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Islam Elsayed
56ae39bdcc
The active health check body is user-supplied and commonly JSON, but it
was expanded with ReplaceAll, which blanks any `{...}` the replacer does
not recognize. Only globals are available here, so a JSON
health_request_body was sent as an empty body.
This is not limited to bodies without placeholders. A body that does use
one is mangled too: `{"token":"{env.SOME_VAR}"}` is sent as `"}`, since
the opening `{"token":"` is consumed as an unrecognized placeholder
before the real one is reached.
Use ReplaceKnown, matching the header values a few lines below, so
unrecognized braces are left intact and real placeholders still expand.
Only the body is changed. The Host header on the same path keeps
ReplaceAll deliberately: Go's HTTP server blanks a Host containing
braces, so leaving `{...}` intact there would send a Host the upstream
discards, where blanking it lets Go fall back to the URL host.