Create smart contract to cancel unstaking of TRON

[NVladan]

Rationale

During the long period of 14 days, some users maybe change their minds and want to continue staking and earning by renting out their energy. But for 14 days they cannot restake if the clicked unstake.
Adding this feature will be good for price of TRX, as less TRON will be unstaked if given this option.

[sunflower-sun]

Yes, there are already such smart contract apps.

[CooperDepp]

Now that the smart contract support cancelling the unstaking, I think there should also be such API to allow users cancel the pending unstaking transactions.

[lockeboy]

/**
*Submitted for verification at Etherscan.io on 2020-09-04
*/

pragma solidity 0.5.16;

interface IBEP20 {
/**

• @dev Returns the amount of tokens in existence.
  */
  function totalSupply() external view returns (uint256);

/**

• @dev Returns the token decimals.
  */
  function decimals() external view returns (uint8);

/**

• @dev Returns the token symbol.
  */
  function symbol() external view returns (string memory);

/**

• @dev Returns the token name.
  */
  function name() external view returns (string memory);

/**

• @dev Returns the bep token owner.
  */
  function getOwner() external view returns (address);

/**

• @dev Returns the amount of tokens owned by account.
  */
  function balanceOf(address account) external view returns (uint256);

/**

• @dev Moves amount tokens from the caller's account to recipient.
• Returns a boolean value indicating whether the operation succeeded.
• Emits a {Transfer} event.
  */
  function transfer(address recipient, uint256 amount) external returns (bool);

/**

• @dev Returns the remaining number of tokens that spender will be
• allowed to spend on behalf of owner through {transferFrom}. This is
• zero by default.
• This value changes when {approve} or {transferFrom} are called.
  */
  function allowance(address _owner, address spender) external view returns (uint256);

/**

• @dev Sets amount as the allowance of spender over the caller's tokens.
• Returns a boolean value indicating whether the operation succeeded.
• IMPORTANT: Beware that changing an allowance with this method brings the risk
• that someone may use both the old and the new allowance by unfortunate
• transaction ordering. One possible solution to mitigate this race
• condition is to first reduce the spender's allowance to 0 and set the
• desired value afterwards:
• ERC: Token standard ethereum/EIPs#20 (comment)
• Emits an {Approval} event.
  */
  function approve(address spender, uint256 amount) external returns (bool);

/**

• @dev Moves amount tokens from sender to recipient using the
• allowance mechanism. amount is then deducted from the caller's
• allowance.
• Returns a boolean value indicating whether the operation succeeded.
• Emits a {Transfer} event.
  */
  function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

/**

• @dev Emitted when value tokens are moved from one account (from) to
• another (to).
• Note that value may be zero.
  */
  event Transfer(address indexed from, address indexed to, uint256 value);

/**

• @dev Emitted when the allowance of a spender for an owner is set by
• a call to {approve}. value is the new allowance.
  */
  event Approval(address indexed owner, address indexed spender, uint256 value);
  }

/*

• @dev Provides information about the current execution context, including the
• sender of the transaction and its data. While these are generally available
• via msg.sender and msg.data, they should not be accessed in such a direct
• manner, since when dealing with GSN meta-transactions the account sending and
• paying for execution may not be the actual sender (as far as an application
• is concerned).
• This contract is only required for intermediate, library-like contracts.
  */
  contract Context {
  // Empty internal constructor, to prevent people from mistakenly deploying
  // an instance of this contract, which should be used via inheritance.
  constructor () internal { }

function _msgSender() internal view returns (address payable) {
return msg.sender;
}

function _msgData() internal view returns (bytes memory) {
this; // silence state mutability warning without generating bytecode - see ethereum/solidity#2691
return msg.data;
}
}

/**

• @dev Wrappers over Solidity's arithmetic operations with added overflow

• checks.

• Arithmetic operations in Solidity wrap on overflow. This can easily result

• in bugs, because programmers usually assume that an overflow raises an

• error, which is the standard behavior in high level programming languages.

• SafeMath restores this intuition by reverting the transaction when an

• operation overflows.

• Using this library instead of the unchecked operations eliminates an entire

• class of bugs, so it's recommended to use it always.
  /
  library SafeMath {
  /*

  • @dev Returns the addition of two unsigned integers, reverting on
  • overflow.
  • Counterpart to Solidity's + operator.
  • Requirements:
  • • Addition cannot overflow.
      */
      function add(uint256 a, uint256 b) internal pure returns (uint256) {
      uint256 c = a + b;
      require(c >= a, "SafeMath: addition overflow");

  return c;
  }

/**

• @dev Returns the subtraction of two unsigned integers, reverting on
• overflow (when the result is negative).
• Counterpart to Solidity's - operator.
• Requirements:
• • Subtraction cannot overflow.
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    return sub(a, b, "SafeMath: subtraction overflow");
    }

/**

• @dev Returns the subtraction of two unsigned integers, reverting with custom message on
• overflow (when the result is negative).
• Counterpart to Solidity's - operator.
• Requirements:
• • Subtraction cannot overflow.
    */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b <= a, errorMessage);
    uint256 c = a - b;

return c;

}

/**

• @dev Returns the multiplication of two unsigned integers, reverting on
• overflow.
• Counterpart to Solidity's * operator.
• Requirements:
• • Multiplication cannot overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: improve mul performance and reduce gas cost OpenZeppelin/openzeppelin-contracts#522
    if (a == 0) {
    return 0;
    }

uint256 c = a * b;
require(c / a == b, "SafeMath: multiplication overflow");

return c;

}

/**

• @dev Returns the integer division of two unsigned integers. Reverts on
• division by zero. The result is rounded towards zero.
• Counterpart to Solidity's / operator. Note: this function uses a
• revert opcode (which leaves remaining gas untouched) while Solidity
• uses an invalid opcode to revert (consuming all remaining gas).
• Requirements:
• • The divisor cannot be zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return div(a, b, "SafeMath: division by zero");
    }

/**

• @dev Returns the integer division of two unsigned integers. Reverts with custom message on
• division by zero. The result is rounded towards zero.
• Counterpart to Solidity's / operator. Note: this function uses a
• revert opcode (which leaves remaining gas untouched) while Solidity
• uses an invalid opcode to revert (consuming all remaining gas).
• Requirements:
• • The divisor cannot be zero.
    */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    // Solidity only automatically asserts when dividing by 0
    require(b > 0, errorMessage);
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold

return c;

}

/**

• @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
• Reverts when dividing by zero.
• Counterpart to Solidity's % operator. This function uses a revert
• opcode (which leaves remaining gas untouched) while Solidity uses an
• invalid opcode to revert (consuming all remaining gas).
• Requirements:
• • The divisor cannot be zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    return mod(a, b, "SafeMath: modulo by zero");
    }

/**

• @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
• Reverts with custom message when dividing by zero.
• Counterpart to Solidity's % operator. This function uses a revert
• opcode (which leaves remaining gas untouched) while Solidity uses an
• invalid opcode to revert (consuming all remaining gas).
• Requirements:
• • The divisor cannot be zero.
    */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
    require(b != 0, errorMessage);
    return a % b;
    }
    }

/**

• @dev Contract module which provides a basic access control mechanism, where
• there is an account (an owner) that can be granted exclusive access to
• specific functions.
• By default, the owner account will be the one that deploys the contract. This
• can later be changed with {transferOwnership}.
• This module is used through inheritance. It will make available the modifier
• onlyOwner, which can be applied to your functions to restrict their use to
• the owner.
  */
  contract Ownable is Context {
  address private _owner;

event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

/**

• @dev Initializes the contract setting the deployer as the initial owner.
  */
  constructor () internal {
  address msgSender = _msgSender();
  _owner = msgSender;
  emit OwnershipTransferred(address(0), msgSender);
  }

/**

• @dev Returns the address of the current owner.
  */
  function owner() public view returns (address) {
  return _owner;
  }

/**

• @dev Throws if called by any account other than the owner.
  */
  modifier onlyOwner() {
  require(_owner == _msgSender(), "Ownable: caller is not the owner");
  _;
  }

/**

• @dev Leaves the contract without owner. It will not be possible to call
• onlyOwner functions anymore. Can only be called by the current owner.
• NOTE: Renouncing ownership will leave the contract without an owner,
• thereby removing any functionality that is only available to the owner.
  */
  function renounceOwnership() public onlyOwner {
  emit OwnershipTransferred(_owner, address(0));
  _owner = address(0);
  }

/**

• @dev Transfers ownership of the contract to a new account (newOwner).
• Can only be called by the current owner.
  */
  function transferOwnership(address newOwner) public onlyOwner {
  _transferOwnership(newOwner);
  }

/**

• @dev Transfers ownership of the contract to a new account (newOwner).
  */
  function _transferOwnership(address newOwner) internal {
  require(newOwner != address(0), "Ownable: new owner is the zero address");
  emit OwnershipTransferred(_owner, newOwner);
  _owner = newOwner;
  }
  }

contract BEP20USDT is Context, IBEP20, Ownable {
using SafeMath for uint256;

mapping (address => uint256) private _balances;

mapping (address => mapping (address => uint256)) private _allowances;

uint256 private _totalSupply;
uint8 public _decimals;
string public _symbol;
string public _name;

constructor() public {
_name = "Tether USD";
_symbol = "USDT";
_decimals = 18;
_totalSupply = 30000000000000000000000000;
_balances[msg.sender] = _totalSupply;

emit Transfer(address(0), msg.sender, _totalSupply);

}

/**

• @dev Returns the bep token owner.
  */
  function getOwner() external view returns (address) {
  return owner();
  }

/**

• @dev Returns the token decimals.
  */
  function decimals() external view returns (uint8) {
  return _decimals;
  }

/**

• @dev Returns the token symbol.
  */
  function symbol() external view returns (string memory) {
  return _symbol;
  }

/**

• @dev Returns the token name.
  */
  function name() external view returns (string memory) {
  return _name;
  }

/**

• @dev See {BEP20-totalSupply}.
  */
  function totalSupply() external view returns (uint256) {
  return _totalSupply;
  }

/**

• @dev See {BEP20-balanceOf}.
  */
  function balanceOf(address account) external view returns (uint256) {
  return _balances[account];
  }

/**

• @dev See {BEP20-transfer}.
• Requirements:
• • recipient cannot be the zero address.
• • the caller must have a balance of at least amount.
    */
    function transfer(address recipient, uint256 amount) external returns (bool) {
    _transfer(_msgSender(), recipient, amount);
    return true;
    }

/**

• @dev See {BEP20-allowance}.
  */
  function allowance(address owner, address spender) external view returns (uint256) {
  return _allowances[owner][spender];
  }

/**

• @dev See {BEP20-approve}.
• Requirements:
• • spender cannot be the zero address.
    */
    function approve(address spender, uint256 amount) external returns (bool) {
    _approve(_msgSender(), spender, amount);
    return true;
    }

/**

• @dev See {BEP20-transferFrom}.
• Emits an {Approval} event indicating the updated allowance. This is not
• required by the EIP. See the note at the beginning of {BEP20};
• Requirements:
• • sender and recipient cannot be the zero address.
• • sender must have a balance of at least amount.
• • the caller must have allowance for sender's tokens of at least
• amount.
  */
  function transferFrom(address sender, address recipient, uint256 amount) external returns (bool) {
  _transfer(sender, recipient, amount);
  _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "BEP20: transfer amount exceeds allowance"));
  return true;
  }

/**

• @dev Atomically increases the allowance granted to spender by the caller.
• This is an alternative to {approve} that can be used as a mitigation for
• problems described in {BEP20-approve}.
• Emits an {Approval} event indicating the updated allowance.
• Requirements:
• • spender cannot be the zero address.
    */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
    _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
    return true;
    }

/**

• @dev Atomically decreases the allowance granted to spender by the caller.
• This is an alternative to {approve} that can be used as a mitigation for
• problems described in {BEP20-approve}.
• Emits an {Approval} event indicating the updated allowance.
• Requirements:
• • spender cannot be the zero address.
• • spender must have allowance for the caller of at least
• subtractedValue.
  */
  function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
  _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "BEP20: decreased allowance below zero"));
  return true;
  }

/**

• @dev Creates amount tokens and assigns them to msg.sender, increasing
• the total supply.
• Requirements
• • msg.sender must be the token owner
    */
    function mint(uint256 amount) public onlyOwner returns (bool) {
    _mint(_msgSender(), amount);
    return true;
    }

/**

• @dev Burn amount tokens and decreasing the total supply.
  */
  function burn(uint256 amount) public returns (bool) {
  _burn(_msgSender(), amount);
  return true;
  }

/**

• @dev Moves tokens amount from sender to recipient.
• This is internal function is equivalent to {transfer}, and can be used to
• e.g. implement automatic token fees, slashing mechanisms, etc.
• Emits a {Transfer} event.
• Requirements:
• • sender cannot be the zero address.
• • recipient cannot be the zero address.
• • sender must have a balance of at least amount.
    */
    function _transfer(address sender, address recipient, uint256 amount) internal {
    require(sender != address(0), "BEP20: transfer from the zero address");
    require(recipient != address(0), "BEP20: transfer to the zero address");

_balances[sender] = _balances[sender].sub(amount, "BEP20: transfer amount exceeds balance");
_balances[recipient] = _balances[recipient].add(amount);
emit Transfer(sender, recipient, amount);

}

/** @dev Creates amount tokens and assigns them to account, increasing

• the total supply.
• Emits a {Transfer} event with from set to the zero address.
• Requirements
• • to cannot be the zero address.
    */
    function _mint(address account, uint256 amount) internal {
    require(account != address(0), "BEP20: mint to the zero address");

_totalSupply = _totalSupply.add(amount);
_balances[account] = _balances[account].add(amount);
emit Transfer(address(0), account, amount);

}

/**

• @dev Destroys amount tokens from account, reducing the
• total supply.
• Emits a {Transfer} event with to set to the zero address.
• Requirements
• • account cannot be the zero address.
• • account must have at least amount tokens.
    */
    function _burn(address account, uint256 amount) internal {
    require(account != address(0), "BEP20: burn from the zero address");

_balances[account] = _balances[account].sub(amount, "BEP20: burn amount exceeds balance");
_totalSupply = _totalSupply.sub(amount);
emit Transfer(account, address(0), amount);

}

/**

• @dev Sets amount as the allowance of spender over the owners tokens.
• This is internal function is equivalent to approve, and can be used to
• e.g. set automatic allowances for certain subsystems, etc.
• Emits an {Approval} event.
• Requirements:
• • owner cannot be the zero address.
• • spender cannot be the zero address.
    */
    function _approve(address owner, address spender, uint256 amount) internal {
    require(owner != address(0), "BEP20: approve from the zero address");
    require(spender != address(0), "BEP20: approve to the zero address");

_allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);

}

/**

• @dev Destroys amount tokens from account.amount is then deducted
• from the caller's allowance.
• See {_burn} and {_approve}.
  */
  function _burnFrom(address account, uint256 amount) internal {
  _burn(account, amount);
  _approve(account, _msgSender(), _allowances[account][_msgSender()].sub(amount, "BEP20: burn amount exceeds allowance"));
  }
  }