +232,11 @@ namespace S7.Net.Types
             {
                 if (property.PropertyType.IsArray)
                 {
-                    Array array = (Array)property.GetValue(sourceClass, null);
+                    Array array = (Array?) property.GetValue(sourceClass, null) ??
+                        throw new ArgumentException($"Property {property.Name} on sourceClass must be an array instance.", nameof(sourceClass));
+
                     IncrementToEven(ref numBytes);
-                    Type elementType = property.PropertyType.GetElementType();
+                    Type elementType = property.PropertyType.GetElementType()!;
                     for (int i = 0; i < array.Length && numBytes < bytes.Length; i++)
                     {
                         array.SetValue(
@@ -320,26 +331,30 @@ namespace S7.Net.Types
         /// <summary>
         /// Creates a byte array depending on the struct type.
         /// </summary>
-        /// <param name="sourceClass">The struct object</param>
+        /// <param name="sourceClass">The struct object.</param>
+        /// <param name="bytes">The target byte array.</param>
+        /// <param name="numBytes">The offset for the current field.</param>
         /// <returns>A byte array or null if fails.</returns>
         public static double ToBytes(object sourceClass, byte[] bytes, double numBytes = 0.0)
         {
             var properties = GetAccessableProperties(sourceClass.GetType());
             foreach (var property in properties)
             {
+                var value = property.GetValue(sourceClass, null) ??
+                    throw new ArgumentException($"Property {property.Name} on sourceClass can't be null.", nameof(sourceClass));
+
                 if (property.PropertyType.IsArray)
                 {
-                    Array array = (Array)property.GetValue(sourceClass, null);
+                    Array array = (Array) value;
                     IncrementToEven(ref numBytes);
-                    Type elementType = property.PropertyType.GetElementType();
                     for (int i = 0; i < array.Length && numBytes < bytes.Length; i++)
                     {
-                        numBytes = SetBytesFromProperty(array.GetValue(i), property, bytes, numBytes);
+                        numBytes = SetBytesFromProperty(array.GetValue(i)!, property, bytes, numBytes);
                     }
                 }
                 else
                 {
-                    numBytes = SetBytesFromProperty(property.GetValue(sourceClass, null), property, bytes, numBytes);
+                    numBytes = SetBytesFromProperty(value, property, bytes, numBytes);
                 }
             }
             return numBytes;

S7.Net/Types/DateTime.cs

@@ -141,7 +141,7 @@ namespace S7.Net.Types
         /// Converts an array of <see cref="T:System.DateTime"/> values to a byte array.
         /// </summary>
         /// <param name="dateTimes">The DateTime values to convert.</param>
-        /// <returns>A byte array containing the S7 date time representations of <paramref name="dateTime"/>.</returns>
+        /// <returns>A byte array containing the S7 date time representations of <paramref name="dateTimes"/>.</returns>
         /// <exception cref="ArgumentOutOfRangeException">Thrown when any value of
         ///   <paramref name="dateTimes"/> is before <see cref="P:SpecMinimumDateTime"/>
         ///   or after <see cref="P:SpecMaximumDateTime"/>.</exception>

S7.Net/Types/S7String.cs

@@ -8,17 +8,17 @@ namespace S7.Net.Types
     /// An S7 String has a preceeding 2 byte header containing its capacity and length
     /// </summary>
     public static class S7String
-    {
-        private static Encoding stringEncoding = Encoding.ASCII;
-
+    {
+        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));
+        /// <exception cref="ArgumentNullException">StringEncoding must not be null</exception>
+        public static Encoding StringEncoding
+        {
+            get => stringEncoding;
+            set => stringEncoding = value ?? throw new ArgumentNullException(nameof(StringEncoding));
         }
 
         /// <summary>
@@ -58,7 +58,7 @@ namespace S7.Net.Types
         /// <param name="value">The string to convert to byte array.</param>
         /// <param name="reservedLength">The length (in characters) allocated in PLC for the string.</param>
         /// <returns>A <see cref="T:byte[]" /> containing the string header and string value with a maximum length of <paramref name="reservedLength"/> + 2.</returns>
-        public static byte[] ToByteArray(string value, int reservedLength)
+        public static byte[] ToByteArray(string? value, int reservedLength)
         {
             if (value is null)
             {

S7.Net/Types/S7WString.cs

@@ -48,7 +48,7 @@ namespace S7.Net.Types
         /// <param name="value">The string to convert to byte array.</param>
         /// <param name="reservedLength">The length (in characters) allocated in PLC for the string.</param>
         /// <returns>A <see cref="T:byte[]" /> containing the string header and string value with a maximum length of <paramref name="reservedLength"/> + 4.</returns>
-        public static byte[] ToByteArray(string value, int reservedLength)
+        public static byte[] ToByteArray(string? value, int reservedLength)
         {
             if (value is null)
             {

S7.Net/Types/String.cs

@@ -12,13 +12,15 @@
         /// <param name="reservedLength">The amount of bytes reserved for the <paramref name="value"/> in the PLC.</param>
         public static byte[] ToByteArray(string value, int reservedLength)
         {
-            var length = value?.Length;
-            if (length > reservedLength) length = reservedLength;
             var bytes = new byte[reservedLength];
+            if (value == null) return bytes;
 
-            if (length == null || length == 0) return bytes;
+            var length = value.Length;
+            if (length == 0) return bytes;
 
-            System.Text.Encoding.ASCII.GetBytes(value, 0, length.Value, bytes, 0);
+            if (length > reservedLength) length = reservedLength;
+
+            System.Text.Encoding.ASCII.GetBytes(value, 0, length, bytes, 0);
 
             return bytes;
         }

S7.Net/Types/Struct.cs

@@ -98,8 +98,8 @@ namespace S7.Net.Types
             int bytePos = 0;
             int bitPos = 0;
             double numBytes = 0.0;
-            object structValue = Activator.CreateInstance(structType);
-
+            object structValue = Activator.CreateInstance(structType) ??
+                throw new ArgumentException($"Failed to create an instance of the type {structType}.", nameof(structType));
 
             var infos = structValue.GetType()
 #if NETSTANDARD1_3
@@ -254,6 +254,14 @@ namespace S7.Net.Types
 
             foreach (var info in infos)
             {
+                static TValue GetValueOrThrow<TValue>(FieldInfo fi, object structValue) where TValue : struct
+                {
+                    var value = fi.GetValue(structValue) as TValue? ??
+                        throw new ArgumentException($"Failed to convert value of field {fi.Name} of {structValue} to type {typeof(TValue)}");
+
+                    return value;
+                }
+
                 bytes2 = null;
                 switch (info.FieldType.Name)
                 {
@@ -261,7 +269,7 @@ namespace S7.Net.Types
                         // get the value
                         bytePos = (int)Math.Floor(numBytes);
                         bitPos = (int)((numBytes - (double)bytePos) / 0.125);
-                        if ((bool)info.GetValue(structValue))
+                        if (GetValueOrThrow<bool>(info, structValue))
                             bytes[bytePos] |= (byte)Math.Pow(2, bitPos);            // is true
                         else
                             bytes[bytePos] &= (byte)(~(byte)Math.Pow(2, bitPos));   // is false
@@ -270,26 +278,26 @@ namespace S7.Net.Types
                     case "Byte":
                         numBytes = (int)Math.Ceiling(numBytes);
                         bytePos = (int)numBytes;
-                        bytes[bytePos] = (byte)info.GetValue(structValue);
+                        bytes[bytePos] = GetValueOrThrow<byte>(info, structValue);
                         numBytes++;
                         break;
                     case "Int16":
-                        bytes2 = Int.ToByteArray((Int16)info.GetValue(structValue));
+                        bytes2 = Int.ToByteArray(GetValueOrThrow<short>(info, structValue));
                         break;
                     case "UInt16":
-                        bytes2 = Word.ToByteArray((UInt16)info.GetValue(structValue));
+                        bytes2 = Word.ToByteArray(GetValueOrThrow<ushort>(info, structValue));
                         break;
                     case "Int32":
-                        bytes2 = DInt.ToByteArray((Int32)info.GetValue(structValue));
+                        bytes2 = DInt.ToByteArray(GetValueOrThrow<int>(info, structValue));
                         break;
                     case "UInt32":
-                        bytes2 = DWord.ToByteArray((UInt32)info.GetValue(structValue));
+                        bytes2 = DWord.ToByteArray(GetValueOrThrow<uint>(info, structValue));
                         break;
                     case "Single":
-                        bytes2 = Real.ToByteArray((float)info.GetValue(structValue));
+                        bytes2 = Real.ToByteArray(GetValueOrThrow<float>(info, structValue));
                         break;
                     case "Double":
-                        bytes2 = LReal.ToByteArray((double)info.GetValue(structValue));
+                        bytes2 = LReal.ToByteArray(GetValueOrThrow<double>(info, structValue));
                         break;
                     case "String":
                         S7StringAttribute? attribute = info.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
@@ -298,8 +306,8 @@ namespace S7.Net.Types
 
                         bytes2 = attribute.Type switch
                         {
-                            S7StringType.S7String => S7String.ToByteArray((string)info.GetValue(structValue), attribute.ReservedLength),
-                            S7StringType.S7WString => S7WString.ToByteArray((string)info.GetValue(structValue), attribute.ReservedLength),
+                            S7StringType.S7String => S7String.ToByteArray((string?)info.GetValue(structValue), attribute.ReservedLength),
+                            S7StringType.S7WString => S7WString.ToByteArray((string?)info.GetValue(structValue), attribute.ReservedLength),
                             _ => throw new ArgumentException("Please use a valid string type for the S7StringAttribute")
                         };
                         break;