docs.waku.org/docs/guides/js-waku/light-send-receive.md

title
Send and Receive Messages Using Light Push and Filter

This guide provides detailed steps to start using the @waku/sdk package by setting up a Light Node to send messages using the Light Push protocol, and receive messages using the Filter protocol. Have a look at the installation guide for steps on adding @waku/sdk to your project.

Create a Light Node

Use the createLightNode() function to create a Light Node and interact with the Waku Network:

import { createLightNode } from "@waku/sdk";

// Create and start a Light Node
const node = await createLightNode({ defaultBootstrap: true });
await node.start();

// Use the stop() function to stop a running node
// await node.stop();

:::info When the defaultBootstrap option is set to true, your node will be bootstrapped using the default bootstrap method. Have a look at the Bootstrap Nodes and Discover Peers guide to learn more methods to bootstrap nodes. :::

Connect to Remote Peers

Use the waitForRemotePeer() function to wait for the node to connect with peers on the Waku Network:

import { waitForRemotePeer } from "@waku/sdk";

// Wait for a successful peer connection
await waitForRemotePeer(node);

The protocols option allows you to specify the protocols that the remote peers should have enabled:

import { waitForRemotePeer, Protocols } from "@waku/sdk";

// Wait for peer connections with specific protocols
await waitForRemotePeer(node, [
	Protocols.LightPush,
	Protocols.Filter,
]);

Choose a Content Topic

Choose a content topic for your application and create a message encoder and decoder:

import { createEncoder, createDecoder } from "@waku/sdk";

// Choose a content topic
const contentTopic = "/light-guide/1/message/proto";

// Create a message encoder and decoder
const encoder = createEncoder({ contentTopic });
const decoder = createDecoder(contentTopic);

The ephemeral option allows you to specify whether your messages should be persisted by Store peers:

const encoder = createEncoder({
	contentTopic: contentTopic, // message content topic
	ephemeral: true, // allows messages to be stored or not
});

:::info In this example, users send and receive messages on a shared content topic. However, real applications may have users broadcasting messages while others listen or only have 1:1 exchanges. Waku supports all these use cases. :::

Create a Message Structure

Create your application's message structure using Protobuf's valid message fields:

import protobuf from "protobufjs";

// Create a message structure using Protobuf
const ChatMessage = new protobuf.Type("ChatMessage")
    .add(new protobuf.Field("timestamp", 1, "uint64"))
    .add(new protobuf.Field("sender", 2, "string"))
    .add(new protobuf.Field("message", 3, "string"));

:::info Have a look at the Protobuf installation guide for adding the protobufjs package to your project. :::

Send Messages Using Light Push

To send messages over the Waku Network using the Light Push protocol, create a new message object and use the lightPush.send() function:

// Create a new message object
const protoMessage = ChatMessage.create({
    timestamp: Date.now(),
    sender: "Alice",
    message: "Hello, World!",
});

// Serialise the message using Protobuf
const serialisedMessage = ChatMessage.encode(protoMessage).finish();

// Send the message using Light Push
await node.lightPush.send(encoder, {
    payload: serialisedMessage,
});

Receive Messages Using Filter

To receive messages using the Filter protocol, create a callback function for message processing, then use the filter.subscribe() function to subscribe to a content topic:

// Create the callback function
const callback = (wakuMessage) => {
    // Check if there is a payload on the message
    if (!wakuMessage.payload) return;
    // Render the messageObj as desired in your application
    const messageObj = ChatMessage.decode(wakuMessage.payload);
    console.log(messageObj);
};

// Subscribe to content topics and display new messages
const unsubscribe = await node.filter.subscribe([decoder], callback);

// Use the unsubscribe() function to stop receiving messages
// await unsubscribe();

:::tip Congratulations! You have successfully sent and received messages over the Waku Network using the Light Push and Filter protocols. Have a look at the light-js and light-chat examples for working demos. :::