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Pub/Sub in NodeJS

This is a quickstart guide on creating your first stream using the Streamr TypeScript SDK in a NodeJS script.

Prerequisites:

  • NPM v8 or greater
  • NodeJS 16.13.x or greater
  • A small amount of MATIC to pay for gas on Polygon mainnet. You can reachout to us on the #dev channel of Discord for some tokens.

Streamr SDK

The Streamr SDK is available on NPM and can be installed simply with:

$ npm install streamr-client

Having trouble installing the SDK? Maybe our troubleshooting section will help.

Initialize the SDK

// Import Streamr
const Streamr = require("streamr-client")
const { StreamrClient } = require('streamr-client')

// Initialize the client with an Ethereum account
const streamr = new Streamr({
auth: {
privateKey: "ethereum-private-key",
},
})
Key Point:

Ethereum accounts are used for authentication on Streamr.

You can generate an Ethereum private key using any Ethereum wallet, or you can use the utility function StreamrClient.generateEthereumAccount(), which returns the address and private key of a fresh Ethereum account.

Learn more about authentication

Create the stream

A stream is simply a sequence of data points in time, i.e. an append only log. This is semantically equivalent to topics in traditional pub/sub networks.

// Requires MATIC tokens (Polygon blockchain gas token)
const stream = await streamr.createStream({
id: "/foo/bar",
})

console.log(stream.id) // e.g. `0x123.../foo/bar`

We have created a stream with a stream ID that resembles 0x123.../foo/bar. The 0x address is your Ethereum account's public address and /foo/bar has been added to the end.

Key Point:

Take care to not mix up stream with streamr!

Learn more about streams

Alternatively, you can use getOrCreateStream to use an existing stream.

const stream = await streamr.getOrCreateStream({
id: streamId,
})

Set stream permissions

By default, the creator of the stream has full read, write and manage permissions over the stream, but if you'd like different addresses or public access controls to read and write (publish and subscribe) to your stream, then you'll need to add these permissions.

// Requires MATIC tokens (Polygon blockchain gas token)
await stream.grantPermissions({
user: "0x12345...",
permissions: [StreamPermission.PUBLISH],
})
Key Point:

Learn more about setting stream permissions in authenticate.

Publish data to the stream

You can either push data using the stream ID,

const msg = { hello: "world" }
await streamr.publish(streamId, msg)

Or, by using the stream object,

const msg = { hello: "world" }
const stream = await streamr.getStream(streamId)
await stream.publish(msg)
Important:

You must give PUBLISH permission to the address you have authenticated StreamrClient with before publishing data to the stream.

Learn more about setting stream permissions in authentication.

Subscribe to the stream

Just like publishing, you can either use the stream ID,

streamr.subscribe(streamId, (message) => {
// handle for individual messages
})

Or, by using the stream object.

Summary

Congrats! You've managed to create a stream and publish/subscribe data to it! 💪