zzlib

Copyright (c) 2019-2024 by François Galea (fgalea à free.fr)

This is a pure Lua implementation of a depacker for the zlib DEFLATE(RFC1951)/GZIP(RFC1952) file format. zzlib also allows the decoding of zlib-compressed data (RFC1950). Also featured is basic support for extracting files from DEFLATE-compressed ZIP archives (no support for encryption).

The implementation is pretty fast. It makes use of the built-in bit32 (PUC-Rio Lua) or bit (LuaJIT) libraries for bitwise operations. Typical run times to depack lua-5.3.3.tar.gz on a single Core i7-6600U are 0.87s with Lua ≤ 5.2, 0.50s with Lua 5.3, and 0.17s with LuaJIT 2.1.0.

zzlib is distributed under the WTFPL licence. See the COPYING file or http://www.wtfpl.net/ for more details.

Usage

There are various ways of using the library.

Stream from a GZIP file

-- import the zzlib library
zzlib = require("zzlib")

-- get the unpacked contents of the file in the 'output' string
local output,err = zzlib.gunzipf("input.gz")
if not output then error(err) end

Read GZIP/zlib data from a string

Read a file into a string, call the depacker, and get a string with the unpacked file contents, as follows:

-- import the zzlib library
zzlib = require("zzlib")
...

if use_gzip then
  -- unpack the gzip input data to the 'output' string
  output = zzlib.gunzip(input)
else
  -- unpack the zlib input data to the 'output' string
  output = zzlib.inflate(input)
end

Extract a file from a ZIP archive stored in a string

Read a file into a string, call the depacker, and get a string with the unpacked contents of the chosen file, as follows:

-- import the zzlib library
zzlib = require("zzlib")
...

-- extract a specific file from the input zip file
output = zzlib.unzip(input,"lua-5.3.4/README")

Process the list of files from a ZIP archive stored in a string

The zzlib.files() iterator function allows you to span the whole list of files in a ZIP archive, as follows:

for _,name,offset,size,packed,crc in zzlib.files(input) do
  print(string.format("%10d",size),name)
end

During such a loop, the packed boolean variable is set to true if the current file is packed. You may then decide to unpack it using this function call:

output = zzlib.unzip(input,offset,crc)

If the file is not packed, then you can directly extract its contents using string.sub:

output = input:sub(offset,offset+size-1)