Identify the codec that produced a compressed stream

Detection is a property of the codec registry, not a hardcoded list: a codec registered by another package becomes detectable as soon as it advertises magic bytes.

Usage

komp_detect(x)

Arguments

x

A raw vector; only the leading bytes are examined.

Value

The codec's name, or NA_character_ if nothing matched.

Details

Not every format can be detected. Raw DEFLATE, raw LZ4 blocks, raw Snappy and brotli have no header to recognise, so they return NA and must be named explicitly. This is deliberate: guessing wrong for a headerless format means silently returning the wrong bytes.

zlib is recognised by a header predicate rather than a constant, so it carries a small false-positive rate – roughly one arbitrary byte pair in a thousand looks like a valid zlib header. Codecs with real magic are always tested first.

See also

komp_codecs(), whose detectable column says which codecs can be found this way.

Examples

komp_detect(komp_compress(charToRaw("hello"), "gzip"))
#> [1] "gzip"
komp_detect(komp_compress(charToRaw("hello"), "zlib"))
#> [1] "zlib"

# headerless formats are not guessed at
komp_detect(komp_compress(charToRaw("hello"), "deflate-raw"))
#> [1] NA