Hemera-avro package

This is a plugin to use Avro with Hemera.

Apache Avro™ is a data serialization system.

Features

• No schema for you pattern is required
• The request and response schema of a server method (add) is validated by Avro™
• Flexible base schema
• Easy to start

Example without payload schema

Only the protocol schema will be validated with Avro

const Hemera = require('nats-hemera')
// Use NATS driver >= 0.7.2
const nats = require('nats').connect({ 
  preserveBuffers: true
})
const HemeraAvro = require('hemera-avro')
 
const hemera = new Hemera(nats, {
  logLevel: 'info'
})
 
hemera.use(HemeraAvro)

Example with payload schema

hemera.ready(() => {
 
  let Avro = hemera.avro
 
  const type = Avro.parse({
  name: 'Person',
  type: 'record',
  fields: [{
      name: 'a',
      type: 'int'
    }]
  })
 
  hemera.add({
    topic: 'peopleDirectory',
    cmd: 'create',
    avro$: type // We know how to encode the request
  }, (req, cb) => {
 
    cb(null, { a: 1 })
  })
 
  hemera.act({
    topic: 'peopleDirectory',
    cmd: 'create',
    name: 'peter',
    avro$: type // We know how to decode the response
  }, function (err, resp) {
 
    this.log.info('Result', resp)
  })
})

Use Type inference to auto-generate your schema

const type = avro.Type.forValue([1, 4.5, 8])
// We can now encode or any array of floats using this type:
const buf = type.toBuffer([4, 6.1])
const val = type.fromBuffer(buf) // [4, 6.1]
// We can also access the auto-generated schema:
const schema = type.schema()
const JSON = JSON.stringify(schema) // Copy & Paste

Base Schema

The pattern is encoded to JSON byte-array when it's from type object or array. Primitive values (boolean, strings, numbers) are encoded with Avro. The error, delegate, meta and request data are predefined with a fixed schema. Here a list of the specification.

• delegate: Can be a Map of strings, boolean, number
• meta: Can be a Map of strings, boolean, number
• result: You can use your own schema. If you don't define it the message is interpreted as binary (JSON encoded schema-less)
• error:
  • name: Name of the error
  • message: Message of the error
  • stack: Stack of the error
  • code: Code of the error
  • statusCode: Code of the error when using hemera-web
  • details: Can be a Map of strings, boolean, number to add additional data
  • hops: An array of services which were involved in this request