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.

Note: the correlator middleware should be placed after any other middleware.

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

const app = express();
// app.use other middleware here
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([options])

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. The header name is configurable, see options below. To ensure the correlation id is available to other middleware, ensure that it's applied after them.

const app = express();
// app.use other middleware here
app.use(correlator());

options

Options to configure the correlator middleware.

header

Configures the name of the inbound header to check for a correlation id.

const app = express();
app.use(correlator({header: "x-my-correlation-header-name"}));

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

License

MIT