The Deactivation Pattern applies when a smart contract should be removed from an Ethereum-based distributed ledger.
Applies to: [] EOSIO [X] Ethereum [] Hyperledger Fabric
In Ethereum, smart contracts can be removed from the distributed ledger by calling the selfdestruct(...) operation. Calling selfdestruct(...) initiates the transfer of assets kept by that contract to be sent to a predefined target, and both storage and code are removed from the distributed ledger. When assets are transferred to the destroyed smart contract, the assets will be lost. The aim of the Deactivation Pattern is to mitigate risks associated with the removal or deactivation of smart contracts.
The forces involved in the Deactivation Pattern are regulated executability and semantic soundness. Executability of the smart contract is regulated as all executions of the respective smart contract are prevented. Also, semantic soundness is improved as the possible loss of assets associated with the removal of smart contracts from the distributed ledger are prevented.
Instead of using the selfdestruct(...) operation developers should disable the smart contract by changing the internal state in a way that causes all functions to revert.
pragma solidity 0.7.0;
contract DeactivationAntipattern {
address payable owner;
modifier onlyOwner(){
require (owner == msg.sender, ”Not authorized”);
_;
}
// ...
function close() public onlyOwner {
selfdestruct(owner);
}
}pragma solidity 0.7.0;
contract DeactivationPattern {
address payable owner;
bool activated = true;
modifier checkActive(){
require (activated);
_;
}
modifier onlyOwner(){
require (owner == msg.sender, ”Not authorized”);
_;
}
// ...
function anyFunction() checkActive public {
// Code will not be executed after deactivation
}
function setActive(bool _active) onlyOwner public {
activated = _active
}
}The application of the Deactivation Pattern ensures that the smart contract cannot be used while mitigating the risk associated with using the selfdesctruct(...) operation to remove the smart contract.
Keeping outdated smart contracts executable on the distributed ledger may result in unintended calls of the respective smart contract. The Deactivation Pattern offers a way to regulate the executability so that it is impossible to use the smart contract because assets are immediately returned.
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