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Make ClientTransportClosedException public and unify transport exception handling (#1467)

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Co-authored-by: halter73 <54385+halter73@users.noreply.github.com>
Co-authored-by: Stephen Toub <stoub@microsoft.com>
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Copilot 2026-03-29 20:21:03 -04:00 • committed by GitHub
commit 7662ce6b70
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1 changed files with 253 additions and 38 deletions
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38
src/ModelContextProtocol.Core/Client/McpClient.Methods.cs
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@ -1,6 +1,7 @@
using Microsoft.Extensions.Logging;
using ModelContextProtocol.Protocol;
using ModelContextProtocol.Server;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json;
using System.Text.Json.Nodes;
@ -52,13 +53,25 @@ public abstract partial class McpClient : McpSession
{
await clientSession.ConnectAsync(cancellationToken).ConfigureAwait(false);
}
catch
catch (Exception ex) when (ex is not OperationCanceledException and not ClientTransportClosedException)
{
try
// ConnectAsync already disposed the session (which includes awaiting Completion).
// Check if the transport provided structured completion details indicating
// why the transport closed that aren't already in the original exception chain.
Debug.Assert(clientSession.Completion.IsCompleted, "Completion should already be finished after ConnectAsync's DisposeAsync.");
var completionDetails = await clientSession.Completion.ConfigureAwait(false);
// If the transport closed with a non-graceful error (e.g., server process exited)
// and the completion details carry an exception that's NOT already in the original
// exception chain, throw a ClientTransportClosedException with the structured details so
// callers can programmatically inspect the closure reason (exit code, stderr, etc.).
// When the same exception is already in the chain (e.g., HttpRequestException from
// an HTTP transport), the original exception is more appropriate to re-throw.
if (completionDetails.Exception is { } detailsException &&
!ExceptionChainContains(ex, detailsException))
{
await clientSession.DisposeAsync().ConfigureAwait(false);
throw new ClientTransportClosedException(completionDetails);
}
catch { } // allow the original exception to propagate
throw;
}
@ -66,6 +79,23 @@ public abstract partial class McpClient : McpSession
return clientSession;
}
/// <summary>
/// Returns <see langword="true"/> if <paramref name="target"/> is the same object as
/// <paramref name="exception"/> or any exception in its <see cref="Exception.InnerException"/> chain.
/// </summary>
private static bool ExceptionChainContains(Exception exception, Exception target)
{
for (Exception? current = exception; current is not null; current = current.InnerException)
{
if (ReferenceEquals(current, target))
{
return true;
}
}
return false;
}
/// <summary>
/// Recreates an <see cref="McpClient"/> using an existing transport session without sending a new initialize request.
/// </summary>