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The codec capability table

Source: R/codecs.R
komp_codecs.Rd

Every codec this build of zukomp knows the name of, whether or not an implementation is present, plus any codec registered by another package. This is the R-visible face of the registry: it is how you discover what can be compressed, at what levels, and which HTTP content-coding each codec corresponds to.

Usage

komp_codecs()

Value

A data frame with one row per codec and the columns:

id

Codec name, as accepted by the codec argument elsewhere.

available

Is an implementation registered?

can_encode, can_decode

Supported directions; NA if unavailable.

level_min, level_max, level_default

Codec-native compression levels. NA when the codec has no level axis, and when it is unavailable. Levels are not comparable between codecs.

level_fast, level_best

Where the abstract levels "fast" and "best" land for this codec. These are not level_min and level_max: for the DEFLATE family level 0 is stored blocks, so "fast" is 1, and a codec whose level is an acceleration factor inverts the mapping entirely. Only the codec knows, so it declares them.

detectable

Can komp_detect() recognise this codec from its bytes? Headerless formats cannot be detected and must be named.

can_flush

Does the codec support a mid-stream flush – "put the bytes on the wire now"? NA if unavailable. A caller streaming a request body should check this before committing to a codec, rather than discovering it mid-body.

content_encoding

The HTTP content-coding token, or NA.

source

Package that registered the implementation, or NA.

Details

A codec that is declared but not installed still gets a row, with available = FALSE and NA for everything capability-shaped. That is deliberate: "zstd exists but you need the zukomp.zstd package" is a more useful answer than pretending the codec does not exist.

References

The built-in codecs implement the formats specified in Deutsch, P. (1996) "DEFLATE Compressed Data Format Specification version 1.3", RFC 1951, doi:10.17487/RFC1951 ; Deutsch, P. and Gailly, J-L. (1996) "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, doi:10.17487/RFC1950 ; and Deutsch, P. (1996) "GZIP file format specification version 4.3", RFC 1952, doi:10.17487/RFC1952 .

Examples

codecs <- komp_codecs()
codecs[, c("id", "available", "content_encoding")]
#>              id available content_encoding
#> 1      identity      TRUE         identity
#> 2   deflate-raw      TRUE             <NA>
#> 3          zlib      TRUE          deflate
#> 4          gzip      TRUE             gzip
#> 5        brotli     FALSE               br
#> 6          zstd     FALSE             zstd
#> 7     lz4-frame     FALSE             <NA>
#> 8     lz4-block     FALSE             <NA>
#> 9  snappy-frame     FALSE             <NA>
#> 10   snappy-raw     FALSE             <NA>

# what this build can actually decompress right now
codecs$id[which(codecs$can_decode)]
#> [1] "identity"    "deflate-raw" "zlib"        "gzip"