How can i create a logger middleware in express without any package or library

Question

I've trying to create a custom logger middleware without any package or library It's as simple as saving the endpoint, the method and the status code response.

I have the problem when I try to save the status code, since my response has not yet reached the controller. I was trying to understand how morgan does it, because it is the first middleware I use and when my backend responds, it logs the status code.

Is there a simple way without me having to modify all my backend controllers?

Or rather, how can I access the res.status of a controller from this middleware?

const createLog = (req, res, next) => {
  const { method, url } = req;
  const { statusCode, statusMessage } = res;

  console.log(statusCode, statusMessage); // Both null when reach the middleware
  next();
};

Answer 1

The following middleware logs the request method, URL and status (which is available only when the request has finished):

const createLog = (req, res, next) => {
  res.on("finish", function() {
    console.log(req.method, decodeURI(req.url), res.statusCode, res.statusMessage);
  });
  next();
};

Alternatively, you can register the following event handler on your HTTP(S) server, which logs all HTTP requests (>) and responses (<), but this may be overwhelmingly much:

server.on("connection", function(socket) {
  const write = socket.write.bind(socket);
  socket.on("data", function(chunk) {
    console.log(">", chunk.toString());
  });
  socket.write = function(chunk, encoding, callback) {
    write(chunk, encoding, function (err) {
      console.log("<", chunk.toString(encoding || "utf8"));
      if (callback) callback(err);
    });
  };
});