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.\" ========================================================================
.\"
.IX Title "IO::Compress::Gzip 3perl"
.TH IO::Compress::Gzip 3perl "2023-11-25" "perl v5.36.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
IO::Compress::Gzip \- Write RFC 1952 files/buffers
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use IO::Compress::Gzip qw(gzip $GzipError) ;
\&
\&    my $status = gzip $input => $output [,OPTS]
\&        or die "gzip failed: $GzipError\en";
\&
\&    my $z = IO::Compress::Gzip\->new( $output [,OPTS] )
\&        or die "gzip failed: $GzipError\en";
\&
\&    $z\->print($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\->opened();
\&    $z\->autoflush();
\&    $z\->input_line_number();
\&    $z\->newStream( [OPTS] );
\&
\&    $z\->deflateParams();
\&
\&    $z\->close() ;
\&
\&    $GzipError ;
\&
\&    # IO::File mode
\&
\&    print $z $string;
\&    printf $z $format, $string;
\&    tell $z
\&    eof $z
\&    seek $z, $position, $whence
\&    binmode $z
\&    fileno $z
\&    close $z ;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module provides a Perl interface that allows writing compressed
data to files or buffer as defined in \s-1RFC 1952.\s0
.PP
All the gzip headers defined in \s-1RFC 1952\s0 can be created using
this module.
.PP
For reading \s-1RFC 1952\s0 files/buffers, see the companion module
IO::Uncompress::Gunzip.
.SH "Functional Interface"
.IX Header "Functional Interface"
A top-level function, \f(CW\*(C`gzip\*(C'\fR, is provided to carry out
\&\*(L"one-shot\*(R" compression between buffers and/or files. For finer
control over the compression process, see the \*(L"\s-1OO\s0 Interface\*(R"
section.
.PP
.Vb 1
\&    use IO::Compress::Gzip qw(gzip $GzipError) ;
\&
\&    gzip $input_filename_or_reference => $output_filename_or_reference [,OPTS]
\&        or die "gzip failed: $GzipError\en";
.Ve
.PP
The functional interface needs Perl5.005 or better.
.ie n .SS "gzip $input_filename_or_reference => $output_filename_or_reference [, \s-1OPTS\s0]"
.el .SS "gzip \f(CW$input_filename_or_reference\fP => \f(CW$output_filename_or_reference\fP [, \s-1OPTS\s0]"
.IX Subsection "gzip $input_filename_or_reference => $output_filename_or_reference [, OPTS]"
\&\f(CW\*(C`gzip\*(C'\fR expects at least two parameters,
\&\f(CW$input_filename_or_reference\fR and \f(CW$output_filename_or_reference\fR
and zero or more optional parameters (see \*(L"Optional Parameters\*(R")
.PP
\fIThe \f(CI$input_filename_or_reference\fI parameter\fR
.IX Subsection "The $input_filename_or_reference parameter"
.PP
The parameter, \f(CW$input_filename_or_reference\fR, is used to define the
source of the uncompressed data.
.PP
It can take one of the following forms:
.IP "A filename" 5
.IX Item "A filename"
If the \f(CW$input_filename_or_reference\fR parameter is a simple scalar, it is
assumed to be a filename. This file will be opened for reading and the
input data will be read from it.
.IP "A filehandle" 5
.IX Item "A filehandle"
If the \f(CW$input_filename_or_reference\fR parameter is a filehandle, the input
data will be read from it.  The string '\-' can be used as an alias for
standard input.
.IP "A scalar reference" 5
.IX Item "A scalar reference"
If \f(CW$input_filename_or_reference\fR is a scalar reference, the input data
will be read from \f(CW$$input_filename_or_reference\fR.
.IP "An array reference" 5
.IX Item "An array reference"
If \f(CW$input_filename_or_reference\fR is an array reference, each element in
the array must be a filename.
.Sp
The input data will be read from each file in turn.
.Sp
The complete array will be walked to ensure that it only
contains valid filenames before any data is compressed.
.IP "An Input FileGlob string" 5
.IX Item "An Input FileGlob string"
If \f(CW$input_filename_or_reference\fR is a string that is delimited by the
characters \*(L"<\*(R" and \*(L">\*(R" \f(CW\*(C`gzip\*(C'\fR will assume that it is an
\&\fIinput fileglob string\fR. The input is the list of files that match the
fileglob.
.Sp
See File::GlobMapper for more details.
.PP
If the \f(CW$input_filename_or_reference\fR parameter is any other type,
\&\f(CW\*(C`undef\*(C'\fR will be returned.
.PP
In addition, if \f(CW$input_filename_or_reference\fR is a simple filename,
the default values for
the \f(CW\*(C`Name\*(C'\fR and \f(CW\*(C`Time\*(C'\fR options will be sourced from that file.
.PP
If you do not want to use these defaults they can be overridden by
explicitly setting the \f(CW\*(C`Name\*(C'\fR and \f(CW\*(C`Time\*(C'\fR options or by setting the
\&\f(CW\*(C`Minimal\*(C'\fR parameter.
.PP
\fIThe \f(CI$output_filename_or_reference\fI parameter\fR
.IX Subsection "The $output_filename_or_reference parameter"
.PP
The parameter \f(CW$output_filename_or_reference\fR is used to control the
destination of the compressed data. This parameter can take one of
these forms.
.IP "A filename" 5
.IX Item "A filename"
If the \f(CW$output_filename_or_reference\fR 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.
.IP "A filehandle" 5
.IX Item "A filehandle"
If the \f(CW$output_filename_or_reference\fR parameter is a filehandle, the
compressed data will be written to it.  The string '\-' can be used as
an alias for standard output.
.IP "A scalar reference" 5
.IX Item "A scalar reference"
If \f(CW$output_filename_or_reference\fR is a scalar reference, the
compressed data will be stored in \f(CW$$output_filename_or_reference\fR.
.IP "An Array Reference" 5
.IX Item "An Array Reference"
If \f(CW$output_filename_or_reference\fR is an array reference,
the compressed data will be pushed onto the array.
.IP "An Output FileGlob" 5
.IX Item "An Output FileGlob"
If \f(CW$output_filename_or_reference\fR is a string that is delimited by the
characters \*(L"<\*(R" and \*(L">\*(R" \f(CW\*(C`gzip\*(C'\fR will assume that it is an
\&\fIoutput fileglob string\fR. The output is the list of files that match the
fileglob.
.Sp
When \f(CW$output_filename_or_reference\fR is an fileglob string,
\&\f(CW$input_filename_or_reference\fR must also be a fileglob string. Anything
else is an error.
.Sp
See File::GlobMapper for more details.
.PP
If the \f(CW$output_filename_or_reference\fR parameter is any other type,
\&\f(CW\*(C`undef\*(C'\fR will be returned.
.SS "Notes"
.IX Subsection "Notes"
When \f(CW$input_filename_or_reference\fR maps to multiple files/buffers and
\&\f(CW$output_filename_or_reference\fR is a single
file/buffer the input files/buffers will be stored
in \f(CW$output_filename_or_reference\fR as a concatenated series of compressed data streams.
.SS "Optional Parameters"
.IX Subsection "Optional Parameters"
The optional parameters for the one-shot function \f(CW\*(C`gzip\*(C'\fR
are (for the most part) identical to those used with the \s-1OO\s0 interface defined in the
\&\*(L"Constructor Options\*(R" section. The exceptions are listed below
.ie n .IP """AutoClose => 0|1""" 5
.el .IP "\f(CWAutoClose => 0|1\fR" 5
.IX Item "AutoClose => 0|1"
This option applies to any input or output data streams to
\&\f(CW\*(C`gzip\*(C'\fR that are filehandles.
.Sp
If \f(CW\*(C`AutoClose\*(C'\fR is specified, and the value is true, it will result in all
input and/or output filehandles being closed once \f(CW\*(C`gzip\*(C'\fR has
completed.
.Sp
This parameter defaults to 0.
.ie n .IP """BinModeIn => 0|1""" 5
.el .IP "\f(CWBinModeIn => 0|1\fR" 5
.IX Item "BinModeIn => 0|1"
This option is now a no-op. All files will be read in binmode.
.ie n .IP """Append => 0|1""" 5
.el .IP "\f(CWAppend => 0|1\fR" 5
.IX Item "Append => 0|1"
The behaviour of this option is dependent on the type of output data
stream.
.RS 5
.IP "\(bu" 5
A Buffer
.Sp
If \f(CW\*(C`Append\*(C'\fR is enabled, all compressed data will be append to the end of
the output buffer. Otherwise the output buffer will be cleared before any
compressed data is written to it.
.IP "\(bu" 5
A Filename
.Sp
If \f(CW\*(C`Append\*(C'\fR 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.
.IP "\(bu" 5
A Filehandle
.Sp
If \f(CW\*(C`Append\*(C'\fR is enabled, the filehandle will be positioned to the end of
the file via a call to \f(CW\*(C`seek\*(C'\fR before any compressed data is
written to it.  Otherwise the file pointer will not be moved.
.RE
.RS 5
.Sp
When \f(CW\*(C`Append\*(C'\fR is specified, and set to true, it will \fIappend\fR all compressed
data to the output data stream.
.Sp
So when the output is a filehandle it will carry out a seek to the eof
before writing any compressed data. If the output is a filename, it will be opened for
appending. If the output is a buffer, all compressed data will be
appended to the existing buffer.
.Sp
Conversely when \f(CW\*(C`Append\*(C'\fR is not specified, or it is present and is set to
false, it will operate as follows.
.Sp
When the output is a filename, it will truncate the contents of the file
before writing any compressed data. If the output is a filehandle
its position will not be changed. If the output is a buffer, it will be
wiped before any compressed data is output.
.Sp
Defaults to 0.
.RE
.SS "Examples"
.IX Subsection "Examples"
Here are a few example that show the capabilities of the module.
.PP
\fIStreaming\fR
.IX Subsection "Streaming"
.PP
This very simple command line example demonstrates the streaming capabilities of the module.
The code reads data from \s-1STDIN,\s0 compresses it, and writes the compressed data to \s-1STDOUT.\s0
.PP
.Vb 1
\&    $ echo hello world | perl \-MIO::Compress::Gzip=gzip \-e \*(Aqgzip \e*STDIN => \e*STDOUT\*(Aq >output.gz
.Ve
.PP
The special filename \*(L"\-\*(R" can be used as a standin for both \f(CW\*(C`\e*STDIN\*(C'\fR and \f(CW\*(C`\e*STDOUT\*(C'\fR,
so the above can be rewritten as
.PP
.Vb 1
\&    $ echo hello world | perl \-MIO::Compress::Gzip=gzip \-e \*(Aqgzip "\-" => "\-"\*(Aq >output.gz
.Ve
.PP
\fICompressing a file from the filesystem\fR
.IX Subsection "Compressing a file from the filesystem"
.PP
To read the contents of the file \f(CW\*(C`file1.txt\*(C'\fR and write the compressed
data to the file \f(CW\*(C`file1.txt.gz\*(C'\fR.
.PP
.Vb 3
\&    use strict ;
\&    use warnings ;
\&    use IO::Compress::Gzip qw(gzip $GzipError) ;
\&
\&    my $input = "file1.txt";
\&    gzip $input => "$input.gz"
\&        or die "gzip failed: $GzipError\en";
.Ve
.PP
\fIReading from a Filehandle and writing to an in-memory buffer\fR
.IX Subsection "Reading from a Filehandle and writing to an in-memory buffer"
.PP
To read from an existing Perl filehandle, \f(CW$input\fR, and write the
compressed data to a buffer, \f(CW$buffer\fR.
.PP
.Vb 4
\&    use strict ;
\&    use warnings ;
\&    use IO::Compress::Gzip qw(gzip $GzipError) ;
\&    use IO::File ;
\&
\&    my $input = IO::File\->new( "<file1.txt" )
\&        or die "Cannot open \*(Aqfile1.txt\*(Aq: $!\en" ;
\&    my $buffer ;
\&    gzip $input => \e$buffer
\&        or die "gzip failed: $GzipError\en";
.Ve
.PP
\fICompressing multiple files\fR
.IX Subsection "Compressing multiple files"
.PP
To compress all files in the directory \*(L"/my/home\*(R" that match \*(L"*.txt\*(R"
and store the compressed data in the same directory
.PP
.Vb 3
\&    use strict ;
\&    use warnings ;
\&    use IO::Compress::Gzip qw(gzip $GzipError) ;
\&
\&    gzip \*(Aq</my/home/*.txt>\*(Aq => \*(Aq<*.gz>\*(Aq
\&        or die "gzip failed: $GzipError\en";
.Ve
.PP
and if you want to compress each file one at a time, this will do the trick
.PP
.Vb 3
\&    use strict ;
\&    use warnings ;
\&    use IO::Compress::Gzip qw(gzip $GzipError) ;
\&
\&    for my $input ( glob "/my/home/*.txt" )
\&    {
\&        my $output = "$input.gz" ;
\&        gzip $input => $output
\&            or die "Error compressing \*(Aq$input\*(Aq: $GzipError\en";
\&    }
.Ve
.SH "OO Interface"
.IX Header "OO Interface"
.SS "Constructor"
.IX Subsection "Constructor"
The format of the constructor for \f(CW\*(C`IO::Compress::Gzip\*(C'\fR is shown below
.PP
.Vb 2
\&    my $z = IO::Compress::Gzip\->new( $output [,OPTS] )
\&        or die "IO::Compress::Gzip failed: $GzipError\en";
.Ve
.PP
It returns an \f(CW\*(C`IO::Compress::Gzip\*(C'\fR object on success and undef on failure.
The variable \f(CW$GzipError\fR will contain an error message on failure.
.PP
If you are running Perl 5.005 or better the object, \f(CW$z\fR, returned from
IO::Compress::Gzip can be used exactly like an IO::File filehandle.
This means that all normal output file operations can be carried out
with \f(CW$z\fR.
For example, to write to a compressed file/buffer you can use either of
these forms
.PP
.Vb 2
\&    $z\->print("hello world\en");
\&    print $z "hello world\en";
.Ve
.PP
The mandatory parameter \f(CW$output\fR is used to control the destination
of the compressed data. This parameter can take one of these forms.
.IP "A filename" 5
.IX Item "A filename"
If the \f(CW$output\fR parameter is a simple scalar, it is assumed to be a
filename. This file will be opened for writing and the compressed data
will be written to it.
.IP "A filehandle" 5
.IX Item "A filehandle"
If the \f(CW$output\fR parameter is a filehandle, the compressed data will be
written to it.
The string '\-' can be used as an alias for standard output.
.IP "A scalar reference" 5
.IX Item "A scalar reference"
If \f(CW$output\fR is a scalar reference, the compressed data will be stored
in \f(CW$$output\fR.
.PP
If the \f(CW$output\fR parameter is any other type, \f(CW\*(C`IO::Compress::Gzip\*(C'\fR::new will
return undef.
.SS "Constructor Options"
.IX Subsection "Constructor Options"
\&\f(CW\*(C`OPTS\*(C'\fR is any combination of zero or more the following options:
.ie n .IP """AutoClose => 0|1""" 5
.el .IP "\f(CWAutoClose => 0|1\fR" 5
.IX Item "AutoClose => 0|1"
This option is only valid when the \f(CW$output\fR parameter is a filehandle. If
specified, and the value is true, it will result in the \f(CW$output\fR being
closed once either the \f(CW\*(C`close\*(C'\fR method is called or the \f(CW\*(C`IO::Compress::Gzip\*(C'\fR
object is destroyed.
.Sp
This parameter defaults to 0.
.ie n .IP """Append => 0|1""" 5
.el .IP "\f(CWAppend => 0|1\fR" 5
.IX Item "Append => 0|1"
Opens \f(CW$output\fR in append mode.
.Sp
The behaviour of this option is dependent on the type of \f(CW$output\fR.
.RS 5
.IP "\(bu" 5
A Buffer
.Sp
If \f(CW$output\fR is a buffer and \f(CW\*(C`Append\*(C'\fR is enabled, all compressed data
will be append to the end of \f(CW$output\fR. Otherwise \f(CW$output\fR will be
cleared before any data is written to it.
.IP "\(bu" 5
A Filename
.Sp
If \f(CW$output\fR is a filename and \f(CW\*(C`Append\*(C'\fR 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.
.IP "\(bu" 5
A Filehandle
.Sp
If \f(CW$output\fR is a filehandle, the file pointer will be positioned to the
end of the file via a call to \f(CW\*(C`seek\*(C'\fR before any compressed data is written
to it.  Otherwise the file pointer will not be moved.
.RE
.RS 5
.Sp
This parameter defaults to 0.
.RE
.ie n .IP """Merge => 0|1""" 5
.el .IP "\f(CWMerge => 0|1\fR" 5
.IX Item "Merge => 0|1"
This option is used to compress input data and append it to an existing
compressed data stream in \f(CW$output\fR. The end result is a single compressed
data stream stored in \f(CW$output\fR.
.Sp
It is a fatal error to attempt to use this option when \f(CW$output\fR is not an
\&\s-1RFC 1952\s0 data stream.
.Sp
There are a number of other limitations with the \f(CW\*(C`Merge\*(C'\fR option:
.RS 5
.IP "1." 5
This module needs to have been built with zlib 1.2.1 or better to work. A
fatal error will be thrown if \f(CW\*(C`Merge\*(C'\fR is used with an older version of
zlib.
.IP "2." 5
If \f(CW$output\fR is a file or a filehandle, it must be seekable.
.RE
.RS 5
.Sp
This parameter defaults to 0.
.RE
.IP "\-Level" 5
.IX Item "-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.
.Sp
.Vb 4
\&   Z_NO_COMPRESSION
\&   Z_BEST_SPEED
\&   Z_BEST_COMPRESSION
\&   Z_DEFAULT_COMPRESSION
.Ve
.Sp
The default is Z_DEFAULT_COMPRESSION.
.Sp
Note, these constants are not imported by \f(CW\*(C`IO::Compress::Gzip\*(C'\fR by default.
.Sp
.Vb 3
\&    use IO::Compress::Gzip qw(:strategy);
\&    use IO::Compress::Gzip qw(:constants);
\&    use IO::Compress::Gzip qw(:all);
.Ve
.IP "\-Strategy" 5
.IX Item "-Strategy"
Defines the strategy used to tune the compression. Use one of the symbolic
constants defined below.
.Sp
.Vb 5
\&   Z_FILTERED
\&   Z_HUFFMAN_ONLY
\&   Z_RLE
\&   Z_FIXED
\&   Z_DEFAULT_STRATEGY
.Ve
.Sp
The default is Z_DEFAULT_STRATEGY.
.ie n .IP """Minimal => 0|1""" 5
.el .IP "\f(CWMinimal => 0|1\fR" 5
.IX Item "Minimal => 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
\&\s-1RFC 1952.\s0
.Sp
See the section titled \*(L"Compliance\*(R" in \s-1RFC 1952\s0 for a definition
of the values used for the fields in the gzip header.
.Sp
All other parameters that control the content of the gzip header will
be ignored if this parameter is set to 1.
.Sp
This parameter defaults to 0.
.ie n .IP """Comment => $comment""" 5
.el .IP "\f(CWComment => $comment\fR" 5
.IX Item "Comment => $comment"
Stores the contents of \f(CW$comment\fR in the \s-1COMMENT\s0 field in
the gzip header.
By default, no comment field is written to the gzip file.
.Sp
If the \f(CW\*(C`\-Strict\*(C'\fR option is enabled, the comment can only consist of \s-1ISO
8859\-1\s0 characters plus line feed.
.Sp
If the \f(CW\*(C`\-Strict\*(C'\fR option is disabled, the comment field can contain any
character except \s-1NULL.\s0 If any null characters are present, the field
will be truncated at the first \s-1NULL.\s0
.ie n .IP """Name => $string""" 5
.el .IP "\f(CWName => $string\fR" 5
.IX Item "Name => $string"
Stores the contents of \f(CW$string\fR in the gzip \s-1NAME\s0 header field. If
\&\f(CW\*(C`Name\*(C'\fR is not specified, no gzip \s-1NAME\s0 field will be created.
.Sp
If the \f(CW\*(C`\-Strict\*(C'\fR option is enabled, \f(CW$string\fR can only consist of \s-1ISO
8859\-1\s0 characters.
.Sp
If \f(CW\*(C`\-Strict\*(C'\fR is disabled, then \f(CW$string\fR can contain any character
except \s-1NULL.\s0 If any null characters are present, the field will be
truncated at the first \s-1NULL.\s0
.ie n .IP """Time => $number""" 5
.el .IP "\f(CWTime => $number\fR" 5
.IX Item "Time => $number"
Sets the \s-1MTIME\s0 field in the gzip header to \f(CW$number\fR.
.Sp
This field defaults to the time the \f(CW\*(C`IO::Compress::Gzip\*(C'\fR object was created
if this option is not specified.
.ie n .IP """TextFlag => 0|1""" 5
.el .IP "\f(CWTextFlag => 0|1\fR" 5
.IX Item "TextFlag => 0|1"
This parameter controls the setting of the \s-1FLG.FTEXT\s0 bit in the gzip
header. It is used to signal that the data stored in the gzip file/buffer
is probably text.
.Sp
The default is 0.
.ie n .IP """HeaderCRC => 0|1""" 5
.el .IP "\f(CWHeaderCRC => 0|1\fR" 5
.IX Item "HeaderCRC => 0|1"
When true this parameter will set the \s-1FLG.FHCRC\s0 bit to 1 in the gzip header
and set the \s-1CRC16\s0 header field to the \s-1CRC\s0 of the complete gzip header
except the \s-1CRC16\s0 field itself.
.Sp
\&\fBNote\fR that gzip files created with the \f(CW\*(C`HeaderCRC\*(C'\fR flag set to 1 cannot
be read by most, if not all, of the standard gunzip utilities, most
notably gzip version 1.2.4. You should therefore avoid using this option if
you want to maximize the portability of your gzip files.
.Sp
This parameter defaults to 0.
.ie n .IP """OS_Code => $value""" 5
.el .IP "\f(CWOS_Code => $value\fR" 5
.IX Item "OS_Code => $value"
Stores \f(CW$value\fR in the gzip \s-1OS\s0 header field. A number between 0 and 255 is
valid.
.Sp
If not specified, this parameter defaults to the \s-1OS\s0 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.
.ie n .IP """ExtraField => $data""" 5
.el .IP "\f(CWExtraField => $data\fR" 5
.IX Item "ExtraField => $data"
This parameter allows additional metadata to be stored in the ExtraField in
the gzip header. An \s-1RFC 1952\s0 compliant ExtraField consists of zero or more
subfields. Each subfield consists of a two byte header followed by the
subfield data.
.Sp
The list of subfields can be supplied in any of the following formats
.Sp
.Vb 12
\&    \-ExtraField => [$id1, $data1,
\&                    $id2, $data2,
\&                     ...
\&                   ]
\&    \-ExtraField => [ [$id1 => $data1],
\&                     [$id2 => $data2],
\&                     ...
\&                   ]
\&    \-ExtraField => { $id1 => $data1,
\&                     $id2 => $data2,
\&                     ...
\&                   }
.Ve
.Sp
Where \f(CW$id1\fR, \f(CW$id2\fR are two byte subfield \s-1ID\s0's. The second byte of
the \s-1ID\s0 cannot be 0, unless the \f(CW\*(C`Strict\*(C'\fR option has been disabled.
.Sp
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 \s-1ID.\s0
.Sp
Alternatively the list of subfields can by supplied as a scalar, thus
.Sp
.Vb 1
\&    \-ExtraField => $rawdata
.Ve
.Sp
If you use the raw format, and the \f(CW\*(C`Strict\*(C'\fR option is enabled,
\&\f(CW\*(C`IO::Compress::Gzip\*(C'\fR will check that \f(CW$rawdata\fR consists of zero or more
conformant sub-fields. When \f(CW\*(C`Strict\*(C'\fR is disabled, \f(CW$rawdata\fR can
consist of any arbitrary byte stream.
.Sp
The maximum size of the Extra Field 65535 bytes.
.ie n .IP """ExtraFlags => $value""" 5
.el .IP "\f(CWExtraFlags => $value\fR" 5
.IX Item "ExtraFlags => $value"
Sets the \s-1XFL\s0 byte in the gzip header to \f(CW$value\fR.
.Sp
If this option is not present, the value stored in \s-1XFL\s0 field will be
determined by the setting of the \f(CW\*(C`Level\*(C'\fR option.
.Sp
If \f(CW\*(C`Level => Z_BEST_SPEED\*(C'\fR has been specified then \s-1XFL\s0 is set to 2.
If \f(CW\*(C`Level => Z_BEST_COMPRESSION\*(C'\fR has been specified then \s-1XFL\s0 is set to 4.
Otherwise \s-1XFL\s0 is set to 0.
.ie n .IP """Strict => 0|1""" 5
.el .IP "\f(CWStrict => 0|1\fR" 5
.IX Item "Strict => 0|1"
\&\f(CW\*(C`Strict\*(C'\fR will optionally police the values supplied with other options
to ensure they are compliant with \s-1RFC1952.\s0
.Sp
This option is enabled by default.
.Sp
If \f(CW\*(C`Strict\*(C'\fR is enabled the following behaviour will be policed:
.RS 5
.IP "\(bu" 5
The value supplied with the \f(CW\*(C`Name\*(C'\fR option can only contain \s-1ISO 8859\-1\s0
characters.
.IP "\(bu" 5
The value supplied with the \f(CW\*(C`Comment\*(C'\fR option can only contain \s-1ISO 8859\-1\s0
characters plus line-feed.
.IP "\(bu" 5
The values supplied with the \f(CW\*(C`\-Name\*(C'\fR and \f(CW\*(C`\-Comment\*(C'\fR options cannot
contain multiple embedded nulls.
.IP "\(bu" 5
If an \f(CW\*(C`ExtraField\*(C'\fR option is specified and it is a simple scalar,
it must conform to the sub-field structure as defined in \s-1RFC 1952.\s0
.IP "\(bu" 5
If an \f(CW\*(C`ExtraField\*(C'\fR option is specified the second byte of the \s-1ID\s0 will be
checked in each subfield to ensure that it does not contain the reserved
value 0x00.
.RE
.RS 5
.Sp
When \f(CW\*(C`Strict\*(C'\fR is disabled the following behaviour will be policed:
.IP "\(bu" 5
The value supplied with \f(CW\*(C`\-Name\*(C'\fR option can contain
any character except \s-1NULL.\s0
.IP "\(bu" 5
The value supplied with \f(CW\*(C`\-Comment\*(C'\fR option can contain any character
except \s-1NULL.\s0
.IP "\(bu" 5
The values supplied with the \f(CW\*(C`\-Name\*(C'\fR and \f(CW\*(C`\-Comment\*(C'\fR 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
\&\s-1NULL.\s0
.IP "\(bu" 5
If an \f(CW\*(C`ExtraField\*(C'\fR 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.
.IP "\(bu" 5
The \s-1ID\s0 header in an \f(CW\*(C`ExtraField\*(C'\fR sub-field can consist of any two bytes.
.RE
.RS 5
.RE
.SS "Examples"
.IX Subsection "Examples"
\&\s-1TODO\s0
.SH "Methods"
.IX Header "Methods"
.SS "print"
.IX Subsection "print"
Usage is
.PP
.Vb 2
\&    $z\->print($data)
\&    print $z $data
.Ve
.PP
Compresses and outputs the contents of the \f(CW$data\fR parameter. This
has the same behaviour as the \f(CW\*(C`print\*(C'\fR built-in.
.PP
Returns true if successful.
.SS "printf"
.IX Subsection "printf"
Usage is
.PP
.Vb 2
\&    $z\->printf($format, $data)
\&    printf $z $format, $data
.Ve
.PP
Compresses and outputs the contents of the \f(CW$data\fR parameter.
.PP
Returns true if successful.
.SS "syswrite"
.IX Subsection "syswrite"
Usage is
.PP
.Vb 3
\&    $z\->syswrite $data
\&    $z\->syswrite $data, $length
\&    $z\->syswrite $data, $length, $offset
.Ve
.PP
Compresses and outputs the contents of the \f(CW$data\fR parameter.
.PP
Returns the number of uncompressed bytes written, or \f(CW\*(C`undef\*(C'\fR if
unsuccessful.
.SS "write"
.IX Subsection "write"
Usage is
.PP
.Vb 3
\&    $z\->write $data
\&    $z\->write $data, $length
\&    $z\->write $data, $length, $offset
.Ve
.PP
Compresses and outputs the contents of the \f(CW$data\fR parameter.
.PP
Returns the number of uncompressed bytes written, or \f(CW\*(C`undef\*(C'\fR if
unsuccessful.
.SS "flush"
.IX Subsection "flush"
Usage is
.PP
.Vb 2
\&    $z\->flush;
\&    $z\->flush($flush_type);
.Ve
.PP
Flushes any pending compressed data to the output file/buffer.
.PP
This method takes an optional parameter, \f(CW$flush_type\fR, that controls
how the flushing will be carried out. By default the \f(CW$flush_type\fR
used is \f(CW\*(C`Z_FINISH\*(C'\fR. Other valid values for \f(CW$flush_type\fR are
\&\f(CW\*(C`Z_NO_FLUSH\*(C'\fR, \f(CW\*(C`Z_SYNC_FLUSH\*(C'\fR, \f(CW\*(C`Z_FULL_FLUSH\*(C'\fR and \f(CW\*(C`Z_BLOCK\*(C'\fR. It is
strongly recommended that you only set the \f(CW\*(C`flush_type\*(C'\fR parameter if
you fully understand the implications of what it does \- overuse of \f(CW\*(C`flush\*(C'\fR
can seriously degrade the level of compression achieved. See the \f(CW\*(C`zlib\*(C'\fR
documentation for details.
.PP
Returns true on success.
.SS "tell"
.IX Subsection "tell"
Usage is
.PP
.Vb 2
\&    $z\->tell()
\&    tell $z
.Ve
.PP
Returns the uncompressed file offset.
.SS "eof"
.IX Subsection "eof"
Usage is
.PP
.Vb 2
\&    $z\->eof();
\&    eof($z);
.Ve
.PP
Returns true if the \f(CW\*(C`close\*(C'\fR method has been called.
.SS "seek"
.IX Subsection "seek"
.Vb 2
\&    $z\->seek($position, $whence);
\&    seek($z, $position, $whence);
.Ve
.PP
Provides a sub-set of the \f(CW\*(C`seek\*(C'\fR functionality, with the restriction
that it is only legal to seek forward in the output file/buffer.
It is a fatal error to attempt to seek backward.
.PP
Empty parts of the file/buffer will have \s-1NULL\s0 (0x00) bytes written to them.
.PP
The \f(CW$whence\fR parameter takes one the usual values, namely \s-1SEEK_SET,
SEEK_CUR\s0 or \s-1SEEK_END.\s0
.PP
Returns 1 on success, 0 on failure.
.SS "binmode"
.IX Subsection "binmode"
Usage is
.PP
.Vb 2
\&    $z\->binmode
\&    binmode $z ;
.Ve
.PP
This is a noop provided for completeness.
.SS "opened"
.IX Subsection "opened"
.Vb 1
\&    $z\->opened()
.Ve
.PP
Returns true if the object currently refers to a opened file/buffer.
.SS "autoflush"
.IX Subsection "autoflush"
.Vb 2
\&    my $prev = $z\->autoflush()
\&    my $prev = $z\->autoflush(EXPR)
.Ve
.PP
If the \f(CW$z\fR object is associated with a file or a filehandle, this method
returns the current autoflush setting for the underlying filehandle. If
\&\f(CW\*(C`EXPR\*(C'\fR is present, and is non-zero, it will enable flushing after every
write/print operation.
.PP
If \f(CW$z\fR is associated with a buffer, this method has no effect and always
returns \f(CW\*(C`undef\*(C'\fR.
.PP
\&\fBNote\fR that the special variable \f(CW$|\fR \fBcannot\fR be used to set or
retrieve the autoflush setting.
.SS "input_line_number"
.IX Subsection "input_line_number"
.Vb 2
\&    $z\->input_line_number()
\&    $z\->input_line_number(EXPR)
.Ve
.PP
This method always returns \f(CW\*(C`undef\*(C'\fR when compressing.
.SS "fileno"
.IX Subsection "fileno"
.Vb 2
\&    $z\->fileno()
\&    fileno($z)
.Ve
.PP
If the \f(CW$z\fR object is associated with a file or a filehandle, \f(CW\*(C`fileno\*(C'\fR
will return the underlying file descriptor. Once the \f(CW\*(C`close\*(C'\fR method is
called \f(CW\*(C`fileno\*(C'\fR will return \f(CW\*(C`undef\*(C'\fR.
.PP
If the \f(CW$z\fR object is associated with a buffer, this method will return
\&\f(CW\*(C`undef\*(C'\fR.
.SS "close"
.IX Subsection "close"
.Vb 2
\&    $z\->close() ;
\&    close $z ;
.Ve
.PP
Flushes any pending compressed data and then closes the output file/buffer.
.PP
For most versions of Perl this method will be automatically invoked if
the IO::Compress::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 \f(CW\*(C`close\*(C'\fR method will be called automatically, but
not until global destruction of all live objects when the program is
terminating.
.PP
Therefore, if you want your scripts to be able to run on all versions
of Perl, you should call \f(CW\*(C`close\*(C'\fR explicitly and not rely on automatic
closing.
.PP
Returns true on success, otherwise 0.
.PP
If the \f(CW\*(C`AutoClose\*(C'\fR option has been enabled when the IO::Compress::Gzip
object was created, and the object is associated with a file, the
underlying file will also be closed.
.SS "newStream([\s-1OPTS\s0])"
.IX Subsection "newStream([OPTS])"
Usage is
.PP
.Vb 1
\&    $z\->newStream( [OPTS] )
.Ve
.PP
Closes the current compressed data stream and starts a new one.
.PP
\&\s-1OPTS\s0 consists of any of the options that are available when creating
the \f(CW$z\fR object.
.PP
See the \*(L"Constructor Options\*(R" section for more details.
.SS "deflateParams"
.IX Subsection "deflateParams"
Usage is
.PP
.Vb 1
\&    $z\->deflateParams
.Ve
.PP
\&\s-1TODO\s0
.SH "Importing"
.IX Header "Importing"
A number of symbolic constants are required by some methods in
\&\f(CW\*(C`IO::Compress::Gzip\*(C'\fR. None are imported by default.
.IP ":all" 5
.IX Item ":all"
Imports \f(CW\*(C`gzip\*(C'\fR, \f(CW$GzipError\fR and all symbolic
constants that can be used by \f(CW\*(C`IO::Compress::Gzip\*(C'\fR. Same as doing this
.Sp
.Vb 1
\&    use IO::Compress::Gzip qw(gzip $GzipError :constants) ;
.Ve
.IP ":constants" 5
.IX Item ":constants"
Import all symbolic constants. Same as doing this
.Sp
.Vb 1
\&    use IO::Compress::Gzip qw(:flush :level :strategy) ;
.Ve
.IP ":flush" 5
.IX Item ":flush"
These symbolic constants are used by the \f(CW\*(C`flush\*(C'\fR method.
.Sp
.Vb 6
\&    Z_NO_FLUSH
\&    Z_PARTIAL_FLUSH
\&    Z_SYNC_FLUSH
\&    Z_FULL_FLUSH
\&    Z_FINISH
\&    Z_BLOCK
.Ve
.IP ":level" 5
.IX Item ":level"
These symbolic constants are used by the \f(CW\*(C`Level\*(C'\fR option in the constructor.
.Sp
.Vb 4
\&    Z_NO_COMPRESSION
\&    Z_BEST_SPEED
\&    Z_BEST_COMPRESSION
\&    Z_DEFAULT_COMPRESSION
.Ve
.IP ":strategy" 5
.IX Item ":strategy"
These symbolic constants are used by the \f(CW\*(C`Strategy\*(C'\fR option in the constructor.
.Sp
.Vb 5
\&    Z_FILTERED
\&    Z_HUFFMAN_ONLY
\&    Z_RLE
\&    Z_FIXED
\&    Z_DEFAULT_STRATEGY
.Ve
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.SS "Apache::GZip Revisited"
.IX Subsection "Apache::GZip Revisited"
See IO::Compress::FAQ
.SS "Working with Net::FTP"
.IX Subsection "Working with Net::FTP"
See IO::Compress::FAQ
.SH "SUPPORT"
.IX Header "SUPPORT"
General feedback/questions/bug reports should be sent to
<https://github.com/pmqs/IO\-Copress/issues> (preferred) or
<https://rt.cpan.org/Public/Dist/Display.html?Name=IO\-Copress>.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Compress::Zlib, 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
.PP
IO::Compress::FAQ
.PP
File::GlobMapper, Archive::Zip,
Archive::Tar,
IO::Zlib
.PP
For \s-1RFC 1950, 1951\s0 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>
.PP
The \fIzlib\fR compression library was written by Jean-loup Gailly
\&\f(CW\*(C`gzip@prep.ai.mit.edu\*(C'\fR and Mark Adler \f(CW\*(C`madler@alumni.caltech.edu\*(C'\fR.
.PP
The primary site for the \fIzlib\fR compression library is
<http://www.zlib.org>.
.PP
The primary site for gzip is <http://www.gzip.org>.
.SH "AUTHOR"
.IX Header "AUTHOR"
This module was written by Paul Marquess, \f(CW\*(C`pmqs@cpan.org\*(C'\fR.
.SH "MODIFICATION HISTORY"
.IX Header "MODIFICATION HISTORY"
See the Changes file.
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright (c) 2005\-2022 Paul Marquess. All rights reserved.
.PP
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.