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Bled - Base Library for Easy Decompression

What's this then?

This is Bled, the Base Library for Easy Decompression. It is based almost entirely on the native decompression code found in BusyBox.

What's it for?

It's a library, that can be used in applications to handle the decompression of .Z, .gz, .bz2, .lzma, .xz, .zip compressed files and/or archives.

Why are you doing that?

Because I need this stuff for Rufus, mostly to handle compressed disk images, and nobody outside of BusyBox seems to have put much effort providing a compact, one-size-fits-all Open Source library, for decompressing the most common formats.

As I am very conscious of size in Rufus, and Busybox is targeted at embedded systems, its decompression library seemed like a natural choice. Sure, the 7-Zip LZMA SDK is nice, and compiles nicely on Windows, but it only supports lzma/lzma2/xz (+.7z archives), so you'll need to add stuff like miniz, and then some more, and soon enough you're dealing with multiple APIs and a lot of duplicated code. Plus these libraries also provide compression support, which we don't need, so the whole thing becomes quite large.

What's the license?

GPLv2 or later.

While the BusyBox project as a whole is GPLv2 only, this library is GPLv2 or later, which means it can be used indiscriminately in GPLv2 or GPLv3 projects. This is possible because the BusyBox sources we used were all explictly tagged GPLv2 or later and any source that wasn't (libbb.h, crc32.c, decompress_unxz.c) has been recreated/replaced with versions that are. Also, since we're not using any part of bzlib there's no additional license notice required. So this really is a pure GPLv2 or later decompression library, for the most common compression formats.

What about compressed tar archives?

I'm not planning to handle these, because I have no need for tar extraction in Rufus. However, since tar archive handling is present in the BusyBox sources, I may accept a patch if you feel like adding support for it.

What about .rar?

Not planning to add support for RAR, unless a truly Free Source (GPL) RAR decompression comes along.

Are there any limitations?

  • Only Windows is supported for now (MinGW/gcc and MSVC). That's because:
    • Windows is the only platform I need for Rufus
    • The original libbb.h was GPLv2 only, so I had to recreate my own from scratch that is GPLv2 or later. This was a bit of a pain, so I don't want to bother recreating a GPLv2+ libbb.h for Linux or other platforms.
  • Can't query the uncompressed file size. This is mostly due to the limitation of the compression formats being used, as most of them are stream formats and do not store that information anywhere.
  • .7z archive extraction is not supported.
  • No multithreading and not optimized for speed at all!
  • There probably exist limitations with regards to advanced compression and/or newer compression formats.

Alright I'm sold. What do I need?

Either:

  • Visual Studio 2022
  • MinGW

Then use the .sln file or run configure + make.

Is the name a reference to Bled, Slovenia?

It is. You should visit Slovenia too, if you ever have a chance.