Realtime Pub/Sub Client

The realtime-pubsub-client is a JavaScript client library for interacting with Realtime Pub/Sub applications. It enables developers to manage real-time WebSocket connections, handle subscriptions, and process messages efficiently. The library provides a simple and flexible API to interact with realtime applications, supporting features like publishing/sending messages, subscribing to topics, handling acknowledgements, and waiting for replies with timeout support.

Features

• WebSocket Connection Management: Seamlessly connect and disconnect from the Realtime Pub/Sub service with automatic reconnection support.
• Topic Subscription: Subscribe and unsubscribe to topics for receiving messages.
• Topic Publishing: Publish messages to specific topics with optional message types and compression.
• Message Sending: Send messages to backend applications with optional message types and compression.
• Event Handling: Handle incoming messages with custom event listeners.
• Acknowledgements and Replies: Wait for gateway acknowledgements or replies to messages with timeout support.
• Error Handling: Robust error handling and logging capabilities.
• TypeScript Support: Strongly typed classes for better development experience.

Installation

Install the realtime-pubsub-client library via npm:

npm install realtime-pubsub-client

Or via yarn:

yarn add realtime-pubsub-client

Getting Started

This guide will help you set up and use the realtime-pubsub-client library in your TypeScript or JavaScript project.

Connecting to the Server

First, import the RealtimeClient class and create a new instance with the required configuration:

import {
  RealtimeClient,
  ClientOptions,
  ConnectionInfo,
} from 'realtime-pubsub-client'

const APP_ID = 'your-app-id'

const clientOptions: ClientOptions = {
  websocketOptions: {
    // https://www.npmjs.com/package/reconnecting-websocket#available-options
    maxRetries: 10,
    urlProvider: async () => {
      // Implement getAuthToken according to your auth mechanism
      const ACCESS_TOKEN = await getAuthToken()

      return `wss://genesis.r7.21no.de/apps/${APP_ID}?access_token=${ACCESS_TOKEN}`
    },
  },
  // Optional: Pass a custom logger implementing the Logger interface
  logger: console,
}

const client = new RealtimeClient(clientOptions)

Connecting to the server and handling the session.started event:

client.on('session.started', (connectionInfo: ConnectionInfo) => {
  console.log('Connection ID:', connectionInfo.id)

  // subscribe to topics here
  client.subscribeRemoteTopic('topic1')
  client.subscribeRemoteTopic('topic2')
  // ...
})

await client.connect()
await client.waitFor('session.started')

Subscribing to incoming messages

You can handle messages for specific topics and message types:

Note: The topic and message type are separated by a dot (.) in the event name.

client.on('topic1.action1', (message: IncomingMessage) => {
  // message handling logic here
  console.log('Received message:', message.data.payload)
})

Wildcard subscriptions are also supported:

client.on('topic1.*', (message: IncomingMessage) => {
  // ...
})

Publishing Messages

Publish messages to a topic:

client.publish('topic1', 'Hello, world!', {
  messageType: 'text-message',
})

Responding to Incoming Messages

Set up event listeners to handle incoming messages:

client.on(
  'topic1.text-message',
  (message: IncomingMessage, reply: ReplyFunction) => {
    // ...

    // sending a reply
    reply('Message received!', 'ok')
  },
)

Waiting for Acknowledgements and Replies

• waitForAck(timeout?: number): Waits for an acknowledgement of the message, with an optional timeout in milliseconds.
• waitForReply(timeout?: number): Waits for a reply to the message, with an optional timeout in milliseconds.

Wait for the Realtime Gateway acknowledgement after publishing a message:

await client
  .publish('secure/peer-to-peer1', 'Hi', {
    messageType: 'greeting',
  })
  .waitForAck()

Wait for the Realtime Gateway acknowledgement after sending a message:

await client
  .send(
    {
      /*...*/
    },
    {
      messageType: 'create',
    },
  )
  .waitForAck()

Wait for a reply with a timeout:

await client
  .send(
    {
      /*...*/
    },
    {
      messageType: 'create',
    },
  )
  .waitForReply(5000) // Wait for up to 5 seconds

Error Handling

Handle errors and disconnections:

client.on('error', (error: Error) => {
  console.error('WebSocket error:', error)
})

client.on('close', (event: CloseEvent) => {
  console.log('WebSocket closed:', event.reason)
})

API Reference

RealtimeClient

Constructor

new RealtimeClient(config: ClientOptions);

Creates a new RealtimeClient instance.

• config: Configuration options for the client.

Methods

• connect(): Connects client to the WebSocket Messaging Gateway.

  async connect(): Promise<void>;

  Returns a promise that resolves when the connection is established.

• disconnect(): Terminates the WebSocket connection.

  disconnect(): RealtimeClient;

  Returns the RealtimeClient instance.

• subscribeRemoteTopic(topic: string): Subscribes connection to a remote topic.

  subscribeRemoteTopic(topic: string): RealtimeClient;

  Returns the RealtimeClient instance.

• unsubscribeRemoteTopic(topic: string): Unsubscribes connection from a remote topic.

  unsubscribeRemoteTopic(topic: string): RealtimeClient;

  Returns the RealtimeClient instance.

• publish(topic: string, payload: string | Record<string, any>, options?: MessageOptions): Publishes a message to a topic.

  publish(topic: string, payload: string | Record<string, any>, options?: MessageOptions): WaitForFactory;

  Returns a WaitForFactory instance to wait for acknowledgements or replies.

• send(payload: string | Record<string, any>, options?: MessageOptions): Sends a message to the server.

  send(payload: string | Record<string, any>, options?: MessageOptions): WaitForFactory;

  Returns a WaitForFactory instance to wait for acknowledgements or replies.

• wait(ms: number): Waits for a specified duration. Utility function for waiting in async functions.

  wait(ms: number): Promise<void>;

  Returns a promise that resolves after the specified time.

Events

• 'session.started': Emitted when the session starts.

  client.on('session.started', (connectionInfo: ConnectionInfo) => { ... });

• 'error': Emitted on WebSocket errors.

  client.on('error', (error: Error) => { ... });

• 'close': Emitted when the WebSocket connection closes.

  client.on('close', (event: CloseEvent) => { ... });

• Custom Events: Handle custom events based on topic and message type.

  client.on('TOPIC_NAME.MESSAGE_TYPE', (message: IncomingMessage, reply: ReplyFunction) => { ... });

  Wildcard subscriptions are also supported. See:

License

This library is licensed under the MIT License.

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For more detailed examples and advanced configurations, please refer to the documentation.

Notes

• Ensure that you have an account and an app set up with Realtime Pub/Sub.
• Customize the urlProvider function to retrieve the access token for connecting to your realtime application.
• Implement the getAuthToken function according to your authentication mechanism.
• Optionally use the logger option to integrate with your application's logging system.
• Handle errors and disconnections gracefully to improve the robustness of your application.
• Make sure to handle timeouts when waiting for replies to avoid hanging operations.

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Feel free to contribute to this project by submitting issues or pull requests on GitHub.