Local::SiteRobot - a simple web crawling module

[rob_au]

Category:

Web Stuff

Description:

Earlier this month, George_Sherston posted a node, where he submitted code for a site indexer and search engine - I took this code and decided to build upon it for my own site and in evaluating it and other options available, I found HTML::Index. This code offered the ability to create site indexes for both local and remote files (through the use of WWW::SimpleRobot by the same author) - This ability for indexing based upon URL was important to me as a great deal of content on the site is dynamic in nature. This was where my journey hit a stumbling block ... WWW::SimpleRobot didn't work!

So, I set about writing my own simplified robot code which had one and only one function - return a list of crawled URLs from a start URL address.

#!/usr/bin/perl -w

use Local::SiteRobot;
use strict;

my $robot = Local::SiteRobot->new(
    DEPTH           =>  10,
    FOLLOW_REGEX    =>  '^http://www.cowsnet.com',
    URLS            =>  [ 'http://www.cowsnet.com.au' ]
);
my @pages = $robot->crawl;
print STDOUT $_, "\n" foreach @pages;

The code I feel is quite self explanatory - /msg me if you have any questions on usage.

package Local::SiteRobot;

use HTML::LinkExtor;
use LWP::Simple;
use URI;
use strict;

sub new {
    my $class = shift;
    my %options = (
        DEPTH           =>  undef,
        FOLLOW_REGEX    =>  '',
        URLS            =>  [],
        VERBOSE         =>  0
    );
    my %args = (%options, @_);
    foreach (keys %args) {
        die "Local::SiteRobot->new : Unknown argument option - $_" unl
+ess exists $options{$_};
    };
    my $self = bless \%args, (ref($class) || $class);
    $self->_verbose("Local::SiteRobot->new : Created new Local::SiteRo
+bot object");
    return $self;
}

sub crawl {
    my $self = shift;
    return undef unless @{$self->{URLS}};
    my @pages;
    foreach my $url (@{$self->{URLS}}) {
        my $uri = URI->new($url);
        next unless $uri->scheme;
        next unless $uri->scheme eq 'http';
        $self->_verbose("Local::SiteRobot->crawl : Crawling from URL "
+, $uri->canonical->as_string);
        push (@pages, $self->_crawl($uri->canonical->as_string));
        $self->_verbose("Local::SiteRobot->crawl : Crawling from URL "
+, $uri->canonical->as_string, " returned ", scalar(@pages), " pages")
+;
    }
    return @pages;
}

sub _crawl {
    my ($self, $url, $depth) = @_;
    my @pages;
    my $uri = URI->new($url);
    $self->_verbose("Local::SiteRobot->_crawl : GET ", $uri->canonical
+->as_string);
    my $html = get($uri->canonical->as_string);
    return unless $html;
    return $uri->canonical->as_string if ((defined $self->{DEPTH}) && 
+($self->{DEPTH} == ($depth || 0)));
    ${$self->{pages}}{$uri->canonical->as_string} = 1;
    push (@pages, $uri->canonical->as_string);
    my $linkextor = HTML::LinkExtor->new(undef, $uri->canonical->as_st
+ring);
    $linkextor->parse($html);
    foreach my $link ($linkextor->links) {
        my ($tag, %attr) = @{$link};
        next unless ($tag eq 'a');
        next unless (defined $attr{'href'});
        my $href = URI->new($attr{'href'});
        next unless ($href->canonical->as_string =~ /$self->{FOLLOW_RE
+GEX}/);
        next if exists ${$self->{pages}}{$href};
        ${$self->{pages}}{$href} = 1;
        push (@pages, $self->_crawl($href, ($depth || 0) + 1));
    }
    return @pages;
}

sub _verbose {
    my $self = shift;
    return unless $self->{VERBOSE};
    print STDERR @_, "\n";
}

1;


__END__

[merlyn]

This was where my journey hit a stumbling block ... WWW::SimpleRobot didn't work!

Rather than partially reinvent a wheel, did you try to work with the author to figure out why it "didn't work"? And can you please explain what "didn't work" for you? I've used the module successfully, as have many hundreds of others.

"forking" a codebase should be considered carefully, otherwise the open source users as a community all lose.

-- Randal L. Schwartz, Perl hacker

[rob_au]

The problems which I encountered with WWW::SimpleRobot related to the traverse function not returning traversal results via the $object->pages and $object->urls methods - The problem appeared to relate to the shift method by which the author was iterating through the constructed queue undefining the @pages results array before it was returned at the end of the function.

Better than just reporting this to the author, I have submitted a fix patch which corrects this behaviour by pushing results into a separate array to the queue.

115a116
>     my @results;
150a152
>             push (@results, $page);
165,166c167,168
<     $self->{pages} = \@pages;
<     $self->{urls} = [ map { $_->{url} } @pages ];
---
>     $self->{pages} = \@results;
>     $self->{urls} = [ map { $_->{url} } @results ];

Note that I never meant for my little piece of code to be viewed as a code fork from WWW::SimpleRobot but rather just an additional available option.

 

Ooohhh, Rob no beer function well without!