Solidity – How to Destroy a Smart Contract and Collect Its Funds?

contract-designcontract-developmentremixselfdestructsolidity

I'm quite new at smart contracts/Solidity, which I'm learning for a postgraduate course.

In one of the assignments, we have to implement a short example of dutch auction (wiki link). Now my question is that in one of methods, specifically finalize(), the owner of contract must destroy it and collect its funds. And here is my code:

    function finalize() public creatorOnly biddingClosedOnly {
      selfdestruct(_creator);
      if(finalPrice > 0) {
        _creator.transfer(finalPrice);
      }
    }

The rest of contract's methods are running well in Remix but when I call finalize method, the smart contract is not destroyed and still exists so that anyone can call the other functions as before. What am I doing wrong ?

Best Answer

All you need to do is have the selfdestruct(address payable recipient) function. selfdestruct takes a single parameter that sends all ETH in the contract to that address. In your case, you can do:

function finalize() public creatorOnly biddingClosedOnly {
    selfdestruct(_creator);
}

From the docs:

selfdestruct(address payable recipient): destroy the current contract, sending its funds to the given address

The reason you can still call the function after the contract has been selfdestructed is because technically the address is still valid. However, no contract (data) lives there any more.

Because of this, you can still send ETH to the address and you can still send transactions with data to the address, but the EVM will not execute the function as it would with a non-selfdestructed address.

Edit: You can use the get_code RPC method to verify that the contract was, in fact, destroyed.

Using ethers.js, the following output will be given:

// Deploy contract

ethersProvider.getCode('0xDCcd6331401b62ebcE7F3a22e966b26ACe27559d').then(console.log)
> 0x608060405260043610603f576000357c0100000000000000000000000000000000000000000000000000000000900463ffffffff1680634bb278f3146044575b600080fd5b348015604f57600080fd5b5060566058565b005b3373ffffffffffffffffffffffffffffffffffffffff16ff00a165627a7a7230582077ca7684f4d93293e360c5c695d0e416f54dde89713426cc4d6fddb9f9963faa0029

// Self destruct contract

ethersProvider.getCode('0xDCcd6331401b62ebcE7F3a22e966b26ACe27559d').then(console.log)
> 0x

Related Solutions

Selfdestruct – How to Destroy a Contract Using Suicide Accounts in Solidity

To start my answer, I have to say that once you put something on the blockchain it is "immutable", and by that I mean that it can not be modified or deleted.

(there is a special type of "upgradable" contracts but this is not the answer for that)

You can find here a lot of information about self-destruction.

Why would you need to destroy others? For example, to make a contract not accessible, you can not delete it from the chain but you can disable it.

Can my smart contract destroy a contract owned by another person? This requires a long explanation and has multiple factors at play. But, in summary, no, you can't do it.

How is this destruction implemented? You can use selfdestruct/destroy (The old mean suicide/kill). You can find some information here and a good but old tutorial here - the latter explains how this implementation works. Also, here's yet another link with information on the topic.

Do we actually modify previous blocks' contents related to destructed accounts? or we just update the change in the tree structure? We never can modify other blocks, we can only put a new block in the blockchain with more information. Blocks are permanent and they contain the information of the transactions and the contracts. Maybe this can help you with the block concepts.

Contract Design – Can You Create and Destroy a Contract in a Single Transaction?

Yes, it's possible. The following code does just that if you were to call the create function on a deployed Creator:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Created {

    event AnEvent(uint256);

    function aFunction(uint256 value) public {
        emit AnEvent(value);
    }

    function kill() public {
        selfdestruct(payable(msg.sender));
    }
}

contract Creator {

    function create() public {

        Created tmp = new Created{salt: 0}();
        tmp.aFunction(1);
        tmp.kill();
    }
}

Second part of the question. If that is possible would the account submitting the transaction need to have the full gas amount to deploy the contract or would I only need to provide the deployment cost minus the refund from self-destruct?

The refunds are only processed after the transaction is executed, in go-ethereum : transaction execution followed by refund. So you must provide the whole cost upfront, but it will only cost you that amount minus the refund.

Refunds are no longer as interesting as they used to economically speaking (see EIP-3529), plus for anyone to profit on it there needs to be some variation (i.e., time delay) between the creation and selfdestruct, that is not the case if everything happens inside a single transaction.

I hope that answers your question.

Best Answer

Related Solutions

Selfdestruct – How to Destroy a Contract Using Suicide Accounts in Solidity

Contract Design – Can You Create and Destroy a Contract in a Single Transaction?

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