Rethinkdbdash bug #103 posted on 29 June 2015

I just fixed a sneaky but in rethinkdbdash and thought it would be worth to quickly write about it.

Here is the broken snippet:

// Opening a socket
self.connection = net.connect({
  port: self.port,
  family: family

self.connection.on('end', function(error) {
  // ...
self.connection.on('close', function(error) {
  // ...
self.connection.on('connect', function() {
  // Do the handshake
  // var initBuffer = ...
  // var lengthBuffer = ...
  // var authBuffer ...
  // var protocolBuffer = ...
  self.connection.write(Buffer.concat([initBuffer, lengthBuffer, authBuffer, protocolBuffer]));
self.connection.once('error', function(error) {
  // ...
self.connection.once('end', function() { = false;

self.connection.on('data', function(buffer) {
  // Handle handshake and responses

I have cleaned a bit the code, but the main idea is to open a TCP connection, send a “handshake” and listen for data (the response of the handshake and the response for the queries we will send).

This code however can throw with

Process exit at 2015-06-27T15:15:18.897Z
      throw er; // Unhandled 'error' event
Error: write after end
    at writeAfterEnd (_stream_writable.js:158:12)
    at Socket.Writable.write (_stream_writable.js:203:5)
    at Socket.write (net.js:615:40)
    at /home/u/app/node_modules/rethinkdbdash/lib/connection.js:81:23
    at Object.tryCatch (/home/u/app/node_modules/rethinkdbdash/lib/helper.js:156:3)
    at Socket.<anonymous> (/home/u/app/node_modules/rethinkdbdash/lib/connection.js:80:12)
    at emitNone (events.js:72:20)
    at Socket.emit (events.js:166:7)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1029:10)

The reason is that self.connection.write is not safe there.

The main problem is that the TCP connection can be already closed when you enter the callback for the connect event. In this case, we will try to write on the socket, but this will immediately emit an error. Because we bind the listener for error after the one for connect, we end up with an error that nothing will catch that will eventually crash the worker.

The solution is simply to bind your listener for error before trying to write anything on the socket. A better solution would probably be for node to emit the event at the next tick like mentionned in the TODO.