fs.createWriteStream does not immediately create file?

Problem

I have made a simple download from http function as below (error handling is omitted for simplifcation):

function download(url, tempFilepath, filepath, callback) {
    var tempFile = fs.createWriteStream(tempFilepath);
    http.request(url, function(res) {
        res.on('data', function(chunk) {
            tempFile.write(chunk);
        }).on('end', function() {
            tempFile.end();
            fs.renameSync(tempFile.path, filepath);
            return callback(filepath);
        })
    });
}

However, as I call download() tens of times asynchronously, it seldom reports error on fs.renameSync complaining it cannot find file at tempFile.path.

Error: ENOENT, no such file or directory 'xxx'

I used the same list of urls to test it, and it failed about 30% of time. The same list of urls worked when downloaded one by one.

Testing some more, I found out that the following code

fs.createWriteStream('anypath');
console.log(fs.exist('anypath'));
console.log(fs.exist('anypath'));
console.log(fs.exist('anypath'));

does not always print true, but sometimes the first answer prints false.

I am suspecting that too many asynchronous fs.createWriteStream calls cannot guarantee the file creation. Is this true? Are there any methods to guarantee file creation?

Problem courtesy of: Jang-hwan Kim

Solution

You shouldn't call write on your tempFile write stream until you've received the 'open' event from the stream. The file won't exist until you see that event.

For your function:

function download(url, tempFilepath, filepath, callback) {
    var tempFile = fs.createWriteStream(tempFilepath);
    tempFile.on('open', function(fd) {
        http.request(url, function(res) {
            res.on('data', function(chunk) {
                tempFile.write(chunk);
            }).on('end', function() {
                tempFile.end();
                fs.renameSync(tempFile.path, filepath);
                return callback(filepath);
            });
        });
    });
}

For your test:

var ws = fs.createWriteStream('anypath');
ws.on('open', function(fd) {
    console.log(fs.existsSync('anypath'));
    console.log(fs.existsSync('anypath'));
    console.log(fs.existsSync('anypath'));
});
Solution courtesy of: JohnnyHK

Discussion

The accepted answer didn't download some of the last bytes for me.
Here's a Q version that works correctly (but without the temp file).

'use strict';

var fs = require('fs'),
    http = require('http'),
    path = require('path'),
    Q = require('q');

function download(url, filepath) {
  var fileStream = fs.createWriteStream(filepath),
      deferred = Q.defer();

  fileStream.on('open', function () {
    http.get(url, function (res) {
      res.on('error', function (err) {
        deferred.reject(err);
      });

      res.pipe(fileStream);
    });
  }).on('error', function (err) {
    deferred.reject(err);
  }).on('finish', function () {
    deferred.resolve(filepath);
  });

  return deferred.promise;
}

module.exports = {
  'download': download
};

Note I'm listening to finish on file stream instead of end on response.

Discussion courtesy of: Dan Abramov

This recipe can be found in it's original form on Stack Over Flow.