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Prevent cancellation of initialize request per MCP spec (#1350)

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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>
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Copilot 2026-02-23 15:40:17 -05:00 • committed by GitHub
commit 4f7095453c
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1 changed files with 99 additions and 3 deletions
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12
src/ModelContextProtocol.Core/McpSessionHandler.cs
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@ -190,11 +190,16 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
{
// Register before we yield, so that the tracking is guaranteed to be there
// when subsequent messages arrive, even if the asynchronous processing happens
// out of order.
// out of order. Per spec, "The initialize request MUST NOT be cancelled by clients",
// so we don't track it in _handlingRequests to prevent cancellation notifications from
// canceling it.
if (messageWithId is not null)
{
combinedCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
_handlingRequests[messageWithId.Id] = combinedCts;
if (message is not JsonRpcRequest { Method: RequestMethods.Initialize })
{
_handlingRequests[messageWithId.Id] = combinedCts;
}
}
// If we await the handler without yielding first, the transport may not be able to read more messages,
@ -528,9 +533,10 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
// Now that the request has been sent, register for cancellation. If we registered before,
// a cancellation request could arrive before the server knew about that request ID, in which
// case the server could ignore it.
// Per spec, "The initialize request MUST NOT be cancelled by clients", so skip registration for initialize.
LogRequestSentAwaitingResponse(EndpointName, request.Method, request.Id);
JsonRpcMessage? response;
using (var registration = RegisterCancellation(cancellationToken, request))
using (var registration = method != RequestMethods.Initialize ? RegisterCancellation(cancellationToken, request) : default)
{
response = await tcs.Task.WaitAsync(cancellationToken).ConfigureAwait(false);
}