How to log JSON HTTP Responses using Winston/Morgan

Question

I'm using Winston and Morgan for all the back-end logging in Sails.js and I need to be able to log the responses from HTTP get requests. I need to log them in a file. My logFile currently takes shows all the http requests but it does not show the responses. I have searched all the options for Morgan and Winston and can't find a way/option to do this. I was just wondering if any of you had any advice on how to accomplish this? Thanks!

Answer 1

You can write a middleware function for ExpressJS that will log the body once a response is sent. Basing it off of Node's http module to see how Connect (and therefore Express) manages the response body (which is a stream): you can hook into the two methods that write to that stream to grab the chunks and then concat/decode them to log it. Simple solution and could be made more robust but it shows the concept works.

function bodyLog(req, res, next) {
  var write = res.write;
  var end = res.end;
  var chunks = [];

  res.write = function newWrite(chunk) {
    chunks.push(chunk);

    write.apply(res, arguments);
  };

  res.end = function newEnd(chunk) {
    if (chunk) { chunks.push(chunk); }

    end.apply(res, arguments);
  };

  res.once('finish', function logIt() {
    var body = Buffer.concat(chunks).toString('utf8');

    // LOG BODY
  });

  next();
}

And then set it before any routes are assigned in the main app router:

app.use(bodyLog);
// assign routes

I would assume you could also use this as an assignment for a variable in Morgan but I haven't looked into how async variable assignment would work.