fs.createWriteStream does not immediately create file?

Question

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?

Answer 1

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')); }); 

Answer 2

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.