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

       HTTP::Headers - Class encapsulating HTTP Message headers

	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 ini‐
	   tial attribute-value pairs as parameters to the constructor.	 E.g.:

	    $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 invo‐

	   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 pro‐
	   vided as "undef" then the field is removed.	If the $value is not
	   given, then that header field will remain unchanged.

	   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) promise 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 previ‐
	   ous 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-"
	   falls into this category, as well as "Allow", "Expires" and
	   "Last-Modified".  RFC 2616 denote 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 rou‐
	   tine 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.

       $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 recom‐
	   mended "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 fol‐
       lowing 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 mes‐
	   sage 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 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 con‐

	   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 ini‐
	   tialized automatically from the <TITLE>...</TITLE> element of HTML
	   documents.  This header is no longer part of the HTTP standard.

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


	   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-Authoriza‐
	   tion" 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 spe‐
       cific 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 this:

	 $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.

       Copyright 1995-2005 Gisle Aas.

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

perl v5.8.8			  2008-09-24		      HTTP::Headers(3)

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