Crate flate2

A DEFLATE-based stream compression/decompression library

This library provides support for compression and decompression of DEFLATE-based streams:

• the DEFLATE format itself
• the zlib format
• gzip

These three formats are all closely related and largely only differ in their headers/footers. This crate has three types in each submodule for dealing with these three formats.

Implementation

In addition to supporting three formats, this crate supports several different backends, controlled through this crate’s features:

• default, or rust_backend - this implementation uses the miniz_oxide crate which is a port of miniz.c (below) to Rust. This feature does not require a C compiler and only requires Rust code.

• zlib - this feature will enable linking against the libz library, typically found on most Linux systems by default. If the library isn’t found to already be on the system it will be compiled from source (this is a C library).

There’s various tradeoffs associated with each implementation, but in general you probably won’t have to tweak the defaults. The default choice is selected to avoid the need for a C compiler at build time. zlib-ng-compat is useful if you’re using zlib for compatibility but want performance via zlib-ng’s zlib-compat mode. zlib is useful if something else in your dependencies links the original zlib so you cannot use zlib-ng-compat. The compression ratios and performance of each of these feature should be roughly comparable, but you’ll likely want to run your own tests if you’re curious about the performance.

Organization

This crate consists mainly of three modules, read, write, and bufread. Each module contains a number of types used to encode and decode various streams of data.

All types in the write module work on instances of Write, whereas all types in the read module work on instances of Read and bufread works with BufRead. If you are decoding directly from a &[u8], use the bufread types.

use flate2::write::GzEncoder;
use flate2::Compression;
use std::io;
use std::io::prelude::*;

let mut encoder = GzEncoder::new(Vec::new(), Compression::default());
encoder.write_all(b"Example")?;

Other various types are provided at the top-level of the crate for management and dealing with encoders/decoders. Also note that types which operate over a specific trait often implement the mirroring trait as well. For example a flate2::read::DeflateDecoder<T> also implements the Write trait if T: Write. That is, the “dual trait” is forwarded directly to the underlying object if available.

About multi-member Gzip files

While most gzip files one encounters will have a single member that can be read with the GzDecoder, there may be some files which have multiple members.

A GzDecoder will only read the first member of gzip data, which may unexpectedly provide partial results when a multi-member gzip file is encountered. GzDecoder is appropriate for data that is designed to be read as single members from a multi-member file. bufread::GzDecoder and write::GzDecoder also allow non-gzip data following gzip data to be handled.

The MultiGzDecoder on the other hand will decode all members of a gzip file into one consecutive stream of bytes, which hides the underlying members entirely. If a file contains non-gzip data after the gzip data, MultiGzDecoder will emit an error after decoding the gzip data. This behavior matches the gzip, gunzip, and zcat command line tools.

Modules

• bufread
  Types which operate over BufRead streams, both encoders and decoders for various formats.
• read
  Types which operate over Read streams, both encoders and decoders for various formats.
• write
  Types which operate over Write streams, both encoders and decoders for various formats.

Structs

• Compress
  Raw in-memory compression stream for blocks of data.
• CompressError
  Error returned when a compression object is used incorrectly or otherwise generates an error.
• Compression
  When compressing data, the compression level can be specified by a value in this struct.
• Crc
  The CRC calculated by a CrcReader.
• CrcReader
  A wrapper around a Read that calculates the CRC.
• CrcWriter
  A wrapper around a Write that calculates the CRC.
• Decompress
  Raw in-memory decompression stream for blocks of data.
• DecompressError
  Error returned when a decompression object finds that the input stream of bytes was not a valid input stream of bytes.
• GzBuilder
  A builder structure to create a new gzip Encoder.
• GzHeader
  A structure representing the header of a gzip stream.

Enums

• FlushCompress
  Values which indicate the form of flushing to be used when compressing in-memory data.
• FlushDecompress
  Values which indicate the form of flushing to be used when decompressing in-memory data.
• Status
  Possible status results of compressing some data or successfully decompressing a block of data.