cloudevents

What is cloudevents?

The 'cloudevents' npm package is a library for working with CloudEvents, which are a specification for describing event data in a common way. This package allows you to create, validate, and serialize/deserialize CloudEvents, making it easier to work with event-driven architectures.

What are cloudevents's main functionalities?

Create CloudEvent

This feature allows you to create a new CloudEvent instance with specified attributes such as type, source, and data.

const { CloudEvent } = require('cloudevents');

const myEvent = new CloudEvent({
  type: 'com.example.someevent',
  source: '/mycontext',
  data: {
    foo: 'bar'
  }
});

console.log(myEvent);

Validate CloudEvent

This feature allows you to validate a CloudEvent instance to ensure it conforms to the CloudEvents specification.

const { CloudEvent, ValidationError } = require('cloudevents');

const myEvent = new CloudEvent({
  type: 'com.example.someevent',
  source: '/mycontext',
  data: {
    foo: 'bar'
  }
});

try {
  myEvent.validate();
  console.log('Event is valid');
} catch (e) {
  if (e instanceof ValidationError) {
    console.error('Event is invalid:', e.errors);
  }
}

Serialize CloudEvent

This feature allows you to serialize a CloudEvent instance to a JSON string, which can be useful for transmitting the event over a network.

const { CloudEvent } = require('cloudevents');

const myEvent = new CloudEvent({
  type: 'com.example.someevent',
  source: '/mycontext',
  data: {
    foo: 'bar'
  }
});

const serializedEvent = myEvent.toString();
console.log(serializedEvent);

Deserialize CloudEvent

This feature allows you to deserialize a JSON string back into a CloudEvent instance, making it easier to work with received events.

const { CloudEvent } = require('cloudevents');

const serializedEvent = '{"type":"com.example.someevent","source":"/mycontext","data":{"foo":"bar"}}';
const myEvent = CloudEvent.parse(serializedEvent);

console.log(myEvent);

Other packages similar to cloudevents

eventemitter3

EventEmitter3 is a high-performance event emitter for Node.js and the browser. While it does not specifically adhere to the CloudEvents specification, it provides a robust way to handle events in an application.

node-eventstore-client

Node EventStore Client is a client for EventStore, a database optimized for event sourcing. It provides more advanced features for event storage and retrieval but is more complex and specific to EventStore.

aws-sdk

The AWS SDK for JavaScript provides a way to interact with AWS services, including event-driven services like AWS Lambda and Amazon EventBridge. It offers broader functionality but is specific to the AWS ecosystem.

README

JavaScript SDK for CloudEvents

The CloudEvents SDK for JavaScript.

Features

• Represent CloudEvents in memory
• Serialize and deserialize CloudEvents in different event formats.
• Send and recieve CloudEvents with via different protocol bindings.

Note: Supports CloudEvent versions 0.3, 1.0

Installation

The CloudEvents SDK requires a current LTS version of Node.js. At the moment those are Node.js 10.x and Node.js 12.x. To install in your Node.js project:

npm install cloudevents

Receiving and Emitting Events

Receiving Events

You can choose any popular web framework for port binding. A CloudEvent object can be created by simply providing the HTTP protocol binding the incoming headers and request body.

const app = require("express")();
const { HTTP } = require("cloudevents");

app.post("/", (req, res) => {
  // body and headers come from an incoming HTTP request, e.g. express.js
  const receivedEvent = HTTP.toEvent({ headers: req.headers, body: req.body });
  console.log(receivedEvent);
});

Emitting Events

You can send events over HTTP in either binary or structured format using the HTTP binding to create a Message which has properties for headers and body.

const axios = require("axios").default;
const { HTTP, CloudEvent } = require("cloudevents");

const ce = new CloudEvent({ type, source, data });
const message = HTTP.binary(ce); // Or HTTP.structured(ce)

axios({
  method: "post",
  url: "...",
  data: message.body,
  headers: message.headers,
});

You may also use the emitterFor() function as a convenience.

const axios = require("axios").default;
const { emitterFor, Mode, CloudEvent } = require("cloudevents");

function sendWithAxios(message) {
  // Do what you need with the message headers
  // and body in this function, then send the
  // event
  axios({
    method: "post",
    url: "...",
    data: message.body,
    headers: message.headers,
  });
}

const emit = emitterFor(sendWithAxios, { mode: Mode.BINARY });
emit(new CloudEvent({ type, source, data }));

You may also use the Emitter singleton

const axios = require("axios").default;
const { emitterFor, Mode, CloudEvent, Emitter } = require("cloudevents");

function sendWithAxios(message) {
  // Do what you need with the message headers
  // and body in this function, then send the
  // event
  axios({
    method: "post",
    url: "...",
    data: message.body,
    headers: message.headers,
  });
}

const emit = emitterFor(sendWithAxios, { mode: Mode.BINARY });
// Set the emit
Emitter.on("cloudevent", emit);

...
// In any part of the code will send the event
new CloudEvent({ type, source, data }).emit();

// You can also have several listener to send the event to several endpoint

CloudEvent Objects

All created CloudEvent objects are read-only. If you need to update a property or add a new extension to an existing cloud event object, you can use the cloneWith method. This will return a new CloudEvent with any update or new properties. For example:

const {
  CloudEvent,
} = require("cloudevents");

// Create a new CloudEvent
const ce = new CloudEvent({...});

// Add a new extension to an existing CloudEvent
const ce2 = ce.cloneWith({extension: "Value"});

Example Applications

There are a few trivial example applications in the examples folder. There you will find Express.js, TypeScript and Websocket examples.

API Transition Guide

Guide Link

Supported specification features

Core Specification	v0.3	v1.0
CloudEvents Core	:heavy_check_mark:	:heavy_check_mark:

---

Event Formats	v0.3	v1.0
AVRO Event Format	:x:	:x:
JSON Event Format	:heavy_check_mark:	:heavy_check_mark:

---

Transport Protocols	v0.3	v1.0
AMQP Protocol Binding	:x:	:x:
HTTP Protocol Binding	:heavy_check_mark:	:heavy_check_mark:
Kafka Protocol Binding	:x:	:x:
MQTT Protocol Binding	:x:	:x:
NATS Protocol Binding	:x:	:x:

Community

• There are bi-weekly calls immediately following the Serverless/CloudEvents call at 9am PT (US Pacific). Which means they will typically start at 10am PT, but if the other call ends early then the SDK call will start early as well. See the CloudEvents meeting minutes to determine which week will have the call.
• Slack: #cloudeventssdk channel under CNCF's Slack workspace.
• Maintainers typically available on Slack
  • Lance Ball
  • Lucas Holmquist
  • Grant Timmerman
• Email: https://lists.cncf.io/g/cncf-cloudevents-sdk

Contributing

We love contributions from the community! Please check the Contributor's Guide for information on how to get involved.

Each SDK may have its own unique processes, tooling and guidelines, common governance related material can be found in the CloudEvents community directory. In particular, in there you will find information concerning how SDK projects are managed, guidelines for how PR reviews and approval, and our Code of Conduct information.

Changelog

4.0.3 (2021-07-06)

Bug Fixes

• do not modify incoming event's specversion (#419) (22e42dd)
• do not modify incoming event's specversion (#419) (7c05ade)
• throw on validation if extensions are improperly named (#420) (7f6b658)

Miscellaneous

• add copyrights header and lint rules (#418) (80d987c)
• add Lance Ball to maintainers in package.json (#411) (d68b85a)
• be more forgiving parsing JSON as a string (#417) (db4be6b)