phpman > man > HTTP::Headers(3pm)

NAME
    HTTP::Headers - Class encapsulating HTTP Message headers

VERSION
    version 6.36

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 )
    $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 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. In addition to being a
        string, $value may be something that stringifies.

        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.

        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 )
    $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 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-" fall into this category, as well as "Allow", "Expires"
        and "Last-Modified". RFC 2616 denotes 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->flatten()
        Returns the list of pairs of keys and values.

    $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.
    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.

    $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_type_charset
        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.

    $h->content_is_text
        Returns TRUE if the Content-Type header field indicate that the content is textual.

    $h->content_is_html
        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.

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

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

    $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/5.0 (compatible; MSIE 7.0; Windows NT 6.0)');

    $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 <king AT kong.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.

AUTHOR
    Gisle Aas <gisle AT activestate.com>

COPYRIGHT AND LICENSE
    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.