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Improve exception diagnostics for stdio client (#376)

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* Improve exception diagnostics for stdio client

Track the last several lines of stderr and include those in an exception created as part of CleanupAsync if the server process has already exited. This is based on an assumption that the server should never exit prior to CleanupAsync being called.

* Address feedback and fix test failure
This commit is contained in:
Stephen Toub 2025-05-14 10:46:49 -04:00 • committed by GitHub
commit c11c634945
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1 changed files with 222 additions and 131 deletions
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73
src/ModelContextProtocol/Protocol/Transport/TransportBase.cs
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@ -1,7 +1,8 @@
using System.Diagnostics;
using System.Threading.Channels;
using Microsoft.Extensions.Logging;
using ModelContextProtocol.Protocol.Messages;
using Microsoft.Extensions.Logging.Abstractions;
using ModelContextProtocol.Protocol.Messages;
namespace ModelContextProtocol.Protocol.Transport;
@ -23,7 +24,14 @@ public abstract partial class TransportBase : ITransport
{
private readonly Channel<JsonRpcMessage> _messageChannel;
private readonly ILogger _logger;
private int _isConnected;
private volatile int _state = StateInitial;
/// <summary>The transport has not yet been connected.</summary>
private const int StateInitial = 0;
/// <summary>The transport is connected.</summary>
private const int StateConnected = 1;
/// <summary>The transport was previously connected and is now disconnected.</summary>
private const int StateDisconnected = 2;
/// <summary>
/// Initializes a new instance of the <see cref="TransportBase"/> class.
@ -53,7 +61,7 @@ public abstract partial class TransportBase : ITransport
protected string Name { get; }
/// <inheritdoc/>
public bool IsConnected => _isConnected == 1;
public bool IsConnected => _state == StateConnected;
/// <inheritdoc/>
public ChannelReader<JsonRpcMessage> MessageReader => _messageChannel.Reader;
@ -73,7 +81,7 @@ public abstract partial class TransportBase : ITransport
{
if (!IsConnected)
{
throw new InvalidOperationException("Transport is not connected");
throw new InvalidOperationException("Transport is not connected.");
}
if (_logger.IsEnabled(LogLevel.Debug))
@ -82,24 +90,61 @@ public abstract partial class TransportBase : ITransport
LogTransportReceivedMessage(Name, messageId);
}
await _messageChannel.Writer.WriteAsync(message, cancellationToken).ConfigureAwait(false);
bool wrote = _messageChannel.Writer.TryWrite(message);
Debug.Assert(wrote || !IsConnected, "_messageChannel is unbounded; this should only ever return false if the channel has been closed.");
}
/// <summary>
/// Sets the connected state of the transport.
/// Sets the transport to a connected state.
/// </summary>
/// <param name="isConnected">Whether the transport is connected.</param>
protected void SetConnected(bool isConnected)
protected void SetConnected()
{
var newIsConnected = isConnected ? 1 : 0;
if (Interlocked.Exchange(ref _isConnected, newIsConnected) == newIsConnected)
while (true)
{
return;
}
int state = _state;
switch (state)
{
case StateInitial:
if (Interlocked.CompareExchange(ref _state, StateConnected, StateInitial) == StateInitial)
{
return;
}
break;
if (!isConnected)
case StateConnected:
return;
case StateDisconnected:
throw new IOException("Transport is already disconnected and can't be reconnected.");
default:
Debug.Fail($"Unexpected state: {state}");
return;
}
}
}
/// <summary>
/// Sets the transport to a disconnected state.
/// </summary>
/// <param name="error">Optional error information associated with the transport disconnecting. Should be <see langwor="null"/> if the disconnect was graceful and expected.</param>
protected void SetDisconnected(Exception? error = null)
{
int state = _state;
switch (state)
{
_messageChannel.Writer.Complete();
case StateInitial:
case StateConnected:
_state = StateDisconnected;
_messageChannel.Writer.TryComplete(error);
break;
case StateDisconnected:
return;
default:
Debug.Fail($"Unexpected state: {state}");
break;
}
}