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fix(streamable_http): stop sending a spec-incorrect Origin header - #154
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build_common_headers set `Origin` to the MCP endpoint's own URL, path included. RFC 6454 §7 defines Origin as scheme + host [+ port] only, so that value can never match a server allowlist. The MCP Streamable HTTP spec asks servers to validate Origin against DNS rebinding, and servers that do (GitHub's remote MCP, Metabase, Grafana...) reject every request with 403. A server-to-server client has no browser origin to report, and the reference TypeScript and Python SDKs send none. Drop the automatic header. An Origin passed explicitly through the `headers` option is still forwarded untouched. Fixes patvice#140
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Heads up @guizaols: I pushed an empty commit ( |
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CI passes and this change looks good. Thanks for the contribution @guizaols |
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Problem
StreamableHTTP#build_common_headerssetsOriginto the MCP endpoint's own URL, path included — e.g.Origin: https://api.githubcopilot.com/mcp/.Originvalue asscheme "://" host [ ":" port ]. A path is never part of it, so no server allowlist can match what the gem sends.Originto prevent DNS rebinding. Servers that do so (GitHub's remote MCP server, Metabase's MCP endpoint, Grafana, …) reject every request with403/"Origin not allowed", regardless of how the server-side allowlist is configured.Originheader at all.Reproduction and sources are in #140. The
prependworkaround posted there (removingOriginfrombuild_common_headers) is what affected users are running in production today; this PR makes it unnecessary.Fix
Remove the one line that sets the header. Nothing else changes:
Originpassed explicitly via theheadersoption is still forwarded untouched, for anyone who genuinely needs one.Origin, so it is unaffected.Tests
Two specs added to
streamable_http_spec.rb:OriginOriginis preservedThe first spec fails on
mainand passes with this change.bundle exec rspec spec/ruby_llm/mcp/native/transports/streamable_http_spec.rbis green (142 examples),rubocopclean.Fixes #140