Retrying a RPC Subscription with Web3.js 2.0
When using Web3.js 2.0, establishing a long-lived WebSocket connection can be a bit more challenging than in earlier versions of the library. One common issue is reconnecting after disconnection, which can lead to lost transactions or data being sent multiple times.
In this article, we’ll explore how to retry a RPC subscription using Web3.js 2.0.
Why Retry?
RPC (Remote Procedure Call) subscriptions allow you to execute blockchain functions remotely, without having to worry about establishing a direct connection between the client and server. However, as with any asynchronous operation, there’s always a chance of disconnection or failure.
When a disconnection occurs, your application may lose its position on the block chain transactions being processed. As a result, it might re-sender all pending transactions multiple times, leading to wasted gas and lost value.
Solution: Retry Mechanism
To address this issue, we’ll implement a retry mechanism using Web3.js 2.0’s built-in error handling features. Our solution will use the retry function from the web3 package to automatically reconnect when necessary.
Here’s an example of how you can modify your code to include retry:
const web3 = require('web3');
const { retry } = require('web3');
// Replace with your Web3.js provider URL
const provider = new web3.providers.HttpProvider("
// Initialize the connection to the blockchain network
async function connectToBlockchain() {
const chainId = await web3.eth.getChainId();
console.log(Connected to ${chainId} blockchain...);
// Create a new Web3 instance with your provider
const web3Instance = new web3(provider);
return web3Instance;
}
// Establish an RPC subscription
async function establishRpcSubscription() {
try {
const wsSubscription = await createWeb3RpcSubscription(
'0xYourPublicKey', // Your RPC endpoint
{ network: 'mainnet' } // Specify the blockchain network (e.g., mainnet, testnet)
);
console.log(RPC Subscription established successfully!);
return wsSubscription;
} catch (error) {
if (error.message.includes('Disconnected')) {
// Retry connection after disconnection
retry(error, 5);
}
console.error('Error establishing RPC subscription:', error);
throw error;
}
}
// Main entry point for your application
async function main() {
const web3Instance = await connectToBlockchain();
const wsSubscription = await establishRpcSubscription();
// Handle any errors that occur during connection
try {
console.log('Websocket connection established.');
} catch (error) {
throw error;
}
return wsSubscription;
}
How it Works:
- The
connectToBlockchainfunction establishes a new Web3 instance with your provider.
- The
establishRpcSubscriptionfunction attempts to create an RPC subscription using the established connection.
- If the subscription is successfully created, it returns the newly established WebSocket object (
wsSubscription).
- Otherwise, if disconnection occurs, the retry mechanism kicks in after a brief delay (5 seconds) using the
retryfunction from web3.
- Once retries are exhausted or successful, the original error is re-throwing.
Conclusion:
By implementing a retry mechanism like this, you can ensure that your Web3.js applications remain responsive and efficient even when dealing with disconnections or failures in blockchain transactions. This approach also helps minimize wasted gas and lost value due to repeated retries.
