squiz-box ~fix-zip

Squiz-Box

A D library that handles compression / decompression and archiving.

In the Squiz-Box terminology, squiz refers to compression/decompression, while box refers to archiving. Squiz-Box API consists almost exclusively of range algorithms. squiz related algorithms map a range of bytes to another range of bytes where one is the compressed stream of the other. box and unbox related algorithms map a range of file entries to/from a range of bytes.

Squiz-Box provides both compile time known structures and dynamic types over all algorithms.

Compression / decompression

The range based design makes squizing suitable for streaming and for transforming data from any kind of source to any kind of destination.

Algorithms and formats

An algorithm refers to the compression algorithm properly, and format refers to a header and a trailer attached to the compressed data that gives information about decompression parameters and integrity checking. A raw format refers to data compressed without such header and trailer and can be used only in applications or archive that know how to decompress the stream by other means.

Algorithms	Squiz structs	Available formats
Deflate	Deflate (compression), Inflate (decompression)	Zlib, Gzip, Raw
Bzip2	CompressBzip2, DecompressBzip2	Bzip2
LZMA1 (legacy compression)	CompressLzma, DecompressLzma	Xz, Lzma (legacy format), Raw
LZMA (aka. LZMA2)	CompressLzma, DecompressLzma	Xz, Raw
Zstandard	CompressZstd, DecompressZstd	Zstandard

In addition, the LZMA1 and LZMA compression also support additional filters that transorm the data before the compression stage in order to increase the compression ratio:

• Delta
• higher compression of repetitive binary data such as audio PCM, RGB...
• BCJ (Branch/Call/Jump)
• higher compression of compiled executable
• available for different architectures (X86, ARM, ...)

API

Algorithms are represented by structs that share a common interface. Constructed objects from those structs carry parameters for compression / decompression and can instantiate a stream (class that derives SquizStream) that will carry the necessary state as well as input and output buffer.

To process these algorithms and streams as D ranges, you use the squiz function. The squiz function works for both compression and decompression and there are many helpers built upon it (deflate, inflate, compressXz, ...). See code examples below for usage.

Archiving

Whenever possible, archving and de-archiving are implemented as the transformation of a range of file entries to a range of bytes. It is never required to have the full archive in memory at the same time, so it is possible to create or extract archives of dozens of giga-bytes with minimal memory foot print.

The following formats are supported:

• Tar (including .tar.gz, .tar.bz2, .tar.xz)
• Zip

There is also WIP for 7z.

Archive update is not supported at this stage.

Code examples

Compress data with zlib

import squiz_box;
import std.range;

const ubyte[] data = myDataToCompress();

auto algo = Deflate.init; // defaults to zlib format

only(data)              // InputRange of const(ubyte)[] (uncompressed)
  .squiz(algo)          // also InputRange of const(ubyte)[] (deflated)
  .sendOverNetwork();

// the following code is equivalent
only(data)
  .deflate()
  .sendOverNetwork();

Re-inflate data with zlib

import squiz_box;
import std.array;

const data = receiveFromNetwork() // InputRange of const(ubyte)[]
  .inflate()
  .join();                        // const(ubyte)[]

Create an archive from a directory

Zip a directory:

import squiz_box;

import std.algorithm;
import std.file;

const root = buildNormalizedPath(someDir);

dirEntries(root, SpanMode.breadth, false)
    .filter!(e => !e.isDir)
    .map!(e => fileEntry(e.name, root, null))    // range of FileBoxEntry
    .boxZip()                                    // range of bytes
    .writeBinaryFile("some-dir.zip");

Create a .tar.xz file from a directory (with little bit more control):

import squiz_box;

import std.algorithm;
import std.file;
import std.path;

const root = squizBoxDir;

// prefix all files path in the archive
// don't forget the trailing '/'!
const prefix = "squiz-box-12.5/";

const exclusion = [".git", ".dub", ".vscode", "libsquiz-box.a", "build"];

dirEntries(root, SpanMode.breadth, false)
    .filter!(e => !e.isDir)
    .filter!(e => !exclusion.any!(ex => e.name.canFind(ex)))
    .map!(e => fileEntry(e.name, root, prefix))
    .boxTar()
    .compressXz()
    .writeBinaryFile("squiz-box-12.5.tar.xz");

Extract an archive into a directory

import squiz_box;

const archive = "my-archive.tar.gz";
const extractionSite = "some-dir";

mkdir(extractionSite);

readBinaryFile(archive)
    .inflateGz()
    .unboxTar()                               // range of UnboxEntry
    .each!(e => e.extractTo(extractionSite));

Compression/Decompression with algorithm known at runtime

import squiz_box;

// SquizAlgo is a D interface
// it must be instantiated from a compile-time known algorithm
SquizAlgo algo = squizAlgo(Deflate.init);

// the rest is the same as previously

const ubyte[] data = myDataToCompress();

only(data)
  .squiz(algo)
  .sendOverNetwork();

Boxing/Unboxing with algorithm known at runtime

import squiz_box;

import std.algorithm;
import std.file;
import std.path;

const filename = "squiz-box-12.5.tar.xz";

/// BoxAlgo is a D interface
/// It can be instantiated from a filename with archive extension
/// or directly with the implementing classes (ZipBox, TarXzBox, ...)
BoxAlgo algo = BoxAlgo.fromFilename(filename);

/// the rest is (almost) the same as before

const root = squizBoxDir;

// prefix all files path in the archive
// don't forget the trailing '/'!
const prefix = "squiz-box-12.5/";

const exclusion = [".git", ".dub", ".vscode", "libsquiz-box.a", "build"];

// no need to collect entries in an array
auto entries = dirEntries(root, SpanMode.breadth, false)
    .filter!(e => !e.isDir)
    .filter!(e => !exclusion.any!(ex => e.name.canFind(ex)))
    .map!(e => fileEntry(e.name, root, prefix));

// algo.box is a template function that can receive any range of BoxEntry
algo.box(entries).writeBinaryFile(filename);

Full control over the streaming process

Sometimes, D ranges are not practical. Think of a receiver thread that receives data, compresses it and sends it over network with low latency. You will not wait to receive the full data before to start streaming, and a D range is probably not well suited to receive the data from a different thread. In that situation you can use the streaming API directly.

The following code gives the spirit of it.

import squiz_box;

// Zstandard is a good fit for low latency streaming
auto algo = CompressZstd.init;
auto stream = algo.initialize();

// repeat for as many chunks of memory as necessary
stream.input = dataChunk;
stream.output = buffer;
auto streamEnded = algo.process(stream, No.lastChunk);
// send buffer content out
// at some point we send the last chunk and receive notification that the stream is done.

// we can reset the stream and keep the allocated resources for a new round
algo.reset(stream);

// more streaming...

// finally we can release the resources
algo.end(stream);

Download, build, install

To use squiz-box, the easiest is to use the Dub package from the registry. On Linux, you will need liblzma, libbz2 and libzstd installed. On Windows, a compiled copy of these libraries is shipped with the package (only Windows 64 bit is supported).

Squiz-box is developped with Meson, which will build the C libraries if they are not found. If you want to use squiz-box in a Meson project, you should use it as a subproject.

To build, test on Linux:

meson builddir
cd builddir
ninja && ./squiz-test

To build test on Windows:

rem Visual Studio prompt is required
rem A script is provided to help this (needs vswhere)
win_env_vs.bat
meson builddir
cd builddir
ninja && squiz-test.exe