stacklok / toolhive / 30076713529

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push

github

Committed by web-flow

Commit Message

Add opt-in strict MCP-Protocol-Version validation (#5957)

The streamable HTTP proxy accepted any MCP-Protocol-Version header
(isSupportedMCPVersion always returned true). This was an undocumented,
deliberately permissive stance: defensible for a transport-level proxy
that does not depend on a specific MCP revision, but the spec says a
server MUST reject an invalid/unsupported version with HTTP 400, and
operators had no way to opt into that behavior.

Add a --strict-protocol-validation flag (default off, preserving the
version-agnostic behavior byte-for-byte). When enabled, the proxy rejects
a request whose MCP-Protocol-Version header names an unknown MCP revision
with HTTP 400; an absent header is still accepted (the spec says to assume
2025-03-26). The known-version set is checked against a small map, with
the upcoming stateless revision sourced from mcp.MCPVersionModern so the
strict gate and the ClassifyRevision routing path cannot drift.

The flag is threaded end-to-end mirroring TrustProxyHeaders: CLI ->
RunConfig -> types.Config -> StdioTransport -> streamable proxy option,
and is preserved across thv upgrade via the config applier. The default
version-agnostic stance and the opt-in flag are documented in
docs/arch/03-transport-architecture.md.

Closes #5764.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Coverage Stats

38 of 39 new or added lines in 8 files covered. (97.44%)

12 existing lines in 4 files now uncovered.

77834 of 112417 relevant lines covered (69.24%)

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