NodeJS write response to browser multiple times

Question

I have a simple nodeJS server that fetches data from another server and store them in a JSON files, i need to write a status about each file fetched and generated, but that doesn't work, because i have to execute response.end(), which implies that i can't write to the stream again, without ending the stream

here's my code:

      var http = require('http');
  var module = require('fs');
  var APIs = [ '/servlet/en', '/servlet/fr' ];
  var langs =[ 'en', 'fr' ];
  var finish = false;
  var host = 'http://www.localtest';
  const port = process.argv[2] || 9000;
  var responses = [];

  http.createServer(function (req, response) {

    for (x in APIs){
      console.log(x);
    var options = {
      host: 'localtest',
      port: 8888,
      path: APIs[x],
      lang: langs[x]
    };

    http.get(options, function(res) {
        res.setEncoding('utf8');
        var body='';
        res.on('data', function(chunk){
          body += chunk;
        });
        res.on('end', function(chunk){
          responses.push(body);

          if (responses.length == 2){
          var d = JSON.parse(responses[1]);
          var d2 = JSON.parse(responses[0]);

        module.writeFileSync("options.lang1"+".json",JSON.stringify(d) , 'utf-8');
        module.writeFileSync("options.lang2"+".json",JSON.stringify(d2) , 'utf-8');
        }
        });

    });

  }

  }).listen(parseInt(port));

  console.log(`Server listening on port ${port}`);

An example, i tried to write a message to the user after the line : responses.push(body); using response.write(), but this method needs an response.end() in order to be executed and displayed on the browser, If i do that i can't write to the stream anymore!

Possible duplicate of [Callback after all asynchronous forEach callbacks are completed](http://stackoverflow.com/questions/18983138/callback-after-all-asynchronous-foreach-callbacks-are-completed) — E_net4, Dec 04 '16 at 23:43
Maybe I have misinterpreted the question. Care to clarify it then? Why do you think doing "response.end()" can become an issue? — E_net4, Dec 05 '16 at 00:05
I don't know, i'm new to nodeJS, but when i write to the stream for the first time, i can't do that any more! — M1M6, Dec 05 '16 at 00:09
Consider showing what you've tried to actually solve the problem, in code. — E_net4, Dec 05 '16 at 00:12

score 0 · Accepted Answer · answered Dec 05 '16 at 00:19

Couple issues with your code here. First off, you shouldn't use module as a variable, as that is a word that's already used in node's moduling system, e.g. in module.exports

Second, You really want to have some control flow in there. here's a complete example using the async library, though others prefer Promises.

 var http = require('http');
  var fs = require('fs');
  var APIs = [ '/servlet/en', '/servlet/fr' ];
  var langs =[ 'en', 'fr' ];
  var host = 'http://www.localtest';
  const port = process.argv[2] || 9000;

  const async = require('async');
  let responses = [];

  function fetchAndWriteFile(lang, callback){
    var options = {
      host: 'localtest',
      port: 8888,
      path: '/servlet/'+lang,
      lang: lang
    };

    http.get(options, function(res) {
        res.setEncoding('utf8');
        const filename = 'options.'+lang+'.json';
        const fileStream = fs.createWriteStream(filename, {defaultEncoding: 'utf-8'});
        fileStream.on('end', (e)=> {
            if(e) return callback(e);
            return callback(null, filename);
        });

        res.pipe(fileStream)
    });
  }

  http.createServer(function (req, response) {
    // this will run the fetchAndWriteFile once for each lang in langs
    async.map(langs, fetchAndWriteFile, (e, files) => {
        response.end(files); // files will be an array of filenames saved
    });

  }).listen(parseInt(port));

  console.log(`Server listening on port ${port}`);

Thanks, it works as of my code, when i run the script the browser will always show the loading icon (although the files are generated and saved), my main problem is with writing some text to the browser — M1M6, Dec 05 '16 at 00:32
yes, and what I have shows how to do that (writing the response to the browser after both are saved). — Paul, Dec 05 '16 at 00:34

NodeJS write response to browser multiple times

1 Answers1