Is there anyway to burn/get tokens back from a contract address?

Question

I have a case here. Created a contract and sent some tokens to it. As of now, the contract is of not usable. The contract had destroy function as below.

  function destroy() onlyOwner {
    // Transfer tokens back to owner
    uint256 balance = token.balanceOf(this);
    assert(balance > 0);
    token.transfer(owner, balance);
  }

But, when the token contract was created, the transfer function was coded as below.

/**
* Internal transfer, only can be called by this contract
*/
function _transfer(address _from, address _to, uint _value) internal {
    // Prevent transfer to 0x0 address. Use burn() instead
    require(_to != 0x0);
    // Check if the sender has enough
    require(balanceOf[_from] >= _value);
    // Check for overflows
    require(balanceOf[_to] + _value > balanceOf[_to]);
    // Save this for an assertion in the future
    uint previousBalances = balanceOf[_from] + balanceOf[_to];
    // Subtract from the sender
    balanceOf[_from] -= _value;
    // Add the same to the recipient
    balanceOf[_to] += _value;
    Transfer(_from, _to, _value);
    // Asserts are used to use static analysis to find bugs in your code. They should never fail
    assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
}

The line require(balanceOf[_to] + _value > balanceOf[_to]); is not allowing to destory as the require always fails during send all the available tokens.

Had created another contract just test the drain function with a different name as below which worked properly. And the contract in consideration was not coded like this (that has the destroy function as above)

  /**
   * @notice Terminate contract and refund to owner
   */
  function withdraw() onlyOwner external {
    address myAddress = this;
    if(myAddress.balance > 0)
        owner.transfer(myAddress.balance);
    uint256 tokBalance = token.balanceOf(this);
    tokBalance = tokBalance - (1 wei);
    if(tokBalance > 0)
        token.transfer(owner, tokBalance);
  }

Is there a way to burn/get back tokens from that contract? Though we can freeze the account, that doesn't help as we want to burn the tokens. Second contract (from where to withdraw or burn token) is here and 0x1798F533e0cE9501dac8a831A0b02A4f35304FFd is the address of it

Answer 1

From your link the issue is that you override _transfer in RETNToken

function _transfer(address _from, address _to, uint _value) internal {
    require (_to != 0x0);                               // Prevent transfer to 0x0 address. Use burn() instead

--->require (balanceOf[_from] > _value);                // Check if the sender has enough

    require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
    require(!frozenAccount[_from]);                     // Check if sender is frozen
    require(!frozenAccount[_to]);                       // Check if recipient is frozen
    balanceOf[_from] -= _value;                         // Subtract from the sender
    balanceOf[_to] += _value;                           // Add the same to the recipient
    Transfer(_from, _to, _value);
}

The solution is to replace that line by the correct one

require (balanceOf[_from] >= _value);