4.7 KiB
Retrieve Messages Using Waku Store
DApps running on a phone or in a browser are often offline: The browser could be closed or mobile app in the background.
Waku Relay is a gossip protocol. As a user, it means that your peers forward you messages they just received. If you cannot be reached by your peers, then messages are not relayed; relay peers do not save messages for later.
However, Waku Store peers do save messages they relay, allowing you to retrieve them at a later time. The Waku Store protocol is best-effort and does not guarantee data availability. Waku Relay should still be preferred when online; Waku Store can be used after resuming connectivity: For example, when the dApp starts.
In this guide, we'll review how you can use Waku Store to retrieve messages.
Before starting, you need to choose a Content Topic for your dApp. Check out the how to choose a content topic guide to learn more about content topics.
For this guide, we are using a single content topic: /store-guide/1/news/proto
.
Installation
You can install js-waku using your favorite package manager:
npm install js-waku
Create Waku Instance
In order to interact with the Waku network, you first need a Waku instance:
import { Waku } from 'js-waku';
const wakuNode = await Waku.create({ bootstrap: true });
Passing the bootstrap
option will connect your node to predefined Waku nodes.
If you want to bootstrap to your own nodes, you can pass an array of multiaddresses instead:
import { Waku } from 'js-waku';
const wakuNode = await Waku.create({
bootstrap: [
'/dns4/node-01.ac-cn-hongkong-c.wakuv2.test.statusim.net/tcp/443/wss/p2p/16Uiu2HAkvWiyFsgRhuJEb9JfjYxEkoHLgnUQmr1N5mKWnYjxYRVm',
'/dns4/node-01.do-ams3.wakuv2.test.statusim.net/tcp/443/wss/p2p/16Uiu2HAmPLe7Mzm8TsYUubgCAW1aJoeFScxrLj8ppHFivPo97bUZ'
]
});
Wait to be connected
When using the bootstrap
option, it may take some times to connect to other peers.
To ensure that you have store peers available to retrieve historical messages from,
use the following function:
await waku.waitForConnectedPeer();
The returned Promise will resolve once you are connected to a Waku Store peer.
Use Protobuf
Waku v2 protocols use protobuf by default.
Let's review how you can use protobuf to send structured data.
First, define a data structure. For this guide, we will use a simple news article that contains a date of publication, title and body:
{
date: Date;
title: string;
body: string;
}
To encode and decode protobuf payloads, you can use the protons package.
Install Protobuf Library
First, install protons:
npm install protons
Protobuf Definition
Then specify the data structure:
import protons from 'protons';
const proto = protons(`
message ArticleMessage {
uint64 date = 1;
string title = 2;
string body = 3;
}
`);
You can learn about protobuf message definitions here: Protocol Buffers Language Guide.
Decode Messages
To decode the messages retrieved from a Waku Store node,
you need to extract the protobuf payload and decode it using protons
.
const decodeWakuMessage = (wakuMessage) => {
// No need to attempt to decode a message if the payload is absent
if (!wakuMessage.payload) return;
const { date, title, body } = proto.SimpleChatMessage.decode(
wakuMessage.payload
);
// In protobuf, fields are optional so best to check
if (!date || !title || !body) return;
const publishDate = new Date();
publishDate.setTime(date);
return { publishDate, title, body };
};
Retrieve messages
You now have all the building blocks to retrieve and decode messages for a store node.
Retrieve messages from a store node:
const ContentTopic = '/store-guide/1/news/proto';
waku.store
.queryHistory([ContentTopic])
.catch((e) => {
// Be sure to catch any potential error
console.log('Failed to retrieve messages', e);
})
.then((retrievedMessages) => {
const articles = retrievedMessages
.map(decodeWakuMessage) // Decode messages
.filter(Boolean); // Filter out undefined values
console.log(`${articles.length} articles have been retrieved`);
});
Note that WakuStore.queryHistory
select an available store node for you.
However, it can only select a connected node, which is why the bootstrapping is necessary.
It will throw an error if no store node is available.