Transact on AssetHub & Parachain

A guide on using the Snowbridge TypeScript SDK for integration.

Uses the @snowbridge/api SDK.

Transact On AssetHub

To specify XCM to be executed on AssetHub, define your XCM:

const remarkCall = moonbeam.tx.system.remarkWithEvent(remarkMessage)
const callHex = remarkCall.method.toHex()

// Get weight info for the call
const paymentInfo = await remarkCall.paymentInfo(POLKADOT_ACCOUNT_PUBLIC)
const weight = paymentInfo.weight

const customXcm = [
   {
       transact: {
           originKind: "SovereignAccount",
           fallbackMaxWeight: {
               refTime: weight.refTime.toBigInt(),
               proofSize: weight.proofSize.toBigInt(),
           },
           call: {
               encoded: callHex,
           },
       },
   },
]

This XCM uses the system.remarkWithEvent extrinsic, wrapped in a Transact XCM instruction.

Transact Execution

To execute the XCM program on AssetHub, the SDK integration is identical to the token transfer steps, with the extra customXcm parameter:

import { createApi } from "@snowbridge/api"
import { EthersEthereumProvider } from "@snowbridge/provider-ethers"
import { polkadot_mainnet } from "@snowbridge/registry"

const {
    chains: { ethereum, assetHub },
} = polkadot_mainnet
const api = createApi({ info: polkadot_mainnet, ethereumProvider: new EthersEthereumProvider() })

const sender = api.sender(ethereum, assetHub)

const transfer = await sender.build(
    "0x...", // source Ethereum account
    "5...", // beneficiary Polkadot account
    "0x0000000000000000000000000000000000000000", // Ether address
    15_000_000_000_000n, // amount: 0.000015 ETH
    {
        customXcm,
    },
)

The returned transfer.tx can then be submitted to the wallet by your application.

Transact on Parachain

To transact on another parachain, like Hydration or NeuroWeb, use the same steps as above with concrete destructuring such as const { chains: { ethereum, hydration } } = polkadot_mainnet.

Your custom XCM program will be appended to the InitiateTransfer instruction that is built up in the SDK.

Message Origin

It is important to note that the origin of the message on AssetHub or destination parachain is the original sender account on Ethereum, e.g.

{
    parents: 2,
    interior: {
        x2: [
            {
                GlobalConsensus: {
                    Ethereum: {
                        chainId: 1,
                    },
                },
            },
            {
                AccountKey20: {
                    key: "0xa84670..."
                }
            }
        ],
    },
}

The destination parachain should support XCM instruction AliasOrigin , and the destination parachain should be able to map the origin location into an account, e.g. using HashedDescription.