Relay Bridge with Callback - Enso Developer Documentation

This workflow demonstrates bridging tokens using Relay protocol with automatic post-bridge execution. Relay uses a placeholder-based design for dynamic amount resolution, making it ideal for complex workflows where amounts are determined at execution time. Route Mechanics: This bundle swaps USDC to ETH, bridges to Arbitrum via Relay, then wraps to WETH:

Swap USDC to native ETH on Ethereum using Enso routing
Bridge ETH from Ethereum to Arbitrum using Relay (supports native tokens)
Check ETH balance on Arbitrum after successful bridge
Wrap ETH to WETH on Arbitrum

relayBridgeWithCallback.ts

import { EnsoClient } from "@ensofinance/sdk";

// Chain IDs
const ETHEREUM_ID = 1;
const ARBITRUM_ID = 42161;

// Common addresses
const WALLET_ADDRESS = "0xd8da6bf26964af9d7eed9e03e53415d37aa96045";

// Token addresses
const USDC_ETHEREUM = "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48";
const WETH_ARBITRUM = "0x82aF49447D8a07e3bd95BD0d56f35241523fBab1";
const NATIVE_TOKEN = "0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee";

const client = new EnsoClient({
  apiKey: process.env.ENSO_API_KEY!,
});

const bundle = await client.getBundleData(
  {
    chainId: ETHEREUM_ID,
    fromAddress: WALLET_ADDRESS,
    routingStrategy: "router",
  },
  [
    // Step 1: Swap USDC to ETH on Ethereum
    {
      protocol: "enso",
      action: "route",
      args: {
        tokenIn: USDC_ETHEREUM,
        tokenOut: NATIVE_TOKEN,
        amountIn: "10000000", // 10 USDC
      },
    },
    // Step 2: Bridge ETH to Arbitrum via Relay
    {
      protocol: "relay",
      action: "bridge",
      args: {
        primaryAddress: "0xa5f565650890fba1824ee0f21ebbbf660a179934",
        destinationChainId: ARBITRUM_ID,
        tokenIn: NATIVE_TOKEN, // Relay supports native tokens
        amountIn: { useOutputOfCallAt: 0 },
        receiver: WALLET_ADDRESS,
        callback: [
          // Step 3: Check ETH balance on Arbitrum
          {
            protocol: "enso",
            action: "balance",
            args: {
              token: NATIVE_TOKEN,
            },
          },
          // Step 4: Wrap ETH to WETH on Arbitrum
          {
            protocol: "wrapped-native",
            action: "deposit",
            args: {
              primaryAddress: WETH_ARBITRUM,
              tokenIn: NATIVE_TOKEN,
              tokenOut: WETH_ARBITRUM,
              amountIn: { useOutputOfCallAt: 0 },
            },
          },
        ],
      },
    },
  ]
);

return bundle;

Important Considerations:

Relay supports both ERC20 and native token bridging
No callback data limit - uses placeholder-based design for dynamic amounts
Fee is taken from the bridged token amount (no separate fee token)
API-based quote system determines optimal routing
For Relay, primaryAddress is the token address itself

Key Differences from Other Bridges

Feature	Relay	CCIP	Stargate
Native Token	Yes	No	Yes
Callback Limit	Unlimited	~30KB	~9.5KB
Fee Token	Token itself	Native	Native
Amount Resolution	Dynamic (placeholders)	Pre-computed	Pre-computed

Resources

Crosschain Routing Guide - Complete guide to crosschain operations
Bridge Action Reference - Technical details on bridge parameters

Updated

Use Cases

​Key Differences from Other Bridges

​Resources

Key Differences from Other Bridges

Resources