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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
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1 changed files with 99 additions and 3 deletions
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53
tests/ModelContextProtocol.Tests/Server/McpServerTests.cs
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@ -861,6 +861,59 @@ public class McpServerTests : LoggedTest
Assert.Same(logNotification, transport.SentMessages[0]);
}
[Fact]
public async Task Server_IgnoresCancellationNotificationForInitializeRequest()
{
// Arrange
await using var transport = new TestServerTransport();
await using McpServer server = McpServer.Create(transport, _options, LoggerFactory);
var runTask = server.RunAsync(TestContext.Current.CancellationToken);
// Set up to capture the initialize response
var initializeRequest = new JsonRpcRequest
{
Id = new RequestId("init-cancel-test"),
Method = RequestMethods.Initialize,
Params = JsonSerializer.SerializeToNode(new InitializeRequestParams
{
ProtocolVersion = "2024-11-05",
Capabilities = new ClientCapabilities(),
ClientInfo = new Implementation { Name = "test-client", Version = "1.0.0" }
}, McpJsonUtilities.DefaultOptions)
};
var initResponseTcs = new TaskCompletionSource<JsonRpcResponse>();
transport.OnMessageSent = (message) =>
{
if (message is JsonRpcResponse response && response.Id == initializeRequest.Id)
{
initResponseTcs.TrySetResult(response);
}
};
// Act: Send initialize request and immediately send a cancellation notification for it.
// Per spec, "The initialize request MUST NOT be cancelled by clients", so the server
// should ignore the cancellation and still complete the initialize request.
await transport.SendClientMessageAsync(initializeRequest, TestContext.Current.CancellationToken);
await transport.SendClientMessageAsync(new JsonRpcNotification
{
Method = NotificationMethods.CancelledNotification,
Params = JsonSerializer.SerializeToNode(
new CancelledNotificationParams { RequestId = initializeRequest.Id },
McpJsonUtilities.DefaultOptions),
}, TestContext.Current.CancellationToken);
// Assert: The initialize response should still arrive (not cancelled)
var response = await initResponseTcs.Task.WaitAsync(TestConstants.DefaultTimeout, TestContext.Current.CancellationToken);
Assert.NotNull(response.Result);
var initResult = JsonSerializer.Deserialize<InitializeResult>(response.Result, McpJsonUtilities.DefaultOptions);
Assert.NotNull(initResult);
Assert.NotNull(initResult.ServerInfo);
await transport.DisposeAsync();
await runTask;
}
private static async Task InitializeServerAsync(TestServerTransport transport, ClientCapabilities capabilities, CancellationToken cancellationToken = default)
{
var initializeRequest = new JsonRpcRequest