`ping` and `logging/setLevel` still sent for protocol 2026-07-28

Aperta
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Dal 13/11/2026.

Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
65/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
go
Ambito
api, backend

Direzione di ricerca

Start in the client session methods ClientSession.Ping and ClientSession.SetLoggingLevel, then read the keepalive loop and the protocol-version negotiation path. Check how other requests handle protocol metadata and how server.go rejects removed methods. Done means these calls and keepalive do not send unsupported methods for protocol 2026-07-28, and the session remains usable afterward.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Checklist
  • I searched the existing issues, and this has not been reported before.
  • This is a real problem that I ran into myself, using the latest release of the SDK.
  • I ran into it in a production system, not in a toy example, a benchmark, or an automated or AI-driven scan of the code.
  • I (a human) examined the relevant SDK code, and wrote or reviewed every line of this report. It is not unreviewed AI output.
  • This report is brief and concise, and sticks to the facts needed to understand the problem.
What happened?

SEP-2575 (protocol 2026-07-28) removed ping and logging/setLevel. The SDK's own server rejects them on the new protocol (server.go, the case methodInitialize, methodPing, ..., methodSetLevel branch). On the client side, however, ClientSession.Ping and ClientSession.SetLoggingLevel still send them on a session that negotiated 2026-07-28:

  • the Mcp-Protocol-Version: 2026-07-28 header is set (the streamable transport falls back to the negotiated version);
  • unlike ListTools, CallTool, etc., neither method calls injectRequestMeta, so the body has no params._meta envelope. Ping goes out as {"jsonrpc":"2.0","id":N,"method":"ping"}.

A strict 2026-07-28 server such as python mcp 2.3.0 answers HTTP 400 / -32602 ("params._meta must be an object carrying the required 'io.modelcontextprotocol/protocolVersion' and 'io.modelcontextprotocol/clientCapabilities' envelope keys"). With the envelope present it answers HTTP 404 / -32601. In both cases streamableClientConn.Write treats the non-2xx as fatal and calls c.fail(err), so the whole session is closed. Every later request fails with client is closing: sending "ping": ... Bad Request.

Anything that pings for liveness or keepalive (for example ClientOptions.KeepAlive, or an application health check) therefore kills a healthy session against such servers.

Reproduce
See below.

Expected

On a session with ProtocolVersion >= 2026-07-28, Ping and SetLoggingLevel should not put a removed method on the wire. Returning a client-side error, for example "ping is not supported in protocol 2026-07-28", would let callers fall back. The keepalive loop should likewise not use ping on such sessions. Adding _meta alone would not fix this, because the methods no longer exist and the server answers 404, which also closes the session.

Workaround

Check sess.InitializeResult().ProtocolVersion and, on 2026-07-28 sessions, use a supported request (for example tools/list) for liveness, and skip SetLoggingLevel.

How to reproduce
1. Run a python `mcp` 2.3.0 server (for example FastMCP 4.0.11, `http_app(stateless_http=True)`).

2. Connect with go-sdk: `server/discover` succeeds and `2026-07-28` is negotiated.

3. `sess.ListTools(ctx, nil)` succeeds.

4. `sess.Ping(ctx, nil)` returns `... envelope keys: Bad Request`.

5. `sess.ListTools(ctx, nil)` now returns `connection closed: ... client is closing ...`.
Where did you hit this?

In production at work.

Go MCP SDK version

1.7

Go version

latest

Logs
No logs available.
Lingua principale
Go
Stelle
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Fork
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Merge medio
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