[omrzk]

MatchReader assumes one Read fills its header buffer. A valid PNG or JPEG supplied through iotest.OneByteReader therefore returns unknown, while a three-byte ICO prefix is accepted after zero padding supplies a missing signature byte.

Read at most 8192 bytes across short reads and pass only the received bytes to Match. EOF after a short header is accepted; empty input now returns ErrEmptyBuffer, consistently with Match. Other read errors propagate. The reader remains consumed; an unclosed stream may wait for the full prefix or EOF.

Validation: the new fragmented-header, truncated-ICO, empty-input, read-limit and read-error regressions fail on current master. All tests pass with Go 1.16.15 and with Go 1.26.10 under the race detector (five repetitions, vet disabled). Formatting and git diff --check pass. Go 1.26 vet's existing sync.Map copy diagnostic in filetype.go:11 was already reproduced on this unchanged master in the previous contribution; it is outside this patch. Hosted Go 1.19–1.21 CI has not run locally.