Fallback Provider

// Without fallback - single point of failure
const provider = new HttpProvider('https://eth-mainnet.g.alchemy.com/v2/...');
// If Alchemy is down, your app is down

// With fallback - automatic failover
const provider = FallbackProvider([
  'https://eth-mainnet.g.alchemy.com/v2/...',
  'https://mainnet.infura.io/v3/...',
  'https://eth.llamarpc.com',
]);
// Tries each endpoint until one works

const provider = FallbackProvider({
  endpoints: [
    { url: 'https://eth-mainnet.g.alchemy.com/v2/KEY', priority: 1 },
    { url: 'https://mainnet.infura.io/v3/KEY', priority: 2 },
    { url: 'https://eth.llamarpc.com', priority: 3 },
  ],
  // Try next endpoint after 5s timeout
  timeout: 5000,
  // Retry failed endpoint after 30s
  retryDelay: 30000,
});

// Uses highest priority available endpoint
const balance = await provider.request({
  method: 'eth_getBalance',
  params: [address, 'latest']
});

// Require multiple endpoints to agree (for critical operations)
const provider = FallbackProvider({
  endpoints: [...],
  quorum: 2, // Need 2 endpoints to return same result
  quorumWeight: {
    'eth_getBalance': 1,      // Single endpoint OK for reads
    'eth_sendRawTransaction': 2, // Require quorum for sends
  }
});

const provider = FallbackProvider({
  endpoints: [...],
  healthCheck: {
    interval: 10000, // Check every 10s
    method: 'eth_blockNumber',
    // Mark unhealthy if >5 blocks behind
    staleness: 5,
  }
});

// Get endpoint health status
const health = provider.getHealth();
// [{ url: '...', healthy: true, latency: 45, blockNumber: 12345678 }, ...]

const provider = FallbackProvider({
  endpoints: [...],
  // Stick to working endpoint instead of always trying primary
  sticky: true,
  // Re-check primary every 60s
  primaryCheckInterval: 60000,
});