Fallback RPC URLs

There are times where it’s beneficial to have a fallback URL when initializing your TezosToolkit instance. While this behaviour is not support by Taquito directly, you can extend the TezosToolkit class using a proxy to achieve the fallback behaviour yourself.

import { RpcClient, type RpcClientInterface } from '@taquito/rpc';

export function createFallbackRpcClient(rpcUrls: string[], chain: string = 'main'): RpcClientInterface {
	if (rpcUrls.length === 0) {
		throw new Error('At least one RPC URL is required');
	}

	const clients = rpcUrls.map(url => new RpcClient(url, chain));
	let currentIndex = 0;

	const handler: ProxyHandler<RpcClient> = {
		get(target, prop, receiver) {
		const value = Reflect.get(target, prop, receiver);
		
		// Only wrap methods (functions), not properties
		if (typeof value !== 'function') {
			return value;
		}

		// Return a wrapped function with fallback logic
		return async (...args: unknown[]) => {
			const startIndex = currentIndex;
			let lastError: unknown;

			do {
				try {
					const client = clients[currentIndex];
					const method = client[prop as keyof RpcClient];
					if (typeof method === 'function') {
						return await method.apply(client, args);
					}
				} catch (error) {
					lastError = error;
					console.warn(`RPC ${clients[currentIndex].getRpcUrl()} failed, trying next...`);
					currentIndex = (currentIndex + 1) % clients.length;
				}
			} while (currentIndex !== startIndex);

			throw lastError;
		};
		},
	};

	// Used for TypeScript type inference
	return new Proxy({} as RpcClientInterface, handler);
}

You can then import the createFallbackRpcClient function where you initialize your TezosToolkit and use it like so:

  const fallbackClient = createFallbackRpcClient([
    'https://example.com',
    'https://example.org',
	'https://ghostnet.tezos.ecadinfra.com'
  ])

  const Tezos = new TezosToolkit(fallbackClient);