利用Redis和JavaScript构建简单的网络爬虫：如何快速抓取数据

const redis = require('redis');
const client = redis.createClient();

// 添加待抓取的URL到队列
const enqueueUrl = (url, priority = 0) => {
  client.zadd('urls', priority, url);
}

// 从队列中获取待抓取的URL
const dequeueUrl = () => {
  return new Promise((resolve, reject) => {
    client.zrange('urls', 0, 0, (err, urls) => {
      if (err) reject(err);
      else resolve(urls[0]);
    })
  })
}

// 判断URL是否已经被抓取过
const isUrlVisited = (url) => {
  return new Promise((resolve, reject) => {
    client.sismember('visited_urls', url, (err, result) => {
      if (err) reject(err);
      else resolve(!!result);
    })
  })
}

// 将URL标记为已经被抓取过
const markUrlVisited = (url) => {
  client.sadd('visited_urls', url);
}

const request = require('request');
const cheerio = require('cheerio');

// 从指定的URL中解析数据
const parseData = (url) => {
  return new Promise((resolve, reject) => {
    request(url, (error, response, body) => {
      if (error) reject(error);
      else {
        const $ = cheerio.load(body);
        // 在这里对页面进行解析，并提取数据
        // ...

        resolve(data);
      }
    })
  })
}

// 爬虫节点的主逻辑
const crawler = async () => {
  while (true) {
    const url = await dequeueUrl();
    if (!url) break;

    if (await isUrlVisited(url)) continue;

    try {
      const data = await parseData(url);

      // 在这里将数据存储到Redis中
      // ...

      markUrlVisited(url);
    } catch (error) {
      console.error(`Failed to parse data from ${url}`, error);
    }
  }
}

crawler();