Smart Contracts

You are referring to the Legacy version of KyberSwap docs.

For the most updated information, please refer to:

• Classic

• Elastic

• Limit Order

• Aggregator

Introduction​

This guide will walk you through on how you can interact with our protocol implementation at a smart contract level. The most common group of users that can benefit from this guide are Dapps.

We break the guide into 2 sections:

1. Trading Tokens - The section covers what contract interfaces to import, and functions to call to fetch rates and perform a simple trade.

2. Reserve Routing - This section covers the reserve routing feature to include / exclude reserves, or to split trades amongst multiple reserves.

Things To Note​

1. If possible, minimise the use of msg.sender within your smart contract. If you were to call a function within the wrapper contract, msg.sender is the wrapper contract address instead of your wallet address.

2. If the source token is not ETH (ie. an ERC20 token), the user is required to first call the ERC20 approve function to give an allowance to the smart contract executing the transferFrom function.

3. To prevent front running, the contract limits the gas price trade transactions can have. The transaction will be reverted if the limit is exceeded. To query for the maximum gas limit, check the public variable maxGasPrice.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

let maxGasPrice = await KyberNetworkProxyContract.maxGasPrice();

Trading Tokens​

File Import​

We will use Solidity compiler version 0.6.6 for deploying our sample contract. The following interfaces are imported for these functionalities:

• IERC20.sol: Token approvals and transfers. We recommend the usage of OpenZeppelin's SafeERC20 contract for these purposes.
• IKyberNetworkProxy.sol: Fetch rates and execute trades

pragma solidity 0.6.6;

import "./IERC20.sol";
import "./IKyberNetworkProxy.sol";

Proxy Contract Declaration​

The network proxy contract can be instantiated as such:

IKyberNetworkProxy kyberProxy;

Fetching Rates​

Call the getExpectedRateAfterFee function of the network proxy contract. The input parameters are explained below.

Parameter	Type	Description
src	IERC20	source ERC20 token contract address
dest	IERC20	destination ERC20 token contract address
srcQty	uint256	src token wei amount
platformFeeBps	uint256	platform fee to be charged, in basis points. Read more about platform fees here
hint	bytes	hint for reserve routing. hint for reserve routing. Refer to this section

Returns\ Expected rate for a trade after deducting network and platform fees. To get a 'readable' rate, divide it by 10**18. Refer to the example below.

Example​

Get the conversion rate of 1 WBTC -> KNC, with a platform fee of 0.25%.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

uint256 expectedRate = kyberNetworkProxyContract.getExpectedRateAfterFee(
    0x2260fac5e5542a773aa44fbcfedf7c193bc2c599, // WBTC token address
    0xdd974d5c2e2928dea5f71b9825b8b646686bd200, // KNC token address
    100000000, // 1 WBTC
    25, // 0.25%
    '' // empty hint
    );

// expectedRate = 7980824281140923034320
// 7980824281140923034320 / 1e18 = 7980.824 => 1 WBTC = 7980.824 KNC

Trade Execution​

Call the tradeWithHintAndFee function of the network proxy contract. The input parameters are explained below.

Parameter	Type	Description
src	IERC20	source ERC20 token contract address
srcAmount	uint256	src token wei amount
dest	IERC20	destination ERC20 token contract address
destAddress	address	recipient address of dest tokens
maxDestAmount	uint256	limit on maximum dest token wei receivable
minConversionRate	uint256	minimal conversion rate. If actual rate is lower, trade reverts
platformWallet	address	wallet address for receiving platform fees.
<!-- Read more about platform fees here	-->
platformFeeBps	uint256	platform fee to be charged, in basis points.
<!-- Read more about platform fees here	-->
hint	bytes	hint for reserve routing.
<!-- Refer to this section	-->

Returns\ Actual dest token wei amount sent to destAddress

Example​

Convert 1 ETH to KNC, specifying 0.25% platform fee.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

// Note: msg.value should be the srcQty if src == ETH, 0 otherwise
uint256 actualDestAmount = kyberNetworkProxyContract.tradeWithHintAndFee{value: msg.value}(
    0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee, // ETH address
    1000000000000000000, // 1 ETH
    0xdd974d5c2e2928dea5f71b9825b8b646686bd200, // KNC address
    0xbeE6fFAFDE4A9cB252a5eA357a53f558dc8A6876, // destAddress
    9999999999999999999999999999999, // maxDestAmount: arbitarily large to swap full amount
    expectedRate, // minConversionRate: value from getExpectedRate call
    0xbeE6fFAFDE4A9cB252a5eA357a53f558dc8A6876, // platform wallet
    25, // 0.25%
    '' // empty hint
    );

Code Example​

Note: The following code is not audited and should not be used in production. If so, it is done at your own risk.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

pragma solidity 0.6.6;

import "./IERC20.sol";
import "./IKyberNetworkProxy.sol";

contract MyContract {
    IERC20 internal constant ETH_TOKEN_ADDRESS = IERC20(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE);
    IKyberNetworkProxy kyberProxy;
    address payable public platformWallet;
    uint256 public platformFeeBps;

    // constructor
    // _platformWallet: To receive platform fees
    // _platformFeeBps: Platform fee amount in basis points
    constructor(
        IKyberNetworkProxy _kyberProxy,
        address payable _platformWallet,
        uint256 _platformFeeBps
        ) public
    {
        kyberProxy = _kyberProxy;
        platformWallet = _platformWallet;
        platformFeeBps = _platformFeeBps;
    }

    /// @dev Get the conversion rate for exchanging srcQty of srcToken to destToken
    function getConversionRates(
        IERC20 srcToken,
        IERC20 destToken,
        uint256 srcQty
    ) public
      view
      returns (uint256)
    {
      return kyberProxy.getExpectedRateAfterFee(srcToken, destToken, srcQty, platformFeeBps, '');
    }

    /// @dev Swap from srcToken to destToken (including ether)
    function executeSwap(
        IERC20 srcToken,
        uint256 srcQty,
        IERC20 destToken,
        address payable destAddress,
        uint256 maxDestAmount
    ) external payable {
        if (srcToken != ETH_TOKEN_ADDRESS) {
            // check that the token transferFrom has succeeded
            // we recommend using OpenZeppelin's SafeERC20 contract instead
            // NOTE: msg.sender must have called srcToken.approve(thisContractAddress, srcQty)
            require(srcToken.transferFrom(msg.sender, address(this), srcQty), "transferFrom failed");

            // mitigate ERC20 Approve front-running attack, by initially setting
            // allowance to 0
            require(srcToken.approve(address(kyberProxy), 0), "approval to 0 failed");

            // set the spender's token allowance to tokenQty
            require(srcToken.approve(address(kyberProxy), srcQty), "approval to srcQty failed");
        }

        // Get the minimum conversion rate
        uint256 minConversionRate = kyberProxy.getExpectedRateAfterFee(
            srcToken,
            destToken,
            srcQty,
            platformFeeBps,
            '' // empty hint
        );

        // Execute the trade and send to destAddress
        kyberProxy.tradeWithHintAndFee{value: msg.value}(
            srcToken,
            srcQty,
            destToken,
            destAddress,
            maxDestAmount,
            minConversionRate,
            platformWallet,
            platformFeeBps,
            '' // empty hint
        );
    }
}

Reserve Routing​

Overview​

In previous network versions, the hint parameter was used to filter permissionless reserves. With Katalyst, we utilise this parameter for routing trades to specific reserves.

There are 4 optional routing rules:

1. BestOfAll - This is the default routing rule when no hint is provided, and is the classic reserve matching algorithm used by the Kyber smart contracts since the beginning.

2. MaskIn (Whitelist) - Specify a list of reserves to be included and perform the BestOfAll routing on them

3. MaskOut (Blacklist) - Specify a list of reserves to be excluded and perform the BestOfAll routing on the remaining reserves

4. Split - Specify a list of reserves and their respective percentages of the total srcQty that will be routed to each reserve.

For token -> token trades, you can specify a routing rule for each half. For example, a MaskIn route can be used for the token -> ether side, while a Split route can be used for the ether -> token side.

Recommendation​

We strongly recommend for the building of hints to be performed off-chain to save gas costs, and we have not discovered a use case for it to be done on-chain yet. You can do so using ethers or the /hint RESTful API. Nevertheless, this guide explains how you may do the building of hints on-chain.

File Import​

We will use Solidity compiler version 0.6.6 for deploying our sample contract. The following interfaces are imported for these functionalities:

• IKyberStorage.sol: Fetching reserve IDs. For more information about reserve IDs, refer to this section.
• IKyberHint.sol: Building and parsing of hints
• IERC20.sol: The IERC20 input parameter of building / parsing hints

pragma solidity 0.6.6;

import "./IKyberHint.sol";
import "./IKyberStorage.sol";

Contract Variable Declarations​

The kyberStorage and kyberHintHandler contracts can be instantiated as such:

IKyberHint kyberHintHandler;
IKyberStorage kyberStorage;

Fetching Reserve IDs​

For the token -> ether side of the trade, call getReserveIdsPerTokenSrc of the kyberStorage contract. For the ether -> token side of the trade, call getReserveIdsPerTokenDest of the kyberStorage contract.

Examples​

Get reserve IDs for WBTC -> ETH

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

bytes32[] memory reserveIds = kyberStorage.getReserveIdsPerTokenSrc(WBTC_ADDRESS);

Get reserve IDs for ETH -> KNC

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

bytes32[] memory reserveIds = kyberStorage.getReserveIdsPerTokenDest(KNC_ADDRESS);

Building Hints​

• For token -> ether trades, call the buildTokenToEthHint function

• For ether -> token trades, call the buildTokenToEthHint function

• For token -> token trades, call the buildTokenToTokenHint function

Their input parameters are explained below:

Parameter	Type	Description
tokenSrc	IERC20	source ERC20 token contract address
tokenToEthType	TradeType	BestOfAll, MaskIn, MaskOut or Split
tokenToEthReserveIds	bytes32[]	list of reserve IDs for token -> ether trade
tokenToEthSplits	uint256[]	percentages (in basis points) for Split trade
tokenDest	IERC20	source ERC20 token contract address
ethToTokenType	TradeType	BestOfAll, MaskIn, MaskOut or Split
ethToTokenReserveIds	bytes32[]	list of reserve IDs for token -> ether trade
ethToTokenSplits	uint256[]	percentages (in basis points) for Split trade

Notes​

• The correct builder hint function must be used for the correct trade type. Otherwise, the hint will not be built correctly, and will result in transaction failure.

• For token -> token trades, a combination of TradeTypes are allowed. For example, the token -> eth trade can be BestOfAll, while the eth -> token trade can be Split.

MaskIn TradeType​

Note that the splits parameter must be empty.

Example​

Select the first reserve for a WBTC -> ETH trade.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

bytes32[] memory reserveIds = kyberStorage.getReserveIdsPerTokenSrc(WBTC_ADDRESS);
bytes32[] memory includedReserveIds = new bytes32[](1);
includedReserveIds[0] = reserveIds[0];
uint256[] memory emptySplits;

bytes memory hint = kyberHintHandler.buildTokenToEthHint(
    WBTC_ADDRESS,
    IKyberHint.TradeType.MaskIn,
    includedReserveIds,
    emptySplits
);

MaskOut TradeType​

Note that the splits parameter must be empty.

Example​

Exclude the first reserve from a WBTC -> ETH trade.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

bytes32[] memory reserveIds = kyberStorage.getReserveIdsPerTokenSrc(WBTC_ADDRESS);
bytes32[] memory excludedReserveIds = new bytes32[](1);
excludedReserveIds[0] = reserveIds[0];
uint256[] memory emptySplits;

bytes memory hint = kyberHintHandler.buildTokenToEthHint(
    WBTC_ADDRESS,
    IKyberHint.TradeType.MaskIn,
    excludedReserveIds,
    emptySplits
);

Split TradeType​

Note that the splits values must add up to 10000 (100%).

Example​

Split evenly among 2 reserves for a ETH -> KNC trade.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

bytes32[] memory reserveIds = kyberStorage.getReserveIdsPerTokenDest(KNC_ADDRESS);
bytes32[] memory splitReserveIds = new bytes32[](2);
splitReserveIds[0] = reserveIds[0];
splitReserveIds[1] = reserveIds[1];
uint256[] memory splits = new uint256[](2);
splits[0] = 5000;
splits[1] = 5000;

bytes memory hint = kyberHintHandler.buildEthToTokenHint(
    KNC_ADDRESS,
    IKyberHint.TradeType.Split,
    splitReserveIds,
    splits
);

BestOfAll TradeType​

• The BestOfAll TradeType is primarily for specifying the BestOfAll behaviour for one side of token -> token trades. It is not needed for token -> ether and ether -> token trades.

• The reserveIds and splits parameters must be empty.

Example​

For a WBTC -> KNC trade, do a MaskIn route for WBTC -> ETH, and BestOfAll route for ETH -> KNC.

// DISCLAIMER: Code snippets in this guide are just examples and you
// should always do your own testing. If you have questions, visit our
// https://t.me/KyberDeveloper.

bytes32[] memory reserveIds = kyberStorage.getReserveIdsPerTokenSrc(WBTC_ADDRESS);
bytes32[] memory includedReserveIds = new bytes32[](1);
includedReserveIds[0] = reserveIds[0];
bytes32[] memory emptyReserveIds;
uint256[] memory emptySplits;

bytes memory hint = kyberHintHandler.buildTokenToTokenHint(
    WBTC_ADDRESS,
    IKyberHint.TradeType.MaskIn,
    includedReserveIds,
    emptySplits,
    KNC_ADDRESS,
    IKyberHint.TradeType.BestOfAll,
    emptyReserveIds,
    emptySplits
);