(Legacy) Bridge Example

This is a simple bridge request (without invoking swap) example

Please note that directly interacting with the smart contract means your bridge request may not be completed on the target chain since you are initiating a request regardless of the liquidity on the other side. If unfortunately you found your transaction hasn't been processed for more than 30 minutes, please contact us via telegram or discord!

See more detail of available liquidity.

In this example, we try to bridge 100 USDT from Ethereum to Polygon.

The function we're going interact with is the swap of the XSwapper on Ethereum.

From (Legacy) Integrate X Swap Contract we can find the interface of swap:

function swap(
    address aggregatorAdaptor,
    IDexAggregatorAdaptor.SwapDescription memory swapDesc,
    bytes memory aggregatorData,
    ToChainDescription calldata toChainDesc

There are four parameters we need to prepare: - aggregatorAdaptor - swapDesc - aggregatorData - toChainDesc


Since we're just bridging USDT, no swap actions would be involved. That is, we don't need aggregator and so is its adaptor aggregatorAdaptor. In this kind of situation aggregatorAdaptor should be 0x0000000000000000000000000000000000000000


Normally, we put the data that is going to be executed by the aggregator to this field. However in this case we're not going to swap tokens, so the aggregatorData we put is 0x.


struct SwapDescription {
    IERC20 fromToken;
    IERC20 toToken;
    address receiver;
    uint256 amount;
    uint256 minReturnAmount;

A SwapDescription describes the swap happening on the source chain. In this case, we don't need to swap USDT to something else so both the fromToken and toToken should be the address of USDT on Ethereum, which is 0xdAC17F958D2ee523a2206206994597C13D831ec7.

The receiver is the one who's going to receive the USDT on target chain (Polygon).

The amount is the swap amount with padding zeroes. In this case it should be 100000000 since the decimals of USDT on Ethereum is 6.

The minReturnAmount is used to make sure the return amount of the swap happening on the source chain. In this case we could just put the same amount as amount.


struct ToChainDescription {
    uint32 toChainId;
    IERC20 toChainToken;
    uint256 expectedToChainTokenAmount;
    uint32 slippage;

As for ToChainDescription, it describes what should be achieved on the target chain.

The toChainId is the ID of the target chain, 137 in this case.

The toChainToken represents the desired token on the target chain, the USDT address on Polygon in this case, which is 0xc2132D05D31c914a87C6611C10748AEb04B58e8F

The expectedToChainTokenAmount will be used for the swap on the target chain. To keep it simple, we could put the same value as the amount of the swapDesc. In this case it would be 100000000 since the decimals of Polygon USDT is also 6. However, please note that the amount you're going to received will be a bit less owing to the XY Fee.

The slippage will be used to calculate the minimum received amount from expectedToChainTokenAmount and it's as well only used when a swap is happening on the target chain. In this case, again, there's no swap involved therefore we put 0 in this field.

To Sum up

The parameters we need to bridge 100 USDT from Ethereum to Polygon would look like:

    0x0000000000000000000000000000000000000000, // aggregatorAdaptor
    (0xdAC17F958D2ee523a2206206994597C13D831ec7, 0xdAC17F958D2ee523a2206206994597C13D831ec7, receiver, 100000000, 100000000), // swapDesc
    0x, // aggregatorData
    (137, 0xc2132D05D31c914a87C6611C10748AEb04B58e8F, 100000000, 0) // toChainDesc

Check on the Target Chain

After sending a swap request from the source chain, we can get the SwapRequested event from logs. The _swapId in the event is the ID of the swap request. We can check whether the swap request is processed or not on the target chain by invoking getEverClosed(_srcChainId, _swapId).

If you are looking for more details of the request such as the amount, you should monitor the SwappedForUser event emitted from the XSwapper on the target chain.

See more of events and functions of XSwapper here. See addresses of XSwapper across all chains here.

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