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HTTP::Headers(3)      User Contributed Perl Documentation     HTTP::Headers(3)

       HTTP::Headers - Class encapsulating HTTP	Message	headers

       version 6.33

	require	HTTP::Headers;
	$h = HTTP::Headers->new;

	$h->header('Content-Type' => 'text/plain');  # set
	$ct = $h->header('Content-Type');	     # get
	$h->remove_header('Content-Type');	     # delete

       The "HTTP::Headers" class encapsulates HTTP-style message headers.  The
       headers consist of attribute-value pairs	also called fields, which may
       be repeated, and	which are printed in a particular order.  The field
       names are cases insensitive.

       Instances of this class are usually created as member variables of the
       "HTTP::Request" and "HTTP::Response" classes, internal to the library.

       The following methods are available:

       $h = HTTP::Headers->new
	   Constructs a	new "HTTP::Headers" object.  You might pass some
	   initial attribute-value pairs as parameters to the constructor.

	    $h = HTTP::Headers->new(
		  Date	       => 'Thu,	03 Feb 1994 00:00:00 GMT',
		  Content_Type => 'text/html; version=3.2',
		  Content_Base => '');

	   The constructor arguments are passed	to the "header"	method which
	   is described	below.

	   Returns a copy of this "HTTP::Headers" object.

       $h->header( $field )
       $h->header( $field => $value )
       $h->header( $f1 => $v1, $f2 => $v2, ... )
	   Get or set the value	of one or more header fields.  The header
	   field name ($field) is not case sensitive.  To make the life	easier
	   for perl users who wants to avoid quoting before the	=> operator,
	   you can use '_' as a	replacement for	'-' in header names.

	   The header()	method accepts multiple	($field	=> $value) pairs,
	   which means that you	can update several fields with a single

	   The $value argument may be a	plain string or	a reference to an
	   array of strings for	a multi-valued field. If the $value is
	   provided as "undef" then the	field is removed.  If the $value is
	   not given, then that	header field will remain unchanged. In
	   addition to being a string, $value may be something that

	   The old value (or values) of	the last of the	header fields is
	   returned.  If no such field exists "undef" will be returned.

	   A multi-valued field	will be	returned as separate values in list
	   context and will be concatenated with ", " as separator in scalar
	   context.  The HTTP spec (RFC	2616) promises that joining multiple
	   values in this way will not change the semantic of a	header field,
	   but in practice there are cases like	old-style Netscape cookies
	   (see	HTTP::Cookies) where "," is used as part of the	syntax of a
	   single field	value.


	    $header->header(MIME_Version => '1.0',
			    User_Agent	 => 'My-Web-Client/0.01');
	    $header->header(Accept => "text/html, text/plain, image/*");
	    $header->header(Accept => [qw(text/html text/plain image/*)]);
	    @accepts = $header->header('Accept');  # get multiple values
	    $accepts = $header->header('Accept');  # get values	as a single string

       $h->push_header(	$field => $value )
       $h->push_header(	$f1 => $v1, $f2	=> $v2,	... )
	   Add a new field value for the specified header field.  Previous
	   values for the same field are retained.

	   As for the header() method, the field name ($field) is not case
	   sensitive and '_' can be used as a replacement for '-'.

	   The $value argument may be a	scalar or a reference to a list	of

	    $header->push_header(Accept	=> 'image/jpeg');
	    $header->push_header(Accept	=> [map	"image/$_", qw(gif png tiff)]);

       $h->init_header(	$field => $value )
	   Set the specified header to the given value,	but only if no
	   previous value for that field is set.

	   The header field name ($field) is not case sensitive	and '_'	can be
	   used	as a replacement for '-'.

	   The $value argument may be a	scalar or a reference to a list	of

       $h->remove_header( $field, ... )
	   This	function removes the header fields with	the specified names.

	   The header field names ($field) are not case	sensitive and '_' can
	   be used as a	replacement for	'-'.

	   The return value is the values of the fields	removed.  In scalar
	   context the number of fields	removed	is returned.

	   Note	that if	you pass in multiple field names then it is generally
	   not possible	to tell	which of the returned values belonged to which

	   This	will remove all	the header fields used to describe the content
	   of a	message.  All header field names prefixed with "Content-" fall
	   into	this category, as well as "Allow", "Expires" and
	   "Last-Modified".  RFC 2616 denotes these fields as Entity Header

	   The return value is a new "HTTP::Headers" object that contains the
	   removed headers only.

	   This	will remove all	header fields.

	   Returns the list of distinct	names for the fields present in	the
	   header.  The	field names have case as suggested by HTTP spec, and
	   the names are returned in the recommended "Good Practice" order.

	   In scalar context return the	number of distinct field names.

       $h->scan( \&process_header_field	)
	   Apply a subroutine to each header field in turn.  The callback
	   routine is called with two parameters; the name of the field	and a
	   single value	(a string).  If	a header field is multi-valued,	then
	   the routine is called once for each value.  The field name passed
	   to the callback routine has case as suggested by HTTP spec, and the
	   headers will	be visited in the recommended "Good Practice" order.

	   Any return values of	the callback routine are ignored.  The loop
	   can be broken by raising an exception ("die"), but the caller of
	   scan() would	have to	trap the exception itself.

	   Returns the list of pairs of	keys and values.

       $h->as_string( $eol )
	   Return the header fields as a formatted MIME	header.	 Since it
	   internally uses the "scan" method to	build the string, the result
	   will	use case as suggested by HTTP spec, and	it will	follow
	   recommended "Good Practice" of ordering the header fields.  Long
	   header values are not folded.

	   The optional	$eol parameter specifies the line ending sequence to
	   use.	 The default is	"\n".  Embedded	"\n" characters	in header
	   field values	will be	substituted with this line ending sequence.

       The most	frequently used	headers	can also be accessed through the
       following convenience methods.  Most of these methods can both be used
       to read and to set the value of a header.  The header value is set if
       you pass	an argument to the method.  The	old header value is always
       returned.  If the given header did not exist then "undef" is returned.

       Methods that deal with dates/times always convert their value to	system
       time (seconds since Jan 1, 1970)	and they also expect this kind of
       value when the header value is set.

	   This	header represents the date and time at which the message was
	   originated. E.g.:

	     $h->date(time);  #	set current date

	   This	header gives the date and time after which the entity should
	   be considered stale.

	   These header	fields are used	to make	a request conditional.	If the
	   requested resource has (or has not) been modified since the time
	   specified in	this field, then the server will return	a "304 Not
	   Modified" response instead of the document itself.

	   This	header indicates the date and time at which the	resource was
	   last	modified. E.g.:

	     # check if	document is more than 1	hour old
	     if	(my $last_mod =	$h->last_modified) {
		 if ($last_mod < time -	60*60) {

	   The Content-Type header field indicates the media type of the
	   message content. E.g.:


	   The value returned will be converted	to lower case, and potential
	   parameters will be chopped off and returned as a separate value if
	   in an array context.	 If there is no	such header field, then	the
	   empty string	is returned.  This makes it safe to do the following:

	     if	($h->content_type eq 'text/html') {
		# we enter this	place even if the real header value happens to
		# be 'TEXT/HTML; version=3.0'

	   Returns the upper-cased charset specified in	the Content-Type
	   header.  In list context return the lower-cased bare	content	type
	   followed by the upper-cased charset.	 Both values will be "undef"
	   if not specified in the header.

	   Returns TRUE	if the Content-Type header field indicate that the
	   content is textual.

	   Returns TRUE	if the Content-Type header field indicate that the
	   content is some kind	of HTML	(including XHTML).  This method	can't
	   be used to set Content-Type.

	   Returns TRUE	if the Content-Type header field indicate that the
	   content is XHTML.  This method can't	be used	to set Content-Type.

	   Returns TRUE	if the Content-Type header field indicate that the
	   content is XML.  This method	can't be used to set Content-Type.

	   The Content-Encoding	header field is	used as	a modifier to the
	   media type.	When present, its value	indicates what additional
	   encoding mechanism has been applied to the resource.

	   A decimal number indicating the size	in bytes of the	message

	   The natural language(s) of the intended audience for	the message
	   content.  The value is one or more language tags as defined by RFC
	   1766.  Eg. "no" for some kind of Norwegian and "en-US" for English
	   the way it is written in the	US.

	   The title of	the document.  In libwww-perl this header will be
	   initialized automatically from the <TITLE>...</TITLE> element of
	   HTML	documents.  This header	is no longer part of the HTTP

	   This	header field is	used in	request	messages and contains
	   information about the user agent originating	the request.  E.g.:

	     $h->user_agent('Mozilla/5.0 (compatible; MSIE 7.0;	Windows	NT 6.0)');

	   The server header field contains information	about the software
	   being used by the originating server	program	handling the request.

	   This	header should contain an Internet e-mail address for the human
	   user	who controls the requesting user agent.	 The address should be
	   machine-usable, as defined by RFC822.  E.g.:

	     $h->from('King Kong <>');

	   This	header is no longer part of the	HTTP standard.

	   Used	to specify the address (URI) of	the document from which	the
	   requested resource address was obtained.

	   The "Free On-line Dictionary	of Computing" as this to say about the
	   word	referer:

		<World-Wide Web> A misspelling of "referrer" which
		somehow	made it	into the {HTTP}	standard.  A given {web
		page}'s	referer	(sic) is the {URL} of whatever web page
		contains the link that the user	followed to the	current
		page.  Most browsers pass this information as part of a


	   By popular demand "referrer"	exists as an alias for this method so
	   you can avoid this misspelling in your programs and still send the
	   right thing on the wire.

	   When	setting	the referrer, this method removes the fragment from
	   the given URI if it is present, as mandated by RFC2616.  Note that
	   the removal does not	happen automatically if	using the header(),
	   push_header() or init_header() methods to set the referrer.

	   This	header must be included	as part	of a "401 Unauthorized"
	   response.  The field	value consist of a challenge that indicates
	   the authentication scheme and parameters applicable to the
	   requested URI.

	   This	header must be included	in a "407 Proxy	Authentication
	   Required" response.

	   A user agent	that wishes to authenticate itself with	a server or a
	   proxy, may do so by including these headers.

	   This	method is used to get or set an	authorization header that use
	   the "Basic Authentication Scheme".  In array	context	it will	return
	   two values; the user	name and the password.	In scalar context it
	   will	return "uname:password"	as a single string value.

	   When	used to	set the	header value, it expects two arguments.	 E.g.:

	     $h->authorization_basic($uname, $password);

	   The method will croak if the	$uname contains	a colon	':'.

	   Same	as authorization_basic() but will set the "Proxy-
	   Authorization" header instead.

       The header field	name spelling is normally canonicalized	including the
       '_' to '-' translation.	There are some application where this is not
       appropriate.  Prefixing field names with	':' allow you to force a
       specific	spelling.  For example if you really want a header field name
       to show up as "foo_bar" instead of "Foo-Bar", you might set it like

	 $h->header(":foo_bar" => 1);

       These field names are returned with the ':' intact for
       $h->header_field_names and the $h->scan callback, but the colons	do not
       show in $h->as_string.

       Gisle Aas <>

       This software is	copyright (c) 1994 by Gisle Aas.

       This is free software; you can redistribute it and/or modify it under
       the same	terms as the Perl 5 programming	language system	itself.

perl v5.32.1			  2021-11-04		      HTTP::Headers(3)


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