I'm using node.js and express to handle HTTP requests and responses. By using the http.ServerRequest 'request' event, I can add a hook in and log HTTP requests. There doesn't seem to be a similiar event for http.ServerResponse and I am wondering how to log all the HTTP responses with one piece of code that my server sends?

I created a package that does such a thing, out of a similar need. Check out express-request-logger

The heart of the program is like this, it contains some extra code so you can have your own key-value map of data that gets logged per request:

// Save the real end that we will wrap
var rEnd = res.end;

// To track response time
req._rlStartTime = new Date();

// Proxy the real end function
res.end = function(chunk, encoding) {
  // Do the work expected
  res.end = rEnd;
  res.end(chunk, encoding);

  // And do the work we want now (logging!)

  // Save a few more variables that we can only get at the end
  req.kvLog.status = res.statusCode;
  req.kvLog.response_time = (new Date() - req._rlStartTime);

  // Send the log off to winston
  var level = req.kvLog._rlLevel;
  delete req.kvLog._rlLevel;
  logger.log(level, '', req.kvLog);
};

The above code runs as middleware in express. Take a look at the code, and if you have further questions, get in touch with me on here or github.