Why doesn't piping work inside a callback

node.js, stream

Solution

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);

Problem

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?

Original source