Swap Tokens for HBAR

Swap HTS fungible tokens for HBAR

Below are two methods available to swap tokens for HBAR:

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.

When providing HBAR in the path array, use the Wrapped HBAR token ID (WHBAR).

Swap Exact Tokens for HBAR

Swap an exact amount of tokens for a minimum HBAR 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 for a 0.05% fee.

Include unwrapWHBAR function in your call to convert the Wrapped HBAR (WHBAR) output token back into the native HBAR cryptocurrency following the swap.

For the ExactInputParams recipient, use the SwapRouter contract address. This is required for unwrapWHBAR to function correctly. The unwrapped HBAR will then be sent to the user's recipient address.

When the output token is not HBAR, use the user's address as the recipient instead.

Code Overview

Resources:

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 {..} from @hashgraph/sdk

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

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

//ExactInputParams
const params = {
  path: routeDataWithFee, //'0x...'
  recipient: swapRouterAddress, //'0x...' - use the SwapRouter id here for unwrapWHBAR to work
  deadline: deadline, //Unix seconds
  amountIn: inputAmount, //in token's smallest unit
  amountOutMinimum: outputTinybarMin //in Tinybar
};

//encode each function individually
const swapEncoded = abiInterfaces.encodeFunctionData('exactInput', [params]);

//Provide the user's address to receive the unwrapped HBAR
const unwrapEncoded = abiInterfaces.encodeFunctionData('unwrapWHBAR', [0, recipient]); 

//multi-call parameter: bytes[]
const multiCallParam = [swapEncoded, unwrapEncoded];

//get encoded data for the multicall involving both functions
const encodedData = abiInterfaces.encodeFunctionData('multicall', [multiCallParam]);  

//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 - Tinybar

Swap Tokens for Exact HBAR

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

Include unwrapWHBAR function in your call to convert the Wrapped HBAR output token back into the native HBAR cryptocurrency following the swap.

When the output token is not HBAR, use the user's address as the recipient instead.

Code Overview

Resources:

import * as ethers from 'ethers'; //V6
//import {..} from @hashgraph/sdk

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

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

//ExactOutputParams
const params = {
  path: routeDataWithFee, //'0x...' (reversed route path)
  recipient: swapRouterAddress, //'0x...' - use the SwapRouter id here for unwrapWHBAR to work
  deadline: deadline, //Unix seconds
  amountOut: outputTinybar, //in Tinybar
  amountInMaximum: inputAmountMax //in token's smallest unit
};

//encode each function individually
const swapEncoded = abiInterfaces.encodeFunctionData('exactOutput', [params]);

//Provide the user's address to receive the unwrapped HBAR
const unwrapEncoded = abiInterfaces.encodeFunctionData('unwrapWHBAR', [0, recipient]);

//multi-call parameter: bytes[]
const multiCallParam = [swapEncoded, unwrapEncoded];

//get encoded data for the multicall involving both functions
const encodedData = abiInterfaces.encodeFunctionData('multicall', [multiCallParam]);  

//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

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Last updated 11 months ago