fix: allow mcp-protocol-version request header in CORS preflight - #137
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shoemoney wants to merge 1 commit into
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fix: allow mcp-protocol-version request header in CORS preflight#137shoemoney wants to merge 1 commit into
shoemoney wants to merge 1 commit into
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The cors() options already expose mcp-protocol-version via exposedHeaders, but allowedHeaders omitted it. The official StreamableHTTPClientTransport sends mcp-protocol-version on every request after initialize, so any browser-based client permitted via ALLOWED_ORIGINS failed the CORS preflight once initialization completed. Add the header to allowedHeaders in the server and in the mirrored transport test fixture, and add a preflight regression test.
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The cors() options in src/http.ts list
mcp-protocol-versioninexposedHeadersbut omit it fromallowedHeaders, which only permitsContent-Typeandmcp-session-id. The official @modelcontextprotocol/sdk StreamableHTTPClientTransport sends themcp-protocol-versionheader on every request after initialization, so a browser-based client permitted via ALLOWED_ORIGINS (per SECURITY.md) completes initialize and then fails every subsequent request at the CORS preflight.Since
exposedHeadersalready lists the header, the intent to support it is clear. This adds it toallowedHeadersin the server and in the mirrored fixture in src/transport.test.ts, plus a preflight regression test in src/http.config.test.ts assertingAccess-Control-Allow-Headersincludesmcp-protocol-version.Full suite passes (90 tests) and tsc builds clean.