this.log should be replaced with req.log

[GuskiS]

I tried this:

req.log = req.log.child({ something: true });

but it didn't work. After digging into sourcecode I found this:

pino-http/logger.js

Line 44 in a7c82bc

var log = this.log

this refers to res object, so that would mean res.log. After changing that code, something appeared in my output.

This is very misleading since all examples suggest to use req.log. Also there isn't res.log doesn't have typescript type definition.

[mcollina]

Can you add an example to reproduce the problem you are facing?

[GuskiS]

I have something like this:

router.use(pinoHttp(), (req, res, next) => {
  req.log = req.log.child({  something: true })
  next();
});

router.get("/example", (req, res) => {
  req.log.info("some message")
  res.json({ ok: true });
});

req.log.info("some message") will have something: true in its output, however, the request completed will not have it, because that one relays on res.

I hope this make it more clear.

[davidmarkclements]

if you're always binding the same value, this isn't a good pattern, instead do

const logger = require('pino')().child({ something: true })
const pinoHttp = require('pino-http')({ logger })
router.use(pinoHttp)

[davidmarkclements]

for injecting values on a per request basis use the serializers

[GuskiS]

Value changes per request. I tried setting that value on req object, however that didn't show up in serializers from req.raw.

[mcollina]

I think it would be helpful to have a full example of what you are trying to do.

[GuskiS]

#74 (comment)
This is almost the same thing as I'm doing, but here goes:
1.

app.use(pinoHttp());

const originalRouteMiddleware = (originalRoute) => (req, res, next) => {
  req.log = req.log.child({ originalRoute });
  next();
});

app.use(pinoHttp({
  serializers: {
    req(req) {
      req.originalRoute = req.raw.originalRoute;
      return req;
    },
  },
}));

const originalRouteMiddleware = (originalRoute) => (req, res, next) => {
  req.originalRoute = originalRoute;
  next();
});

Route:

router.get("/user/:userId", originalRouteMiddleware("/user/:userId"), (req, res) => {
  req.log.info("some message");
  res.json({ ok: true });
});

So the issues I'm facing:

1. I would need to do req.log = res.log = res.log.child({ originalRoute }); to make it work, which is misleading and not obvious if you don't take a look at sourcecode. Also, as suggested, not a good pattern.
2. In this case req.raw doesn't contain my originalRoute, not sure why tho. Maybe .child creates copy of original object? 🤔

[mcollina]

May I get a full example that I can run? Ideally without express (or maybe this is express-only).

[GuskiS]

Here it is: https://github.com/GuskiS/pino-express-failure

[mcollina]

In this case req.raw doesn't contain my originalRoute, not sure why tho. Maybe .child creates copy of original object?

Child serializes the request object once at the time the log line is created. In order for that property to show up, you'd have to add it in a middleware before the pino-http one.

I do not think there is any other way than req.log = res.log = res.log.child({ originalRoute }); tbh.
You could potentially disable autoLogging and log after you have set that value.