How do I make a simple crawler in PHP? [closed]

Question

Meh. Don't parse HTML with regexes.

Here's a DOM version inspired by Tatu's:

<?php
function crawl_page($url, $depth = 5)
{
    static $seen = array();
    if (isset($seen[$url]) || $depth === 0) {
        return;
    }

    $seen[$url] = true;

    $dom = new DOMDocument('1.0');
    @$dom->loadHTMLFile($url);

    $anchors = $dom->getElementsByTagName('a');
    foreach ($anchors as $element) {
        $href = $element->getAttribute('href');
        if (0 !== strpos($href, 'http')) {
            $path = '/' . ltrim($href, '/');
            if (extension_loaded('http')) {
                $href = http_build_url($url, array('path' => $path));
            } else {
                $parts = parse_url($url);
                $href = $parts['scheme'] . '://';
                if (isset($parts['user']) && isset($parts['pass'])) {
                    $href .= $parts['user'] . ':' . $parts['pass'] . '@';
                }
                $href .= $parts['host'];
                if (isset($parts['port'])) {
                    $href .= ':' . $parts['port'];
                }
                $href .= dirname($parts['path'], 1).$path;
            }
        }
        crawl_page($href, $depth - 1);
    }
    echo "URL:",$url,PHP_EOL,"CONTENT:",PHP_EOL,$dom->saveHTML(),PHP_EOL,PHP_EOL;
}
crawl_page("http://hobodave.com", 2);

Edit: I fixed some bugs from Tatu's version (works with relative URLs now).

Edit: I added a new bit of functionality that prevents it from following the same URL twice.

Edit: echoing output to STDOUT now so you can redirect it to whatever file you want

Edit: Fixed a bug pointed out by George in his answer. Relative urls will no longer append to the end of the url path, but overwrite it. Thanks to George for this. Note that George's answer doesn't account for any of: https, user, pass, or port. If you have the http PECL extension loaded this is quite simply done using http_build_url. Otherwise, I have to manually glue together using parse_url. Thanks again George.

Here my implementation based on the above example/answer.

1. It is class based
2. uses Curl
3. support HTTP Auth
4. Skip Url not belonging to the base domain
5. Return Http header Response Code for each page
6. Return time for each page

CRAWL CLASS:

class crawler
{
    protected $_url;
    protected $_depth;
    protected $_host;
    protected $_useHttpAuth = false;
    protected $_user;
    protected $_pass;
    protected $_seen = array();
    protected $_filter = array();

    public function __construct($url, $depth = 5)
    {
        $this->_url = $url;
        $this->_depth = $depth;
        $parse = parse_url($url);
        $this->_host = $parse['host'];
    }

    protected function _processAnchors($content, $url, $depth)
    {
        $dom = new DOMDocument('1.0');
        @$dom->loadHTML($content);
        $anchors = $dom->getElementsByTagName('a');

        foreach ($anchors as $element) {
            $href = $element->getAttribute('href');
            if (0 !== strpos($href, 'http')) {
                $path = '/' . ltrim($href, '/');
                if (extension_loaded('http')) {
                    $href = http_build_url($url, array('path' => $path));
                } else {
                    $parts = parse_url($url);
                    $href = $parts['scheme'] . '://';
                    if (isset($parts['user']) && isset($parts['pass'])) {
                        $href .= $parts['user'] . ':' . $parts['pass'] . '@';
                    }
                    $href .= $parts['host'];
                    if (isset($parts['port'])) {
                        $href .= ':' . $parts['port'];
                    }
                    $href .= $path;
                }
            }
            // Crawl only link that belongs to the start domain
            $this->crawl_page($href, $depth - 1);
        }
    }

    protected function _getContent($url)
    {
        $handle = curl_init($url);
        if ($this->_useHttpAuth) {
            curl_setopt($handle, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
            curl_setopt($handle, CURLOPT_USERPWD, $this->_user . ":" . $this->_pass);
        }
        // follows 302 redirect, creates problem wiht authentication
//        curl_setopt($handle, CURLOPT_FOLLOWLOCATION, TRUE);
        // return the content
        curl_setopt($handle, CURLOPT_RETURNTRANSFER, TRUE);

        /* Get the HTML or whatever is linked in $url. */
        $response = curl_exec($handle);
        // response total time
        $time = curl_getinfo($handle, CURLINFO_TOTAL_TIME);
        /* Check for 404 (file not found). */
        $httpCode = curl_getinfo($handle, CURLINFO_HTTP_CODE);

        curl_close($handle);
        return array($response, $httpCode, $time);
    }

    protected function _printResult($url, $depth, $httpcode, $time)
    {
        ob_end_flush();
        $currentDepth = $this->_depth - $depth;
        $count = count($this->_seen);
        echo "N::$count,CODE::$httpcode,TIME::$time,DEPTH::$currentDepth URL::$url <br>";
        ob_start();
        flush();
    }

    protected function isValid($url, $depth)
    {
        if (strpos($url, $this->_host) === false
            || $depth === 0
            || isset($this->_seen[$url])
        ) {
            return false;
        }
        foreach ($this->_filter as $excludePath) {
            if (strpos($url, $excludePath) !== false) {
                return false;
            }
        }
        return true;
    }

    public function crawl_page($url, $depth)
    {
        if (!$this->isValid($url, $depth)) {
            return;
        }
        // add to the seen URL
        $this->_seen[$url] = true;
        // get Content and Return Code
        list($content, $httpcode, $time) = $this->_getContent($url);
        // print Result for current Page
        $this->_printResult($url, $depth, $httpcode, $time);
        // process subPages
        $this->_processAnchors($content, $url, $depth);
    }

    public function setHttpAuth($user, $pass)
    {
        $this->_useHttpAuth = true;
        $this->_user = $user;
        $this->_pass = $pass;
    }

    public function addFilterPath($path)
    {
        $this->_filter[] = $path;
    }

    public function run()
    {
        $this->crawl_page($this->_url, $this->_depth);
    }
}

USAGE:

// USAGE
$startURL = 'http://YOUR_URL/';
$depth = 6;
$username = 'YOURUSER';
$password = 'YOURPASS';
$crawler = new crawler($startURL, $depth);
$crawler->setHttpAuth($username, $password);
// Exclude path with the following structure to be processed 
$crawler->addFilterPath('customer/account/login/referer');
$crawler->run();

Check out PHP Crawler

http://sourceforge.net/projects/php-crawler/

See if it helps.

In it's simplest form:

function crawl_page($url, $depth = 5) {
    if($depth > 0) {
        $html = file_get_contents($url);

        preg_match_all('~<a.*?href="(.*?)".*?>~', $html, $matches);

        foreach($matches[1] as $newurl) {
            crawl_page($newurl, $depth - 1);
        }

        file_put_contents('results.txt', $newurl."\n\n".$html."\n\n", FILE_APPEND);
    }
}

crawl_page('http://www.domain.com/index.php', 5);

That function will get contents from a page, then crawl all found links and save the contents to 'results.txt'. The functions accepts an second parameter, depth, which defines how long the links should be followed. Pass 1 there if you want to parse only links from the given page.

Why use PHP for this, when you can use wget, e.g.

wget -r -l 1 http://www.example.com

For how to parse the contents, see Best Methods to parse HTML and use the search function for examples. How to parse HTML has been answered multiple times before.

With some little changes to hobodave's code, here is a codesnippet you can use to crawl pages. This needs the curl extension to be enabled in your server.

<?php
//set_time_limit (0);
function crawl_page($url, $depth = 5){
$seen = array();
if(($depth == 0) or (in_array($url, $seen))){
    return;
}   
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_TIMEOUT, 30);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
$result = curl_exec ($ch);
curl_close ($ch);
if( $result ){
    $stripped_file = strip_tags($result, "<a>");
    preg_match_all("/<a[\s]+[^>]*?href[\s]?=[\s\"\']+"."(.*?)[\"\']+.*?>"."([^<]+|.*?)?<\/a>/", $stripped_file, $matches, PREG_SET_ORDER ); 
    foreach($matches as $match){
        $href = $match[1];
            if (0 !== strpos($href, 'http')) {
                $path = '/' . ltrim($href, '/');
                if (extension_loaded('http')) {
                    $href = http_build_url($href , array('path' => $path));
                } else {
                    $parts = parse_url($href);
                    $href = $parts['scheme'] . '://';
                    if (isset($parts['user']) && isset($parts['pass'])) {
                        $href .= $parts['user'] . ':' . $parts['pass'] . '@';
                    }
                    $href .= $parts['host'];
                    if (isset($parts['port'])) {
                        $href .= ':' . $parts['port'];
                    }
                    $href .= $path;
                }
            }
            crawl_page($href, $depth - 1);
        }
}   
echo "Crawled {$href}";
}   
crawl_page("http://www.sitename.com/",3);
?>

I have explained this tutorial in this crawler script tutorial