Swoole Advanced: Using coroutines for web crawler development

With the continuous development of Internet technology, Web crawlers have become an indispensable part of today's Internet applications. They have a wide range of application scenarios in data collection, business discovery, and public opinion monitoring. However, traditional web crawlers usually use multi-threads or multi-processes to implement concurrent requests, and face problems such as context switching overhead and excessive memory usage. In recent years, Swoole has become a new star in PHP applications. Its coroutine feature can provide efficient solutions for concurrent requests of web crawlers.

In this article, we will introduce how to use Swoole coroutine to implement a lightweight and efficient web crawler.

Swoole Introduction

Swoole is a high-performance network communication framework based on PHP language. Its biggest feature is that it supports coroutines. Coroutines are lightweight threads in user mode. Compared with traditional threads and processes, coroutines have less context switching overhead and less memory usage, and can better utilize the performance of the CPU.

Using Swoole to implement Web crawlers

The coroutine feature of Swoole provides a very good platform for the development of Web crawlers. Traditional web crawlers often consume a large amount of system resources when making concurrent requests. Using Swoole coroutines can easily achieve high concurrent requests while avoiding the overhead caused by traditional thread switching.

The following is a simple example of a web crawler implemented using Swoole:

<?php
// 1. 创建Swoole HTTP服务器
$http = new SwooleHttpServer("0.0.0.0", 9501);

// 2. 处理请求
$http->on('request', function ($request, $response) {
    // 3. 发送HTTP请求
    $cli = new SwooleCoroutineHttpClient('www.baidu.com', 80);
    $cli->setHeaders([
        'Host' => "www.baidu.com",
        "User-Agent" => 'Chrome/49.0.2587.3',
        'Accept' => 'text/html,application/xhtml+xml,application/xml',
        'Accept-Encoding' => 'gzip',
    ]);
    $cli->get('/');

    // 4. 响应HTML内容
    $response->header("Content-Type", "text/html; charset=utf-8");
    $response->end($cli->body);
});

// 5. 启动HTTP服务器
$http->start();

The above example code creates a Swoole HTTP server and listens to port number 9501. When an HTTP request arrives, the server will send the HTTP request to the Baidu website and respond with HTML content.

Swoole coroutine HTTP client

Swoole provides a coroutine-based HTTP client. Through the coroutine, multiple HTTP requests can be initiated simultaneously in a single process and the requests can be executed in parallel without the need for Start multiple threads or processes.

The use of coroutine HTTP client is very simple. The following is a usage example:

<?php
// 1. 创建协程HTTP客户端
$cli = new SwooleCoroutineHttpClient('www.baidu.com', 80);

// 2. 配置请求头
$cli->setHeaders([
    'Host' => "www.baidu.com",
    "User-Agent" => 'Chrome/49.0.2587.3',
    'Accept' => 'text/html,application/xhtml+xml,application/xml',
    'Accept-Encoding' => 'gzip',
]);

// 3. 发送HTTP请求
$cli->get('/');

// 4. 输出响应内容
echo $cli->body;

The above example code creates a coroutine HTTP client, sets the request header, sends an HTTP request, and outputs Response content.

Use coroutines to implement crawlers

Using the Swoole coroutine HTTP client, we can easily implement high-performance web crawlers. The following is an example of a crawler implemented using coroutines:

<?php
// 1. 抓取百度搜索结果的页面
$html = file_get_contents('https://www.baidu.com/s?ie=UTF-8&wd=swoole');

// 2. 解析HTML，提取搜索结果列表的URL
preg_match_all('/<a.*?href="(.*?)".*?>/is', $html, $matches);
$urls = $matches[1];

// 3. 并发请求搜索结果列表的URL
$cli = new SwooleCoroutineHttpClient('www.baidu.com', 80);
foreach ($urls as $url) {
    $cli->setHeaders([
        'Host' => "www.baidu.com",
        "User-Agent" => 'Chrome/49.0.2587.3',
        'Accept' => 'text/html,application/xhtml+xml,application/xml',
        'Accept-Encoding' => 'gzip',
    ]);
    $cli->get($url);
    echo $cli->body;
}

// 4. 关闭HTTP客户端
$cli->close();

The above example code first crawls the page where Baidu searches for the "swoole" keyword, parses the HTML, extracts the URLs of the search result list, and requests these URLs concurrently .

Summary

Swoole is a high-performance network communication framework, and its coroutine feature provides an efficient solution for the development of web crawlers. Using the Swoole coroutine HTTP client can greatly improve the concurrent request capabilities of web crawlers while avoiding resource consumption and context switching overhead caused by multi-threads or multi-processes.

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