module Zlib - zlib: Ruby Standard Library Documentation

# module Zlib

This module provides access to the zlib library. `Zlib` is designed to be a portable, free, general-purpose, legally unencumbered – that is, not covered by any patents – lossless data-compression library for use on virtually any computer hardware and operating system.

The zlib compression library provides in-memory compression and decompression functions, including integrity checks of the uncompressed data.

The zlib compressed data format is described in RFC 1950, which is a wrapper around a deflate stream which is described in RFC 1951.

The library also supports reading and writing files in gzip (.gz) format with an interface similar to that of IO. The gzip format is described in RFC 1952 which is also a wrapper around a deflate stream.

The zlib format was designed to be compact and fast for use in memory and on communications channels. The gzip format was designed for single-file compression on file systems, has a larger header than zlib to maintain directory information, and uses a different, slower check method than zlib.

See your system’s zlib.h for further information about zlib

## Sample usage¶ ↑

Using the wrapper to compress strings with default parameters is quite simple:

    require "zlib"

    data_to_compress = File.read("don_quixote.txt")

    puts "Input size: #{data_to_compress.size}"
    #=> Input size: 2347740

    data_compressed = Zlib::Deflate.deflate(data_to_compress)

    puts "Compressed size: #{data_compressed.size}"
    #=> Compressed size: 887238

    uncompressed_data = Zlib::Inflate.inflate(data_compressed)

    puts "Uncompressed data is: #{uncompressed_data}"
    #=> Uncompressed data is: The Project Gutenberg EBook of Don Quixote...

## Class tree¶ ↑

- `Zlib::Deflate`

- `Zlib::Inflate`

- `Zlib::ZStream`

- `Zlib::Error`

  - `Zlib::StreamEnd`

  - `Zlib::NeedDict`

  - `Zlib::DataError`

  - `Zlib::StreamError`

  - `Zlib::MemError`

  - `Zlib::BufError`

  - `Zlib::VersionError`

  - `Zlib::InProgressError`

(if you have GZIP_SUPPORT)

- `Zlib::GzipReader`

- `Zlib::GzipWriter`

- `Zlib::GzipFile`

- `Zlib::GzipFile::Error`

  - `Zlib::GzipFile::LengthError`

  - `Zlib::GzipFile::CRCError`

  - `Zlib::GzipFile::NoFooter`

### Constants

ASCII

  Represents text data as guessed by deflate.

  NOTE: The underlying constant Z_ASCII was deprecated in favor of Z_TEXT in zlib 1.2.2. New applications should not use this constant.

  See `Zlib::Deflate#data_type`.

BEST_COMPRESSION

  Slowest compression level, but with the best space savings.

BEST_SPEED

  Fastest compression level, but with the lowest space savings.

BINARY

  Represents binary data as guessed by deflate.

  See `Zlib::Deflate#data_type`.

DEFAULT_COMPRESSION

  Default compression level which is a good trade-off between space and time

DEFAULT_STRATEGY

  Default deflate strategy which is used for normal data.

DEF_MEM_LEVEL

  The default memory level for allocating zlib deflate compression state.

FILTERED

  `Deflate` strategy for data produced by a filter (or predictor). The effect of `FILTERED` is to force more Huffman codes and less string matching; it is somewhat intermediate between `DEFAULT_STRATEGY` and `HUFFMAN_ONLY`. Filtered data consists mostly of small values with a somewhat random distribution.

FINISH

  Processes all pending input and flushes pending output.

FIXED

  `Deflate` strategy which prevents the use of dynamic Huffman codes, allowing for a simpler decoder for specialized applications.

FULL_FLUSH

  Flushes all output as with `SYNC_FLUSH`, and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. Like `SYNC_FLUSH`, using `FULL_FLUSH` too often can seriously degrade compression.

HUFFMAN_ONLY

  `Deflate` strategy which uses Huffman codes only (no string matching).

MAX_MEM_LEVEL

  The maximum memory level for allocating zlib deflate compression state.

MAX_WBITS

  The maximum size of the zlib history buffer. Note that zlib allows larger values to enable different inflate modes. See `Zlib::Inflate.new` for details.

NO_COMPRESSION

  No compression, passes through data untouched. Use this for appending pre-compressed data to a deflate stream.

NO_FLUSH

  `NO_FLUSH` is the default flush method and allows deflate to decide how much data to accumulate before producing output in order to maximize compression.

OS_AMIGA

  OS code for Amiga hosts

OS_ATARI

  OS code for Atari hosts

OS_CODE

  The OS code of current host

OS_CPM

  OS code for CP/M hosts

OS_MACOS

  OS code for Mac OS hosts

OS_MSDOS

  OS code for MSDOS hosts

OS_OS2

  OS code for OS2 hosts

OS_QDOS

  OS code for QDOS hosts

OS_RISCOS

  OS code for RISC OS hosts

OS_TOPS20

  OS code for TOPS-20 hosts

OS_UNIX

  OS code for UNIX hosts

OS_UNKNOWN

  OS code for unknown hosts

OS_VMCMS

  OS code for VM OS hosts

OS_VMS

  OS code for VMS hosts

OS_WIN32

  OS code for Win32 hosts

OS_ZSYSTEM

  OS code for Z-System hosts

RLE

  `Deflate` compression strategy designed to be almost as fast as `HUFFMAN_ONLY`, but give better compression for PNG image data.

SYNC_FLUSH

  The `SYNC_FLUSH` method flushes all pending output to the output buffer and the output is aligned on a byte boundary. Flushing may degrade compression so it should be used only when necessary, such as at a request or response boundary for a network stream.

TEXT

  Represents text data as guessed by deflate.

  See `Zlib::Deflate#data_type`.

UNKNOWN

  Represents an unknown data type as guessed by deflate.

  See `Zlib::Deflate#data_type`.

VERSION

  The Ruby/zlib version string.

ZLIB_VERSION

  The string which represents the version of zlib.h

### Public Class Methods

adler32(string, adler) click to toggle source

Calculates Adler-32 checksum for `string`, and returns updated value of `adler`. If `string` is omitted, it returns the Adler-32 initial value. If `adler` is omitted, it assumes that the initial value is given to `adler`. If `string` is an IO instance, reads from the IO until the IO returns nil and returns Adler-32 of all read data.

Example usage:

    require "zlib"

    data = "foo"
    puts "Adler32 checksum: #{Zlib.adler32(data).to_s(16)}"
    #=> Adler32 checksum: 2820145

    static VALUE
    rb_zlib_adler32(int argc, VALUE *argv, VALUE klass)
    {
        return do_checksum(argc, argv, adler32);
    }

adler32_combine(adler1, adler2, len2) click to toggle source

Combine two Adler-32 check values in to one. `adler1` is the first Adler-32 value, `adler2` is the second Adler-32 value. `len2` is the length of the string used to generate `adler2`.

    static VALUE
    rb_zlib_adler32_combine(VALUE klass, VALUE adler1, VALUE adler2, VALUE len2)
    {
        return ULONG2NUM(
            adler32_combine(NUM2ULONG(adler1), NUM2ULONG(adler2), NUM2LONG(len2)));
    }

crc32(string, crc) click to toggle source

Calculates CRC checksum for `string`, and returns updated value of `crc`. If `string` is omitted, it returns the CRC initial value. If `crc` is omitted, it assumes that the initial value is given to `crc`. If `string` is an IO instance, reads from the IO until the IO returns nil and returns CRC checksum of all read data.

FIXME: expression.

    static VALUE
    rb_zlib_crc32(int argc, VALUE *argv, VALUE klass)
    {
        return do_checksum(argc, argv, crc32);
    }

crc32_combine(crc1, crc2, len2) click to toggle source

Combine two CRC-32 check values in to one. `crc1` is the first CRC-32 value, `crc2` is the second CRC-32 value. `len2` is the length of the string used to generate `crc2`.

    static VALUE
    rb_zlib_crc32_combine(VALUE klass, VALUE crc1, VALUE crc2, VALUE len2)
    {
        return ULONG2NUM(
            crc32_combine(NUM2ULONG(crc1), NUM2ULONG(crc2), NUM2LONG(len2)));
    }

crc_table() click to toggle source

Returns the table for calculating CRC checksum as an array.

    static VALUE
    rb_zlib_crc_table(VALUE obj)
    {
    #if !defined(HAVE_TYPE_Z_CRC_T)
        /* z_crc_t is defined since zlib-1.2.7. */
        typedef unsigned long z_crc_t;
    #endif
        const z_crc_t *crctbl;
        VALUE dst;
        int i;

        crctbl = get_crc_table();
        dst = rb_ary_new2(256);

        for (i = 0; i < 256; i++) {
            rb_ary_push(dst, rb_uint2inum(crctbl[i]));
        }
        return dst;
    }

deflate(string[, level]) click to toggle source
Zlib::Deflate.deflate(string[, level])

Compresses the given `string`. Valid values of level are `Zlib::NO_COMPRESSION`, `Zlib::BEST_SPEED`, `Zlib::BEST_COMPRESSION`, `Zlib::DEFAULT_COMPRESSION`, or an integer from 0 to 9.

This method is almost equivalent to the following code:

    def deflate(string, level)
      z = Zlib::Deflate.new(level)
      dst = z.deflate(string, Zlib::FINISH)
      z.close
      dst
    end

See also `Zlib.inflate`

    static VALUE
    rb_deflate_s_deflate(int argc, VALUE *argv, VALUE klass)
    {
        struct zstream z;
        VALUE src, level, dst, args[2];
        int err, lev;

        rb_scan_args(argc, argv, "11", &src, &level);

        lev = ARG_LEVEL(level);
        StringValue(src);
        zstream_init_deflate(&z);
        err = deflateInit(&z.stream, lev);
        if (err != Z_OK) {
            raise_zlib_error(err, z.stream.msg);
        }
        ZSTREAM_READY(&z);

        args[0] = (VALUE)&z;
        args[1] = src;
        dst = rb_ensure(deflate_run, (VALUE)args, zstream_ensure_end, (VALUE)&z);

        return dst;
    }

gunzip(src) → String click to toggle source

Decode the given gzipped `string`.

This method is almost equivalent to the following code:

    def gunzip(string)
      sio = StringIO.new(string)
      gz = Zlib::GzipReader.new(sio, encoding: Encoding::ASCII_8BIT)
      gz.read
    ensure
      gz&.close
    end

See also `Zlib.gzip`

    static VALUE
    zlib_gunzip(VALUE klass, VALUE src)
    {
        struct gzfile gz0;
        struct gzfile *gz = &gz0;
        int err;

        StringValue(src);

        gzfile_init(gz, &inflate_funcs, zlib_gunzip_end);
        err = inflateInit2(&gz->z.stream, -MAX_WBITS);
        if (err != Z_OK) {
            raise_zlib_error(err, gz->z.stream.msg);
        }
        gz->io = Qundef;
        gz->z.input = src;
        ZSTREAM_READY(&gz->z);
        return rb_ensure(zlib_gunzip_run, (VALUE)gz, zlib_gzip_ensure, (VALUE)gz);
    }

gzip(src, level: nil, strategy: nil) → String click to toggle source

Gzip the given `string`. Valid values of level are `Zlib::NO_COMPRESSION`, `Zlib::BEST_SPEED`, `Zlib::BEST_COMPRESSION`, `Zlib::DEFAULT_COMPRESSION` (default), or an integer from 0 to 9.

This method is almost equivalent to the following code:

    def gzip(string, level: nil, strategy: nil)
      sio = StringIO.new
      sio.binmode
      gz = Zlib::GzipWriter.new(sio, level, strategy)
      gz.write(string)
      gz.close
      sio.string
    end

See also `Zlib.gunzip`

    static VALUE
    zlib_s_gzip(int argc, VALUE *argv, VALUE klass)
    {
        struct gzfile gz0;
        struct gzfile *gz = &gz0;
        int err;
        VALUE src, opts, level=Qnil, strategy=Qnil, args[2];

        if (OPTHASH_GIVEN_P(opts)) {
            ID keyword_ids[2];
            VALUE kwargs[2];
            keyword_ids[0] = id_level;
            keyword_ids[1] = id_strategy;
            rb_get_kwargs(opts, keyword_ids, 0, 2, kwargs);
            if (kwargs[0] != Qundef) {
                level = kwargs[0];
            }
            if (kwargs[1] != Qundef) {
                strategy = kwargs[1];
            }
        }
        rb_scan_args(argc, argv, "10", &src);
        StringValue(src);
        gzfile_init(gz, &deflate_funcs, zlib_gzip_end);
        gz->level = ARG_LEVEL(level);
        err = deflateInit2(&gz->z.stream, gz->level, Z_DEFLATED,
                           -MAX_WBITS, DEF_MEM_LEVEL, ARG_STRATEGY(strategy));
        if (err != Z_OK) {
            zlib_gzip_end(gz);
            raise_zlib_error(err, gz->z.stream.msg);
        }
        ZSTREAM_READY(&gz->z);
        args[0] = (VALUE)gz;
        args[1] = src;
        return rb_ensure(zlib_gzip_run, (VALUE)args, zlib_gzip_ensure, (VALUE)gz);
    }

inflate(string) click to toggle source
Zlib::Inflate.inflate(string)

Decompresses `string`. Raises a `Zlib::NeedDict` exception if a preset dictionary is needed for decompression.

This method is almost equivalent to the following code:

    def inflate(string)
      zstream = Zlib::Inflate.new
      buf = zstream.inflate(string)
      zstream.finish
      zstream.close
      buf
    end

See also `Zlib.deflate`

    static VALUE
    rb_inflate_s_inflate(VALUE obj, VALUE src)
    {
        struct zstream z;
        VALUE dst, args[2];
        int err;

        StringValue(src);
        zstream_init_inflate(&z);
        err = inflateInit(&z.stream);
        if (err != Z_OK) {
            raise_zlib_error(err, z.stream.msg);
        }
        ZSTREAM_READY(&z);

        args[0] = (VALUE)&z;
        args[1] = src;
        dst = rb_ensure(inflate_run, (VALUE)args, zstream_ensure_end, (VALUE)&z);

        return dst;
    }

zlib_version() click to toggle source

Returns the string which represents the version of zlib library.

    static VALUE
    rb_zlib_version(VALUE klass)
    {
        return rb_str_new2(zlibVersion());
    }