Multiple child_process exec on node js

Question

I am trying to get data using curl on nodejs. I need to run more than one child_process for each query in order to retrieve the data without delays.

router.post('/curl/', function* () {

      var urls = this.request.body.url;
      var exec = require('child_process').exec;

      var promise = new Promise((resolve, reject) => {

                var count = urls.length;

                var res = _.map(urls, (stream) => {
                     // stream = {url:'http://url1.com'};

                     var command = 'curl '+stream.url+';

                     exec(command, (error, stdout, stderr) => {
                          if (error !== null) {
                              console.log('exec error: ' + error);
                          }
                          return stdout;
                     });
                });

                resolve(res);
     });

      this.body = yield promise;
 });

This resolve '[null, null]'; I was tried to use Promise.map, but it was failed too.

If I make a single request (without _.map()) - it returns HTML of the requested page, as I expect. How to run more than one child_process for my requests?

Sangharsh · Accepted Answer · 2017-02-10 06:48:15Z

1

Here is a variant without generator (function*). It is unclear what are you trying to do with generator.

var exec = require('child_process').exec;

router.post('/curl/', function() {

  function processUrl(url) {
    return new Promise((resolve, reject) => {
      var command = 'curl ' + stream.url;
      exec(command, (error, stdout, stderr) => {
        if (error)
          return reject(error);
        return resolve(stdout);
      });
    });
  }

  var urls = this.request.body.url;

  var allPromises = urls.map(url => {
    return processUrl(url);
  });

  Promise.all(allPromises)
    .then(htmls => {
      console.log('HTML of pages:', htmls.length);
    });
});

answered Feb 10, 2017 at 6:48

Sangharsh

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1 Comment

Mike Over a year ago

I use generator to wrap all the code into Promise, and run it as 'this.body = yield promise'.

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