NodeJS + PhantomJS 抓取頁面信息以及截圖

利用PhantomJS做網頁截圖經濟適用，但其API較少，做其他功能就比較吃力了。例如，其自帶的Web Server Mongoose最高只能同時支持10個請求，指望他能獨立成為一個服務是不怎么實際的。所以這里需要另一個語言來支撐服務，這里選用NodeJS來完成。

 

源碼地址

對源代碼感興趣的朋友可以在Github獲取：

https://github.com/miniflycn/url-extract

 

安裝PhantomJS

首先，去PhantomJS官網下載對應平台的版本，或者下載源代碼自行編譯。然后將PhantomJS配置進環境變量，輸入

$ phantomjs

如果有反應，那么就可以進行下一步了。

 

利用PhantomJS進行簡單截圖

var webpage = require('webpage')
  , page = webpage.create();
page.viewportSize = { width: 1024, height: 800 };
page.clipRect = { top: 0, left: 0, width: 1024, height: 800 };
page.settings = {
  javascriptEnabled: false,
  loadImages: true,
  userAgent: 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.31 (KHTML, like Gecko) PhantomJS/19.0'
};
page.open('http://www.baidu.com', function (status) {
  var data;
  if (status === 'fail') {
    console.log('open page fail!');
  } else { 
    page.render('./snapshot/test.png');
  }
  // release the memory
  page.close();
});

這里我們設置了窗口大小為1024 * 800：

page.viewportSize = { width: 1024, height: 800 };

截取從(0, 0)為起點的1024 * 800大小的圖像：

page.clipRect = { top: 0, left: 0, width: 1024, height: 800 };

禁止Javascript，允許圖片載入，並將userAgent改為"Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.31 (KHTML, like Gecko) PhantomJS/19.0"：

page.settings = {
  javascriptEnabled: false,
  loadImages: true,
  userAgent: 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.31 (KHTML, like Gecko) PhantomJS/19.0'
};

然后利用page.open打開頁面，最后截圖輸出到./snapshot/test.png中：

page.render('./snapshot/test.png');

 

NodeJS與PhantomJS通訊

我們先來看看PhantomJS能做什么通訊。

• 命令行傳參

例如：

phantomjs snapshot.js http://www.baidu.com

命令行傳參只能在PhantomJS開啟時進行傳參，在運行過程中就無能為力了。

• 標准輸出

標准輸出能從PhantomJS向NodeJS輸出數據，但卻沒法從NodeJS傳數據給PhantomJS。

不過測試中，標准輸出是這幾種方式傳輸最快的，在大量數據傳輸中應當考慮。

•  HTTP

PhantomJS向NodeJS服務發出HTTP請求，然后NodeJS返回相應的數據。

這種方式很簡單，但是請求只能由PhantomJS發出。

• Websocket

值得注意的是PhantomJS 1.9.0支持Websocket了，不過可惜是hixie-76 Websocket，不過畢竟還是提供了一種NodeJS主動向PhantomJS通訊的方案了。

測試中，我們發現PhantomJS連上本地的Websocket服務居然需要1秒左右，暫時不考慮這種方法吧。

• phantomjs-node

phantomjs-node成功將PhantomJS作為NodeJS的一個模塊來使用，但我們看看作者的原理解釋：

I will answer that question with a question. How do you communicate with a process that doesn't support shared memory, sockets, FIFOs, or standard input?

Well, there's one thing PhantomJS does support, and that's opening webpages. In fact, it's really good at opening web pages. So we communicate with PhantomJS by spinning up an instance of ExpressJS, opening Phantom in a subprocess, and pointing it at a special webpage that turns socket.io messages into alert()calls. Those alert() calls are picked up by Phantom and there you go!

The communication itself happens via James Halliday's fantastic dnode library, which fortunately works well enough when combined with browserify to run straight out of PhantomJS's pidgin Javascript environment.

實際上phantomjs-node使用的也是HTTP或者Websocket來進行通訊，不過其依賴龐大，我們只想做一個簡單的東西，暫時還是不考慮這個東東吧。

 

設計圖

 

讓我們開始吧

我們在第一版中選用HTTP進行實現。

首先利用cluster進行簡單的進程守護（index.js）：

module.exports = (function () {
  "use strict"
  var cluster = require('cluster')
    , fs = require('fs');

  if(!fs.existsSync('./snapshot')) {
    fs.mkdirSync('./snapshot');
  }

  if (cluster.isMaster) {
    cluster.fork();

    cluster.on('exit', function (worker) {
      console.log('Worker' + worker.id + ' died :(');
      process.nextTick(function () {
        cluster.fork();
      });
    })
  } else {
    require('./extract.js');
  }
})();

然后利用connect做我們的對外API（extract.js）：

module.exports = (function () {
  "use strict"
  var connect = require('connect')
    , fs = require('fs')
    , spawn = require('child_process').spawn
    , jobMan = require('./lib/jobMan.js')
    , bridge = require('./lib/bridge.js')
    , pkg = JSON.parse(fs.readFileSync('./package.json'));

  var app = connect()
    .use(connect.logger('dev'))
    .use('/snapshot', connect.static(__dirname + '/snapshot', { maxAge: pkg.maxAge }))
    .use(connect.bodyParser())
    .use('/bridge', bridge)
    .use('/api', function (req, res, next) {
      if (req.method !== "POST" || !req.body.campaignId) return next();
      if (!req.body.urls || !req.body.urls.length) return jobMan.watch(req.body.campaignId, req, res, next);

      var campaignId = req.body.campaignId
        , imagesPath = './snapshot/' + campaignId + '/'
        , urls = []
        , url
        , imagePath;

      function _deal(id, url, imagePath) {
        // just push into urls list
        urls.push({
          id: id,
          url: url,
          imagePath: imagePath
        });
      }
      
      for (var i = req.body.urls.length; i--;) {
        url = req.body.urls[i];
        imagePath = imagesPath + i + '.png';
        _deal(i, url, imagePath);
      }

      jobMan.register(campaignId, urls, req, res, next);
      var snapshot = spawn('phantomjs', ['snapshot.js', campaignId]);
      snapshot.stdout.on('data', function (data) {
        console.log('stdout: ' + data);
      });
      snapshot.stderr.on('data', function (data) {
        console.log('stderr: ' + data);
      });
      snapshot.on('close', function (code) {
        console.log('snapshot exited with code ' + code);
      });

    })
    .use(connect.static(__dirname + '/html', { maxAge: pkg.maxAge }))
    .listen(pkg.port, function () { console.log('listen: ' + 'http://localhost:' + pkg.port); });

})();

這里我們引用了兩個模塊bridge和jobMan。

其中bridge是HTTP通訊橋梁，jobMan是工作管理器。我們通過campaignId來對應一個job，然后將job和response委托給jobMan管理。然后啟動PhantomJS進行處理。

通訊橋梁負責接受或者返回job的相關信息，並交給jobMan（bridge.js）：

module.exports = (function () {
  "use strict"
  var jobMan = require('./jobMan.js')
    , fs = require('fs')
    , pkg = JSON.parse(fs.readFileSync('./package.json'));

  return function (req, res, next) {
      if (req.headers.secret !== pkg.secret) return next();
      // Snapshot APP can post url information
      if (req.method === "POST") {
        var body = JSON.parse(JSON.stringify(req.body));
        jobMan.fire(body);
        res.end('');
      // Snapshot APP can get the urls should extract
      } else {
        var urls = jobMan.getUrls(req.url.match(/campaignId=([^&]*)(\s|&|$)/)[1]);
        res.writeHead(200, {'Content-Type': 'application/json'});
        res.statuCode = 200;
        res.end(JSON.stringify({ urls: urls }));
      }
  };

})();

如果request method為POST，則我們認為PhantomJS正在給我們推送job的相關信息。而為GET時，則認為其要獲取job的信息。

jobMan負責管理job，並發送目前得到的job信息通過response返回給client（jobMan.js）：

module.exports = (function () {
  "use strict"
  var fs = require('fs')
    , fetch = require('./fetch.js')
    , _jobs = {};

  function _send(campaignId){
    var job = _jobs[campaignId];
    if (!job) return;
    if (job.waiting) {
      job.waiting = false;
      clearTimeout(job.timeout);
      var finished = (job.urlsNum === job.finishNum)
        , data = {
        campaignId: campaignId,
        urls: job.urls,
        finished: finished
      };
      job.urls = [];
      var res = job.res;
      if (finished) {
        _jobs[campaignId] = null;
        delete _jobs[campaignId]
      }
      res.writeHead(200, {'Content-Type': 'application/json'});
      res.statuCode = 200;
      res.end(JSON.stringify(data));
    }
  }
  
  function register(campaignId, urls, req, res, next) {
    _jobs[campaignId] = {
      urlsNum: urls.length,
      finishNum: 0,
      urls: [],
      cacheUrls: urls,
      res: null,
      waiting: false,
      timeout: null
    };
    watch(campaignId, req, res, next);
  }

  function watch(campaignId, req, res, next) {
    _jobs[campaignId].res = res;
    // 20s timeout
    _jobs[campaignId].timeout = setTimeout(function () {
      _send(campaignId);
    }, 20000);
  }

  function fire(opts) {
    var campaignId = opts.campaignId
      , job = _jobs[campaignId]
      , fetchObj = fetch(opts.html);

    if (job) {
      if (+opts.status && fetchObj.title) {
        job.urls.push({
          id: opts.id,
          url: opts.url,
          image: opts.image,
          title: fetchObj.title,
          description: fetchObj.description,
          status: +opts.status
        });
      } else {
        job.urls.push({
          id: opts.id,
          url: opts.url,
          status: +opts.status
        });
      }

      if (!job.waiting) {
        job.waiting = true;
        setTimeout(function () {
          _send(campaignId);
        }, 500);
      }
      job.finishNum ++;
    } else {
      console.log('job can not found!');
    }
  }

  function getUrls(campaignId) {
    var job = _jobs[campaignId];
    if (job) return job.cacheUrls;
  }

  return {
    register: register,
    watch: watch,
    fire: fire,
    getUrls: getUrls
  };

})();

這里我們用到fetch對html進行抓取其title和description，fetch實現比較簡單（fetch.js）：

module.exports = (function () {
  "use strict"

  return function (html) {
    if (!html) return { title: false, description: false };

    var title = html.match(/\<title\>(.*?)\<\/title\>/)
      , meta = html.match(/\<meta\s(.*?)\/?\>/g)
      , description;

    if (meta) {
      for (var i = meta.length; i--;) {
        if(meta[i].indexOf('name="description"') > -1 || meta[i].indexOf('name="Description"') > -1){
          description = meta[i].match(/content\=\"(.*?)\"/)[1];
        }
      }
    }

    (title && title[1] !== '') ? (title = title[1]) : (title = 'No Title');
    description || (description = 'No Description');

    return {
      title: title,
      description: description
    };
  };

})();

最后是PhantomJS運行的源代碼，其啟動后通過HTTP向bridge獲取job信息，然后每完成job的其中一個url就通過HTTP返回給bridge（snapshot.js）：

var webpage = require('webpage')
  , args = require('system').args
  , fs = require('fs')
  , campaignId = args[1]
  , pkg = JSON.parse(fs.read('./package.json'));

function snapshot(id, url, imagePath) {
  var page = webpage.create()
    , send
    , begin
    , save
    , end;
  page.viewportSize = { width: 1024, height: 800 };
  page.clipRect = { top: 0, left: 0, width: 1024, height: 800 };
  page.settings = {
    javascriptEnabled: false,
    loadImages: true,
    userAgent: 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.31 (KHTML, like Gecko) PhantomJS/1.9.0'
  };
  page.open(url, function (status) {
    var data;
    if (status === 'fail') {
      data = [
        'campaignId=',
        campaignId,
        '&url=',
        encodeURIComponent(url),
        '&id=',
        id,
        '&status=',
        0
      ].join('');
      postPage.open('http://localhost:' + pkg.port + '/bridge', 'POST', data, function () {});
    } else { 
      page.render(imagePath);
      var html = page.content;
      // callback NodeJS
      data = [
        'campaignId=',
        campaignId,
        '&html=',
        encodeURIComponent(html),
        '&url=',
        encodeURIComponent(url),
        '&image=',
        encodeURIComponent(imagePath),
        '&id=',
        id,
        '&status=',
        1
      ].join('');
      postMan.post(data);
    }
    // release the memory
    page.close();
  });
}

var postMan = {
  postPage: null,
  posting: false,
  datas: [],
  len: 0,
  currentNum: 0,
  init: function (snapshot) {
    var postPage = webpage.create();
    postPage.customHeaders = {
      'secret': pkg.secret
    };
    postPage.open('http://localhost:' + pkg.port + '/bridge?campaignId=' + campaignId, function () {
      var urls = JSON.parse(postPage.plainText).urls
        , url;

      this.len = urls.length;

      if (this.len) {
        for (var i = this.len; i--;) {
          url = urls[i];
          snapshot(url.id, url.url, url.imagePath);
        }
      }
    });
    this.postPage = postPage;
  },
  post: function (data) {
    this.datas.push(data);
    if (!this.posting) {
      this.posting = true;
      this.fire();
    }
  },
  fire: function () {
    if (this.datas.length) {
      var data = this.datas.shift()
        , that = this;
      this.postPage.open('http://localhost:' + pkg.port + '/bridge', 'POST', data, function () {
        that.fire();
        // kill child process
        setTimeout(function () {
          if (++this.currentNum === this.len) {
            that.postPage.close();
            phantom.exit();
          }
        }, 500);
      });
    } else {
      this.posting = false;
    }
  }
};
postMan.init(snapshot);

 

效果