From 0fe9097f63b8049419a776eb735ba1b2c7db04f3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Sim=C3=B5es?= <jose.simoes@eclo.solutions>
Date: Thu, 24 Sep 2026 02:27:09 +0100
Subject: [PATCH] Fix NetworkStream write core

- Add back check for bytes sent.
- Add unit tests to cover NetworkStream.
---
 Tests/SocketTests/NetworkStreamTests.cs       | 129 ++++++++++++++++++
 Tests/SocketTests/SocketTests.nfproj          |   1 +
 .../Sockets/NetworkStream.cs                  |   2 +-
 3 files changed, 131 insertions(+), 1 deletion(-)
 create mode 100644 Tests/SocketTests/NetworkStreamTests.cs

diff --git a/Tests/SocketTests/NetworkStreamTests.cs b/Tests/SocketTests/NetworkStreamTests.cs
new file mode 100644
index 0000000..94c2162
--- /dev/null
+++ b/Tests/SocketTests/NetworkStreamTests.cs
@@ -0,0 +1,129 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using nanoFramework.TestFramework;
+using System;
+using System.Net;
+using System.Net.Sockets;
+
+namespace NFUnitTestSocketTests
+{
+    [TestClass]
+    public class NetworkStreamTests
+    {
+        private const int ServerPort = 7010;
+
+        [Setup]
+        public void SetupNetworkStreamTests()
+        {
+            // Comment next line to run the tests on a real hardware
+            Assert.SkipTest("Skipping tests using nanoCLR Win32 in a pipeline");
+        }
+
+        [TestMethod]
+        public void NetworkStream_Write_ByteArray_SendsData()
+        {
+            byte[] sent = new byte[] { 0x01, 0x02, 0x03, 0x04, 0x05 };
+
+            RunLoopbackTest((stream, peer) =>
+            {
+                stream.Write(sent, 0, sent.Length);
+
+                AssertReceived(peer, sent);
+            });
+        }
+
+        [TestMethod]
+        public void NetworkStream_Write_ByteArrayWithOffset_SendsData()
+        {
+            byte[] buffer = new byte[] { 0xFF, 0x11, 0x22, 0x33, 0xFF };
+
+            RunLoopbackTest((stream, peer) =>
+            {
+                stream.Write(buffer, 1, 3);
+
+                AssertReceived(peer, new byte[] { 0x11, 0x22, 0x33 });
+            });
+        }
+
+        [TestMethod]
+        public void NetworkStream_Write_Span_SendsData()
+        {
+            byte[] sent = new byte[] { 0xAB, 0xCD, 0xEF };
+
+            RunLoopbackTest((stream, peer) =>
+            {
+                stream.Write(new ReadOnlySpan<byte>(sent));
+
+                AssertReceived(peer, sent);
+            });
+        }
+
+        [TestMethod]
+        public void NetworkStream_Write_ZeroLength_DoesNotThrow()
+        {
+            RunLoopbackTest((stream, peer) =>
+            {
+                stream.Write(new byte[0], 0, 0);
+            });
+        }
+
+        private delegate void LoopbackTestAction(NetworkStream stream, Socket peer);
+
+        private static void RunLoopbackTest(LoopbackTestAction test)
+        {
+            Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            Socket peer = null;
+            NetworkStream stream = null;
+
+            try
+            {
+                listener.Bind(new IPEndPoint(IPAddress.Loopback, ServerPort));
+                listener.Listen(1);
+
+                client.Connect(new IPEndPoint(IPAddress.Loopback, ServerPort));
+                peer = listener.Accept();
+
+                stream = new NetworkStream(client, true);
+
+                test(stream, peer);
+            }
+            finally
+            {
+                if (stream != null)
+                {
+                    // stream owns the client socket
+                    stream.Close();
+                }
+                else
+                {
+                    client.Close();
+                }
+
+                peer?.Close();
+                listener.Close();
+            }
+        }
+
+        private static void AssertReceived(Socket peer, byte[] expected)
+        {
+            byte[] received = new byte[expected.Length];
+            int totalRead = 0;
+
+            while (totalRead < expected.Length)
+            {
+                int read = peer.Receive(received, totalRead, expected.Length - totalRead, SocketFlags.None);
+
+                Assert.IsTrue(read > 0, "Connection closed before all data was received");
+
+                totalRead += read;
+            }
+
+            for (int i = 0; i < expected.Length; i++)
+            {
+                Assert.AreEqual(expected[i], received[i], $"Data mismatch at index {i}");
+            }
+        }
+    }
+}
diff --git a/Tests/SocketTests/SocketTests.nfproj b/Tests/SocketTests/SocketTests.nfproj
index b6f0608..0be3bc0 100644
--- a/Tests/SocketTests/SocketTests.nfproj
+++ b/Tests/SocketTests/SocketTests.nfproj
@@ -27,6 +27,7 @@
   <Import Project="$(NanoFrameworkProjectSystemPath)NFProjectSystem.props" Condition="Exists('$(NanoFrameworkProjectSystemPath)NFProjectSystem.props')" />
   <ItemGroup>
     <Compile Include="CompanionClient.cs" />
+    <Compile Include="NetworkStreamTests.cs" />
     <Compile Include="SocketOptionsTests.cs" />
     <Compile Include="SocketPair.cs" />
     <Compile Include="SocketExceptionsTests.cs" />
diff --git a/nanoFramework.System.Net/Sockets/NetworkStream.cs b/nanoFramework.System.Net/Sockets/NetworkStream.cs
index 3df43fa..225c498 100644
--- a/nanoFramework.System.Net/Sockets/NetworkStream.cs
+++ b/nanoFramework.System.Net/Sockets/NetworkStream.cs
@@ -487,7 +487,7 @@ private void WriteCore(byte[] buffer, int offset, int count)
                 throw new NotSupportedException();
             }
 
-            if (0 != count)
+            if (bytesSent != count)
             {
                 throw new IOException();
             }