Fix: swallow _receiveTask exceptions in SseClientSessionTransport.Clo…#1432
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xue-cai wants to merge 1 commit intomodelcontextprotocol:mainfrom
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Fix: swallow _receiveTask exceptions in SseClientSessionTransport.Clo…#1432xue-cai wants to merge 1 commit intomodelcontextprotocol:mainfrom
xue-cai wants to merge 1 commit intomodelcontextprotocol:mainfrom
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…seAsync
When SseClientSessionTransport.ConnectAsync fails (e.g. server returns 405),
the catch block calls CloseAsync() before wrapping the error in
InvalidOperationException. However, CloseAsync() awaits the already-faulted
_receiveTask without a try-catch, causing the original HttpRequestException
to propagate out of CloseAsync and preempt the InvalidOperationException
wrapping. Callers then receive a bare HttpRequestException instead of the
documented InvalidOperationException("Failed to connect transport", ex).
The fix wraps `await _receiveTask` in CloseAsync with a try-catch to
swallow already-observed exceptions from the faulted task.
Code references:
SseClientSessionTransport.ConnectAsync (catch block calls CloseAsync):
https://github.com/modelcontextprotocol/csharp-sdk/blob/v0.9.0-preview.2/src/ModelContextProtocol.Core/Client/SseClientSessionTransport.cs#L52-L67
SseClientSessionTransport.CloseAsync (awaits _receiveTask without try-catch):
https://github.com/modelcontextprotocol/csharp-sdk/blob/v0.9.0-preview.2/src/ModelContextProtocol.Core/Client/SseClientSessionTransport.cs#L108-L130
Testing:
# Build all frameworks (only netstandard2.0 fails — pre-existing on main):
dotnet build tests/ModelContextProtocol.Tests/ '/p:NoWarn=NU1903%3BMCPEXP001'
# Run full transport suite (74 tests × 3 frameworks = 222 total, 0 failures):
dotnet test tests/ModelContextProtocol.Tests/ '/p:NoWarn=NU1903%3BMCPEXP001' --no-build --filter "FullyQualifiedName~Transport" --framework net10.0
dotnet test tests/ModelContextProtocol.Tests/ '/p:NoWarn=NU1903%3BMCPEXP001' --no-build --filter "FullyQualifiedName~Transport" --framework net9.0
dotnet test tests/ModelContextProtocol.Tests/ '/p:NoWarn=NU1903%3BMCPEXP001' --no-build --filter "FullyQualifiedName~Transport" --framework net8.0
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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…seAsync
When SseClientSessionTransport.ConnectAsync fails (e.g. the SSE GET returns 405), its catch block calls CloseAsync() before wrapping the error in InvalidOperationException("Failed to connect transport", ex).
However, CloseAsync() awaits _receiveTask which is already faulted with the same HttpRequestException. Since there is no try-catch around that await, the exception propagates out of CloseAsync, out of the catch block, and the InvalidOperationException wrapping is never reached.
This means callers of ConnectAsync receive an unwrapped HttpRequestException instead of the documented InvalidOperationException wrapper, which breaks exception filtering in downstream code.
The fix wraps
await _receiveTaskin CloseAsync with a try-catch that swallows both OperationCanceledException (normal shutdown) and other exceptions (already observed and forwarded via_connectionEstablished.TrySetException in ReceiveMessagesAsync).
Includes a regression test that verifies ConnectAsync throws InvalidOperationException (not HttpRequestException) when both Streamable HTTP POST and SSE GET fallback fail.
Motivation and Context
How Has This Been Tested?
Breaking Changes
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