Swap Tokens for Tokens

Swap HTS fungible tokens for HTS fungible tokens.

Below are two methods available to swap tokens for tokens:

• Swap exact tokens for tokens

• Swap tokens for exact tokens

Contract ID: SaucerSwapV2SwapRouter

Consider the token's decimal places when determining input and output values.

Input and output amounts passed to the solidity function should all be in the token's smallest unit. For the SAUCE token, which has 6 decimal places, an input of 123.45 SAUCE should be entered as 123450000 (123.45 multiplied by 10^6).

Granting an spender allowance to the router contract is required when the input token is not native HBAR for security reasons enforced at the native code layer. Ensure that the allowance amount is in token's smallest unit.

Ensure that the "to" account has the output token id associated prior to executing the swap. Failure to do so will result in a TOKEN_NOT_ASSOCIATED_TO_ACCOUNT error.

---

Swap Exact Tokens for Tokens

Swap an exact amount of tokens for a minimum token amount.

Solidity function name: exactInput

Struct Parameter Name	Description
bytes path	A bytes array representing a route path including fees data
address recipient	EVM address of the token recipient
uint256 deadline	Deadline in Unix seconds
uint256 amountIn	The exact input token amount in its smallest unit
uint256 amountOutMinimum	The minimum token amount to receive in its smallest unit

Solidity Interface & Function Body

//ISwapRouter.sol

struct ExactInputParams {
  bytes path;
  address recipient;
  uint256 deadline;
  uint256 amountIn;
  uint256 amountOutMinimum;
}

function exactInput(ExactInputParams calldata params) external payable returns (uint256 amountOut);

//SwapRouter.sol

/// @inheritdoc ISwapRouter
function exactInput(ExactInputParams memory params)
  external
  payable
  override
  checkDeadline(params.deadline)
  returns (uint256 amountOut)
{
  address payer = msg.sender; // msg.sender pays for the first hop

  while (true) {
    bool hasMultiplePools = params.path.hasMultiplePools();

    // the outputs of prior swaps become the inputs to subsequent ones
    params.amountIn = exactInputInternal(
      params.amountIn,
      hasMultiplePools ? address(this) : params.recipient, // for intermediate swaps, this contract custodies
      0,
      SwapCallbackData({
        path: params.path.getFirstPool(), // only the first pool in the path is necessary
        payer: payer
      })
    );

    // decide whether to continue or terminate
    if (hasMultiplePools) {
      payer = address(this); // at this point, the caller has paid
      params.path = params.path.skipToken();
    } else {
      amountOut = params.amountIn;
      break;
    }
  }

  require(amountOut >= params.amountOutMinimum, 'Too little received');
}

Set the minimum output token amount (amountOutMinimum) with caution.

A high minimum might lead to a swap failure due to insufficient liquidity or rapid price movements. Conversely, setting the minimum too low can expose you to significant slippage, potentially resulting in a financial loss as you might receive far fewer tokens than expected.

The data passed to the 'path' parameter follows this format: [token, fee, token, fee, token, ...], with each 'token' in the route being 20 bytes long and each 'fee' being 3 bytes long. Example, 0x0001F4 (500) for a 0.05% fee.

Code Overview

Typescript

Resources:

• Ethers.js docs (v6)

• Hedera JavaScript SDK

• Token approve allowance

• Associate tokens to an account

Note: The Hedera Typescript SDK currently does not support passing complex contract function parameters. Instead, use Ethers.js or Web3.js to obtain the encoded function data and pass that data as a function parameter.

import * as ethers from 'ethers'; //V6
import { 
  ContractExecuteTransaction, 
  AccountAllowanceApproveTransaction.
  TokenAssociateTransaction,
  .. 
} from '@hashgraph/sdk';

//Client pre-checks:
// - Output token is associated
// - Router contract has spender allowance for the input token

//load ABI data containing SwapRouter functions
const abiInterfaces = new ethers.Interface(abi); 

//ExactInputParams
const params = {
  path: routeDataWithFee, //'0x...'
  recipient: recipientAddress, //'0x...' - user's recipient address
  deadline: deadline, //Unix seconds
  amountIn: inputAmount, //in token's smallest unit
  amountOutMinimum: outputAmountMin //in token's smallest unit
};

//get encoded hexdecimal string data ('0x...')
const encodedData = abiInterfaces.encodeFunctionData('exactInput', [params]);

//get encoded data as Uint8Array
const encodedDataAsUint8Array = hexToUint8Array(encodedData);

const response = await new ContractExecuteTransaction()
 .setContractId(swapRouterContractId)
 .setGas(gasLim)
 .setFunctionParameters(encodedDataAsUint8Array)
 .execute(client);
 
const record = await response.getRecord(client);
const result = record.contractFunctionResult!;
const values = result.getResult(['uint256']);
const amountOut = values[0]; //uint256 amountOut - in token's smallest unit

---

Swap Tokens for Exact Tokens

Swap a maximum amount of tokens to receive an exact tokens amount

Solidity function name: exactOutput

Schema parameter name	Description
bytes path	A bytes array representing a route path including fees data
address recipient	EVM address for the token recipient
uint256 deadline	Deadline in Unix seconds
uint256 amountOut	The exact output amount to receive in its smallest unit
uint256 amountInMaximum	The maximum allowed input amount in its smallest unit

Solidity Interface & Function Body

//ISwapRouter.sol

struct ExactOutputParams {
  bytes path;
  address recipient;
  uint256 deadline;
  uint256 amountOut;
  uint256 amountInMaximum;
}

/// @notice Swaps as little as possible of one token for `amountOut` of another along the specified path (reversed)
/// @param params The parameters necessary for the multi-hop swap, encoded as `ExactOutputParams` in calldata
/// @return amountIn The amount of the input token
function exactOutput(ExactOutputParams calldata params) external payable returns (uint256 amountIn);

//SwapRouter.sol

/// @inheritdoc ISwapRouter
function exactOutput(ExactOutputParams calldata params)
  external
  payable
  override
  checkDeadline(params.deadline)
  returns (uint256 amountIn)
{
  // it's okay that the payer is fixed to msg.sender here, as they're only paying for the "final" exact output
  // swap, which happens first, and subsequent swaps are paid for within nested callback frames
  exactOutputInternal(
    params.amountOut,
    params.recipient,
    0,
    SwapCallbackData({path: params.path, payer: msg.sender})
  );

  amountIn = amountInCached;
  require(amountIn <= params.amountInMaximum, 'Too much requested');
  amountInCached = DEFAULT_AMOUNT_IN_CACHED;
}

Set the maximum input token amount (amountInMaximum) with caution.

A low maximum might lead to a swap failure if the required liquidity surpasses this limit or due to rapid price movements. Conversely, setting it too high can expose you to significant slippage, potentially leading to a financial loss as you might spend far more tokens than expected.

The data passed to the 'path' parameter follows this format: [token, fee, token, fee, token, ...], but reversed (i.e. the first token in the array should be output token), with each 'token' in the route being 20 bytes long and each 'fee' being 3 bytes long. Example, 0x000BB8 (3000) for a 0.30% fee.

Code Overview

Typescript SDK

Resources:

• Ethers.js docs (v6)

• Hedera JavaScript SDK

• Token approve allowance

• Associate tokens to an account

Note: The Hedera Typescript SDK currently does not support passing complex contract function parameters. Instead, use Ethers.js or Web3.js to obtain the encoded function data and pass that data as a function parameter.

import * as ethers from 'ethers'; //V6
import {
  ContractExecuteTransaction, 
  AccountAllowanceApproveTransaction.
  TokenAssociateTransaction,
  .. 
} from '@hashgraph/sdk';

//Client pre-checks:
// - Output token is associated
// - Router contract has spender allowance for the input token

//load ABI data containing SwapRouter functions
const abiInterfaces = new ethers.Interface(abi); 

//ExactOutputParams
const params = {
  path: routeDataWithFee, //'0x...' (reversed route path)
  recipient: recipientAddress, //'0x...' - user's recipient address
  deadline: deadline, //Unix seconds
  amountOut: outputAmount, //in token's smallest unit
  amountInMaximum: inputAmountMax //in token's smallest unit
};

//get encoded hexdecimal string data ('0x...')
const encodedData = abiInterfaces.encodeFunctionData('exactOutput', [params]);

//get encoded data as Uint8Array
const encodedDataAsUint8Array = hexToUint8Array(encodedData);

const response = await new ContractExecuteTransaction()
 .setContractId(swapRouterContractId)
 .setGas(gasLim)
 .setFunctionParameters(encodedDataAsUint8Array)
 .execute(client);
 
const record = await response.getRecord(client);
const result = record.contractFunctionResult!;
const values = result.getResult(['uint256']);
const amountIn = values[0]; //uint256 amountIn - in token's smallest unit