ganomede-events

ganomede's system events microservice

ganomede-events

NodeJS events stream library

A server and a library allowing services to register and process system events. Relies on redis.

Table of Contents

Background

This was created part of ganomede, a collection of game-related micro services using NodeJS.

Install

npm install ganomede-events

Usage

Server

Assuming a redis server runs on localhost:6379, you can start a ganomede-events server this way:

ganomede-events-server

For specific setup, you can configure using environment variables:

  • export API_SECRET="my-api-secret-token"
  • export REDIS_EVENTS_PORT_6379_TCP_ADDR="192.168.1.4"
  • export REDIS_EVENTS_PORT_6379_TCP_PORT="34009"
  • export POLL_TIMEOUT="30000"

You can also start a server from the public docker image:

docker run -p 8000:8000 --link redis_events:redis_events ganomede/events

You can also play around with provided docker-compose.test.yml and Dockerfile.

Client Library

Client is an EventEmitter. When you register handler for an event, it will treat eventName as channel you’d like to listen for events on (and start issuing HTTP(S) request). When you remove all listeners for a channel, future HTTP(S) request will stop (but request currently running won’t be aborted!).

const {Client} = require('ganomede-events');
const clientId = 'mailchimp-synchronizer';
const events = new Client(clientId, options); // see Client API for more

// Send @event to a specific @channel with
//   Client#send(channel, event[, callback])
events.send('users/v1:add', {
  from: 'users/v1',
  type: 'add',
  data: {
    thing: 'abc',
    stuff: 123,
    blob: [12, 13, 14]
  }
});

// Our event handler
const handler = (event) => {
  console.dir(event);
  //
    console.log("id: " + event.id);
    console.log("from: " + event.from + " == users/v1");
    console.log("type: " + event.type + " == add");
    console.log("timestamp: " + event.timestamp);
    console.log("data: " + JSON.stringify(event.data));
    // Contains the custom data sent with "send"
    //     event.data.thing
    //     event.data.stuff
    //     event.data.blob
};


events.on('users/v1', handler);     // listen to all events from a channel
events.on('users/v1:add', handler); // or specific type
events.removeListener('users/v1:add', handler); // remove specific handlers

// `error` event is special (like some others, see below for more),
// it won't poll `error` channel and you can't send events to that channel.
// (it will also throw if no handlers are registred)
events.on('error', (channel, error) => { /* handle HTTP(S) error */ });

API

The server REST API is documented here. Find below the API for the NodeJS library.

new Client(clientId, options)

Creates the pub/sub client.

Arguments

  • clientId: string

    • requried
    • a unique identifier for the client
    • used on the server to save/restore state
  • options: object with the following fields:

    • secret: string
      • API_SECRET of remote
      • requried and must be non-empty
    • agenthttp.Agent or https.Agent instance
      • agent to use (useful for enabling things like keepAlive, number of simultaneous requests, etc.)
      • defaults to http.globalAgent or https.globalAgent (depending on protocol)
    • protocol: string
      • protocol used to connect to the notifications service ('http' or 'https')
      • default 'http'
    • hostname: string
      • hostname or ip of the notifications service
      • default 'localhost'
    • port: int
      • port number of the notifications service
      • default 8000
    • pathname: string
      • endpoint’s pathname
      • default config.http.prefix + '/events' ('/events/v1/events')

Client#send(channel, event[, callback])

Publish an event to a given channel.

Arguments

  • channel: string requred — the channel to publish to
  • event: object requred — must contain 2 string props: from and type specifying sender and type of an event. You can also add data prop containing any truthy object with custom data you’d like to attach to the event.
  • callback: Function — will receive two arguments: (error, header), header will containt Event ID and Timestamp (assigned by server). IDs are specific to the channel, so it is possible to have 2 events with ID 1 in different channels.

Client#on(channel, handler)

Start receiving events from a given channel.

Arguments

  • channel: string required;
  • handler: Function required; will receive new events, signature is (event, channel). The shape of event is the same as in #send().

Some channels are special, and you can not listen or send messages to those:

  • newListener / removeListenerEventEmitter’s events;
  • error — used to handle HTTP(S) errors, handler invoked with (error, channel). Non-200 statuses are errors.
  • drain — when there are no channel-listeners and all HTTP(S) request are finished;
  • cycle — after single HTTP(S) request is finished (or errored), all events it might contain are emitted (or error is emitted), and before starting next request. Use this to detach listeners without losing events. Signature: ({finished, next}, channel), finished is Cursor describing pages of completed request, next is Cursor describing pages of next request.

Client#removeListener(eventName, handler)

Same as EventEmitter#removeListener().

If there are no listeners left for a particular channel, no new HTTP(S) request will be issued. Note that any requests in-progress will finish, and events will be discarded.

Arguments

  • channel: string
  • handler: Function

Contribute

PRs accepted.

Small note: If editing the README, please conform to the standard-readme specification.

License

MIT © Jean-Christophe Hoelt [email protected]

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ganomede-events

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