The request Accept-Encoding offered only gzip even though the response
parser already recognized deflate/x-deflate. But the actual decode path
(hts_zunpack) used zlib's gzread, which only inflates gzip and copies any
deflate body through verbatim, so a deflate response would have been
written out still compressed. Advertising deflate without fixing that
would corrupt files.
Rewrite hts_zunpack to inflate via inflateInit2 with format detection:
gzip and zlib (RFC1950) auto-detect with +32 windowBits, everything else
is treated as raw deflate (RFC1951). Then add deflate to the advertised
list through a small hts_acceptencoding() helper shared with the test.
A new -#test=acceptencoding self-test asserts the advertised header
carries both gzip and deflate, and round-trips gzip, zlib and raw-deflate
bodies through hts_zunpack on disk. Both halves fail on the old binary.
Brotli is intentionally out of scope (new dependency, larger change).
Signed-off-by: Xavier Roche <roche@httrack.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
