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core: client notifications carry "id":null; JSON-RPC notifications omit id #1520
Description
core.Request.MarshalJSON always emits "id", so every notification the client sends goes out as {"jsonrpc":"2.0","id":null,"method":"notifications/initialized"}. JSON-RPC 2.0 defines a notification as a request object without an id member. With "id":null it's a request with a null id, which the spec discourages and a strict peer may answer or reject. It applies to every transport, since client.notifyMethod marshals through core.Request.
Seen while fixing #1517 (client/stdio_framing_test.go asserts the method rather than the exact bytes because of it). Both reference SDKs tolerate it today: @modelcontextprotocol/server-everything (TS, via tests/e2e/stdio_interop_test.go) and the Python mcp 2.3.0 client session against our server. So nothing is broken that we know of.
Wanted
- Omit
idwhenRequest.IDis nil (json:"id,omitempty"in the marshal shim), and check the server'sIsNotificationand the stateless wire still classify both shapes the same way. - A wire test pinning a notification's exact bytes.
waiting — trigger: a peer rejects or answers an mcpkit notification, or the 1.0 wire freeze (#1356 is the same kind of decision).
Activity
panyam commentedon Oct 14, 2026
Planned 2026-10-14, parked in favour of #1502. Two more findings for whoever picks it up:
server/dispatch.go:377(panic recovery) checksreq.ID != nil, so a notification sent with"id":nullwhose handler panics gets a-32603response. Everywhere else usesreq.IsNotification(), which treats nil andnullalike; use it here too.omitemptyonidin theRequest.MarshalJSONshim (an explicitjson.RawMessage("null")would still be written).core.Responsestays as is. No fixture in the tree pins"id":null, and server-side notifications already omitidviacore.MarshalNotification. Tightenclient/stdio_framing_test.goback to an exact-bytes check as the wire test.panyam commentedon Oct 16, 2026
P3/waiting → P2: JSON-RPC wire correctness, which mission #1552 covers; it was parked only because no mission held it.