Feature 2: Display Node Alias and Balance

The goal of this feature is pretty straight-forward. When a user connects their node to the site, we want them to be able to see their alias and channel balance, so that it is clear to them how much funds they have available to pay for upvotes.

To implement this feature, we first updated the backend to make this data available from our API. Then we updated the frontend to fetch this info from the backend.

Let’s go to the feat-2 branch to see what’s changed.

git checkout feat-2

Added API endpoint to return node alias and channel balance

To update our backend, we’ll need to add a new route to handle requests to fetch the node’s info.

source: /backend/routes.ts

/**
* GET /api/info
*/
export const getInfo = async (req: Request, res: Response) => {
const { token } = req.body;
if (!token) throw new Error('Your node is not connected!');
// find the node that's making the request
const node = db.getNodeByToken(token);
if (!node) throw new Error('Node not found with this token');
// get the node's pubkey and alias
const rpc = nodeManager.getRpc(node.token);
const { alias, identityPubkey: pubkey } = await rpc.getInfo();
const { balance } = await rpc.channelBalance();
res.send({ alias, balance, pubkey });
};

In the routes.ts file, we added a new route handler function getInfo() which receives the user’s token, and first validates that it is valid. Then it uses the NodeManager class to get the RPC connection to the lnd node. With the rpc, we can not make two calls to lnd to fetch the alias and pubkey from getInfo() and the balance from channelBalance(). Finally, we return this data to the client.

source: /backend/index.ts

app.get('/api/info', catchAsyncErrors(routes.getInfo));

We updated the backend entrypoint file to instruct express to use the getInfo() route handler for GET requests to /api/info.

Display node info in the UI

With the backend updated, we can now fetch the alias and balance from the backend to display in the UI. We’ll start with the api wrapper then work our way up to the UI.

source: /src/lib/api.ts

export const getInfo = async () => {
return await httpGet('info');
};

In the API wrapper module, we just added a function to make the http request and return the result.

source: /src/store/store.ts

init = async () => {
// try to fetch the node's info on startup
try {
await this.fetchInfo();
this.connected = true;
} catch (err) {
// don't display an error, just disconnect
this.connected = false;
}
// fetch the posts from the backend
try {
this.posts = await api.fetchPosts();
} catch (err) {
this.error = err.message;
}
// connect to the backend WebSocket and listen for events
const ws = api.getEventsSocket();
ws.addEventListener('message', this.onSocketMessage);
};
.
.
.
fetchInfo = async () => {
const info = await api.getInfo();
this.alias = info.alias;
this.balance = parseInt(info.balance);
this.pubkey = info.pubkey;
};

In the mobx store, we added the fetchInfo() function that will retrieve the alias, pubkey and balance, then update the app state with the returned values. We also updated the init() function to fetch the node info when the page first loads. If it succeeds, then we set the connected flag to true.

source: /src/App.tsx

<Navbar.Collapse id="basic-navbar-nav">
<Nav className="ml-auto">
{!store.connected ? (
<Nav.Item>
<NavLink onClick={store.gotoConnect}>Connect to LND</NavLink>
</Nav.Item>
) : (
<>
<Navbar.Text>
<Badge variant="info" pill className="mr-3">
{store.balance.toLocaleString()} sats
</Badge>
</Navbar.Text>
<Dropdown id="basic-nav-dropdown" alignRight>
<Dropdown.Toggle as={NavLink}>{store.alias}</Dropdown.Toggle>
<Dropdown.Menu>
<Dropdown.Item onClick={store.disconnect}>Disconnect</Dropdown.Item>
</Dropdown.Menu>
</Dropdown>
</>
)}
</Nav>
</Navbar.Collapse>

Finally, we updated the App component to display the node’s alias and balance in the Navbar when it is connected. We also nested the Disconnect link under a dropdown menu.

Polar welcome screen

If you go back to your browser, refresh the page and connect your node, you should now see the alias and balance at the top right of the screen.

This was a simple feature to implement, which was mostly plumbing code to get the data from lnd, through the backend, to the frontend, and finally displayed in the browser. The important takeaway here is that communicating with the Lightning Network is not very different from communicating with any other third-party APIs.

In the next feature, we’ll work on updating the Post creation process to add some Lightning functionality.