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

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@nahapetyan-serob 已经在做这个了。

开始于 2026年11月13日。

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新手友好度
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Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
go
领域
api, backend

调研方向

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.

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描述

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

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