fix(static): skip magic-number pread under directio (O_DIRECT EINVAL)#75
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When "directio <size>" is configured, ngx_open_cached_file() opens the .zst with O_DIRECT once the file meets the threshold. The static handler's 4-byte magic-number sanity probe then issues a deliberately tiny, unaligned pread() — but an O_DIRECT read requires buffer, offset and length all aligned to the device block size, so the probe fails EINVAL on every request. The handler treated that as a failed read and declined, wrongly refusing to serve every .zst above the directio threshold and spamming NGX_LOG_CRIT once per request. The probe is only a best-effort corruption guard, so skip it when of.is_directio: the precompressed file is still served, just without the magic sanity check (which O_DIRECT alignment makes impossible to run cheaply here anyway). Test (t/01-static.t TEST 26): zstd_static on + directio 1 serves the .zst with 200 + Content-Encoding: zstd and no [error]/CRIT. O_DIRECT is filesystem-dependent, so the test deterministically catches the declined+CRIT regression where O_DIRECT engages and still asserts correct serving elsewhere. Verified to fail on pre-fix code.
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MAJOR from module audit.
Problem
With
directio <size>configured,ngx_open_cached_file()opens the.zstwithO_DIRECTonce the file meets the threshold. The static handler then runs its 4-byte magic-number sanity probe with an unalignedpread()— but anO_DIRECTread requires buffer, offset and length all aligned to the device block size, so the probe fails EINVAL on every request. The handler treated that as a failed read → declined every.zstabove the directio threshold and spammedNGX_LOG_CRITonce per request.Fix
Skip the probe when
of.is_directio. It is only a best-effort corruption guard; the precompressed file is still served, just without the magic check (which O_DIRECT alignment makes impossible to run cheaply here anyway).Test
t/01-static.tTEST 26 —zstd_static on; directio 1;serves the.zstwith200+Content-Encoding: zstd, no[error]/CRIT. O_DIRECT is filesystem-dependent, so the test deterministically catches the declined+CRIT regression where O_DIRECT engages and still asserts correct serving elsewhere. Verified to fail on pre-fix code.Local:
prove t/01-static.t= 303/303 PASS.