gdunzip

Gdunzip is a zip file browser/decompressor written entirely in a single GDScript file. You can use this in games you're building with the Godot game engine. This script is meant for modest zip decompressing purposes, since the inflate algorithm it contains isn't super fast and gdunzip doesn't do CRC checks of the uncompressed files. However, gdunzip works fine if you only need to decompress small files, or when your zip files contain precompressed files like png's.

In order to create gdunzip, I have made a GDScript port of Jørgen Ibsen's excellent tiny inflate library: tinf for decompressing the deflate streams. Since the original was written in C and used some nifty pointer arithmetic, I had to make some minor changes here and there to be able to translate it. However, I tried to stay as close to the original code as possible.

The zip file format parsing is all written from scratch and performs pretty well.

Why I wrote gdunzip

I'm working on a little sideproject in Godot: a memorize app. In this app I will allow the user to import an ODS-file: the spreadsheet file format used by LibreOffice and OpenOffice. ODS-files are actually zip files, containing a bunch of xml files and some other assets. I couldn't find a ready-made ODS library for Godot, so I set out creating one. It would have been faster to just use GDNative and hand all the work to a C++ library, but since this is a hobby project and I haven't got much GDScript experience, I thought it would be fun to create it myself. The first step was of course to get an unzipper up and running. I found out that Godot's PoolByteArray has a "decompress" function that supports deflate streams, however these were all in the Zlib format, so you can't use it with regular zip files (zlib uses an Adler-32 checksum to verify decompressed data, but zip files only contain a CRC-32 checksum).

A more sensible person might have just stepped back and pulled some pre-existing C++ library off the shelf, however I thought it would be fun to dive in and gdunzip is the result :-).

Using gdunzip

• Grab gdunzip.gd.
• Put gdunzip.gd somewhere in your Godot project.
• Make an instance, load a file and start uncompressing:

# Instance the gdunzip script
var gdunzip = load('res://addons/gdunzip/gdunzip.gd').new()

# Load a zip file
var loaded = gdunzip.load('res://test.zip')

# Uncompress a file, getting a PoolByteArray in return 
# (or false if it failed uncompressing) 
if loaded:
    var uncompressed = gdunzip.uncompress('lorem.txt')
    if !uncompressed:
        print('Failed uncompressing lorem.txt')
    else:
        print(uncompressed.get_string_from_utf8())
else:
    print('Failed loading zip file')

• When gdunzip has loaded a zip file, you can iterate over all the files inside, by looping through the "files" attribute:

for f in gdunzip.files:
    print('File name: ' + f['file_name'])

    # "compression_method" will be either -1 for uncompressed data, or
    # File.COMPRESSION_DEFLATE for deflate streams
    print('Compression method: ' + str(f['compression_method']))

    print('Compressed size: ' + str(f['compressed_size']))

    print('Uncompressed size: ' + str(f['uncompressed_size']))

Class documentation

Member functions

Returns	Function name
bool	load(String path)
PoolByteArray	uncompress(String file_name)
PoolByteArray	get_compressed(String file_name)

Member function description

• bool load(String path)

Tries to load a zip file with a given path. Returns false if it failed loading the zip, or true if it was successfull.

• PoolByteArray uncompress(String file_name)

Try to uncompress the given file in the loaded zip. The file_name can include directories. This function returns false if the file can't be found, or if there's an error during uncompression.

• PoolByteArray get_compressed(String file_name)

Returns the compressed data for a given file name (or false if the file can't be found). Depending on the file compression it can be either uncompressed or a raw deflate stream. This function returns false if the file can't be found.

files attribute

After you have loaded a file, the gdunzip instance will have a pre-filled "files" attribute. This is simply an dictionary containing the meta data for the files that reside in the zip. The dictionary is a mapping from file name (including directory) to another dictionary with the following keys:

• file_name: the file name
• compression_method: -1 if uncompressed or File.COMPRESSION_DEFLATE
• file_header_offset: the exact byte location of this file's compressed data inside the zip file
• compressed_size: the compressed file size in bytes
• uncompressed_size: the uncompressed file size in bytes