Express correlation id

Express middleware to set a correlation id per route in express. The correlation id will be consistent across async calls within the handling of a request.

Installation

npm i express-correlation-id --save

Middleware usage example

All middleware and route handlers following the correlator() middleware will be within a single correlation scope. If the incoming request has a header called x-correlation-id then it's value will be used as the id for this request, otherwise the id will be a new uuid.

const correlator = require('express-correlation-id');
const express = require('express');

const app = express();
app.use(correlator());

app.get('/', (req, res) => {
  console.log('ID for this request is:', req.correlationId()); // id for this request
  console.log('ID for this request is:', correlator.getId());  // equal to above, not dependant on the req object
  res.end();
})

API

correlator()

Returns an express middleware that creates a correlation scope for all following middleware and route handlers. If the incoming request has a header with name x-correlation-id then it's value will be used as the id.

const app = express();
app.use(correlator());

correlator.getId()

Returns the id for the current request. If called outside of a request returns undefined. This function is useful if you don't want to pass the req object or correlation id from the handler to downstream code.

correlator.getId(); // Returns the current id or undefined

req.correlationId()

Returns the id for the current request. This function is added to the incoming req by the middleware.

req.correlationId(); // Returns the current id