README.md

This sets up two HTTP servers on port 3000 and 3001. The one on port 3000 works as expected, the one on port 3001 doesn't.

Console log output when requesting server on port 3000:

------- NEW WORKING REQUEST -------
New listener added: end
adding 1st data litener
New listener added: data
New listener added: data
New listener added: readable
New listener added: readable
foo
bar

Console log output when requesting server on port 3001:

------- NEW BROKEN REQUEST -------
New listener added: end
adding 1st data litener
New listener added: data
New listener added: data
New listener added: readable
foo
New listener added: readable

bug.js

var http = require('http');

var listen = function (req, res) {
  var listening = false;

  req.on('newListener', function (event) {
    console.log('New listener added:', event);

    if (!listening && event === 'data') {
      listening = true;

      req.on('data', function () {
        console.log('foo');
        res.write('foo\n');
      });
    }
  });
};

var works = function (req, res) {
  console.log('------- NEW WORKING REQUEST -------');
  listen(req, res);

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

  console.log('adding 1st data litener');
  req.on('data', function () {
    console.log('bar');
    res.write('bar\n');
  });
};

var broken = function (req, res) {
  console.log('------- NEW BROKEN REQUEST -------');
  listen(req, res);

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

  process.nextTick(function () {
    console.log('adding 1st data litener');
    req.on('data', function () {
      console.log('bar');
      res.write('bar\n');
    });
  });
};

http.createServer(works).listen(3000);
http.createServer(broken).listen(3001);

workaround.js

var http = require('http');

var listen = function (req, res) {
  var listening = false;

  req.on('newListener', function (event) {
    console.log('New listener added:', event);

    if (!listening && event === 'data') {
      listening = true;

      var size = Buffer.concat(req._readableState.buffer).length;
      req.once('end', function () {
        console.log('Total request size:', size);
      });

      var attachListener = function () {
        req.on('data', function (chunk) {
          size += chunk.length;
        });
      };

      if (size)
        process.nextTick(attachListener);
      else
        attachListener();
    }
  });
};

var sync = function (req, res) {
  console.log('------- REQUEST: SYNC -------');
  listen(req, res);

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

  console.log('adding 1st data litener');
  req.on('data', function () {
    process.stdout.write('.');
  });
};

var async = function (req, res) {
  console.log('------- REQUEST: ASYNC -------');
  listen(req, res);

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

  process.nextTick(function () {
    console.log('adding 1st data litener');
    req.on('data', function () {
      process.stdout.write('.');
    });
  });
};

http.createServer(sync).listen(3000);
http.createServer(async).listen(3001);