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Livecoding recap: Blockchain-redux now shares blocks between clients in real-time

Sunday was fun. We built a thing! 🎉

Well… we added a thing to the You Can Use Blockchain To Store And Share UI State proof of concept I've been livecoding on. I'd share a live link with you, but… err… the app broke.

This is a Livecoding Recap – an almost-weekly post about interesting things discovered while livecoding. Usually shorter than 500 words. Often with pictures. Livecoding happens almost every Sunday at 2pm PDT on multiple channels. You should subscribe to My Youtube channel to catch me live.

It was working, you see. Then it wasn't. Infinite loop on page load.

Next time! I promise.

We did get something working, however. When you dispatch an action on blockchain-redux, the generated block is shared live with all other clients. That sharing still happens via Firebase, so it's not thaaaat impressive, but it's a step in the right direction.

See, you create new benchmark measurements in one browser window, and the other window reacts. Magic 🧙‍♂️

Here's how it works 👇

How blockchain-redux shares blocks between clients in real timeat

Long validation times got you down? Blockchain-redux is all real-time with the firebaseMiddleware. Soon with the WebRTC middleware too, I hope.

In part that's because there's no real consensus algorithm. Any valid block is accepted to the chain. Longest chain wins by default.

You may have seen how blockchain initialization works before. We read the whole chain from Firebase and replace the local chain stub.

Initializing the blockchain from Firebase

You can read more details about this code in a previous blogpost.

The part that's new is calling listenForNextBlock after replacing the local chain.

Listen for the next block

We have a local chain and want to make sure we catch the next block that shows up. So we fetch the latest index with store.getLastBlock().index, increment by 1, and listen for changes on blockchain/${nextIndex}.

When that block shows up, we call valueHandler.

valueHandler then parses the value and calls store.addBlock(), which validates the block fits our chain, and if it does fit, it gets added. If the block makes it to our local chain, then the redux-y stuff kicks in, wakes up all subscribed components, and re-renders happen.

Completely transparent to your app

All this real-time sharing is completely invisible to your app. You build your code just like it was any other Redux-based app.

To initialize the blockchain and render a live count of nodes, you'd do something like this 👇

// App.js
class App extends Component {
blockchain = {};
componentDidMount = async () => {
const FirebaseApp = firebase.initializeApp({
apiKey: "",
databaseURL: "https://thing.firebaseio.com",
projectId: "thing"
});
this.blockchain = await createStore(
benchmarkReducer,
firebaseMiddleware(FirebaseApp)
);
this.unsubscribe = this.blockchain.subscribe(() => {
console.log("Hello");
this.forceUpdate();
});
this.forceUpdate();
};
componentWillUnmount() {
this.unsubscribe();
}
render() {
console.log("in render", this.blockchain);
if (this.blockchain.getState) {
console.log("Current state", this.blockchain.getState());
}
return (
<div class="App">
<blockchaincontext class="provider" value={this.blockchain}>
<introcopy>
<blockchaincontext class="consumer">
{blockchain => (
<benchmarks blockchain={blockchain}>
)}
</benchmarks></blockchaincontext>
<div style={{ padding: "3vh" }}>
</div>
);
}
}
</introcopy></blockchaincontext></div>

Initialize the store in componentDidMount, subscribe to changes, run forceUpdate to get around async issues, unsubscribe on unmount.

The best way to make this store available to the rest of your app is via the new context API using <Context.Provider value={this.blockchain}>.

Then inside <IntroCopy />, where you display the node count, you do something like this.

// IntroCopy.js
// functional component boilerplate ...
// ... render stuff
<blockchaincontext class="consumer">
{({ getWholeChain = () => [] }) => (
There are {getWholeChain().length} nodes on the chain
)}
</blockchaincontext>
// ... more other render stuff

Value passed into render prop is the whole blockchain store. Take out getWholeChain and show the length. You could use getState() to get the latest block value, for example.

Lots of stuff you can do.

And to add a new block? Just call dispatch and have a reducer. Blockchain-redux handles the rest :)

Next steps

Still have to resolve a few TODO comments around block conflicts. What happens if your network is slow and you add blocks locally that other clients haven't seen and you get blocks from the outside world that conflict? Which do you pick?

I'm not sure yet.

Plus I really want to move away from Firebase. That's gonna be fun.

Join me next Sunday as we continue exploring this experiment.

Did you enjoy this article?

Published on April 10th, 2018 in blockchain, Front End, Livecoding, react, redux

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