=item $h->clone

Returns a copy of this HTTP::Headers object.

=back

=head1 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.

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.

=over 4

=item $h->date

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

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

=item $h->expires

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

=item $h->if_modified_since

=item $h->if_unmodified_since

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

=item $h->last_modified

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

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

=item $h->content_type

The Content-Type header field indicates the media type of the message
content. I<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.  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'
     ...
  }

=item $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.

=item $h->content_length

A decimal number indicating the size in bytes of the message content.

=item $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 Norwegian and "en-US" for US-English.

=item $h->title

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

=item $h->user_agent

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

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

=item $h->server

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

=item $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('Gisle Aas <aas@sn.no>');

=item $h->referer

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

=item $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.

=item $h->proxy_authenticate

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

=item $h->authorization

=item $h->proxy_authorization

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

=item $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 I<"uname:password"> as a single string value.

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

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

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

=item $h->proxy_authorization_basic

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

=back

=head1 COPYRIGHT

Copyright 1995-1998 Gisle Aas.

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

=cut

1;

#__DATA__

sub clone
{
    my $self = shift;
    my $clone = new HTTP::Headers;
    $self->scan(sub { $clone->push_header(@_);} );
    $clone;
}

sub push_header
{
    Carp::croak('Usage: $h->push_header($field, $val)') if @_ != 3;
    shift->_header(@_, 'PUSH');
}


sub remove_header
{
    my($self, @fields) = @_;
    my $field;
    foreach $field (@fields) {
	$field =~ tr/_/-/ if $TRANSLATE_UNDERSCORE;
	delete $self->{lc $field};
    }
}

# Convenience access functions

sub _date_header
{
    require HTTP::Date;
    my($self, $header, $time) = @_;
    my($old) = $self->_header($header);
    if (defined $time) {
	$self->_header($header, HTTP::Date::time2str($time));
    }
    HTTP::Date::str2time($old);
}

sub date                { shift->_date_header('Date',                @_); }
sub expires             { shift->_date_header('Expires',             @_); }
sub if_modified_since   { shift->_date_header('If-Modified-Since',   @_); }
sub if_unmodified_since { shift->_date_header('If-Unmodified-Since', @_); }
sub last_modified       { shift->_date_header('Last-Modified',       @_); }

# This is used as a private LWP extention.  The Client-Date header is
# added as a timestamp to a response when it has been received.
sub client_date         { shift->_date_header('Client-Date',         @_); }

# The retry_after field is dual format (can also be a expressed as
# number of seconds from now), so we don't provide an easy way to
# access it until we have know how both these interfaces can be
# addressed.  One possibility is to return a negative value for
# relative seconds and a positive value for epoch based time values.
#sub retry_after       { shift->_date_header('Retry-After',       @_); }

sub content_type      {
  my $ct = (shift->_header('Content-Type', @_))[0];
  return '' unless defined($ct) && length($ct);
  my @ct = split(/\s*;\s*/, lc($ct));
  wantarray ? @ct : $ct[0];
}

sub title             { (shift->_header('Title',            @_))[0] }
sub content_encoding  { (shift->_header('Content-Encoding', @_))[0] }
sub content_language  { (shift->_header('Content-Language', @_))[0] }
sub content_length    { (shift->_header('Content-Length',   @_))[0] }

sub user_agent        { (shift->_header('User-Agent',       @_))[0] }
sub server            { (shift->_header('Server',           @_))[0] }

sub from              { (shift->_header('From',             @_))[0] }
sub referer           { (shift->_header('Referer',          @_))[0] }
sub warning           { (shift->_header('Warning',          @_))[0] }

sub www_authenticate  { (shift->_header('WWW-Authenticate', @_))[0] }
sub authorization     { (shift->_header('Authorization',    @_))[0] }

sub proxy_authenticate  { (shift->_header('Proxy-Authenticate',  @_))[0] }
sub proxy_authorization { (shift->_header('Proxy-Authorization', @_))[0] }

sub authorization_basic       { shift->_basic_auth("Authorization",       @_) }
sub proxy_authorization_basic { shift->_basic_auth("Proxy-Authorization", @_) }

sub _basic_auth {
    require MIME::Base64;
    my($self, $h, $user, $passwd) = @_;
    my($old) = $self->_header($h);
    if (defined $user) {
	Carp::croak("Basic authorization user name can't contain ':'")
	  if $user =~ /:/;
	$passwd = '' unless defined $passwd;
	$self->_header($h => 'Basic ' .
                             MIME::Base64::encode("$user:$passwd", ''));
    }
    if (defined $old && $old =~ s/^\s*Basic\s+//) {
	my $val = MIME::Base64::decode($old);
	return $val unless wantarray;
	return split(/:/, $val, 2);
    }
    return;
}

1;