Transmit

Transmit is a native opinionated Server-Sent-Event (SSE) module built for AdonisJS. It is a simple and efficient way to send real-time updates to the client, such as notifications, live chat messages, or any other type of real-time data.

Installation

Install and configure the package using the following command :

node ace add @adonisjs/transmit

You will also have to install the Transmit client package to listen for events on the client-side.

npm install @adonisjs/transmit-client

Configuration

The configuration for the transmit package is stored within the config/transmit.ts file.

See also: Config stub

import { defineConfig } from '@adonisjs/transmit'

export default defineConfig({
  pingInterval: false,
  transport: null
  // routeHandlerModifier(route: Route) {}
})

pingInterval

The interval used to send ping messages to the client. The value is in milliseconds or using a string Duration format (i.e: 10s). Set to false to disable ping messages.

transport

Transmit supports syncing events across multiple servers or instances. You can enable the feature by referencing the wanted transport layer (only redis is supported for now). Set to null to disable syncing.

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import env from '#start/env'
import { defineConfig } from '@adonisjs/transmit'
import { redis } from '@adonisjs/transmit/transports'

export default defineConfig({
  transport: {
    driver: redis({
      host: env.get('REDIS_HOST'),
      port: env.get('REDIS_PORT'),
      password: env.get('REDIS_PASSWORD'),
    })
  }
})

Ensure you have ioredis installed when using the redis transport.

routeHandlerModifier

A function that is called before registering transmit routes. It receives the route instance. Use this function to add custom middleware or modify the route handler.

For example, you can use the Rate Limiter and auth middleware to avoid abuse of some transmit route.

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import { defineConfig } from '@adonisjs/transmit'
import { middleware } from '#start/kernel'
import { throttle } from '#start/limiter'

export default defineConfig({
  routeHandlerModifier(route) {
    // Ensure you are authenticated to register your client
    if (route.getPattern() === '/__transmit/events') {
      route.middleware(middleware.auth())
      return
    }
    
    // Add a throttle middleware to other transmit routes
    route.use(throttle)
  }
})

Channels

Channels are used to group events. For example, you can have a channel for notifications, another for chat messages, and so on. They are created on the fly when the client subscribes to them.

Channel Names

Channel names are used to identify the channel. They are case-sensitive and must be a string. You cannot use any special characters or spaces in the channel name except /. The following are some examples of valid channel names:

import transmit from '@adonisjs/transmit/services/main'

transmit.broadcast('global', { message: 'Hello' })
transmit.broadcast('chats/1/messages', { message: 'Hello' })
transmit.broadcast('users/1', { message: 'Hello' })

Channel Authorization

You can authorize or reject a connection to a channel using the authorizeChannel method. The method receives the channel name and the HttpContext. It must return a boolean value.

import transmit from '@adonisjs/transmit/services/main'
import Chat from '#models/chat'
import type { HttpContext } from '@adonisjs/core/http'

transmit.authorizeChannel<{ id: string }>('users/:id', (ctx: HttpContext, { id }) => {
  return ctx.auth.user?.id === +id
})

transmit.authorizeChannel<{ id: string }>('chats/:id/messages', async (ctx: HttpContext, { id }) => {
  const chat = await Chat.findOrFail(+id)
  
  return ctx.bouncer.allows('accessChat', chat)
})

Broadcasting Events

You can broadcast events to a channel using the broadcast method. The method receives the channel name and the data to send.

import transmit from '@adonisjs/transmit/services/main'

transmit.broadcast('global', { message: 'Hello' })

You can also broadcast events to any channel except one using the broadcastExcept method. The method receives the channel name, the data to send, and the UID you want to ignore.

transmit.broadcastExcept('global', { message: 'Hello' }, 'uid-of-sender')

Syncing across multiple servers or instances

By default, broadcasting events works only within the context of an HTTP request. However, you can broadcast events from the background using the transmit service if you register a transport in your configuration.

The transport layer is responsible for syncing events across multiple servers or instances. It works by broadcasting any events (like broadcasted events, subscriptions, and un-subscriptions) to all connected servers or instances using a Message Bus.

The server or instance responsible for your client connection will receive the event and broadcast it to the client.

Transmit Client

You can listen for events on the client-side using the @adonisjs/transmit-client package. The package provides a Transmit class. The client use the EventSource API by default to connect to the server.

import { Transmit } from '@adonisjs/transmit-client'

export const transmit = new Transmit({
  baseUrl: window.location.origin
})

Configuring the Transmit Instance

The Transmit class accepts an object with the following properties:

baseUrl

The base URL of the server. The URL must include the protocol (http or https) and the domain name.

uidGenerator

A function that generates a unique identifier for the client. The function must return a string. It defaults to crypto.randomUUID.

eventSourceFactory

A function that creates a new EventSource instance. It defaults to the WebAPI EventSource. You need to provide a custom implementation if you want to use the client on Node.js, React Native or any other environment that does not support the EventSource API.

eventTargetFactory

A function that creates a new EventTarget instance. It defaults to the WebAPI EventTarget. You need to provide a custom implementation if you want to use the client on Node.js, React Native or any other environment that does not support the EventTarget API. Return null to disable the EventTarget API.

httpClientFactory

A function that creates a new HttpClient instance. It is mainly used for testing purposes.

beforeSubscribe

A function that is called before subscribing to a channel. It receives the channel name and the Request object sent to the server. Use this function to add custom headers or modify the request object.

beforeUnsubscribe

A function that is called before unsubscribing from a channel. It receives the channel name and the Request object sent to the server. Use this function to add custom headers or modify the request object.

maxReconnectAttempts

The maximum number of reconnection attempts. It defaults to 5.

onReconnectAttempt

A function that is called before each reconnection attempt and receives the number of attempts made so far. Use this function to add custom logic.

onReconnectFailed

A function that is called when the reconnection attempts fail. Use this function to add custom logic.

onSubscribeFailed

A function that is called when the subscription fails. It receives the Response object. Use this function to add custom logic.

onSubscription

A function that is called when the subscription is successful. It receives the channel name. Use this function to add custom logic.

onUnsubscription

A function that is called when the unsubscription is successful. It receives the channel name. Use this function to add custom logic.

Creating a Subscription

You can create a subscription to a channel using the subscription method. The method receives the channel name.

const subscription = transmit.subscription('chats/1/messages')
await subscription.create()

The create method registers the subscription on the server. It returns a promise that you can await or void.

Listening for Events

You can listen for events on the subscription using the onMessage method that receives a callback function. You can call the onMessage method multiple times to add different callbacks.

subscription.onMessage((data) => {
  console.log(data)
})

You can also listen to a channel only once using the onMessageOnce method which receives a callback function.

subscription.onMessageOnce(() => {
  console.log('I will be called only once')
})

Stop Listening for Events

The onMessage and onMessageOnce methods return a function that you can call to stop listening for a specific callback.

const stopListening = subscription.onMessage((data) => {
  console.log(data)
})

// Stop listening
stopListening()

Deleting a Subscription

You can delete a subscription using the delete method. The method returns a promise that you can await or void. This method will unregister the subscription on the server.

await subscription.delete()