Add tests validating \n line delimiter for stream transports

Validate that both StreamServerTransport and StreamClientSessionTransport
use \n (not \r\n) as the message delimiter on all platforms, and that both
correctly accept \n-delimited messages on the read side.

Co-authored-by: halter73 <54385+halter73@users.noreply.github.com>

Author: Copilot

tests/ModelContextProtocol.Tests/Transport/StdioServerTransportTests.cs

@@ -227,6 +227,54 @@ public async Task SendMessageAsync_Should_Log_At_Trace_Level()
         Assert.Contains(traceLogMessages, x => x.Message.Contains("\"method\":\"test\"") && x.Message.Contains("\"id\":44"));
     }
 
+    [Fact]
+    public async Task SendMessageAsync_Should_Use_LF_Not_CRLF()
+    {
+        using var output = new MemoryStream();
+
+        await using var transport = new StreamServerTransport(
+            new Pipe().Reader.AsStream(),
+            output,
+            loggerFactory: LoggerFactory);
+
+        var message = new JsonRpcRequest { Method = "test", Id = new RequestId(44) };
+
+        await transport.SendMessageAsync(message, TestContext.Current.CancellationToken);
+
+        byte[] bytes = output.ToArray();
+
+        // The output should end with exactly \n (0x0A), not \r\n (0x0D 0x0A).
+        Assert.True(bytes.Length > 1, "Output should contain message data");
+        Assert.Equal((byte)'\n', bytes[^1]);
+        Assert.NotEqual((byte)'\r', bytes[^2]);
+    }
+
+    [Fact]
+    public async Task ReadMessagesAsync_Should_Accept_LF_Delimited_Messages()
+    {
+        var message = new JsonRpcRequest { Method = "test", Id = new RequestId(44) };
+        var json = JsonSerializer.Serialize(message, McpJsonUtilities.DefaultOptions);
+
+        Pipe pipe = new();
+        using var input = pipe.Reader.AsStream();
+
+        await using var transport = new StreamServerTransport(
+            input,
+            Stream.Null,
+            loggerFactory: LoggerFactory);
+
+        // Write the message with \n line ending (not \r\n)
+        await pipe.Writer.WriteAsync(Encoding.UTF8.GetBytes($"{json}\n"), TestContext.Current.CancellationToken);
+
+        var canRead = await transport.MessageReader.WaitToReadAsync(TestContext.Current.CancellationToken);
+
+        Assert.True(canRead, "Should be able to read a \\n-delimited message");
+        Assert.True(transport.MessageReader.TryPeek(out var readMessage));
+        Assert.NotNull(readMessage);
+        Assert.IsType<JsonRpcRequest>(readMessage);
+        Assert.Equal("44", ((JsonRpcRequest)readMessage).Id.ToString());
+    }
+
     [Fact]
     public async Task ReadMessagesAsync_Should_Log_Received_At_Trace_Level()
     {

tests/ModelContextProtocol.Tests/Transport/StreamClientTransportTests.cs

@@ -0,0 +1,60 @@
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Tests.Utils;
+using System.IO.Pipelines;
+using System.Text;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Tests.Transport;
+
+public class StreamClientTransportTests(ITestOutputHelper testOutputHelper) : LoggedTest(testOutputHelper)
+{
+    [Fact]
+    public async Task SendMessageAsync_Should_Use_LF_Not_CRLF()
+    {
+        using var serverInput = new MemoryStream();
+        Pipe serverOutputPipe = new();
+
+        var transport = new StreamClientTransport(serverInput, serverOutputPipe.Reader.AsStream(), LoggerFactory);
+        await using var sessionTransport = await transport.ConnectAsync(TestContext.Current.CancellationToken);
+
+        var message = new JsonRpcRequest { Method = "test", Id = new RequestId(44) };
+
+        await sessionTransport.SendMessageAsync(message, TestContext.Current.CancellationToken);
+
+        byte[] bytes = serverInput.ToArray();
+
+        // The output should end with exactly \n (0x0A), not \r\n (0x0D 0x0A).
+        Assert.True(bytes.Length > 1, "Output should contain message data");
+        Assert.Equal((byte)'\n', bytes[^1]);
+        Assert.NotEqual((byte)'\r', bytes[^2]);
+
+        // Also verify the JSON content is valid
+        var json = Encoding.UTF8.GetString(bytes).TrimEnd('\n');
+        var expected = JsonSerializer.Serialize(message, McpJsonUtilities.DefaultOptions);
+        Assert.Equal(expected, json);
+    }
+
+    [Fact]
+    public async Task ReadMessagesAsync_Should_Accept_LF_Delimited_Messages()
+    {
+        Pipe serverInputPipe = new();
+        Pipe serverOutputPipe = new();
+
+        var transport = new StreamClientTransport(serverInputPipe.Writer.AsStream(), serverOutputPipe.Reader.AsStream(), LoggerFactory);
+        await using var sessionTransport = await transport.ConnectAsync(TestContext.Current.CancellationToken);
+
+        var message = new JsonRpcRequest { Method = "test", Id = new RequestId(44) };
+        var json = JsonSerializer.Serialize(message, McpJsonUtilities.DefaultOptions);
+
+        // Write a \n-delimited message to the server's output (which the client reads)
+        await serverOutputPipe.Writer.WriteAsync(Encoding.UTF8.GetBytes($"{json}\n"), TestContext.Current.CancellationToken);
+
+        var canRead = await sessionTransport.MessageReader.WaitToReadAsync(TestContext.Current.CancellationToken);
+
+        Assert.True(canRead, "Should be able to read a \\n-delimited message");
+        Assert.True(sessionTransport.MessageReader.TryPeek(out var readMessage));
+        Assert.NotNull(readMessage);
+        Assert.IsType<JsonRpcRequest>(readMessage);
+        Assert.Equal("44", ((JsonRpcRequest)readMessage).Id.ToString());
+    }
+}