Documention for: oneliner-gzip.r3
Created by: vincentecuye
 on: 30-Jan-2013
Last updated by: vincentecuye on: 30-Jan-2013
Format: text/editable
Downloaded on: 30-Apr-2025

oneliner-gzip.r3
    Author: Vincent Ecuyer
    Date: 30-Jan-2013

===Purpose

Creates gzip compatible archives.

===Limitations

To keep the code short, a number of gzip files optional capabilities aren't implemented:

*REBOL 3 only

*No filename in archive (optional : gzip tools assumes the filename is the same as the source without the .gz extension)

*No timestamp in archive (not a big problem with .tar archive, as tar and gzip are often used together)

===Usage

    gzip value (binary!)

===Example

    write %test.tar.gz gzip read/binary %test.tar

===Commented Code

    gzip: func [
        "Compresses a binary and returns it in gzip format"
        value [binary!] "Data to compress"
    ][
        ; In a gzip file, the last four bytes holds the data size, 
        ; and the four bytes before holds the crc32.

        ; 'compress uses another crc method,
        ; so the crc bytes must be replaced 

        ; replaces the crc by a crc32:
        head change at tail 
            ; joins a gzip header to a 'compress stream,
            ; skipping the 'compress zlib header (2 bytes)
            join #{1F8B08000000000002FF} skip compress value 2

            ; "at tail data -8" means at 8 bytes before the end of the data
            -8

            ; builds a four bytes value with the crc-32 in little endian order
            ; ('to-binary on an integer! gives a 8 bytes result)
            reverse skip to-binary checksum/method value 'crc32 4
    ]