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Bridging Plugins

The Klaster SDK enables chain abstracted user experiences by performing the bridging of assets in the background. In order to be able to perform bridging actions, the Klaster SDK needs to know how to encode them.

The Klaster Bridging Plugins rely on the fact that most bridges are triggered by a simple call to a smart contract on some chain - and as such, can be ecnoded as a series of transactions (e.g. Bridge + Approve). The bridging plugin then returns a series of calls to the blockchain (to be encoded into an InterchainTransaction) and how much the user will end up with at the destination chain (after all the bridging and gas fees are paid - this is usually availble information before bridging.)

In order to do so, you pass it an instance of a BridgePlugin. A BridgePlugin is a simple function of type:

type BridgePlugin = (BridgePluginParams) => BridgePluginResult
 
// The BridgePluginParams expose all of the information
// required to encode a bridging action using some existing
// bridging provider
type BridgePluginParams = {
  sourceChainId: number,
  destinationChainId: number,
  account: MutlichainAccount,
  sourceToken: Address,
  destinationToken: Address,
  amount: bigint
}
 
// BridgePluginResult tells the Klaster SDK 
// - how much will be received on the destination chain post bridign
// - which transactions need to be executed to trigger the bridge
type BridgePluginResult = {
  receivedOnDesitnation: bigint,
  steps: TxBatch[]
}

An example of a BridgePlugin for Across

export const acrossBridgePlugin: BridgePlugin = async (data) => {
  // Call Across API to get the bridging fee data, as well as all the other required
  // inforation about the bridging procedure
  const feesResponse = await getAcrossSuggestedFees(data);
 
  // Calculate the amount which you will receive on the destination chain from the
  // response given by the Across API
  const outputAmount = data.amount - BigInt(feesResponse.totalRelayFee.total);
 
  // Encode a transcation approving the Across pool contract to get the
  // required amount of ERC20 tokens from your accoount.
  const acrossApproveTx = encodeApproveTx({
    tokenAddress: data.sourceToken,
    amount: data.amount,
    recipient: feesResponse.spokePoolAddress,
  });
 
  // Encode a transaction to call the Across Pool
  const acrossCallTx = rawTx({
    to: feesResponse.spokePoolAddress,
    data: encodeAcrossCallData(data, feesResponse),
    gasLimit: BigInt(250000),
  });
 
  return {
    // The total amount which the user will receive on the destination chain. This is
    // used by the SDK to calculate how much funds it can count on after bridging.
    receivedOnDestination: outputAmount,
    // The sequence of transactions which need to be executed in order to start the brdging
    // procedure.
    txBatch: batchTx(data.sourceChainId, [acrossApproveTx, acrossCallTx]),
  };
};