normalize-url.php

<?php
/**
 * Given a URL, normalize that URL.
 * @param String URL
 * @return String Normalized URL
 */
function normalizeUrl($url)
{
  $newUrl = "";
  $url = parse_url($url);
  $defaultSchemes = array("http" => 80, "https" => 443);

  if (isset($url['scheme'])) {
    $url['scheme'] = strtolower($url['scheme']);
    // Strip scheme default ports
    if (isset($defaultSchemes[$url['scheme']]) && isset($url['port']) && $defaultSchemes[$url['scheme']] == $url['port'])
      unset($url['port']);
    $newUrl .= "{$url['scheme']}://";
  } else {
    $newUrl .= "http://";
  }

  if (isset($url['host'])) {
    $url['host'] = strtolower($url['host']);
    // Seems like a valid domain, properly validation should be made in higher layers.
    if (preg_match("/[a-z]+\Z/", $url['host'])) {
      if (preg_match("/^www\./", $url['host']) && gethostbyname($url['host']) == gethostbyname(str_replace("www.", "", $url['host'])))
        $newUrl .= str_replace("www.", "", $url['host']); else
        $newUrl .= $url['host'];
    } else
      $newUrl .= $url['host'];
  }

  if (isset($url['port']))
    $newUrl .= ":{$url['port']}";

  if (isset($url['path'])) {
    // Case normalization
    $url['path'] = @preg_replace('/(%([0-9abcdef][0-9abcdef]))/ex', "'%'.strtoupper('\\2')", $url['path']);

    //Strip duplicate slashes
    while (preg_match("/\/\//", $url['path']))
      $url['path'] = preg_replace("/\/\//", "/", $url['path']);

    /*
       * Decode unreserved characters, http://www.apps.ietf.org/rfc/rfc3986.html#sec-2.3
       * Heavily rewritten version of urlDecodeUnreservedChars() in Glen Scott's url-normalizer.
       */

    $u = array();
    for ($o = 65; $o <= 90; $o++)
      $u[] = dechex($o);
    for ($o = 97; $o <= 122; $o++)
      $u[] = dechex($o);
    for ($o = 48; $o <= 57; $o++)
      $u[] = dechex($o);
    $chrs = array('-', '.', '_', '~');
    foreach ($chrs as $chr)
      $u[] = dechex(ord($chr));
    $url['path'] = preg_replace_callback(array_map(create_function('$str', 'return "/%" . strtoupper($str) . "/x";'), $u), create_function('$matches', 'return chr(hexdec($matches[0]));'), $url['path']);
    // Remove directory index
    $defaultIndexes = array("/default\.aspx/" => "default.aspx", "/default\.asp/" => "default.asp", "/index\.html/" => "index.html", "/index\.htm/" => "index.htm", "/default\.html/" => "default.html", "/default\.htm/" => "default.htm", "/index\.php/" => "index.php", "/index\.jsp/" => "index.jsp");
    foreach ($defaultIndexes as $index => $strip) {
      if (preg_match($index, $url['path']))
        $url['path'] = str_replace($strip, "", $url['path']);
    }

    /**
     * Path segment normalization, http://www.apps.ietf.org/rfc/rfc3986.html#sec-5.2.4
     * Heavily rewritten version of removeDotSegments() in Glen Scott's url-normalizer.
     */

    $new_path = '';
    while (!empty($url['path'])) {
      if (preg_match('!^(\.\./|\./)!x', $url['path']))
        $url['path'] = preg_replace('!^(\.\./|\./)!x', '', $url['path']); elseif (preg_match('!^(/\./)!x', $url['path'], $matches) || preg_match('!^(/\.)$!x', $url['path'], $matches))
        $url['path'] = preg_replace("!^" . $matches[1] . "!", '/', $url['path']); elseif (preg_match('!^(/\.\./|/\.\.)!x', $url['path'], $matches)) {
        $url['path'] = preg_replace('!^' . preg_quote($matches[1], '!') . '!x', '/', $url['path']);
        $new_path = preg_replace('!/([^/]+)$!x', '', $new_path);
      } elseif (preg_match('!^(\.|\.\.)$!x', $url['path'])) {
        $url['path'] = preg_replace('!^(\.|\.\.)$!x', $url['path']);
      } else {
        if (preg_match('!(/*[^/]*)!x', $url['path'], $matches)) {
          $first_path_segment = $matches[1];
          $url['path'] = preg_replace('/^' . preg_quote($first_path_segment, '/') . '/', '', $url['path'], 1);
          $new_path .= $first_path_segment;
        }
      }
    }
    $newUrl .= $new_path;
  }

  if (isset($url['fragment']))
    unset($url['fragment']);

  // Sort GET params alphabetically, not because the RFC requires it but because it's cool!
  if (isset($url['query'])) {
    if (preg_match("/&/", $url['query'])) {
      $s = explode("&", $url['query']);
      $url['query'] = "";
      sort($s);
      foreach ($s as $z)
        $url['query'] .= "{$z}&";
      $url['query'] = preg_replace("/&\Z/", "", $url['query']);
    }
    $newUrl .= "?{$url['query']}";
  }

  return $newUrl;
}