remit

Remit

A small set of functionality used to create microservices that don't need to be aware of one-another's existence.

npm install remit

const remit = require('remit')()

;(async function () {
  const endpoint = remit
    .endpoint('user.profile')
    .data((event, callback) => {
      const user = getUser({ id: event.data.id })

      callback(null, user)
    })

  await endpoint.ready()

  try {
    var user = await remit
      .request('user.profile')
      .send({ id: 123 })
  } catch (e) {
    console.error('Error getting user', e)
  }

  if (user) {
    console.log('Got user', user)
  }
})()

Contents

• Getting started
• Concepts
• API reference

Concepts

Basic

Remit, primarily, makes use of four simple commands: request, respond, emit and listen.

request requests data from an endpoint defined using respond. emit "emits" data to any and all "listeners" defined using listen.

Example

A simple example here allows us to define an endpoint that increments a counter and emits that change to the rest of the system.

// This service sets up our counter and incrementer.
const remit = require('remit')()
let counter = 0

remit
    .endpoint('counter.increment')
    .data((event, callback) => {
        remit.emit('counter.incremented').send(++counter)

        return callback(null, counter)
    })

// Here we set up a listener for when the counter's been incremented
const remit = require('remit')()

remit
    .listen('counter.incremented')
    .data((event, callback) => {
        console.log(`Counter is now ${event.data}`)

        return callback()
    })

// And here we increment the counter!
const remit = require('remit')()

remit.request('counter.increment')()

API reference

• Remit
• remit
• Request
• #request / #req
• #emit
• Response
• #respond / #res / #endpoint
• #listen / #on

---

Remit

A Remit instance representing a single connection to the AMQ in use.

Properties

• request (req)
• emit
• respond (res, endpoint)
• listen (on)

---

require('remit')([options]) > Remit ^

Creates a new Remit instance, using the given options, and connects to the message queue.

Arguments

• options (Optional) An object containing a mixture of Remit and AMQ options. Acceptable values are currently:
  • url (Optional, defaults to 'amqp://localhost') The RabbitMQ URI to use to connect to the AMQ instance. If not defined, tries to fall back to the REMIT_URL environment variable before the default. Any query string options defined are overwritten.
  • name (Optional, defaults to '') The friendly connection name to give the service. This is used heavily for load balancing requests, so instances of the same service (that should load balance requests between themselves) should have the same name. If not defined, tries to fall back to the REMIT_NAME environment variable before the default.
  • exchange (Optional, defaults to 'remit') The AMQ exchange to connect to.

Returns Remit

AMQ behaviour

1. Connects to the AMQ

---

Request([data]) ^

A request set up for a specific endpoint, ready to send and receive data.

Arguments

• data (Optional) Can be any JSON-compatible data that you wish to send to the endpoint.

Properties

• send Synonymous with calling the Request object.
• data(callback) Provide a callback to be run when a reply is received from a request.
• sent(callback) Provide a callback to be run when the request successfully sends data to an endpoint.

Returns

Returns a promise that resolves when the reply is received. If timeout or error are emitted, the promise is rejected. If data is emitted with a falsey err, the promise is resolved. If the err is truthy, the promise is rejected.

---

remit.request(endpoint[, options]) > Request ^

Aliases: req

Sets up a request pointed at the specified endpoint with the given options.

Arguments

• endpoint A string representing an endpoint, defined using respond / res / endpoint.
• options (Optional) An object containing a mixture of Remit and AMQ options. Acceptable values are currently:
  • something

Properties

• data(callback) Provide a global callback to be run when a reply is received from any request.
• sent(callback) Provide a global callback to be run when any request successfully sends data to an endpoint.

Returns Request

AMQ behaviour

1. If a reply is sought, follow sub-steps, otherwise skip to step #2
2. Ensure a connection is available
3. Ensure the channel used for publishing is available
4. Start consuming from amq.rabbitmq.reply-to
5. Ensure a connection is available
6. Ensure the channel used for publishing is available
7. Publish the message

---

Response ^

An active endpoint set up and ready to receive data.

Properties

• data Provide a callback to be run when a request is received.
• ready Provide a callback to be run when the endpoint becomes live and ready.

---

remit.respond(endpoint[, options]) > Response ^

Aliases: res, endpoint

Arguments

• endpoint A string representing the name of the endpoint. This is used as a routing key (see the RabbitMQ Topics Tutorial) so the only allowed characters are a-zA-Z0-9_.-.
• options (Optional) An object containing a mixture of Remit and AMQ options. Acceptable values are currently:
  • something

Properties

• data Provide a global callback to be run when any request is received.
• ready Provide a global callback to be run when any endpoint becomes live and ready.

Returns Response

Templates

Some basic options templates are also set up as separate functions to allow for some semantically-pleasing set-ups without having to skim through objects to figure out what's happening

// remit.listen
// remit.on
{
  "some": "thing"
}

AMQ behaviour

1. Ensure a connection is available
2. Ensure the channel used for miscellaneous work is available
3. Assert the presence of the queue named after the event given
4. Ensure the channel used for consuming is available
5. Bind the asserted queue using a duplicate routing key
6. Ensure the channel used for consuming is available
7. Start consuming from the event