XCM SDK

The following is a quick guide on how to use Unique SDK to work with (NFT) XCM. Find how to work with Unique SDK in the official documentation.

IMPORTANT:
The NFT SDK currently functions only in a development environment. For production use, the following tasks still need to be completed:
Implement XcmPaymentApi (Polkadot SDK). Required for handling the payment and fee logic within cross-chain messages.
Implement DryRunApi (Polkadot SDK). Allows for dry-run validation of cross-chain transactions.
Add an XCM Asset Transactor for NFTs. This transactor—using the new XCM + NFT types (currently under review for the Polkadot SDK)—enables native NFT transfers on your chain.
(Optional) Support Receiving External Derivatives: Implement a mechanism for registering external NFT collections. This can be done with a pallet-derivatives approach, which is also under review for inclusion in the Polkadot SDK.
Add an additional XCM Asset Transactor specifically for derivative NFTs.

Prerequisites

Install the @unique-nft/sdk package.

npm install @unique-nft/sdk

Establish a connection

For this demo-stand you can use the following SDK instances:

Unique Network: https://rest.uniquenetwork.dev/v2/xcm-unique
Asset Hub: https://rest.uniquenetwork.dev/v2/xcm-assethub

Below is an example of how to instantiate the Asset Hub SDK:

import { AssetHub } from '@unique-nft/sdk';

const assetHub = AssetHub({ baseUrl: "https://rest.uniquenetwork.dev/v2/xcm-assethub" });

Creating collections and NFTs

Although creating collections and NFTs is outside the scope of XCM functionality, you can learn more about these processes in the official documentation:

Creating derivatives

A derivative is a cross-chain representation of an NFT collection that allows one chain to reference a collection hosted on another chain. On production networks, creating derivatives will be managed through governance processes.

IMPORTANT:
Unique SDK provides the derivative.register method solely for testing. It will not work on production networks and is likely to be removed in future SDK versions.

await assetHub.derivative.register({
  universalLocation: {
    globalConsensus: {
      byGenesis: '0x0000000000000000000000000000000000000000000000000000000000000000'
    },
    parachain: uniqueParaId,
    generalIndex: collectionId,
  }
});

Check if derivative is registered

To confirm whether a derivative is already registered for a specific NFT collection, use the derivative.registered method:

const { registered } = await assetHub.derivative.registered({
  universalLocation: {
    globalConsensus: {
      byGenesis: '0x0000000000000000000000000000000000000000000000000000000000000000'
    },
    parachain: uniqueParaId,
    generalIndex: collectionId,
  }
});

XCM Fees

When performing cross-chain transfers or calls, you typically need to pay fees in an asset recognized by the destination chain. Use the xcm.feeAssets method to retrieve a list of valid fee assets for a particular parachain:

const feeAssets = await assetHub.xcm.feeAssets({ parachainId });

This method returns the universalLocation for the assets accepted as fees on the specified parachain. Once you know the acceptable fee assets, you can estimate fees for a specific transfer:

const fees = assetHub.xcm.transferNft.fee(transferParams);

Transfer NFT

Finally, you can initiate an XCM-based NFT transfer:

const result = await assetHub.xcm.transferNft(params);

const { xcmMessageId, xcmMessageHash } = result;

Here, xcmMessageId and xcmMessageHash serve as identifiers for the cross-chain message, which can be used to track the transfer status.