Docs

Find the full documentation here, for quick start guide read below. All examples can be found here.

Summary: Asset-transfer-api is a library focused on simplifying the construction of asset transfers for Substrate based chains that involves system parachains like Asset Hub (Polkadot and Kusama). It exposes a reduced set of methods which facilitates users to send transfers to other (para) chains or locally.

Current Cross-chain Support

The below chart is focusing on what directions are supported for constructing asset transfers and in what XCM version. The goal is to have everything in green checkmarks. Note that local transfers (intra-chain) are not visualized here.

Direction	V2	V3	V4
System to Relay	✅	✅	✅
System to System	✅	✅	✅
System to Bridge	❌	✅	✅
System to Parachain	✅	✅	✅
Relay to Parachain	✅	✅	✅
Relay to Bridge	❌	✅	✅
Relay to System	✅	✅	✅
Parachain to Parachain	✅	✅	✅
Parachain to Relay	✅	✅	✅
Parachain to System	✅	✅	✅

Note on Parachain to Parachain Support

Parachain To Parachain support is currently limited to XCM V2, with the exception of Parachain primary asset tx construction (e.g. MOVR, SDN, etc.).

Note: System refers to System Parachains like Asset Hub.

Usage

Npm

npm install @substrate/asset-transfer-api

Yarn

yarn add @substrate/asset-transfer-api

NodeJS Version

Recommended: v21 or greater When the API is initalized using the CDN, node:fetch is being used and is stable in node v21. Therefore it is recommended to use v21 or greater.

Example Usage

Note: For more detailed and practical usage examples, please refer to the ./examples directory, where you can find various use cases. To run these examples, follow the steps below:

1. First, install the dependencies:

   yarn install
   
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2. Then, build and run the desired example:

   yarn build:examples && node ./examples/build/examples/<file_to_run>.js
   
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import { AssetTransferApi, constructApiPromise } from '@substrate/asset-transfer-api';

// NOTE: This should all be wrapped in an asynchronous layer.

// This constructs a polkadot-js ApiPromise, it is totally viable for one to construct their
// own ApiPromise, and pass it into AssetTransferApi, but keep in mind the `specName`, and `safeXcmVersion` are also necessary.
const { api, specName, safeXcmVersion } = await constructApiPromise('wss://westmint-rpc.polkadot.io');

const assetsApi = new AssetTransferApi(api, specName, safeXcmVersion);

const call = assetsApi.createTransferTransaction(
	'2001', // destChainId (If the destination is a relay chain put `0`)
	'0x00', // destAddress
	['1', '2'], // Array of AssetIds
	['1000000000', '2000000000'], // Array of amounts of each token to transfer
	{
		format: 'call',
		xcmVersion: 1,
	}, // Options
);
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AssetTransferApi & AssetTransferApiOpts & TransferArgsOpts

// The AssetTransferApi method: `createTransferTransaction`

/**
 * Create an XCM transaction to transfer Assets, or native tokens from one
 * chain to another.
 *
 * @param destChainId ID of the destination (para) chain (‘0’ for Relaychain)
 * @param destAddr Address of destination account
 * @param assetIds Array of assetId's to be transferred
 * @param amounts Array of the amounts of each token to transfer
 * @param opts Options
 */
AssetTransferApi.createTransferTransaction(
  	destChainId: string,
	destAddr: string,
	assetIds: string[],
	amounts: string[],
	opts?: TransferArgsOpts<T>
)
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// The AssetTransferApi method: `fetchFeeInfo`

/**
 * Fetch estimated fee information for an extrinsic
 *
 * @param tx a payload, call or submittable
 * @param format The format the tx is in
 */
AssetTransferApi.fetchFeeInfo(
  	tx: ConstructedFormat<T>,
	format: T,
)
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// AssetTransferApiOpts are the options for the `AssetTransferApi`

type AssetTransferApiOpts = {
	/**
	 * The injectedRegistry allows you to add custom values to the predefined initialized registry.
	 * If you would like to see the registry you may visit https://github.com/paritytech/asset-transfer-api-registry/blob/main/docs/registry.json
	 * When adding a new chain, the `specName` and `tokens` fields are mandatory.
	 *
	 * An example input of the registry would be:
	 * {
	 *     polkadot: {
	 *         '9876': {
	 *             tokens: ['TST'],
	 *             assetsInfo,
	 *             specName: 'testing',
	 *         }
	 *     }
	 * }
	 *
	 * NOTE: It supports adding info for `polkadot`, `kusama`, `westend` and `paseo`.
	 */
	injectedRegistry?: RequireAtLeastOne<ChainInfoRegistry>;
	/**
	 * The overrideRegistry option allows you to modify chain data already present in the registry,
	 * either overriding fields' values or adding new information. If the chain of which data is
	 * being overriden is not present in the registry, it will be treated as if it were
	 * and injectedRegistry and added following the same logic.
	 *
	 * If the chain is present in the registry, it will override only the fields
	 * present in the passed overrideRegistry, leaving the remaining as is.
	 *
	 * An example input for overrideRegistry would be:
	 * {
	 *     westend: {
	 *         '0': {
	 *             tokens: ['WER'],
	 *         }
	 *     }
	 * }
	 *
	 * This would override the existing native token for the Westend Relay Chain
	 * to WER instead of WND.
	 */
	overrideRegistry?: RequireAtLeastOne<ChainInfoRegistry<InjectedChainInfoKeys>>;
	/**
	 * RegistryTypes is a string and can either be 'CDN' or 'NPM'.
	 *
	 * CDN - The registry will be initialized with the up to date version given the CDN
	 * NPM - The registry will be initialized with the NPM version which is updated less frequently.
	 */
	registryType?: RegistryTypes;
};
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// The TransferArgsOpts are options that give the possibility of adding certain customization to the transaction.

interface TransferArgsOpts<T extends Format> {
	/**
	 * Option that specifies the format in which to return a transaction.
	 * It can either be a `payload`, `call`, or `submittable`.
	 *
	 * Note: A `submittable` will return a `SubmittableExtrinsic` polkadot-js type, whereas
	 * a `payload` will return a `GenericExtrinsicPayload` polkadot-js type and a `call` will return a hex. By default a `payload` will be returned if nothing is inputted.
	 */
	format?: T;
	/**
	 * AssetId to pay fees on the current common good parachain.
	 * Polkadot AssetHub: default DOT
	 * Kusama AssetHub: default KSM
	 */
	paysWithFeeOrigin?: string;
	/**
	 * AssetId to pay fees on the destination parachain.
	 */
	paysWithFeeDest?: string;
	/**
	 * Option for applying a custom weightLimit.
	 * If not inputted it will default to `Unlimited`.
	 */
	weightLimit?: { refTime?: string; proofSize?: string };
	/**
	 * Set the xcmVersion for message construction. If this is not present a supported version
	 * will be queried, and if there is no supported version a safe version will be queried.
	 */
	xcmVersion?: number;
	/**
	 * For creating local asset transfers, this will allow for a `transferKeepAlive` as oppose
	 * to a `transfer`.
	 */
	keepAlive?: boolean;
	/**
	 * For creating local asset transfers, this will allow for a `transferAll` as opposed
	 * to a `transfer`.
	 */
	transferAll?: boolean;
	/**
	 * Boolean to declare if this will transfer liquidity tokens.
	 * Default is false.
	 */
	transferLiquidToken?: boolean;
	/**
	 * The XCM `TransferType` used to transfer assets.
	 * Provided to construct `transferAssetsUsingTypeAndThen` transactions.
	 */
	assetTransferType?: string;
	/**
	 * The RemoteReserve location for an XCM transfer.
	 * Should be provided when specifying an `assetTransferType` of `RemoteReserve`.
	 */
	remoteReserveAssetTransferTypeLocation?: string;
	/**
	 * The XCM `TransferType` used to pay fees for an XCM transfer.
	 * Provided to construct `transferAssetsUsingTypeAndThen` transactions.
	 */
	feesTransferType?: string;
	/**
	 * The RemoteReserve location for an XCM transfers' fees.
	 * Should be provided when specfying a `feesTransferType` of `RemoteReserve`.
	 */
	remoteReserveFeesTransferTypeLocation?: string;
	/**
	 * Optional custom XCM message to be executed on destination chain.
	 * Should be provided if a custom xcm message is needed after transfering assets.
	 * Defaults to `Xcm(vec![DepositAsset { assets: Wild(AllCounted(assets.len())), beneficiary }])`
	 */
	customXcmOnDest?: string;
	/**
	 * Optionally allows for dry running the constructed tx in order get the estimated fees and execution result.
	 */
	dryRunCall?: boolean;

	/**
	 * Optional assetId that will be used to pay for fees. Used with the `dryRunCall` option to determine fees in the specified asset.
	 */
	xcmFeeAsset?: string;

	/**
	 * Optionally sets the pallet to be used for the current tx.
	 */
	xcmPalletOverride?: XcmPallet;
}
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Teleport and Reserve Transfer via polkadotXcm pallet

The AssetTransferApi.createTransferTransaction is able to infer what kind of transaction is necessary given the inputs. When sending cross chain transfers, the api does a lot of validation to ensure the inputs are valid, and the assets either exist or don't. This process is done through a registry which is maintained in a separate repo here. If the asset is not in the registry, it will then lookup if that asset exists on-chain and cache it if necessary. On-chain verification is not always possible in respect to the direction the asset is being sent and what the destination chain is since we only maintain one api connection. Therefore, if you would like to inject information into the registry, you can using the injectedRegistry option for the AssetTransferApi.

Transferring assets via xTokens pallet

If the transfer is being sent from a parachain that utilizes the xTokens pallet, the API will detect that and construct the transaction that is necessary. It will construct one of three calls: transferMultiasset, transferMultiassets, or transferMultiassetWithFee. This is only applicable when the intended transfer direction starts from a parachain. The xTokens pallet can be found here.

An example would look like:

api.createTransferTransaction(
	'1000',
	'0xc4db7bcb733e117c0b34ac96354b10d47e84a006b9e7e66a229d174e8ff2a063',
	['xcUSDT'],
	['1000000'],
	{
		format: 'call',
		xcmVersion: 2,
	},
);
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If you would like to run an example to understand the output, run: yarn build:examples && node ./examples/build/examples/paraToSystemTransferMultiAsset.js

Foreign Asset Transfers

Sending a foreign asset requires the input assetIds in createTransferTransaction to include the MultiLocation of the asset you would like to send. If a MultiLocation is not passed it will not know if the asset you are sending is a foreign asset. If the MultiLocation passed in has a Parachain id which matches the destChainId input for the transfer, then the output will be a limited teleport, otherwise it will be a limited reserve backed transfer.

An example would look like:

api.createTransferTransaction(
	'2125', // Note: the Parchain ID matches the MultiLocations 'Parachain' ID, making this a limitedTeleportAssets call
	'5EWNeodpcQ6iYibJ3jmWVe85nsok1EDG8Kk3aFg8ZzpfY1qX',
	['{"parents":"1","interior":{"X2":[{"Parachain":"2125"},{"GeneralIndex":"0"}]}}'],
	['1000000000000'],
	{
		format: 'call',
		xcmVersion: 3,
	},
);
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If you would like to run an example to understand the output run: yarn build:examples && node ./examples/build/examples/systemToParaTeleportForeignAssets.js

Liquid Pool Asset Transfers

Sending a liquidity token (from the poolAssets pallet) in Asset Hub is as simple as setting the option transferLiquidToken to true. That being said, it does have some nuances. A liquidity token cross-chain transfer must be in the direction of a SystemToPara, and the inputted asset must be a valid integer as a string. The api will error if either of these conditions are not met.

An example would look like:

api.createTransferTransaction('2023', '0xF977814e90dA44bFA03b6295A0616a897441aceC', ['0'], ['100000'], {
	format: 'call',
	xcmVersion: 2,
	transferLiquidToken: true,
});
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If you would like to run an example to understand the output run: yarn build:examples && node ./examples/build/examples/systemToParaLpToken.js

Local Transactions

Sending an Asset or Native token locally on a System Parachain is easy. In order to create a transaction, ensure the destChainId is the same as the ID of the System Parachain itself. Note, the only System parachains that are supported are Kusama AssetHub, Polkadot AssetHub, Westend AssetHub, Rococo AssetHub (note on how to use it) and as a side effect the only destChainId that is supported is 1000. In addition to that, ensure the length of the assetId's array and amounts array are 1. As sending assets will only accept one asset at a time. Keep in mind transfer, and transferKeepAlive are the only supported calls.

An example would look like:

api.createTransferTransaction(
	'1000', // destChainId
	'0xf5d5714c084c112843aca74f8c498da06cc5a2d63153b825189baa51043b1f0b', // destAddr
	['1984'], // assetIds
	['10000000000'], // amounts
	{
		format: 'call',
		keepAlive: true,
	}, // opts
);
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The api can also send native tokens as well. Similar to the above you would replace the assetIds with ['DOT']. In addition to that, you may provide an empty array to denote you want to send the chain's native token.

The api can also send local transactions for Relay chains. It is the same principal as above, the only difference being that the destChainId would need to be '0'.

For more information, refer to the docs in the repository.

Note: For other parachains, local transfers are currently supported via the balances and tokens pallets. For local parachain transactions, if an asset id is not passed in it will resolve to the balances pallet, and if a asset id is passed in it will resolve to the tokens pallet.

Claiming Trapped Assets

The api can be used to construct claimAssets calls in order to retrieve assets trapped locally on chain after a failed XCM.

An example would look like:

api.claimAssets(
	[`DOT`], // Asset(s) to claim
	['1000000000000'], // Amount of asset(s) to claim
	'0xf5d5714c084c112843aca74f8c498da06cc5a2d63153b825189baa51043b1f0b', // Beneficiary
	{
		xcmVersion: 4,
		format: 'payload',
		sendersAddr: '5EWNeodpcQ6iYibJ3jmWVe85nsok1EDG8Kk3aFg8ZzpfY1qX',
	}, // opts
);
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Note: claimAssets works when pallet-xcm is configured as the AssetTrap for the given runtime. This is true for all relay chains and system parachains but may not be for other chains.

E2E Testing

You can access the E2E tests and their documentation here.

License

The source code in this repository is distributed under the Apache 2.0 license. See the LICENSE file. This source code comes with absolutely no warranty. Use at your own risk.