komp_codecs: The codec capability table

In zukomp: Portable Byte Compression with a Pluggable Codec Registry

The codec capability table

Description

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()

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.

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.

References

The built-in codecs implement the formats specified in Deutsch, P. (1996) "DEFLATE Compressed Data Format Specification version 1.3", RFC 1951, \Sexpr[results=rd]{tools:::Rd_expr_doi("10.17487/RFC1951")}; Deutsch, P. and Gailly, J-L. (1996) "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, \Sexpr[results=rd]{tools:::Rd_expr_doi("10.17487/RFC1950")}; and Deutsch, P. (1996) "GZIP file format specification version 4.3", RFC 1952, \Sexpr[results=rd]{tools:::Rd_expr_doi("10.17487/RFC1952")}.

Examples

codecs <- komp_codecs()
codecs[, c("id", "available", "content_encoding")]

# what this build can actually decompress right now
codecs$id[which(codecs$can_decode)]

zukomp documentation built on Oct. 16, 2026, 5:09 p.m.