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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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2
mcp/transport.go
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@ -171,7 +171,7 @@ type canceller struct {
// Preempt implements [jsonrpc2.Preempter].
func (c *canceller) Preempt(ctx context.Context, req *jsonrpc.Request) (result any, err error) {
if req.Method == "notifications/cancelled" {
if req.Method == notificationCancelled {
var params CancelledParams
if err := json.Unmarshal(req.Params, &params); err != nil {
return nil, err