docs.waku.org/docs/build/javascript/light-send-receive.md

title	hide_table_of_contents
Send and Receive Messages Using Light Push and Filter	true

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 parameter 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. :::

A node needs to know how to route messages. By default, it will use The Waku Network configuration ({ clusterId: 1, shards: [0,1,2,3,4,5,6,7] }). For most applications, it's recommended to use autosharding:

// Create node with auto sharding (recommended)
const node = await createLightNode({
  defaultBootstrap: true,
  networkConfig: {
    clusterId: 1,
    contentTopics: ["/my-app/1/notifications/proto"],
  },
});

Alternative network configuration

If your project requires a specific network configuration, you can use static sharding:

// Create node with static sharding
const node = await createLightNode({
  defaultBootstrap: true,
  networkConfig: {
    clusterId: 1,
    shards: [0, 1, 2, 3],
  },
});

Connect to remote peers

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

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

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

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

// Wait for peer connections with specific protocols
await node.waitForPeers([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 parameter allows you to specify whether messages should NOT be stored by Store peers:

const encoder = createEncoder({
  contentTopic: contentTopic, // message content topic
  ephemeral: true, // allows messages NOT be stored on the network
});

The pubsubTopicShardInfo parameter allows you to configure a different network configuration for your encoder and decoder:

// Create the network config
const networkConfig = { clusterId: 3, shards: [1, 2] };

// Create encoder and decoder with custom network config
const encoder = createEncoder({
  contentTopic: contentTopic,
  pubsubTopicShardInfo: networkConfig,
});
const decoder = createDecoder(contentTopic, networkConfig);

:::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 DataPacket = new protobuf.Type("DataPacket")
  .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 = DataPacket.create({
  timestamp: Date.now(),
  sender: "Alice",
  message: "Hello, World!",
});

// Serialise the message using Protobuf
const serialisedMessage = DataPacket.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 = DataPacket.decode(wakuMessage.payload);
  console.log(messageObj);
};

// Create a Filter subscription
const { error, subscription } = await node.filter.createSubscription({ contentTopics: [contentTopic] });

if (error) {
    // handle errors if happens
    throw Error(error);
}

// Subscribe to content topics and process new messages
await subscription.subscribe([decoder], callback);

The pubsubTopicShardInfo parameter allows you to configure a different network configuration for your Filter subscription:

// Create the network config
const networkConfig = { clusterId: 3, shards: [1, 2] };

// Create Filter subscription with custom network config
const subscription = await node.filter.createSubscription(networkConfig);

You can use the subscription.unsubscribe() function to stop receiving messages from a content topic:

await subscription.unsubscribe([contentTopic]);

:::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. :::