Unwrap WHBAR for HBAR

🚨 Important Security Notice

DO NOT interact with the WHBAR contract directly.
DO NOT grant allowances to the WHBAR contract.
You MUST use the WhbarHelper contract instead.

WHBAR is not intended for direct use in other applications. Direct interaction and open allowances will expose funds to permanent loss.

Contract ID: WhbarHelper

Granting a spender allowance to the WhbarHelper contract is required for the contract to transfer the WHBAR token from the user’s wallet to the contract.

Function name: unwrapWhbar

Parameter Name	Description
uint256 wad	WHBAR token amount in its smallest unit

/// @notice Safely unwrap whbar to msg.sender
/// @dev This contract needs an allowance from msg.sender to transfer the whbar token
/// @param wad The amount to unwrap
function unwrapWhbar(uint wad) public {
  require(wad > 0, "WhbarHelper: wad cannot be lt zero");
  // transfer the whbar to this contract
  HederaTokenHelper.safeTransferFrom(whbarToken, msg.sender, address(this), wad);

  // approve sending the whbar to the whbar contract
  HederaTokenHelper.safeApprove(whbarToken, whbarContract, wad);

  // use withdraw(address src, address dst, uint wad) and use this contract and msg.sender to withdraw
  // to the contract caller
  IWHBAR(whbarContract).withdraw(address(this), msg.sender, wad);
}

Code overview

Recommended gas limit: 1,000,000

JavaScript SDK

Resources:

import {
  ContractFunctionParameters,
  ContractExecuteTransaction,
  TokenAssociateTransaction,
  Hbar,
  HbarUnit
} from '@hashgraph/sdk';

//Client pre-checks:
// - WhbarHelper contract has spender allowance for WHBAR token

const params = new ContractFunctionParameters();
params.addUint256(withdrawAmount); //amount in token's smallest unit

await new ContractExecuteTransaction()
  .setContractId(whbarHelperContractId)
  .setGas(gasLim)
  .setFunction('unwrapWhbar', params)
  .execute(client);

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