server.js

var fs = require('fs');
var path = require('path');
var http = require('http');

var bind = 9090;
var basedir = '';

var server = http.createServer(function(req, res) {
  if (req.method === 'POST') {
    var d = new Date();
    if (month < 10) {
      month = '0' + month;
    }
    var filename = d.getFullYear() + '-' + month + '-' + d.getDate() + '.txt';

    var s = fs.createWriteStream(path.join(basedir, filename), {flags: 'a'});
    s.on('open', function(fd) {
      fs.write(fd, '\n');
    });

    req.pipe(s);

    req.on('end', function() {
      res.writeHead(200);
      res.end('Ok');
    });

  } else {
    res.writeHead(200);
    res.end('Ok');
  }
});

server.listen(bind);