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fix(mcp): detect 'unknown method' phrasing in ping keepalive fallback

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A server that doesn't implement the optional 'ping' utility answers a
keepalive ping with JSON-RPC method-not-found. _is_method_not_found_error
latches that condition so the probe falls back to list_tools instead of
reconnect-looping.

The substring fallback only matched 'method not found' / '-32601' /
'not found: ping'. Servers that surface method-not-found as the common
'Unknown method: <name>' phrasing without a structural -32601 code (e.g.
agentmemory's MCP server) slipped through, so the fallback never latched
and the keepalive reconnect-looped every cycle.

Add 'unknown method' to the substring fallback so the ping->list_tools
keepalive fallback latches for these servers too.

Fixes #50028.
This commit is contained in:
xxxigm 2026-06-21 14:54:02 +07:00 • committed by kshitij
parent 8ca38d3121
commit 472c068159
1 changed files with 8 additions and 0 deletions
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8
tools/mcp_tool.py
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@ -415,6 +415,13 @@ def _is_method_not_found_error(exc: BaseException) -> bool:
an empty result. Structurally inspect ``McpError.error.code`` first, then
fall back to a substring match so detection survives SDK version drift and
servers that surface the condition as a plain message.
The substring fallback matters when a server reports method-not-found
without a structural ``-32601`` code (e.g. surfaced as a plain exception
string). Besides the canonical "method not found", many JSON-RPC
implementations phrase it as "Unknown method: <name>" — agentmemory's MCP
server is one such case (#50028). Without matching that phrasing the
ping→list_tools fallback never latches and the keepalive reconnect-loops.
"""
# Structural: mcp.shared.exceptions.McpError carries ErrorData.code.
err = getattr(exc, "error", None)
@ -427,6 +434,7 @@ def _is_method_not_found_error(exc: BaseException) -> bool:
return (
str(_JSONRPC_METHOD_NOT_FOUND) in msg
or "method not found" in msg
or "unknown method" in msg
or "not found: ping" in msg
)