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)
3. Usage
gzip value (binary!)
4. Example
write %test.tar.gz gzip read/binary %test.tar
5. 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
]
