NAME¶

Compress::Zlib - Interface to zlib compression library

SYNOPSIS¶

    use Compress::Zlib ;
    ($d, $status) = deflateInit( [OPT] ) ;
    $status = $d->deflate($input, $output) ;
    $status = $d->flush([$flush_type]) ;
    $d->deflateParams(OPTS) ;
    $d->deflateTune(OPTS) ;
    $d->dict_adler() ;
    $d->crc32() ;
    $d->adler32() ;
    $d->total_in() ;
    $d->total_out() ;
    $d->msg() ;
    $d->get_Strategy();
    $d->get_Level();
    $d->get_BufSize();
    ($i, $status) = inflateInit( [OPT] ) ;
    $status = $i->inflate($input, $output [, $eof]) ;
    $status = $i->inflateSync($input) ;
    $i->dict_adler() ;
    $d->crc32() ;
    $d->adler32() ;
    $i->total_in() ;
    $i->total_out() ;
    $i->msg() ;
    $d->get_BufSize();
    $dest = compress($source) ;
    $dest = uncompress($source) ;
    $gz = gzopen($filename or filehandle, $mode) ;
    $bytesread = $gz->gzread($buffer [,$size]) ;
    $bytesread = $gz->gzreadline($line) ;
    $byteswritten = $gz->gzwrite($buffer) ;
    $status = $gz->gzflush($flush) ;
    $offset = $gz->gztell() ;
    $status = $gz->gzseek($offset, $whence) ;
    $status = $gz->gzclose() ;
    $status = $gz->gzeof() ;
    $status = $gz->gzsetparams($level, $strategy) ;
    $errstring = $gz->gzerror() ;
    $gzerrno
    $dest = Compress::Zlib::memGzip($buffer) ;
    $dest = Compress::Zlib::memGunzip($buffer) ;
    $crc = adler32($buffer [,$crc]) ;
    $crc = crc32($buffer [,$crc]) ;
    $crc = crc32_combine($crc1, $crc2, $len2);
    $adler = adler32_combine($adler1, $adler2, $len2);
    my $version = Compress::Raw::Zlib::zlib_version();

DESCRIPTION¶

The Compress::Zlib module provides a Perl interface to the zlib compression library (see "AUTHOR" for details about where to get zlib).

The "Compress::Zlib" module can be split into two general areas of functionality, namely a simple read/write interface to gzip files and a low-level in-memory compression/decompression interface.

Each of these areas will be discussed in the following sections.

GZIP INTERFACE¶

A number of functions are supplied in zlib for reading and writing gzip files that conform to RFC 1952. This module provides an interface to most of them.

If you have previously used "Compress::Zlib" 1.x, the following enhancements/changes have been made to the "gzopen" interface:

1.

If you want to open either STDIN or STDOUT with "gzopen", you can now optionally use the special filename ""-"" as a synonym for "\*STDIN" and "\*STDOUT".

2.

In "Compress::Zlib" version 1.x, "gzopen" used the zlib library to open the underlying file. This made things especially tricky when a Perl filehandle was passed to "gzopen". Behind the scenes the numeric C file descriptor had to be extracted from the Perl filehandle and this passed to the zlib library.

Apart from being non-portable to some operating systems, this made it difficult to use "gzopen" in situations where you wanted to extract/create a gzip data stream that is embedded in a larger file, without having to resort to opening and closing the file multiple times.

It also made it impossible to pass a perl filehandle that wasn't associated with a real filesystem file, like, say, an "IO::String".

In "Compress::Zlib" version 2.x, the "gzopen" interface has been completely rewritten to use the IO::Compress::Gzip for writing gzip files and IO::Uncompress::Gunzip for reading gzip files. None of the limitations mentioned above apply.

3.

Addition of "gzseek" to provide a restricted "seek" interface.

4.

Added "gztell".

A more complete and flexible interface for reading/writing gzip files/buffers is included with the module "IO-Compress-Zlib". See IO::Compress::Gzip and IO::Uncompress::Gunzip for more details.

$gz = gzopen($filename, $mode)

$gz = gzopen($filehandle, $mode)

This function opens either the gzip file $filename for reading or writing or attaches to the opened filehandle, $filehandle. It returns an object on success and "undef" on failure.

When writing a gzip file this interface will always create the smallest possible gzip header (exactly 10 bytes). If you want greater control over what gets stored in the gzip header (like the original filename or a comment) use IO::Compress::Gzip instead. Similarly if you want to read the contents of the gzip header use IO::Uncompress::Gunzip.

The second parameter, $mode, is used to specify whether the file is opened for reading or writing and to optionally specify a compression level and compression strategy when writing. The format of the $mode parameter is similar to the mode parameter to the 'C' function "fopen", so "rb" is used to open for reading, "wb" for writing and "ab" for appending (writing at the end of the file).

To specify a compression level when writing, append a digit between 0 and 9 to the mode string -- 0 means no compression and 9 means maximum compression. If no compression level is specified Z_DEFAULT_COMPRESSION is used.

To specify the compression strategy when writing, append 'f' for filtered data, 'h' for Huffman only compression, or 'R' for run-length encoding. If no strategy is specified Z_DEFAULT_STRATEGY is used.

So, for example, "wb9" means open for writing with the maximum compression using the default strategy and "wb4R" means open for writing with compression level 4 and run-length encoding.

Refer to the zlib documentation for the exact format of the $mode parameter.

$bytesread = $gz->gzread($buffer [, $size]) ;

Reads $size bytes from the compressed file into $buffer. If $size is not specified, it will default to 4096. If the scalar $buffer is not large enough, it will be extended automatically.

Returns the number of bytes actually read. On EOF it returns 0 and in the case of an error, -1.

$bytesread = $gz->gzreadline($line) ;

Reads the next line from the compressed file into $line.

Returns the number of bytes actually read. On EOF it returns 0 and in the case of an error, -1.

It is legal to intermix calls to "gzread" and "gzreadline".

To maintain backward compatibility with version 1.x of this module "gzreadline" ignores the $/ variable - it always uses the string "\n" as the line delimiter.

If you want to read a gzip file a line at a time and have it respect the $/ variable (or $INPUT_RECORD_SEPARATOR, or $RS when "English" is in use) see IO::Uncompress::Gunzip.

$byteswritten = $gz->gzwrite($buffer) ;

Writes the contents of $buffer to the compressed file. Returns the number of bytes actually written, or 0 on error.

$status = $gz->gzflush($flush_type) ;

Flushes all pending output into the compressed file.

This method takes an optional parameter, $flush_type, that controls how the flushing will be carried out. By default the $flush_type used is "Z_FINISH". Other valid values for $flush_type are "Z_NO_FLUSH", "Z_SYNC_FLUSH", "Z_FULL_FLUSH" and "Z_BLOCK". It is strongly recommended that you only set the "flush_type" parameter if you fully understand the implications of what it does - overuse of "flush" can seriously degrade the level of compression achieved. See the "zlib" documentation for details.

Returns 0 on success.

$offset = $gz->gztell() ;

Returns the uncompressed file offset.

$status = $gz->gzseek($offset, $whence) ;

Provides a sub-set of the "seek" functionality, with the restriction that it is only legal to seek forward in the compressed file. It is a fatal error to attempt to seek backward.

When opened for writing, empty parts of the file will have NULL (0x00) bytes written to them.

The $whence parameter should be one of SEEK_SET, SEEK_CUR or SEEK_END.

Returns 1 on success, 0 on failure.

$gz->gzclose

Closes the compressed file. Any pending data is flushed to the file before it is closed.

Returns 0 on success.

$gz->gzsetparams($level, $strategy

Change settings for the deflate stream $gz.

The list of the valid options is shown below. Options not specified will remain unchanged.

Note: This method is only available if you are running zlib 1.0.6 or better.

$gz->gzerror

Returns the zlib error message or number for the last operation associated with $gz. The return value will be the zlib error number when used in a numeric context and the zlib error message when used in a string context. The zlib error number constants, shown below, are available for use.

    Z_OK
    Z_STREAM_END
    Z_ERRNO
    Z_STREAM_ERROR
    Z_DATA_ERROR
    Z_MEM_ERROR
    Z_BUF_ERROR
    

$gzerrno

The $gzerrno scalar holds the error code associated with the most recent gzip routine. Note that unlike gzerror(), the error is not associated with a particular file.

As with gzerror() it returns an error number in numeric context and an error message in string context. Unlike gzerror() though, the error message will correspond to the zlib message when the error is associated with zlib itself, or the UNIX error message when it is not (i.e. zlib returned "Z_ERRORNO").

As there is an overlap between the error numbers used by zlib and UNIX, $gzerrno should only be used to check for the presence of an error in numeric context. Use gzerror() to check for specific zlib errors. The gzcat example below shows how the variable can be used safely.

    use strict ;
    use warnings ;
    use Compress::Zlib ;
    # use stdin if no files supplied
    @ARGV = '-' unless @ARGV ;
    foreach my $file (@ARGV) {
        my $buffer ;
        my $gz = gzopen($file, "rb")
             or die "Cannot open $file: $gzerrno\n" ;
        print $buffer while $gz->gzread($buffer) > 0 ;
        die "Error reading from $file: $gzerrno" . ($gzerrno+0) . "\n"
            if $gzerrno != Z_STREAM_END ;
        $gz->gzclose() ;
    }

    use strict ;
    use warnings ;
    use Compress::Zlib ;
    die "Usage: gzgrep pattern [file...]\n"
        unless @ARGV >= 1;
    my $pattern = shift ;
    # use stdin if no files supplied
    @ARGV = '-' unless @ARGV ;
    foreach my $file (@ARGV) {
        my $gz = gzopen($file, "rb")
             or die "Cannot open $file: $gzerrno\n" ;
        while ($gz->gzreadline($_) > 0) {
            print if /$pattern/ ;
        }
        die "Error reading from $file: $gzerrno\n"
            if $gzerrno != Z_STREAM_END ;
        $gz->gzclose() ;
    }

    use strict ;
    use warnings ;
    use Compress::Zlib ;
    binmode STDOUT;  # gzopen only sets it on the fd
    my $gz = gzopen(\*STDOUT, "wb")
          or die "Cannot open stdout: $gzerrno\n" ;
    while (<>) {
        $gz->gzwrite($_)
          or die "error writing: $gzerrno\n" ;
    }
    $gz->gzclose ;

    $dest = Compress::Zlib::memGzip($buffer)
        or die "Cannot compress: $gzerrno\n";

    $dest = Compress::Zlib::memGunzip($buffer)
        or die "Cannot uncompress: $gzerrno\n";

COMPRESS/UNCOMPRESS¶

Two functions are provided to perform in-memory compression/uncompression of RFC 1950 data streams. They are called "compress" and "uncompress".

$dest = compress($source [, $level] ) ;

Compresses $source. If successful it returns the compressed data. Otherwise it returns undef.

The source buffer, $source, can either be a scalar or a scalar reference.

The $level parameter defines the compression level. Valid values are 0 through 9, "Z_NO_COMPRESSION", "Z_BEST_SPEED", "Z_BEST_COMPRESSION", and "Z_DEFAULT_COMPRESSION". If $level is not specified "Z_DEFAULT_COMPRESSION" will be used.

$dest = uncompress($source) ;

Uncompresses $source. If successful it returns the uncompressed data. Otherwise it returns undef.

The source buffer can either be a scalar or a scalar reference.

Please note: the two functions defined above are not compatible with the Unix commands of the same name.

See IO::Deflate and IO::Inflate included with this distribution for an alternative interface for reading/writing RFC 1950 files/buffers.

Deflate Interface¶

This section defines an interface that allows in-memory compression using the deflate interface provided by zlib.

Here is a definition of the interface available:

    deflateInit( -Bufsize => 300,
                 -Level => Z_BEST_SPEED  ) ;

    use strict ;
    use warnings ;
    use Compress::Zlib ;
    binmode STDIN;
    binmode STDOUT;
    my $x = deflateInit()
       or die "Cannot create a deflation stream\n" ;
    my ($output, $status) ;
    while (<>)
    {
        ($output, $status) = $x->deflate($_) ;
        $status == Z_OK
            or die "deflation failed\n" ;
        print $output ;
    }
    ($output, $status) = $x->flush() ;
    $status == Z_OK
        or die "deflation failed\n" ;
    print $output ;

Inflate Interface¶

This section defines the interface available that allows in-memory uncompression using the deflate interface provided by zlib.

Here is a definition of the interface:

    inflateInit( -Bufsize => 300 ) ;

    use strict ;
    use warnings ;
    use Compress::Zlib ;
    my $x = inflateInit()
       or die "Cannot create a inflation stream\n" ;
    my $input = '' ;
    binmode STDIN;
    binmode STDOUT;
    my ($output, $status) ;
    while (read(STDIN, $input, 4096))
    {
        ($output, $status) = $x->inflate(\$input) ;
        print $output
            if $status == Z_OK or $status == Z_STREAM_END ;
        last if $status != Z_OK ;
    }
    die "inflation failed\n"
        unless $status == Z_STREAM_END ;

CHECKSUM FUNCTIONS¶

Two functions are provided by zlib to calculate checksums. For the Perl interface, the order of the two parameters in both functions has been reversed. This allows both running checksums and one off calculations to be done.

    $crc = adler32($buffer [,$crc]) ;
    $crc = crc32($buffer [,$crc]) ;

The buffer parameters can either be a scalar or a scalar reference.

If the $crc parameters is "undef", the crc value will be reset.

If you have built this module with zlib 1.2.3 or better, two more CRC-related functions are available.

    $crc = crc32_combine($crc1, $crc2, $len2);
    $adler = adler32_combine($adler1, $adler2, $len2);

These functions allow checksums to be merged. Refer to the zlib documentation for more details.

Misc¶

CONSTANTS¶

All the zlib constants are automatically imported when you make use of Compress::Zlib.

SUPPORT¶

General feedback/questions/bug reports should be sent to <https://github.com/pmqs/IO-Compress/issues> (preferred) or <https://rt.cpan.org/Public/Dist/Display.html?Name=IO-Compress>.

SEE ALSO¶

IO::Compress::Gzip, IO::Uncompress::Gunzip, IO::Compress::Deflate, IO::Uncompress::Inflate, IO::Compress::RawDeflate, IO::Uncompress::RawInflate, IO::Compress::Bzip2, IO::Uncompress::Bunzip2, IO::Compress::Lzma, IO::Uncompress::UnLzma, IO::Compress::Xz, IO::Uncompress::UnXz, IO::Compress::Lzip, IO::Uncompress::UnLzip, IO::Compress::Lzop, IO::Uncompress::UnLzop, IO::Compress::Lzf, IO::Uncompress::UnLzf, IO::Compress::Zstd, IO::Uncompress::UnZstd, IO::Uncompress::AnyInflate, IO::Uncompress::AnyUncompress

IO::Compress::FAQ

File::GlobMapper, Archive::Zip, Archive::Tar, IO::Zlib

For RFC 1950, 1951 and 1952 see <https://datatracker.ietf.org/doc/html/rfc1950>, <https://datatracker.ietf.org/doc/html/rfc1951> and <https://datatracker.ietf.org/doc/html/rfc1952>

The zlib compression library was written by Jean-loup Gailly "gzip@prep.ai.mit.edu" and Mark Adler "madler@alumni.caltech.edu".

The primary site for the zlib compression library is <http://www.zlib.org>.

The primary site for the zlib-ng compression library is <https://github.com/zlib-ng/zlib-ng>.

The primary site for gzip is <http://www.gzip.org>.

AUTHOR¶

This module was written by Paul Marquess, "pmqs@cpan.org".

MODIFICATION HISTORY¶

See the Changes file.

COPYRIGHT AND LICENSE¶

Copyright (c) 1995-2024 Paul Marquess. All rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.