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Send messages from XRPL
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Send messages from XRPL

In addition to transferring tokens across chains, Axelar enables cross-chain communication through Axelar's General Message Passing (GMP). GMP enables developers to call any function on any other connected chain. For example, smart contracts on EVM-compatible chains, such as the XRPL EVM, can be triggered directly from the XRP Ledger (XRPL).

To send a message from one chain to another, there are some key aspects to consider:

  • The destination chain must be an EVM-compatible chain, as executing messages requires a smart contract.
  • The destination contract address must inherit from AxelarExecutable

For a deeper dive into GMP, refer to the official documentation. Additionally, Axelar's step-by-step guide provides a detailed walkthrough of the process.

Sending a message from XRP Ledger to XRPL EVM

To send a message from the XRP Ledger (XRPL) to the XRPL EVM, a payment transaction is used with the following key parameters:

  • Amount: Represents the value of the asset to be sent. If the message does not include an asset transfer, this can be set to 1 drop (the smallest XRP unit).
  • Destination: The address of the Gateway on the XRP Ledger.
  • Memos: Encodes additional data required for the function call, including:
    • The destination chain ID on the Axelar network.
    • The contract address on the destination chain to which the message is sent.
    • The payload hash, which contains the data to be sent to the destination contract. This payload must be ABI-encoded. The ethers AbiCoder can be used for encoding the payload.

Important: All fields within Memos must be encoded in hexadecimal format before submission.

Below are two examples (Devnet and Testnet) showing how to call a smart contract function on the XRPL EVM from the XRP Ledger. Both examples use the ethers library to encode the payload and the xrpl.js library to interact with the XRP Ledger.

import { AbiCoder } from "ethers";
import { Wallet, Client, Payment, convertStringToHex } from "xrpl";

// Create the ABI-encoded payload
const payload = AbiCoder.defaultAbiCoder().encode(["string"], ["Hello World"]);

// wallet variable corresponds to xrpl.js Wallet instance
// client variable corresponds to xrpl.js Client instance

// Create the payment transaction object for DEVNET
const payment: Payment = {
  TransactionType: "Payment",
  Account: wallet.address, // Sender's address
  Amount: "10000000", // 10 Million drops = 10 XRP
  // Devnet Gateway address on the XRP Ledger
  Destination: "rGAbJZEzU6WaYv5y1LfyN7LBBcQJ3TxsKC",
  Memos: [
    {
      Memo: {
        // hex(destination_address)
        MemoType: Buffer.from("destination_address")
          .toString("hex")
          .toUpperCase(),
        // Destination contract address (hexadecimal, without 0x prefix)
        MemoData: "ECFA31764C91805B6C8E1D488941E41A86531880",
      },
    },
    {
      Memo: {
        // hex(destination_chain)
        MemoType: Buffer.from("destination_chain")
          .toString("hex")
          .toUpperCase(),
        // The destination chain ID on the Axelar network (hexadecimal)
        // for Devnet
        MemoData: Buffer.from("xrpl-evm-devnet").toString("hex").toUpperCase(),
      },
    },
    {
      Memo: {
        // hex(payload_hash)
        MemoType: "7061796C6F61645F68617368", // "payload_hash" in hex
        // ABI-encoded payload (hexadecimal, without 0x prefix)
        MemoData: payload.slice(2),
      },
    },
  ],
};

// Autofill transaction
const transaction = await client.autofill(payment);

// Sign transaction
const signedTransaction = wallet.sign(transaction).tx_blob;

// Submit transaction
const result = await client.submit(signedTransaction);
console.log(result);