Why doesn't piping work inside a callback

Question

I have the following server:

http.createServer(function (req, res) {

  fs.mkdir(__dirname + '/output', function (err) {

    req.pipe(fs.createWriteStream(__dirname + '/output/file.txt'));
    res.end();

  });

}).listen(3000);

I am then using request to pipe a stream to the server.

var fs = require('fs');
var request = require('request');

var crs = fs.createReadStream(__dirname + '/file.txt');
var r = request.post('http://0.0.0.0:3000');

crs.pipe(r);

Sometimes it works but most of the time /output/file.txt is empty. When I move the req.pipe(...) outside of the mkdir callback it works every time. Could anybody explain why it is happening?

Answer 1

Since mkdir is asynchronous, the data in the request is emitted while the directory is being created. You need to instruct the stream to not emit the data until later by using pause and resume .

http.createServer(function (req, res) {
  req.pause();
  fs.mkdir(__dirname + '/output', function (err) {
    req.pipe(fs.createWriteStream(__dirname + '/output/file.txt'));

    req.resume();
    res.end();
  });
}).listen(3000);