hwzip.zig

What's hwzip.zig?

It's a port in Zig of the program hwzip-2.1 written by Hans Wennborg.

Zip Files: History, Explanation and Implementation
Shrink, Reduce, and Implode: The Legacy Zip Compression Methods

hwzip is an example implementation written in C of the Zip file format.

hwzip.zig is a Zig version in an attempt to make it more accessible.

I tried to make the least amount of changes possible so that one can still follow the article with the Zig code instead of C. This means it's not idiomatic Zig code, it's more a translation than a port.

Why hwzip.zig?

Because you can compile, test and run it without any dependencies (except Zig). The C version requires the usual hell of building utilities, the Info-ZIP binary, and links into zlib.
I needed a way to compress files in Zig.
I wanted to learn about Zip files and Zig is much more readable to me than C.

Building instructions

Download and install Zig 0.9.1

To build the binary in ./zig-out/bin/hwzip you need to run

zig build

Testing instructions

zig build test

Usage

Executing without any arguments print the help message

./hwzip list <zipfile>
./hwzip extract <zipfile>
./hwzip create <zipfile> [-m <method>] [-c <comment>] <files...>

Supported compression methods: 
store, shrink, reduce, implode, deflate (default).

List of changes from hwzip-2.1

The debug field huffman_decoder_t.num_syms is commented out.
Fuzz tests are missing.
Uses std.hash.crc32() from Zig instead of a custom one.
Uses epoch dos date for dates before 1980-01-01 in zip.ctime2dos()
The table reverse8_tbl is replaced by the function bits.reverse8().

Limitations

hwzip.zig comes with no warranties, I may have introduced bugs which are not in the original version hwzip-2.1.

You cannot recursively compress files within a directory, you need to list all files that you want to add to the archive.

This utility is slow and is not meant for daily use, you should use more serious tools like Info-ZIP, 7zip or gzip to compress your files.

License

The ./doc directory contains a copy of the articles explaining the Zip file format which are under Hans Wennborg copyright.

time.zig is a port of some portion of src/time from musl libc and as such this file is under the standard MIT license, see the LICENSE-time-dot-zig file.

The rest is public domain unless specified otherwise, see the LICENSE file.

README