Axelar integration

Axelar Integration

Axelar is a decentralized cross-chain communication network. Unlike bridges with multisig validators (Multichain, Ronin), Axelar uses proof-of-stake network with ~75 validators and threshold signatures. Compromise requires controlling 2/3 of validators by stake — significantly higher attack threshold than 5-of-9 multisig.

What Axelar Can Do

GMP (General Message Passing) — transfer arbitrary messages between chains. Not just tokens: can call function in another chain's smart contract with arbitrary data.

Canonical token bridging — standardized token transfer. USDC via Axelar is either Circle's native USDC (via Circle CCTP) or Axelar Wrapped USDC (axlUSDC), depending on configuration.

Squid — DEX aggregator on top of Axelar, allowing cross-chain swaps in one transaction (swap on source chain + bridge + swap on destination).

GMP Integration

Source Chain Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import { AxelarExecutable } from "@axelar-network/axelar-gmp-sdk-solidity/contracts/executable/AxelarExecutable.sol";
import { IAxelarGateway } from "@axelar-network/axelar-gmp-sdk-solidity/contracts/interfaces/IAxelarGateway.sol";
import { IAxelarGasService } from "@axelar-network/axelar-gmp-sdk-solidity/contracts/interfaces/IAxelarGasService.sol";

contract SourceContract {
    IAxelarGateway public gateway;
    IAxelarGasService public gasService;
    
    constructor(address _gateway, address _gasService) {
        gateway = IAxelarGateway(_gateway);
        gasService = IAxelarGasService(_gasService);
    }
    
    function sendCrossChainMessage(
        string calldata destinationChain,      // "Polygon", "avalanche", "binance"
        string calldata destinationAddress,    // recipient contract address
        bytes calldata payload
    ) external payable {
        // Pay gas for execution on destination chain
        gasService.payNativeGasForContractCall{value: msg.value}(
            address(this),
            destinationChain,
            destinationAddress,
            payload,
            msg.sender
        );
        
        // Send message
        gateway.callContract(destinationChain, destinationAddress, payload);
    }
}

Destination Chain Contract

contract DestinationContract is AxelarExecutable {
    event MessageReceived(string sourceChain, string sourceAddress, bytes payload);
    
    constructor(address gateway) AxelarExecutable(gateway) {}
    
    // Called by Axelar when message delivered
    function _execute(
        string calldata sourceChain,
        string calldata sourceAddress,
        bytes calldata payload
    ) internal override {
        // Decode payload
        (address recipient, uint256 amount) = abi.decode(payload, (address, uint256));
        
        // Execute business logic
        _processMessage(sourceChain, sourceAddress, recipient, amount);
        
        emit MessageReceived(sourceChain, sourceAddress, payload);
    }
}

Gas Payment on Destination Chain

Key Axelar GMP detail — Gas Service. User pays gas for both chains in one transaction (on source chain). Axelar Gas Service converts native token and pays relayers on destination chain.

Calculate needed gas via AxelarGMPRecoveryAPI:

import { AxelarQueryAPI, Environment, GasToken } from "@axelar-network/axelarjs-sdk";

const api = new AxelarQueryAPI({ environment: Environment.MAINNET });

const gasEstimate = await api.estimateGasFee(
  "Ethereum",           // source chain
  "Polygon",            // destination chain
  GasToken.ETH,
  300_000,              // gas limit on destination
  1.1                   // 10% buffer
);

// gasEstimate is sum in wei to pass to payNativeGasForContractCall

Token Transfer with GMP

For token transfer + function call on destination chain — use callContractWithToken:

function sendTokenAndCall(
    string calldata destinationChain,
    string calldata destinationAddress,
    bytes calldata payload,
    string calldata symbol,  // "USDC", "WETH"
    uint256 amount
) external payable {
    IERC20(gateway.tokenAddresses(symbol)).transferFrom(msg.sender, address(this), amount);
    IERC20(gateway.tokenAddresses(symbol)).approve(address(gateway), amount);
    
    gasService.payNativeGasForContractCallWithToken{value: msg.value}(
        address(this), destinationChain, destinationAddress, payload, symbol, amount, msg.sender
    );
    
    gateway.callContractWithToken(destinationChain, destinationAddress, payload, symbol, amount);
}

Supported Chains

Axelar supports 50+ chains: Ethereum, Polygon, Avalanche, BNB Chain, Fantom, Arbitrum, Optimism, Base, Linea, Scroll, Near, Cosmos ecosystem (via IBC).

Cosmos integration is unique Axelar advantage: only major cross-chain protocol with real EVM ↔ Cosmos connection.

Squid Integration for Cross-Chain Swaps

import { Squid } from "@0xsquid/sdk";

const squid = new Squid({ baseUrl: "https://apiplus.squidrouter.com" });
await squid.init();

const { route } = await squid.getRoute({
  fromAddress: userAddress,
  fromChain: "1",                // Ethereum
  fromToken: "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE", // ETH
  fromAmount: "1000000000000000000", // 1 ETH
  toChain: "137",                // Polygon
  toToken: "0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174", // USDC
  toAddress: recipientAddress,
  slippage: 1.0,                 // 1%
  enableBoost: true,
});

// Execute swap
const tx = await signer.sendTransaction(route.transactionRequest);

Axelar GMP integration — 2-4 weeks. Includes: deploy contracts on several chains, setup gas payment, monitor transaction status via AxelarScan API, testnet testing (Axelar testnet supports all major EVM testnets).