NAME

IO::Gzip - Perl interface to write RFC 1952 files/buffers

SYNOPSIS

    use IO::Gzip qw(gzip $GzipError) ;


    my $status = gzip $input => $output [,OPTS] 
        or die "gzip failed: $GzipError\n";

    my $z = new IO::Gzip $output [,OPTS]
        or die "gzip failed: $GzipError\n";

    $z->print($string);
    $z->printf($format, $string);
    $z->write($string);
    $z->syswrite($string [, $length, $offset]);
    $z->flush();
    $z->tell();
    $z->eof();
    $z->seek($position, $whence);
    $z->binmode();
    $z->fileno();
    $z->newStream();
    $z->deflateParams();
    $z->close() ;

    $GzipError ;

    # IO::File mode

    print $z $string;
    printf $z $format, $string;
    syswrite $z, $string [, $length, $offset];
    flush $z, ;
    tell $z
    eof $z
    seek $z, $position, $whence
    binmode $z
    fileno $z
    close $z ;
    

DESCRIPTION

WARNING -- This is a Beta release.

  • DO NOT use in production code.

  • The documentation is incomplete in places.

  • Parts of the interface defined here are tentative.

  • Please report any problems you find.

This module provides a Perl interface that allows writing compressed data to files or buffer as defined in RFC 1952.

All the gzip headers defined in RFC 1952 can be created using this module.

For reading RFC 1952 files/buffers, see the companion module IO::Gunzip.

Functional Interface

A top-level function, gzip, is provided to carry out "one-shot" compression between buffers and/or files. For finer control over the compression process, see the "OO Interface" section.

    use IO::Gzip qw(gzip $GzipError) ;

    gzip $input => $output [,OPTS] 
        or die "gzip failed: $GzipError\n";

    gzip \%hash [,OPTS] 
        or die "gzip failed: $GzipError\n";

The functional interface needs Perl5.005 or better.

gzip $input => $output [, OPTS]

If the first parameter is not a hash reference gzip expects at least two parameters, $input and $output.

The $input parameter

The parameter, $input, is used to define the source of the uncompressed data.

It can take one of the following forms:

A filename

If the $input parameter is a simple scalar, it is assumed to be a filename. This file will be opened for reading and the input data will be read from it.

A filehandle

If the $input parameter is a filehandle, the input data will be read from it. The string '-' can be used as an alias for standard input.

A scalar reference

If $input is a scalar reference, the input data will be read from $$input.

An array reference

If $input is an array reference, the input data will be read from each element of the array in turn. The action taken by gzip with each element of the array will depend on the type of data stored in it. You can mix and match any of the types defined in this list, excluding other array or hash references. The complete array will be walked to ensure that it only contains valid data types before any data is compressed.

An Input FileGlob string

If $input is a string that is delimited by the characters "<" and ">" gzip will assume that it is an input fileglob string. The input is the list of files that match the fileglob.

If the fileglob does not match any files ...

See File::GlobMapper for more details.

If the $input parameter is any other type, undef will be returned.

In addition, if $input is a simple filename, the default values for two of the gzip header fields created by this function will be sourced from that file -- the NAME gzip header field will be populated with the filename itself, and the MTIME header field will be set to the modification time of the file. The intention here is to mirror part of the behavior of the gzip executable. If you do not want to use these defaults they can be overridden by explicitly setting the Name and Time options.

The $output parameter

The parameter $output is used to control the destination of the compressed data. This parameter can take one of these forms.

A filename

If the $output parameter is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.

A filehandle

If the $output parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.

A scalar reference

If $output is a scalar reference, the compressed data will be stored in $$output.

A Hash Reference

If $output is a hash reference, the compressed data will be written to $output{$input} as a scalar reference.

When $output is a hash reference, $input must be either a filename or list of filenames. Anything else is an error.

An Array Reference

If $output is an array reference, the compressed data will be pushed onto the array.

An Output FileGlob

If $output is a string that is delimited by the characters "<" and ">" gzip will assume that it is an output fileglob string. The output is the list of files that match the fileglob.

When $output is an fileglob string, $input must also be a fileglob string. Anything else is an error.

If the $output parameter is any other type, undef will be returned.

gzip \%hash [, OPTS]

If the first parameter is a hash reference, \%hash, this will be used to define both the source of uncompressed data and to control where the compressed data is output. Each key/value pair in the hash defines a mapping between an input filename, stored in the key, and an output file/buffer, stored in the value. Although the input can only be a filename, there is more flexibility to control the destination of the compressed data. This is determined by the type of the value. Valid types are

undef

If the value is undef the compressed data will be written to the value as a scalar reference.

A filename

If the value is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.

A filehandle

If the value is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.

A scalar reference

If the value is a scalar reference, the compressed data will be stored in the buffer that is referenced by the scalar.

A Hash Reference

If the value is a hash reference, the compressed data will be written to $hash{$input} as a scalar reference.

An Array Reference

If $output is an array reference, the compressed data will be pushed onto the array.

Any other type is a error.

Notes

When $input maps to multiple files/buffers and $output is a single file/buffer the compressed input files/buffers will all be stored in $output as a single compressed stream.

Optional Parameters

Unless specified below, the optional parameters for gzip, OPTS, are the same as those used with the OO interface defined in the "Constructor Options" section below.

AutoClose => 0|1

This option applies to any input or output data streams to gzip that are filehandles.

If AutoClose is specified, and the value is true, it will result in all input and/or output filehandles being closed once gzip has completed.

This parameter defaults to 0.

-Append => 0|1

TODO

Examples

To read the contents of the file file1.txt and write the compressed data to the file file1.txt.gz.

    use strict ;
    use warnings ;
    use IO::Gzip qw(gzip $GzipError) ;

    my $input = "file1.txt";
    gzip $input => "$input.gz"
        or die "gzip failed: $GzipError\n";

To read from an existing Perl filehandle, $input, and write the compressed data to a buffer, $buffer.

    use strict ;
    use warnings ;
    use IO::Gzip qw(gzip $GzipError) ;
    use IO::File ;

    my $input = new IO::File "<file1.txt"
        or die "Cannot open 'file1.txt': $!\n" ;
    my $buffer ;
    gzip $input => \$buffer 
        or die "gzip failed: $GzipError\n";

To compress all files in the directory "/my/home" that match "*.txt" and store the compressed data in the same directory

    use strict ;
    use warnings ;
    use IO::Gzip qw(gzip $GzipError) ;

    gzip '</my/home/*.txt>' => '<*.gz>'
        or die "gzip failed: $GzipError\n";

and if you want to compress each file one at a time, this will do the trick

    use strict ;
    use warnings ;
    use IO::Gzip qw(gzip $GzipError) ;

    for my $input ( glob "/my/home/*.txt" )
    {
        my $output = "$input.gz" ;
        gzip $input => $output 
            or die "Error compressing '$input': $GzipError\n";
    }

OO Interface

Constructor

The format of the constructor for IO::Gzip is shown below

    my $z = new IO::Gzip $output [,OPTS]
        or die "IO::Gzip failed: $GzipError\n";

It returns an IO::Gzip object on success and undef on failure. The variable $GzipError will contain an error message on failure.

If you are running Perl 5.005 or better the object, $z, returned from IO::Gzip can be used exactly like an IO::File filehandle. This means that all normal output file operations can be carried out with $z. For example, to write to a compressed file/buffer you can use either of these forms

    $z->print("hello world\n");
    print $z "hello world\n";

The mandatory parameter $output is used to control the destination of the compressed data. This parameter can take one of these forms.

A filename

If the $output parameter is a simple scalar, it is assumed to be a filename. This file will be opened for writing and the compressed data will be written to it.

A filehandle

If the $output parameter is a filehandle, the compressed data will be written to it. The string '-' can be used as an alias for standard output.

A scalar reference

If $output is a scalar reference, the compressed data will be stored in $$output.

If the $output parameter is any other type, IO::Gzip::new will return undef.

Constructor Options

OPTS is any combination of the following options:

-AutoClose => 0|1

This option is only valid when the $output parameter is a filehandle. If specified, and the value is true, it will result in the $output being closed once either the close method is called or the IO::Gzip object is destroyed.

This parameter defaults to 0.

-Append => 0|1

Opens $output in append mode.

The behaviour of this option is dependant on the type of $output.

  • A Buffer

    If $output is a buffer and Append is enabled, all compressed data will be append to the end if $output. Otherwise $output will be cleared before any data is written to it.

  • A Filename

    If $output is a filename and Append is enabled, the file will be opened in append mode. Otherwise the contents of the file, if any, will be truncated before any compressed data is written to it.

  • A Filehandle

    If $output is a filehandle, the file pointer will be positioned to the end of the file via a call to seek before any compressed data is written to it. Otherwise the file pointer will not be moved.

This parameter defaults to 0.

-Merge => 0|1

This option is used to compress input data and append it to an existing compressed data stream in $output. The end result is a single compressed data stream stored in $output.

It is a fatal error to attempt to use this option when $output is not an RFC 1952 data stream.

There are a number of other limitations with the Merge option:

  1. This module needs to have been built with zlib 1.2.1 or better to work. A fatal error will be thrown if Merge is used with an older version of zlib.

  2. If $output is a file or a filehandle, it must be seekable.

This parameter defaults to 0.

-Level

Defines the compression level used by zlib. The value should either be a number between 0 and 9 (0 means no compression and 9 is maximum compression), or one of the symbolic constants defined below.

   Z_NO_COMPRESSION
   Z_BEST_SPEED
   Z_BEST_COMPRESSION
   Z_DEFAULT_COMPRESSION

The default is Z_DEFAULT_COMPRESSION.

Note, these constants are not imported by IO::Gzip by default.

    use IO::Gzip qw(:strategy);
    use IO::Gzip qw(:constants);
    use IO::Gzip qw(:all);
-Strategy

Defines the strategy used to tune the compression. Use one of the symbolic constants defined below.

   Z_FILTERED
   Z_HUFFMAN_ONLY
   Z_RLE
   Z_FIXED
   Z_DEFAULT_STRATEGY

The default is Z_DEFAULT_STRATEGY.

-Mimimal => 0|1

If specified, this option will force the creation of the smallest possible compliant gzip header (which is exactly 10 bytes long) as defined in RFC 1952.

See the section titled "Compliance" in RFC 1952 for a definition of the values used for the fields in the gzip header.

All other parameters that control the content of the gzip header will be ignored if this parameter is set to 1.

This parameter defaults to 0.

-Comment => $comment

Stores the contents of $comment in the COMMENT field in the gzip header. By default, no comment field is written to the gzip file.

If the -Strict option is enabled, the comment can only consist of ISO 8859-1 characters plus line feed.

If the -Strict option is disabled, the comment field can contain any character except NULL. If any null characters are present, the field will be truncated at the first NULL.

-Name => $string

Stores the contents of $string in the gzip NAME header field. If Name is not specified, no gzip NAME field will be created.

If the -Strict option is enabled, $string can only consist of ISO 8859-1 characters.

If -Strict is disabled, then $string can contain any character except NULL. If any null characters are present, the field will be truncated at the first NULL.

-Time => $number

Sets the MTIME field in the gzip header to $number.

This field defaults to the time the IO::Gzip object was created if this option is not specified.

-TextFlag => 0|1

This parameter controls the setting of the FLG.FTEXT bit in the gzip header. It is used to signal that the data stored in the gzip file/buffer is probably text.

The default is 0.

-HeaderCRC => 0|1

When true this parameter will set the FLG.FHCRC bit to 1 in the gzip header and set the CRC16 header field to the CRC of the complete gzip header except the CRC16 field itself.

Note that gzip files created with the HeaderCRC flag set to 1 cannot be read by most, if not all, of the the standard gunzip utilities, most notably gzip version 1.2.4. You should therefore avoid using this option if you want to maximise the portability of your gzip files.

This parameter defaults to 0.

-OS_Code => $value

Stores $value in the gzip OS header field. A number between 0 and 255 is valid.

If not specified, this parameter defaults to the OS code of the Operating System this module was built on. The value 3 is used as a catch-all for all Unix variants and unknown Operating Systems.

-ExtraField => $data

This parameter allows additional metadata to be stored in the ExtraField in the gzip header. An RFC1952 compliant ExtraField consists of zero or more subfields. Each subfield consists of a two byte header followed by the subfield data.

The list of subfields can be supplied in any of the following formats

    -ExtraField => [$id1, $data1,
                    $id2, $data2,
                     ...
                   ]
    -ExtraField => [ [$id1 => $data1],
                     [$id2 => $data2],
                     ...
                   ]
    -ExtraField => { $id1 => $data1,
                     $id2 => $data2,
                     ...
                   }

Where $id1, $id2 are two byte subfield ID's. The second byte of the ID cannot be 0, unless the Strict option has been disabled.

If you use the hash syntax, you have no control over the order in which the ExtraSubFields are stored, plus you cannot have SubFields with duplicate ID.

Alternatively the list of subfields can by supplied as a scalar, thus

    -ExtraField => $rawdata

If you use the raw format, and the Strict option is enabled, IO::Gzip will check that $rawdata consists of zero or more conformant sub-fields. When Strict is disabled, $rawdata can consist of any arbitrary byte stream.

The maximum size of the Extra Field 65535 bytes.

-ExtraFlags => $value

Sets the XFL byte in the gzip header to $value.

If this option is not present, the value stored in XFL field will be determined by the setting of the Level option.

If Level => Z_BEST_SPEED has been specified then XFL is set to 2. If Level => Z_BEST_COMPRESSION has been specified then XFL is set to 4. Otherwise XFL is set to 0.

-Strict => 0|1

Strict will optionally police the values supplied with other options to ensure they are compliant with RFC1952.

This option is enabled by default.

If Strict is enabled the following behavior will be policed:

  • The value supplied with the Name option can only contain ISO 8859-1 characters.

  • The value supplied with the Comment option can only contain ISO 8859-1 characters plus line-feed.

  • The values supplied with the -Name and -Comment options cannot contain multiple embedded nulls.

  • If an ExtraField option is specified and it is a simple scalar, it must conform to the sub-field structure as defined in RFC1952.

  • If an ExtraField option is specified the second byte of the ID will be checked in each subfield to ensure that it does not contain the reserved value 0x00.

When Strict is disabled the following behavior will be policed:

  • The value supplied with -Name option can contain any character except NULL.

  • The value supplied with -Comment option can contain any character except NULL.

  • The values supplied with the -Name and -Comment options can contain multiple embedded nulls. The string written to the gzip header will consist of the characters up to, but not including, the first embedded NULL.

  • If an ExtraField option is specified and it is a simple scalar, the structure will not be checked. The only error is if the length is too big.

  • The ID header in an ExtraField sub-field can consist of any two bytes.

Examples

TODO

Methods

print

Usage is

    $z->print($data)
    print $z $data

Compresses and outputs the contents of the $data parameter. This has the same behavior as the print built-in.

Returns true if successful.

printf

Usage is

    $z->printf($format, $data)
    printf $z $format, $data

Compresses and outputs the contents of the $data parameter.

Returns true if successful.

syswrite

Usage is

    $z->syswrite $data
    $z->syswrite $data, $length
    $z->syswrite $data, $length, $offset

    syswrite $z, $data
    syswrite $z, $data, $length
    syswrite $z, $data, $length, $offset

Compresses and outputs the contents of the $data parameter.

Returns the number of uncompressed bytes written, or undef if unsuccessful.

write

Usage is

    $z->write $data
    $z->write $data, $length
    $z->write $data, $length, $offset

Compresses and outputs the contents of the $data parameter.

Returns the number of uncompressed bytes written, or undef if unsuccessful.

flush

Usage is

    $z->flush;
    $z->flush($flush_type);
    flush $z ;
    flush $z $flush_type;

Flushes any pending compressed data to the output file/buffer.

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 true on success.

tell

Usage is

    $z->tell()
    tell $z

Returns the uncompressed file offset.

eof

Usage is

    $z->eof();
    eof($z);

Returns true if the close method has been called.

seek

    $z->seek($position, $whence);
    seek($z, $position, $whence);

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

Empty parts of the file/buffer will have NULL (0x00) bytes written to them.

The $whence parameter takes one the usual values, namely SEEK_SET, SEEK_CUR or SEEK_END.

Returns 1 on success, 0 on failure.

binmode

Usage is

    $z->binmode
    binmode $z ;

This is a noop provided for completeness.

fileno

    $z->fileno()
    fileno($z)

If the $z object is associated with a file, this method will return the underlying filehandle.

If the $z object is is associated with a buffer, this method will return undef.

close

    $z->close() ;
    close $z ;

Flushes any pending compressed data and then closes the output file/buffer.

For most versions of Perl this method will be automatically invoked if the IO::Gzip object is destroyed (either explicitly or by the variable with the reference to the object going out of scope). The exceptions are Perl versions 5.005 through 5.00504 and 5.8.0. In these cases, the close method will be called automatically, but not until global destruction of all live objects when the program is terminating.

Therefore, if you want your scripts to be able to run on all versions of Perl, you should call close explicitly and not rely on automatic closing.

Returns true on success, otherwise 0.

If the AutoClose option has been enabled when the IO::Gzip object was created, and the object is associated with a file, the underlying file will also be closed.

newStream

Usage is

    $z->newStream

TODO

deflateParams

Usage is

    $z->deflateParams

TODO

Importing

A number of symbolic constants are required by some methods in IO::Gzip. None are imported by default.

:all

Imports gzip, $GzipError and all symbolic constants that can be used by IO::Gzip. Same as doing this

    use IO::Gzip qw(gzip $GzipError :constants) ;
:constants

Import all symbolic constants. Same as doing this

    use IO::Gzip qw(:flush :level :strategy) ;
:flush

These symbolic constants are used by the flush method.

    Z_NO_FLUSH
    Z_PARTIAL_FLUSH
    Z_SYNC_FLUSH
    Z_FULL_FLUSH
    Z_FINISH
    Z_BLOCK
:level

These symbolic constants are used by the Level option in the constructor.

    Z_NO_COMPRESSION
    Z_BEST_SPEED
    Z_BEST_COMPRESSION
    Z_DEFAULT_COMPRESSION
:strategy

These symbolic constants are used by the Strategy option in the constructor.

    Z_FILTERED
    Z_HUFFMAN_ONLY
    Z_RLE
    Z_FIXED
    Z_DEFAULT_STRATEGY

For

EXAMPLES

TODO

SEE ALSO

Compress::Zlib, IO::Gunzip, IO::Deflate, IO::Inflate, IO::RawDeflate, IO::RawInflate, IO::AnyInflate

Compress::Zlib::FAQ

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

For RFC 1950, 1951 and 1952 see http://www.faqs.org/rfcs/rfc1950.html, http://www.faqs.org/rfcs/rfc1951.html and http://www.faqs.org/rfcs/rfc1952.html

The primary site for the gzip program is http://www.gzip.org.

AUTHOR

The IO::Gzip module was written by Paul Marquess, pmqs@cpan.org. The latest copy of the module can be found on CPAN in modules/by-module/Compress/Compress-Zlib-x.x.tar.gz.

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.

MODIFICATION HISTORY

See the Changes file.

COPYRIGHT AND LICENSE

Copyright (c) 2005 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.