Ryo Anazawa > CGI-Header-0.13 > CGI::Header



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Module Version: 0.13   Source   Latest Release: CGI-Header-0.63


CGI::Header - Adapter for CGI::header() function


  use CGI::Header;

  # CGI.pm-compatible HTTP header properties
  my $header = {
      -attachment => 'foo.gif',
      -charset    => 'utf-7',
      -cookie     => [ $cookie1, $cookie2 ], # CGI::Cookie objects
      -expires    => '+3d',
      -nph        => 1,
      -p3p        => [qw/CAO DSP LAW CURa/],
      -target     => 'ResultsWindow',
      -type       => 'image/gif'

  # create a CGI::Header object
  my $h = CGI::Header->new( $header );

  # update $header
  $h->set( 'Content-Length' => 3002 );
  $h->delete( 'Content-Disposition' );

  $h->header; # same reference as $header


This module is a utility class to manipulate a hash reference which CGI's header() function receives. This class is, so to speak, a subclass of Hash because the function behaves like a hash, while Perl5 doesn't provide a built-in class called Hash.

This module isn't the replacement of the function. Although this class implements as_string() method, the function should stringify the reference in most cases.

This module can be used in the following situation:

1. $header is a hash reference which represents CGI response headers

For example, CGI::Application implements header_add() method which can be used to add CGI.pm-compatible HTTP header properties. Instances of CGI applications often hold those properties.

  my $header = { -type => 'text/plain' };
2. Manipulates $header using CGI::Header

Since property names are case-insensitive, application developers have to normalize them manually when they specify header properties. CGI::Header normalizes them automatically.

  use CGI::Header;

  my $h = CGI::Header->new( $header );
  $h->set( 'Content-Length' => 3002 ); # add Content-Length header

  # => {
  #     -type => 'text/plain',
  #     -content_length => '3002',
  # }
3. Passes $header to CGI::header() to stringify the variable
  use CGI;

  print CGI::header( $header );
  # Content-length: 3002
  # Content-Type: text/plain; charset=ISO-8859-1

header() function just stringifies given header properties. This module can be used to generate PSGI-compatible header array references. See also flatten().


$header = CGI::Header->new({ -type => 'text/plain', ... })

Given a header hash reference, returns a CGI::Header object which holds a reference to the original given argument:

  my $header = { -type => 'text/plain' };
  my $h = CGI::Header->new( $header );
  $h->header; # same reference as $header

The object updates the reference when called write methods like set(), delete() or clear():

  # updates $header
  $h->set( 'Content-Length' => 3002 );
  $h->delete( 'Content-Disposition' );
$header = CGI::Header->new( -type => 'text/plain', ... )

A shortcut for:

  my $header = CGI::Header->new({ -type => 'text/plain', ... });



Returns the header hash reference associated with this CGI::Header object.

$self = $header->rehash

Rebuilds the header hash to normalize parameter names without changing the reference. Returns this object itself. If parameter names aren't normalized, the methods listed below won't work as you expect.

  my $h1 = $header->header;
  # => {
  #     '-content_type'   => 'text/plain',
  #     'Set-Cookie'      => 'ID=123456; path=/',
  #     'expires'         => '+3d',
  #     '-target'         => 'ResultsWindow',
  #     '-content-length' => '3002'
  # }


  my $h2 = $header->header; # same reference as $h1
  # => {
  #     '-type'           => 'text/plain',
  #     '-cookie'         => 'ID=123456; path=/',
  #     '-expires'        => '+3d',
  #     '-target'         => 'ResultsWindow',
  #     '-content_length' => '3002'
  # }

Normalized parameter names are:

1. lowercased
  'Content-Length' -> 'content-length'
2. start with a dash
  'content-length' -> '-content-length'
3. use underscores instead of dashes except for the first character
  '-content-length' -> '-content_length'

CGI::header() also accepts aliases of parameter names. This module converts them as follows:

 '-content_type'  -> '-type'
 '-set_cookie'    -> '-cookie'
 '-cookies'       -> '-cookie'
 '-window_target' -> '-target'

NOTE: new() doesn't check whether parameter names are normalized or not at all, and so you have to rehash() the header hash explicitly when you aren't sure that they are normalized.

$value = $header->get( $field )
$value = $header->set( $field => $value )

Get or set the value of the header field. The header field name ($field) is not case sensitive. You can use underscores as a replacement for dashes in header names.

  # field names are case-insensitive
  $header->get( 'Content-Length' );
  $header->get( 'content-length' );

The $value argument may be a plain string or a reference to an array of CGI::Cookie objects for the Set-Cookie header.

  $header->set( 'Content-Length' => 3002 );
  my $length = $header->get( 'Content-Length' ); # => 3002

  # $cookie1 and $cookie2 are CGI::Cookie objects
  $header->set( 'Set-Cookie' => [$cookie1, $cookie2] );
  my $cookies = $header->get( 'Set-Cookie' ); # => [ $cookie1, $cookie2 ]
$bool = $header->exists( $field )

Returns a Boolean value telling whether the specified field exists.

  if ( $header->exists('ETag') ) {
$value = $header->delete( $field )

Deletes the specified field form CGI response headers. Returns the value of the deleted field.

  my $value = $header->delete( 'Content-Disposition' ); # => 'inline'
$self = $header->clear

This will remove all header fields.

$bool = $header->is_empty

Returns true if the header contains no key-value pairs.


  if ( $header->is_empty ) { # true
$clone = $header->clone

Returns a copy of this CGI::Header object. It's identical to:

  my %copy = %{ $header->header }; # shallow copy
  my $clone = CGI::Header->new( \%copy );
$filename = $header->attachment
$header->attachment( $filename )

Can be used to turn the page into an attachment. Represents suggested name for the saved file.

  $header->attachment( 'genome.jpg' );
  my $filename = $header->attachment; # => "genome.jpg"

In this case, the outgoing header will be formatted as:

  Content-Disposition: attachment; filename="genome.jpg"
@tags = $header->p3p_tags
$header->p3p_tags( @tags )

Represents P3P tags. The parameter can be an array or a space-delimited string. Returns a list of P3P tags. (In scalar context, returns the number of P3P tags.)

  $header->p3p_tags(qw/CAO DSP LAW CURa/);
  # or
  $header->p3p_tags( 'CAO DSP LAW CURa' );

  my @tags = $header->p3p_tags; # => ("CAO", "DSP", "LAW", "CURa")
  my $size = $header->p3p_tags; # => 4

In this case, the outgoing header will be formatted as:

  P3P: policyref="/w3c/p3p.xml", CP="CAO DSP LAW CURa"
$format = $header->expires
$header->expires( $format )

The Expires header gives the date and time after which the entity should be considered stale. You can specify an absolute or relative expiration interval. The following forms are all valid for this field:

  $header->expires( '+30s' ); # 30 seconds from now
  $header->expires( '+10m' ); # ten minutes from now
  $header->expires( '+1h'  ); # one hour from now
  $header->expires( 'now'  ); # immediately
  $header->expires( '+3M'  ); # in three months
  $header->expires( '+10y' ); # in ten years time

  # at the indicated time & date
  $header->expires( 'Thu, 25 Apr 1999 00:40:33 GMT' );

If set to a true value, will issue the correct headers to work with a NPH (no-parse-header) script.

  $header->nph( 1 );
  my $nph = $header->nph; # => 1
@fields = $header->field_names

Returns the list of distinct field names present in the header in a random order. The field names have case as returned by CGI::header().

  my @fields = $header->field_names;
  # => ( 'Set-Cookie', 'Content-length', 'Content-Type' )
$self = $header->each( \&callback )

Apply a subroutine to each header field in turn. The callback routine is called with two parameters; the name of the field and a value. If the Set-Cookie header is multi-valued, then the routine is called once for each value. Any return values of the callback routine are ignored.

  my @lines;
  $header->each(sub {
      my ( $field, $value ) = @_;
      push @lines, "$field: $value";

  print join @lines, "\n";
  # Content-length: 3002
  # Content-Type: text/plain
@headers = $header->flatten
@headers = $header->flatten( $is_recursive )

Returns pairs of fields and values. This method flattens the Set-Cookie headers recursively by default. The optional $is_recursive argument determines whether to flatten them recursively.

  my $header = CGI::Header->new( -cookie => ['cookie1', 'cookie2'] );

  # => (
  #     'Set-Cookie'   => 'cookie1',
  #     'Set-Cookie'   => 'cookie2',
  #     'Date'         => 'Thu, 25 Apr 1999 00:40:33 GMT',
  #     'Content-Type' => 'text/html'
  # )

  # => (
  #     'Set-Cookie'   => ['cookie1', 'cookie2'],
  #     'Date'         => 'Thu, 25 Apr 1999 00:40:33 GMT',
  #     'Content-Type' => 'text/html'
  # )

This method can be used to generate PSGI-compatible header array references. For example,

  use parent 'CGI';
  use CGI::Header;

  sub psgi_header {
      my $self   = shift;
      my $header = CGI::Header->new(@_)->rehash;

      my $status = $header->delete('Status') || '200 OK';
      $status =~ s/\D*$//;

      $status, [ $header->flatten ];

Strictly speaking, you have to check charset() attribute of CGI.pm. In addition, if $header->nph is true, $header->flatten will return the Server header which psgi_header() shouldn't return. Moreover, this method depends on a global variable %ENV.

See also CGI::Emulate::PSGI, CGI::PSGI.

$header->as_string( $eol )

Returns the header fields as a formatted MIME header. The optional $eol parameter specifies the line ending sequence to use. The default is \015\012.

When valid multi-line headers are included, this method will always output them back as a single line, according to the folding rules of RFC 2616: the newlines will be removed, while the white space remains.

Unlike CGI.pm, when invalid newlines are included, this module removes them instead of throwing exceptions.

If $header->nph is true, the Status-Line will be added to the beginning of response headers automatically.


  # HTTP/1.1 200 OK
  # Server: Apache/1.3.27 (Unix)
  # ...


  use CGI::Header;

  my $header = { -type => 'text/plain' };
  tie my %header => 'CGI::Header' => $header;

  # update $header
  $header{'Content-Length'} = 3002;
  delete $header{'Content-Disposition'};
  %header = ();

  tied( %header )->header; # same reference as $header

Above methods are aliased as follows:

  TIEHASH -> new
  FETCH   -> get
  STORE   -> set
  DELETE  -> delete
  CLEAR   -> clear
  EXISTS  -> exists
  SCALAR  -> !is_empty

You can also iterate through the tied hash:

  my @fields = keys %header;
  my @values = values %header;
  my ( $field, $value ) = each %header;

See also perltie.



You can set the Content-Type header to neither undef nor an empty:

  # wrong
  $header->set( 'Content-Type' => undef );
  $header->set( 'Content-Type' => q{} );

Use delete() instead:

  $header->delete( 'Content-Type' );

If one of the following conditions is met, the Date header will be set automatically:

  if ( $header->nph or $header->get('Set-Cookie') or $header->expires ) {
      my $date = $header->get( 'Date' ); # => HTTP-Date (current time)

and also the header field will become read-only:

  # wrong
  $header->set( 'Date' => 'Thu, 25 Apr 1999 00:40:33 GMT' );
  $header->delete( 'Date' );

You can't assign to the Expires header directly:

  # wrong
  $header->set( 'Expires' => '+3d' );

Use expires() instead:

  $header->expires( '+3d' );

because the following behavior will surprise us:

  my $value = $header->get( 'Expires' );
  # => "Thu, 25 Apr 1999 00:40:33 GMT" (not "+3d")

You can't assign to the P3P header directly:

  # wrong
  $header->set( 'P3P' => '/path/to/p3p.xml' );

CGI::header() restricts where the policy-reference file is located, and so you can't modify the location (/w3c/p3p.xml). You're allowed to set P3P tags using p3p_tags().


If the following condition is met, the Server header will be set automatically:

  if ( $header->nph ) {
      my $server = $header->get( 'Server' ); # => $ENV{SERVER_SOFTWARE}

and also the header field will become read-only:

  # wrong
  $header->set( 'Server' => 'Apache/1.3.27 (Unix)' );
  $header->delete( 'Server' );


CGI, Plack::Util, HTTP::Headers


There are no known bugs in this module. Please report problems to ANAZAWA (anazawa@cpan.org). Patches are welcome.


Ryo Anazawa (anazawa@cpan.org)


This module is free software; you can redistibute it and/or modify it under the same terms as Perl itself. See perlartistic.

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