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Merged
halter73 merged 8 commits into from
Jan 29, 2026
+90 −2
Merged

Add Trace-level logging for JSON-RPC payloads in transports #1191

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d661159
Initial plan
Copilot Jan 28, 2026
7cd6a01
Add Trace-level logging for JSON-RPC payloads in transports
Copilot Jan 28, 2026
cc7e97c
Remove Debug-level logging, keep only Trace-level logging for sent me…
Copilot Jan 28, 2026
9d9d8af
Guard Trace logging calls with IsEnabled check
Copilot Jan 28, 2026
669781d
Add IsEnabled guards for received message logging
Copilot Jan 28, 2026
a3aa70b
Add LogTransportSendingMessageSensitive overload taking JsonRpcMessage
Copilot Jan 28, 2026
5fd721f
Remove unnecessary IsEnabled guards from logging call sites
Copilot Jan 28, 2026
843ccca
Use LoggedTest.LoggerFactory and MockLoggerProvider in trace logging …
Copilot Jan 29, 2026
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2 changes: 2 additions & 0 deletions src/ModelContextProtocol.Core/Client/SseClientSessionTransport.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,8 @@ public override async Task SendMessageAsync(
messageId = messageWithId.Id.ToString();
}

LogTransportSendingMessageSensitive(message);

using var httpRequestMessage = new HttpRequestMessage(HttpMethod.Post, _messageEndpoint);
StreamableHttpClientSessionTransport.CopyAdditionalHeaders(httpRequestMessage.Headers, _options.AdditionalHeaders, sessionId: null, protocolVersion: null);
var response = await _httpClient.SendAsync(httpRequestMessage, message, cancellationToken).ConfigureAwait(false);
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2 changes: 2 additions & 0 deletions src/ModelContextProtocol.Core/Client/StreamClientSessionTransport.cs
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Expand Up @@ -105,6 +105,8 @@ public override async Task SendMessageAsync(JsonRpcMessage message, Cancellation

var json = JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage);

LogTransportSendingMessageSensitive(Name, json);

using var _ = await _sendLock.LockAsync(cancellationToken).ConfigureAwait(false);
try
{
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2 changes: 2 additions & 0 deletions src/ModelContextProtocol.Core/Client/StreamableHttpClientSessionTransport.cs
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Expand Up @@ -75,6 +75,8 @@ internal async Task<HttpResponseMessage> SendHttpRequestAsync(JsonRpcMessage mes
$"Call {nameof(McpClient)}.{nameof(McpClient.ResumeSessionAsync)} to resume existing sessions.");
}

LogTransportSendingMessageSensitive(message);

using var sendCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, _connectionCts.Token);
cancellationToken = sendCts.Token;

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16 changes: 16 additions & 0 deletions src/ModelContextProtocol.Core/Protocol/TransportBase.cs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using System.Diagnostics;
using System.Text.Json;
using System.Threading.Channels;

namespace ModelContextProtocol.Protocol;
Expand Down Expand Up @@ -166,6 +167,21 @@ protected void SetDisconnected(Exception? error = null)
[LoggerMessage(Level = LogLevel.Error, Message = "{EndpointName} transport send failed for message ID '{MessageId}'.")]
private protected partial void LogTransportSendFailed(string endpointName, string messageId, Exception exception);

[LoggerMessage(Level = LogLevel.Trace, Message = "{EndpointName} transport sending message. Message: '{Message}'.")]
private protected partial void LogTransportSendingMessageSensitive(string endpointName, string message);

/// <summary>
/// Logs a sending message at Trace level if trace logging is enabled.
/// </summary>
/// <param name="message">The JSON-RPC message to log.</param>
private protected void LogTransportSendingMessageSensitive(JsonRpcMessage message)
{
if (_logger.IsEnabled(LogLevel.Trace))
{
LogTransportSendingMessageSensitive(Name, JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage));
}
}

[LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} transport reading messages.")]
private protected partial void LogTransportEnteringReadMessagesLoop(string endpointName);

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4 changes: 3 additions & 1 deletion src/ModelContextProtocol.Core/Server/StreamServerTransport.cs
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Expand Up @@ -74,7 +74,9 @@ public override async Task SendMessageAsync(JsonRpcMessage message, Cancellation

try
{
await JsonSerializer.SerializeAsync(_outputStream, message, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(JsonRpcMessage)), cancellationToken).ConfigureAwait(false);
var json = JsonSerializer.Serialize(message, McpJsonUtilities.JsonContext.Default.JsonRpcMessage);
LogTransportSendingMessageSensitive(Name, json);
await _outputStream.WriteAsync(Encoding.UTF8.GetBytes(json), cancellationToken).ConfigureAwait(false);
await _outputStream.WriteAsync(s_newlineBytes, cancellationToken).ConfigureAwait(false);
await _outputStream.FlushAsync(cancellationToken).ConfigureAwait(false);
}
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66 changes: 65 additions & 1 deletion tests/ModelContextProtocol.Tests/Transport/StdioServerTransportTests.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
using ModelContextProtocol.Protocol;
using Microsoft.Extensions.Logging;
using ModelContextProtocol.Protocol;
using ModelContextProtocol.Server;
using ModelContextProtocol.Tests.Utils;
using System.IO.Pipelines;
Expand All @@ -21,6 +22,14 @@ public StdioServerTransportTests(ITestOutputHelper testOutputHelper)
InitializationTimeout = TimeSpan.FromSeconds(10),
ServerInstructions = "Test Instructions"
};

// Override the LoggerFactory to use Trace level for testing Trace-level logging
LoggerFactory = Microsoft.Extensions.Logging.LoggerFactory.Create(builder =>
{
builder.AddProvider(XunitLoggerProvider);
builder.AddProvider(MockLoggerProvider);
builder.SetMinimumLevel(LogLevel.Trace);
});
}

[Fact(Skip="https://github.com/modelcontextprotocol/csharp-sdk/issues/143")]
Expand Down Expand Up @@ -193,4 +202,59 @@ public async Task SendMessageAsync_Should_Preserve_Unicode_Characters()
Assert.True(magnifyingGlassFound, "Magnifying glass emoji not found in result");
Assert.True(rocketFound, "Rocket emoji not found in result");
}

[Fact]
public async Task SendMessageAsync_Should_Log_At_Trace_Level()
{
// Arrange
using var output = new MemoryStream();

await using var transport = new StreamServerTransport(
new Pipe().Reader.AsStream(),
output,
loggerFactory: LoggerFactory);

// Act
var message = new JsonRpcRequest { Method = "test", Id = new RequestId(44) };
await transport.SendMessageAsync(message, TestContext.Current.CancellationToken);

// Assert
var traceLogMessages = MockLoggerProvider.LogMessages
.Where(x => x.LogLevel == LogLevel.Trace && x.Message.Contains("transport sending message"))
.ToList();

Assert.NotEmpty(traceLogMessages);
Assert.Contains(traceLogMessages, x => x.Message.Contains("\"method\":\"test\"") && x.Message.Contains("\"id\":44"));
}

[Fact]
public async Task ReadMessagesAsync_Should_Log_Received_At_Trace_Level()
{
// Arrange
var message = new JsonRpcRequest { Method = "test", Id = new RequestId(99) };
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);

// Act
await pipe.Writer.WriteAsync(Encoding.UTF8.GetBytes($"{json}\n"), TestContext.Current.CancellationToken);

// Wait for the message to be processed
var canRead = await transport.MessageReader.WaitToReadAsync(TestContext.Current.CancellationToken);
Assert.True(canRead, "Nothing to read here from transport message reader");

// Assert
var traceLogMessages = MockLoggerProvider.LogMessages
.Where(x => x.LogLevel == LogLevel.Trace && x.Message.Contains("transport received message"))
.ToList();

Assert.NotEmpty(traceLogMessages);
Assert.Contains(traceLogMessages, x => x.Message.Contains("\"method\":\"test\"") && x.Message.Contains("\"id\":99"));
}
}
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