fix(router): stop dropping client-sent default headers like anthropic-version#320
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johntmyers merged 1 commit intomainfrom Mar 15, 2026
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…-version The strip_headers list in send_backend_request included default_headers names (e.g. anthropic-version), which removed the client's value. The already_sent check then saw the original input still contained the header and skipped injecting the route default. Neither value reached upstream. Remove default_headers names from strip_headers so client values pass through. The existing already_sent guard still injects defaults only when the client omits them.
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…-version (#320) The strip_headers list in send_backend_request included default_headers names (e.g. anthropic-version), which removed the client's value. The already_sent check then saw the original input still contained the header and skipped injecting the route default. Neither value reached upstream. Remove default_headers names from strip_headers so client values pass through. The existing already_sent guard still injects defaults only when the client omits them.
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Summary
Fix a bug where client-sent headers that match route
default_headersnames (e.g.anthropic-version) are silently dropped, causing upstream API errors for third-party clients like OpenClaw.Related Issue
N/A — reported via direct debugging session.
Changes
default_headersnames from thestrip_headerslist insend_backend_request(backend.rs). Only auth headers (authorization,x-api-key) andhostare stripped now.proxy_forwards_client_anthropic_version_headerthat verifies a client-sentanthropic-versionheader reaches the upstream.Root Cause
send_backend_requestaddeddefault_headersnames tostrip_headers, which removed the client's value in the forwarding loop. The subsequentalready_sentcheck looked at the original input headers, saw the client had sent it, and skipped injecting the route default. Neither the client's value nor the default reached the upstream.After the fix:
already_sent = true, default skipped. Client value wins.already_sent = false, default injected. Route default wins.Auth headers are still unconditionally stripped and re-injected via the route's auth mechanism — no security regression.
Testing
mise run pre-commitpassesChecklist