Basic error handling in Express

express-error-handling.js

app.configure(function() {
  // Setup a socket error handler for all requests
  app.use(socketErrorHandler);
  // Catch any attempts to call res.send multiple times for the same client
  app.use(onlyOneResponse);
});

function socketErrorHandler(req, res, next) {
  // Check if this socket is being reused and already has an error handler
  if (!req.socket.listeners('error').length) {
    // Install an error handler for this socket
    req.socket.addListener('error', function(err) {
      console.warn('Socket error from client ' + req.socket.remoteAddress +
        ': ' + err);
    });
  }
  
  next();
}

function onlyOneResponse(req, res, next) {
  var send = res.send;
  
  // Proxy the send method
  res.send = function(body) {
    if (res._doSend) {
      // send has already been called
      var err = new Error('Response already sent');
      console.error(err.toString());
      return;
    }
    
    res._doSend = send;
    res._doSend(body);
  };
  
  next();
}