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 receive CloudEvents with via different protocol bindings.

Note: Supports CloudEvent version 1.0

Installation

The CloudEvents SDK requires a current LTS version of Node.js. At the moment those are Node.js 16.x, and Node.js 18.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

The easiest way to send events is to use the built-in HTTP emitter.

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

// Create an emitter to send events to a receiver
const emit = emitterFor(httpTransport("https://my.receiver.com/endpoint"));

// Create a new CloudEvent
const ce = new CloudEvent({ type, source, data });

// Send it to the endpoint - encoded as HTTP binary by default
emit(ce);

If you prefer to use another transport mechanism for sending events over HTTP, you can use the HTTP binding to create a Message which has properties for headers and body, allowing greater flexibility and customization. For example, the axios module is used here to send a CloudEvent.

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 to send your CloudEvents.

const { emitterFor, httpTransport, Mode, CloudEvent, Emitter } = require("cloudevents");

// Create a CloudEvent emitter function to send events to our receiver
const emit = emitterFor(httpTransport("https://example.com/receiver"));

// Use the emit() function to send a CloudEvent to its endpoint when a "cloudevent" event is emitted
// (see: https://nodejs.org/api/events.html#class-eventemitter)
Emitter.on("cloudevent", emit);

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

// You can also have several listeners to send the event to several endpoints

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"});

You can create a CloudEvent object in many ways, for example, in TypeScript:

import { CloudEvent, CloudEventV1, CloudEventV1Attributes } from "cloudevents";
const ce: CloudEventV1<string> = {
  specversion: "1.0",
  source: "/some/source",
  type: "example",
  id: "1234"
};
const event = new CloudEvent(ce);
const ce2: CloudEventV1Attributes<string> = {
  specversion: "1.0",
  source: "/some/source",
  type: "example",
};
const event2 = new CloudEvent(ce2);
const event3 = new CloudEvent({
  source: "/some/source",
  type: "example",
});

A Note About Big Integers

When parsing JSON data, if a JSON field value is a number, and that number is really big, JavaScript loses precision. For example, the Twitter API exposes the Tweet ID. This is a large number that exceeds the integer space of Number.

In order to address this situation, you can set the environment variable CE_USE_BIG_INT to the string value "true" to enable the use of the json-bigint package. This package is not used by default due to the resulting slowdown in parse speed by a factor of 7x.

See for more information: https://github.com/cloudevents/sdk-javascript/issues/489

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	:white_check_mark:	:white_check_mark:

---

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

---

Protocol Bindings	v0.3	v1.0
AMQP Protocol Binding	:x:	:x:
HTTP Protocol Binding	:white_check_mark:	:white_check_mark:
Kafka Protocol Binding	:x:	:white_check_mark:
MQTT Protocol Binding	:white_check_mark:	:x:
NATS Protocol Binding	:x:	:x:

---

Content Modes	v0.3	v1.0
HTTP Binary	:white_check_mark:	:white_check_mark:
HTTP Structured	:white_check_mark:	:white_check_mark:
HTTP Batch	:white_check_mark:	:white_check_mark:
Kafka Binary	:white_check_mark:	:white_check_mark:
Kafka Structured	:white_check_mark:	:white_check_mark:
Kafka Batch	:white_check_mark:	:white_check_mark:
MQTT Binary	:white_check_mark:	:white_check_mark:
MQTT Structured	:white_check_mark:	:white_check_mark:

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.
• Email: https://lists.cncf.io/g/cncf-cloudevents-sdk

Maintainers

Currently active maintainers who may be found in the CNCF Slack.

• Lance Ball (@lance)
• Lucas Holmquist (@lholmquist)

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.

If there is a security concern with one of the CloudEvents specifications, or with one of the project's SDKs, please send an email to [e-mail].

Additional SDK Resources

• List of current active maintainers
• How to contribute to the project
• SDK's License
• SDK's Release process

Changelog

8.0.2 (2024-07-22)

Bug Fixes

• creating an event does not error when the event attribute name is too long (#593) (6977113)