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mcp: fix cancellation for HTTP transport

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In #202, I added the checkRequest helper to validate incoming requests,
and invoked it in the stremable transports to preemptively reject
invalid HTTP requests, so that a jsonrpc error could be translated to an
HTTP error.

However, this introduced a bug: since cancellation was handled in the
jsonrpc2 layer, we never had to validate it in the mcp layer, and
therefore never added methodInfo. As a result, it was reported as an
invalid request in the http layer.

Add a test, and a fix. The simplest fix was to create stubs that are
placeholders for cancellation.

This was discovered in the course of investigating #285.
This commit is contained in:
Rob Findley 2025-08-13 15:37:56 +00:00 • committed by Robert Findley
commit bb6dadecca
1 changed files with 72 additions and 26 deletions
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10
mcp/client.go
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@ -305,6 +305,7 @@ var clientMethodInfos = map[string]methodInfo{
methodPing: newClientMethodInfo(clientSessionMethod((*ClientSession).ping), missingParamsOK),
methodListRoots: newClientMethodInfo(clientMethod((*Client).listRoots), missingParamsOK),
methodCreateMessage: newClientMethodInfo(clientMethod((*Client).createMessage), 0),
notificationCancelled: newClientMethodInfo(clientSessionMethod((*ClientSession).cancel), notification|missingParamsOK),
notificationToolListChanged: newClientMethodInfo(clientMethod((*Client).callToolChangedHandler), notification|missingParamsOK),
notificationPromptListChanged: newClientMethodInfo(clientMethod((*Client).callPromptChangedHandler), notification|missingParamsOK),
notificationResourceListChanged: newClientMethodInfo(clientMethod((*Client).callResourceChangedHandler), notification|missingParamsOK),
@ -344,6 +345,15 @@ func (*ClientSession) ping(context.Context, *PingParams) (*emptyResult, error) {
return &emptyResult{}, nil
}
// cancel is a placeholder: cancellation is handled the jsonrpc2 package.
//
// It should never be invoked in practice because cancellation is preempted,
// but having its signature here facilitates the construction of methodInfo
// that can be used to validate incoming cancellation notifications.
func (*ClientSession) cancel(context.Context, *CancelledParams) (Result, error) {
return nil, nil
}
func newClientRequest[P Params](cs *ClientSession, params P) *ClientRequest[P] {
return &ClientRequest[P]{Session: cs, Params: params}
}