Correlation id

Correlation id maintains a consistent id across asynchronous calls in node.js applications. This is extremely useful for logging purposes. For example within a web application, each incoming request can be assigned an id that will be available in all function calls made processing that request, so we can see which requests caused errors.

Installation

npm i correlation-id --save

Simple example

As demonstrated by this example, all calls to getId() within the same withId() block will return the same id. The id can be supplied, otherwise a v4 uuid will be generated.

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

function printCurrentId (name) {
  console.log('%s id: %s', name, correlator.getId());
}

correlator.withId(() => {
  setTimeout(() => {
    printCurrentId('withId block 1, call 1');
  });
  setTimeout(() => {
    printCurrentId('withId block 1, call 2');
  }, 1000);
});

correlator.withId('my-custom-id', () => {
  setTimeout(() => {
    printCurrentId('withId block 2, call 1');
  }, 500);
});

// Output:
// withId block 1, call 1 id: 5816e2d3-6b90-43be-8738-f6e1b2654f39
// withId block 2, call 1 id: my-custom-id
// withId block 1, call 2 id: 5816e2d3-6b90-43be-8738-f6e1b2654f39

API

withId([id,] work)

Executes function work within a correlation scope. Within work and any other function executions (sync or async) calls to getId() will return the same id. The id for the context may be set explicitly with the optional id parameter, otherwise it will be a v4 uuid. Calls to withId() may be nested.

correlator.withId(() => {
  console.log(correlator.getId()); // Writes a uuid to stdout
});
correlator.withId('my-custom-id', () => {
  console.log(correlator.getId()); // Writes 'my-custom-id' to stdout
});

bindId([id,] work)

Returns function work bound with a correlation scope. When work is executed all calls to getId() will return the same id. The id for the context may be set explicitly with the optional id parameter, otherwise it will be a v4 uuid. Arguments passed to the bound function will be applied to work.

const boundFunction = correlator.bindId((p1) => {
  console.log('p1 is', p1);
  console.log(correlator.getId());
});
boundFunction('foo'); // Writes 'p1 is foo' and then a uuid to stdout

const boundFunction2 = correlator.bindId('my-custom-id', (p1) => {
  console.log('p1 is', p1);
  console.log(correlator.getId());
});
boundFunction('foo'); // Writes 'p1 is foo' and then 'my-custom-id' to stdout

getId()

Returns the id for the current correlation scope (created via withId or bindId). If called outside of a correlation scope returns undefined.

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

How does it work?

Currently this module a slim wrapper over continuation-local-storage. I intend to move to async-hook when it's generally available.

License

MIT