如何利用php语法编写web爬虫程序

<?php

// 定义URL
$startUrl = "https://ipkd.cn";
$depth = 2;
 
// 放置已经处理的URL和当前的深度
$processedUrls = [
  $startUrl => 0
];
 
// 运行爬虫
getAllLinks($startUrl, $depth);
 
//获取给定URL的HTML
function getHTML($url) {
  $curl = curl_init();
  curl_setopt($curl, CURLOPT_URL, $url);
  curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
  $html = curl_exec($curl);
  curl_close($curl);
  return $html;
}
 
//获取所有链接
function getAllLinks($url, $depth) {
  global $processedUrls;
   
  if ($depth === 0) {
    return;
  }
   
  $html = getHTML($url);
  $dom = new DOMDocument();
  @$dom->loadHTML($html);
   
  $links = $dom->getElementsByTagName('a');
  foreach ($links as $link) {
    $href = $link->getAttribute('href');
    if (strpos($href, $url) !== false && !array_key_exists($href, $processedUrls)) {
      $processedUrls[$href] = $processedUrls[$url] + 1;
      echo $href . " (Depth: " . $processedUrls[$href] . ")" . PHP_EOL;
      getAllLinks($href, $depth - 1);
    }
  }
}