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



NAME
       HTTP::Headers - Class encapsulating HTTP Message headers

SYNOPSIS
        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

DESCRIPTION
       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.
           E.g.:

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

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

       $h->clone
           Returns a copy of this "HTTP::Headers" object.

       $h->header( $field )
       $h->header( $field => $value, ... )
           Get or set the value of one or more header fields.  The header
           field name ($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
           invocation.

           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.

           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.

           Examples:

            $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 )
           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
           scalars.

            $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
           scalars.

       $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
           field.

       $h->remove_content_headers
           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
           Fields.

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

       $h->clear
           This will remove all header fields.

       $h->header_field_names
           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.

       $h->as_string
       $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.

CONVENIENCE METHODS
       The most frequently used headers can also be accessed through the
       following convenience Methods.  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.

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

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

       $h->expires
           This header gives the date and time after which the entity should
           be considered stale.

       $h->if_modified_since
       $h->if_unmodified_since
           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.

       $h->last_modified
           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) {
                     ...
                 }
             }

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

             $h->content_type('text/html');

           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'
                ...
             }

       $h->content_encoding
           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.

       $h->content_length
           A decimal number indicating the size in bytes of the message
           content.

       $h->content_language
           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.

       $h->title
           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
           standard.

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

             $h->user_agent('Mozilla/1.2');

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

       $h->from
           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 <kingATkong.com>');

           This header is no longer part of the HTTP standard.

       $h->referer
           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
                request.

                (1998-10-19)

           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.

       $h->www_authenticate
           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.

       $h->proxy_authenticate
           This header must be included in a "407 Proxy Authentication
           Required" response.

       $h->authorization
       $h->proxy_authorization
           A user agent that wishes to authenticate itself with a server or a
           proxy, may do so by including these headers.

       $h->authorization_basic
           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 ':'.

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

NON-CANONICALIZED FIELD NAMES
       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
       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
       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 v5.10.0                      2008-04-07                HTTP::Headers(3pm)