fix: allow RESPONSE_CODE_DETAILS and START_TIME in error page#277
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mattdjenkinson merged 2 commits intoJul 15, 2026
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The branded 5xx error page served on the downstream data plane shows a "Status code", "Error details", and "Timestamp" row. Only the first one ever rendered — the other two printed their literal Envoy %OPERATOR% tokens instead of real values. envoyBodyAllowedCommands only permitted %RESPONSE_CODE% through the escaper. Every other %...% token, including %RESPONSE_CODE_DETAILS% and %START_TIME(%Y-%m-%d %H:%M:%S UTC)%, got its percent signs doubled to %%, which Envoy renders back as a literal percent instead of invoking the operator. Add both operators to the allowlist so they resolve like %RESPONSE_CODE% already does.
mattdjenkinson
marked this pull request as ready for review
July 14, 2026 14:32
scotwells
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Jul 14, 2026
mattdjenkinson
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July 15, 2026 09:42
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Summary
The branded 5xx error page served on the downstream data plane has three fields: status code, error details, and a timestamp. Only the status code ever rendered. The other two showed up as literal Envoy
%OPERATOR%tokens instead of real values.The escaper that prepares this page for Envoy (
escapeEnvoyFormatLiterals) only allowlists%RESPONSE_CODE%. Every other%...%token, including%RESPONSE_CODE_DETAILS%and%START_TIME(%Y-%m-%d %H:%M:%S UTC)%, gets its percent signs doubled to%%, which Envoy renders back as a literal%instead of invoking the operator. This is deliberate (issue #243: an unescaped literal%in this page's CSS once caused the whole listener xDS update to be rejected), but the allowlist was never extended past the one operator it shipped with.This adds both operators to
envoyBodyAllowedCommandsso they resolve the same way%RESPONSE_CODE%already does.Verified with new cases in
TestEscapeEnvoyFormatLiteralscovering both operators, plus the existingTestEmbeddedDefaultPageIsEnvoySaferegression guard, all passing.