Building CCIP Messages from EVM to Aptos

Introduction

This guide explains how to construct CCIP Messages from Ethereum Virtual Machine (EVM) chains (e.g., Ethereum, Arbitrum, Base, etc.) to the Aptos blockchain. We'll cover the message structure, required parameters, and implementation details for different message types including token transfers, arbitrary data messaging, and programmatic token transfers (data and tokens).

CCIP Message Structure

CCIP messages from EVM are built using the EVM2AnyMessage struct from the Client.sol library. The EVM2AnyMessage struct is defined as follows:

struct EVM2AnyMessage {
    bytes receiver;
    bytes data;
    EVMTokenAmount[] tokenAmounts;
    address feeToken;
    bytes extraArgs;
}

receiver

Definition: The 32-byte account address of the receiver on Aptos.
For token-only transfers: This is the end user's wallet address on Aptos.
For arbitrary messaging or programmatic token transfers: This must be the account address of your custom Aptos module that is intended to receive and process the message.

Formatting Aptos Addresses

When providing an Aptos account address as the receiver, it must be represented as a 32-byte hex string (bytes32). Standard Aptos addresses are already 32 bytes and represented in hex, so you just need to ensure it includes the 0x prefix.

// An Aptos address is already in the correct format.
const aptosReceiverAddress = "0xca843279e3427144cead5e4d5999a3d0abf820035b3b4104284b792e2a936c86"

// Use the hex string directly in the message.
const message = {
  // ...
  receiver: aptosReceiverAddress,
  // ...
}

data

Definition: Contains the payload to be delivered to the destination chain.
For token-only transfers: Must be empty (0x).
For arbitrary messaging or programmatic token transfers: Contains the custom data the receiver module will process.
Encoding requirement: Must be encoded as a hex string with a 0x prefix.

Data Encoding

import { toUtf8Bytes, hexlify } from "ethers"

// For token-only transfers, data is empty.
const tokenTransferData = "0x"

// For arbitrary data, convert your payload to a hex string.
const arbitraryMessageData = hexlify(toUtf8Bytes("Hello Aptos"))

tokenAmounts

Definition: An array of token addresses and amounts to transfer.
For data-only messages: Must be an empty array ([]).
For token transfers or programmatic token transfers: Each entry specifies a token address and amount. Note: Check the CCIP Directory for the list of supported tokens on each lane.

feeToken

Definition: Specifies which token to use for paying CCIP fees.
For native gas token: Use address(0) (ethers.ZeroAddress) to specify the source chain's native gas token (e.g., ETH on Ethereum).
For ERC-20 tokens: Specify the ERC-20 token address for fee payment. Note: Check the CCIP Directory for the list of supported fee tokens on your source chain.

extraArgs

For Aptos-bound messages, the extraArgs parameter is a byte string composed of a 4-byte tag (0x181dcf10) prepended to the ABI-encoded tuple (uint256 gasLimit, bool allowOutOfOrderExecution). This format is specified in the GenericExtraArgsV2 reference.

gasLimit

Definition: Specifies the amount of gas units to allocate for execution on Aptos.
Usage: For simple token and data transfers as shown in the examples, 0 is a sufficient value. For complex programmatic token transfers involving significant computation in your receiving module, this value must be determined through testing.

allowOutOfOrderExecution

Definition: A boolean flag required for the message.
Usage: The provided example scripts consistently use true for this value. It must be set to true when Aptos is the destination chain.

Encoding extraArgs for Aptos

You must ABI-encode a tuple containing the gasLimit and allowOutOfOrderExecution parameters, and then prepend the 0x181dcf10 tag. You can use the Client.encodeExtraArgsV2 helper function for this.

import { ethers } from "ethers";

function encodeExtraArgsV2(gasLimit: bigint, allowOutOfOrderExecution: boolean): string {
    const abiCoder = ethers.AbiCoder.defaultAbiCoder();

    // Encode the arguments as a tuple
    const encodedArgs = abiCoder.encode(
        ["tuple(uint256 gasLimit, bool allowOutOfOrderExecution)"],
        [[gasLimit, allowOutOfOrderExecution]]
    );

    const GENERIC_EXTRA_ARGS_V2_TAG = "0x181dcf10";

    // Concatenate the tag and the encoded arguments
    return ethers.concat([GENERIC_EXTRA_ARGS_V2_TAG, encodedArgs]);
}

// Example for a simple transfer
const extraArgs = encodeExtraArgsV2(0n, true);

Implementation by Message Type

Token Transfer

Use this configuration when sending only tokens from an EVM chain to a user's wallet on Aptos.

{
  destinationChainSelector: APTOS_CHAIN_SELECTOR,
  receiver: userAptosAddress, // The end user's 32-byte Aptos address
  tokenAmounts: [{ token: tokenAddress, amount: tokenAmount }],
  feeToken: feeTokenAddress, // or address(0) for native
  data: "0x", // Data must be empty
  extraArgs: {
    gasLimit: 0, // Gas limit is 0 for token-only transfers
    allowOutOfOrderExecution: true
  }
}

const aptosRecipient = "0xabf820035b3b4104284b792e2a936c86ca843279e3427144cead5e4d5999a3d0";
const tokenAmount = ethers.parseUnits("0.001", 18); // 0.001 CCIP-BnM

const message = {
  receiver: aptosRecipient,
  data: "0x", // No data for a simple token transfer
  tokenAmounts: [{
    token: "0xFd57b4ddBf88a4e07fF4e34C487b99af2Fe82a05", // CCIP-BnM on Sepolia
    amount: tokenAmount
  }],
  feeToken: ethers.ZeroAddress, // Pay fee in native ETH
  extraArgs: encodeExtraArgsV2(0n, true)
};

Arbitrary Messaging

Use this configuration when sending only a data payload to a custom module on Aptos.

{
  destinationChainSelector: APTOS_CHAIN_SELECTOR,
  receiver: yourAptosModuleAddress,
  tokenAmounts: [], // Empty for data-only
  feeToken: feeTokenAddress, // or address(0) for native
  data: customHexData,
  extraArgs: {
    gasLimit: determinedGasLimit, // Must be tested
    allowOutOfOrderExecution: true
  }
}

const yourAptosModule = "0xca843279e3427144cead5e4d5999a3d0abf820035b3b4104284b792e2a936c86";
const messageData = ethers.hexlify(ethers.toUtf8Bytes("Hello Aptos!"));

const message = {
  receiver: yourAptosModule,
  data: messageData,
  tokenAmounts: [],  // No tokens
  feeToken: "0x779877A7B0D9E8603169DdbD7836e478b4624789", // Pay fee in LINK
  extraArgs: encodeExtraArgsV2(0n, true)
};

Programmatic Token Transfer (Data and Tokens)

Use this configuration when sending both tokens and a data payload to a custom module on Aptos.

{
  destinationChainSelector: APTOS_CHAIN_SELECTOR,
  receiver: yourAptosModuleAddress,
  tokenAmounts: [{ token: tokenAddress, amount: tokenAmount }],
  feeToken: feeTokenAddress,
  data: customHexData,
  extraArgs: {
    gasLimit: determinedGasLimit, // Must be tested
    allowOutOfOrderExecution: true
  }
}

const yourAptosModule = "0xca843279e3427144cead5e4d5999a3d0abf820035b3b4104284b792e2a936c86";
const messageData = ethers.hexlify(ethers.toUtf8Bytes("Deposit for user X"));

const message = {
  receiver: yourAptosModule,
  data: messageData,
  tokenAmounts: [{
    token: "0xFd57b4ddBf88a4e07fF4e34C487b99af2Fe82a05", // CCIP-BnM on Sepolia
    amount: ethers.parseUnits("1.5", 18)
  }],
  feeToken: "0x779877A7B0D9E8603169DdbD7836e478b4624789", // Pay fee in LINK
  extraArgs: encodeExtraArgsV2(200000n, true) // Gas determined from testing
};

To see these concepts in action with step-by-step implementation guides, check out the following tutorials:

Token Transfers: EVM to Aptos - Learn how to implement token-only transfers from EVM chains to Aptos wallets.
Arbitrary Messaging: EVM to Aptos - Learn how to send data messages from EVM chains to Aptos modules.
Programmatic Token Transfers: EVM to Aptos - Learn how to send both tokens and data in a single message to trigger module execution with token transfers on Aptos.

These tutorials provide complete, working examples using the concepts covered in this guide.

Further Resources

CCIP EVM Client API Reference: Complete technical details about the EVM2AnyMessage struct, helper functions, and message construction on EVM chains.
Aptos TS-SDK Docs: For more information on building the receiving Aptos module, refer to the official Aptos TS-SDK docs.

Building CCIP Messages from EVM to Aptos

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