javascript - 如何在node.js中正确实现读取流的回调逻辑？

Question

我正在尝试在node.js 中实现小型RSS 阅读器(它将提要数据呈现为html 页面)。

到目前为止我已经做到了这一点:

var FeedParser = require(__dirname + '/../node_modules/feedparser')
  , request = require(__dirname + '/../node_modules/request');

exports.news = function(req, res){

  var news = []; 
    request('http://feeds.feedburner.com/niebezpiecznik/')
    .pipe(new FeedParser())
      .on('error', function(error) {
        // ...
      })  
      .on('meta', function (meta) {
        console.log('===== %s =====', meta.title);
        console.log('**** %s ****', meta.description);
        console.log();
      })  
      .on('readable', function() {
        var stream = this, item;
        var i = 0;
        while (item = stream.read()) {

          var this_news = { 
            'title': item.title,
            'description': item.description
          }   
          news.push(this_news);
          console.log(i++);
        }   
        res.render('rss', {
          title: 'Node.js based RSS reader',
          newsi: JSON.stringify(news)
        }); 
    }); 

};

带有以下 Jade 模板:

扩展布局

block content
  h1= title
  p Welcome to #{title}
  script(type='text/javascript').
    var inews = JSON.parse('!{newsi}');
    console.log(inews);
  ul  
  for news in newsi
    li= news
  else
    li sorry, no newsHERE!

但我不断收到以下错误:

0
GET /rss 304 532ms
0
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (http.js:691:11)
    at ServerResponse.res.setHeader (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/node_modules/connect/lib/patch.js:63:22)
    at ServerResponse.res.set.res.header (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/response.js:527:10)
    at ServerResponse.res.contentType.res.type (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/response.js:396:15)
    at ServerResponse.res.send (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/response.js:112:14)
    at fn (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/response.js:794:10)
    at View.exports.renderFile [as engine] (/home/XXX/programming/nodejs/node-express-aws/node_modules/jade/lib/jade.js:222:12)
    at View.render (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/view.js:76:8)
    at Function.app.render (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/application.js:504:10)
    at ServerResponse.res.render (/home/XXX/programming/nodejs/node-express-aws/node_modules/express/lib/response.js:798:7)

我应该把这个render部分放在哪里？

Answer 1

我认为，即使您从其处理程序中调用 read ，read 事件也可能会被多次触发。

我不熟悉 Feedparser 模块，但请尝试使用 data 和 end 事件:

.on('data', function(item) {
  var this_news = { 
    'title': item.title,
    'description': item.description
  }   
  news.push(this_news);
  console.log(i++);
})
.on('end', function() {
  res.render('rss', {
    title: 'Node.js based RSS reader',
    newsi: JSON.stringify(news)
  }); 
});

如果这不起作用，您仍然可以使用 read 事件处理程序，但请确保从 end 调用 res.render处理程序。