package HTML::LinkExtor;=head1 NAMEHTML::LinkExtor - Extract links from an HTML document=head1 SYNOPSIS require HTML::LinkExtor; $p = HTML::LinkExtor->new(\&cb, "http://www.sn.no/"); sub cb {     my($tag, %links) = @_;     print "$tag @{[%links]}\n"; } $p->parse_file("index.html");=head1 DESCRIPTIONThe I<HTML::LinkExtor> (link extractor) is an HTML parser that takes acallback routine as parameter.  This routine is then called as thevarious link attributes are recognized.The I<HTML::LinkExtor> is a subclass of I<HTML::Parser>. This meansthat the document should be given to the parser by calling the$p->parse() or $p->parse_file() methods.=cutrequire HTML::Parser;@ISA = qw(HTML::Parser);use URI::URL qw(url);use strict;use vars qw(%LINK_ELEMENT);# Elements that might contain links and the name of the link attribute%LINK_ELEMENT =( body   => 'background', base   => 'href', a      => 'href', img    => [qw(src lowsrc usemap)],   # 'lowsrc' is a Netscape invention form   => 'action', input  => 'src','link'  => 'href',          # need quoting since link is a perl builtin frame  => 'src', applet => [qw(codebase code)], area   => 'href', frame  => 'src',   # Netscape 2.0 extention embed  => 'src',   # used in Netscape 2.0 for Shockwave and things like that);=head2 $p = HTML::LinkExtor->new([$callback[, $base]])The constructor takes two optional argument. The first is a referenceto a callback routine. It will be called as links are found. If acallback is not provided, then links are just accumulated internallyand can be retrieved by calling the $p->links() method. The $base isan optional base URL used to absolutize all URLs found.The callback is called with the lowercase tag name as first argument,and then all link attributes as separate key/value pairs.  Allnon-link attributes are removed.=cutsub new{    my($class, $cb, $base) = @_;    my $self = $class->SUPER::new;    $self->{extractlink_cb} = $cb;    $self->{extractlink_base} = $base;    $self;}sub start{    my($self, $tag, $attr) = @_;  # $attr is reference to a HASH    return unless exists $LINK_ELEMENT{$tag};    my $base = $self->{extractlink_base};    my $links = $LINK_ELEMENT{$tag};    $links = [$links] unless ref $links;    my @links;    my $a;    for $a (@$links) {	next unless exists $attr->{$a};	push(@links, $a, $base ? url($attr->{$a}, $base)->abs : $attr->{$a});    }    return unless @links;    my $cb = $self->{extractlink_cb};    if ($cb) {	&$cb($tag, @links);    } else {	push(@{$self->{'links'}}, [$tag, @links]);    }}=head2 $p->linksReturns a list of all links found in the document.  The returnedvalues will be anonymous arrays with the follwing elements:  [$tag, $attr => $url1, $attr2 => $url2,...]The $p->links method will also truncate the internal link list.  Thismeans that if the method is called twice without any parsing inbetween then the second call will return an empty list.Also note that $p->links will always be empty if a callback routinewas provided when the L<HTML::LinkExtor> was created.=cutsub links{    my $self = shift;    exists($self->{'links'}) ? @{delete $self->{'links'}} : ();}# We override the parse_file() method so that we can clear the links# before we start with a new file.sub parse_file{    my $self = shift;    delete $self->{'links'};    $self->SUPER::parse_file(@_);}=head1 EXAMPLEThis is an example showing how you can extract links as a documentis received using LWP:  use LWP::UserAgent;  use HTML::LinkExtor;  use URI::URL;  $url = "http://www.sn.no/";  # for instance  $ua = new LWP::UserAgent;  # Set up a callback that collect image links  my @imgs = ();  sub callback {     my($tag, %attr) = @_;     return if $tag ne 'img';  # we only look closer at <img ...>     push(@imgs, values %attr);  }  # Make the parser.  Unfortunately, we don't know the base yet (it might  # be diffent from $url)  $p = HTML::LinkExtor->new(\&callback);  # Request document and parse it as it arrives  $res = $ua->request(HTTP::Request->new(GET => $url), sub {$p->parse($_[0])});  # Expand all image URLs to absolute ones  my $base = $res->base;  @imgs = map { $_ = url($_, $base)->abs; } @imgs;  # Print them out  print join("\n", @imgs), "\n";=head1 SEE ALSOL<HTML::Parser>=head1 AUTHORGisle Aas E<lt>aas@sn.no>=cut1;