Logging all requests in Node.js/Express - json

Question

In my small node.js application, using express, I wanted to log all the incoming requests, so I ended up with this:
var bodyParser = require('body-parser');
module.exports = function(app) {
app.set("port", 50001);
app.set("json spaces", 2);
app.use(bodyParser.json());
app.use(function (error, req, res, next) {
app.logger.info("received from "+req.get("X-Forwarded-For")+" : "+req.method+" "+req.originalUrl+" (Authorization: "+req.get("Authorization")+")");
//does not work if json is malformed
//app.logger.info("content :"+JSON.stringify(req.body));
if (error /*instanceof SyntaxError*/) {
res.status(400);
app.logger.error(error);
res.json({ error:{msg: error.message}});
} else {
next();
}
});
app.use(app.auth.initialize());
};
Unfortunately, I only get the logs via the app.logger.info line when there's an error (in my case a malformed JSON string in the body). What am I missing here?

Answer 1

Expressjs adapts its functionality based on what type of callback you give it (this is not common in JS libraries so it is not surprising that people get confused by it).
If you do this where your callback has four arguments:
app.use(function(error, req, res, next) {...});
then Express assumes this is an error-only middleware handler and will only be called when there are errors. In the express doc, see the section labeled Error-handling middleware. Note this specific part of that page:
Define error-handling middleware functions in the same way as other
middleware functions, except with four arguments instead of three,
specifically with the signature (err, req, res, next)):
And, here's a whole section of the documentation devoted to error handling middleware.
If you use just three arguments:
app.use(function(req, res, next) {...});
then, it is a normal middleware that is called when there are not errors. I'm not sure if they provide a single way to get both. But, certainly as a workaround, you could put your logging code into a function and then call that function from two separate middleware handlers, one for errors and one for non-errors.

Answer 2

Use morgan https://github.com/expressjs/morgan
Install morgan
$ npm install morgan
Include morgan in the index.js or app.js or server.js file (The file that pointed by the script tag in the package.json)
var morgan = require('morgan')
Then add below before all the app call.
app.use(morgan('combined'))
Complete example
var express = require('express')
var morgan = require('morgan')
var app = express()
app.use(morgan('combined'))
app.get('/', function (req, res) {
res.send('hello, world!')
})
A sample output line looks like this:
::1 - - [31/May/2021:09:03:14 +0000] "GET / HTTP/1.1" 200 2078 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36"

Answer 3

DEBUG='*' or DEBUG='express:router' environment variable
It does not show a lot of information about the request, but it does show the path and method, which might be enough for basic applications, and is convenient as it does not require any extra setup.
DEBUG='*' enables all logs and is slightly easier to type:
DEBUG='*' ./app.js
or the more specific DEBUG='express:router' is what you will generally want in a complex application with a lot of middleware, otherwise the DEBUG='*' could produce mountains of output:
DEBUG='express:router' ./app.js
E.g. with the hello world:
#!/usr/bin/env node
const express = require('express')
const app = express()
const port = 3000
app.get('/', (req, res) => {
res.send('Hello World!')
})
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`)
})
Then as I play on the browser with different URLs I can see logs such as:
express:router dispatching GET / +3m
express:router query : / +0ms
express:router expressInit : / +0ms
express:router dispatching GET /asdf +10s
express:router query : /asdf +0ms
express:router expressInit : /asdf +0ms
finalhandler default 404 +3m
express:router dispatching GET /asdf?qwer=zxcv +17s
express:router query : /asdf?qwer=zxcv +0ms
express:router expressInit : /asdf?qwer=zxcv +0ms
finalhandler default 404 +17s
Documentation at: https://expressjs.com/en/guide/debugging.html
Tested on express 4.17.1.

Answer 4

npm install body-parser
npm install morgan-body
and use this snippet,
const express = require('express')
const morganBody = require("morgan-body")
const bodyParser = require("body-parser")
const app = express()
const port = 8888
// must parse body before morganBody as body will be logged
app.use(bodyParser.json());
// hook morganBody to express app
morganBody(app, {logAllReqHeader:true, maxBodyLength:5000});
app.get('/', (req, res) => {
res.send('Hello World!')
})
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`)
})

Answer 5

You can just use grackle_tracking npm library to easily log all your traffic out to the console or log it to your database - also tracks uncaugt/caught errors - you can toggle it on/off easily for different environments as well since it's just
grackle_tracking.configure({...configuration...});
app.use(grackle_tracking.track);
so you can comment out both or just the bottom line for environments/users you don't want to track
https://www.getgrackle.com/libraries#grackle_tracking_overview

Answer 6

You could use try/catch
try {
var jsonBody = JSON.stringify(req.body);
app.logger.info("content :" + jsonBody);
} catch (err) {
app.logger.error("content error, error type: invalid json, error msg:" + err);
}