Reentrancy Guard

Contract component that helps prevent reentrant calls to a function.

Dependency

metis_reentrancy_guard  = { git = "https://github.com/patractlabs/metis", default-features = false }

Storage

In most cases, developer not need to consider the storage of reentrancy guard.

const _NOT_ENTERED: u8 = 1;const _ENTERED: u8 = 2;
/// The Data of pausable component#[cfg_attr(feature = "std", derive(::ink_storage::traits::StorageLayout))]#[derive(Debug)]pub struct Data {    /// is contract current paused    status: Lazy<u8>,
    key: ink_primitives::Key,}

Note the key in module, in ink!, all storage will flush to storage after the end of message proccess, so if contract only modifies status, the reentrancy_guard will not work:

    /// set current status to entered    pub fn set_entered(&mut self) {        Lazy::set(&mut self.status, _ENTERED);        self.flush() // flush to storage    }
    /// set current status to not entered    pub fn set_not_entered(&mut self) {        Lazy::set(&mut self.status, _NOT_ENTERED);        self.flush() // flush to storage    }

Internal Function

There is some internal function for reentrancy_guard, the marco will check it automatically:

        #[ink(message)]        #[metis_lang::reentrancy_guard]        pub fn function_can_not_reentrancy(&mut self) {            self._check_nonreentrant();            self._set_entered();
            // logics
            self._set_not_entered();        }

the functions:

• _check_nonreentrant : check if the current status is _NOT_ENTERED

    fn _check_nonreentrant(&self) {        assert!(!self.get().is_entered(), "ReentrancyGuard: reentrant call");    }

• _set_entered : set current status to _ENTERED

    fn _set_entered(&mut self) {        self.get_mut().set_entered();    }

• _set_not_entered : set current status to _NOT_ENTERED

    fn _set_not_entered(&mut self) {        self.get_mut().set_not_entered();    }

Usage Example

To use reentrant_guard component, first is import the component:

    use metis_lang::{        import,        metis,    };        use metis_reentrancy_guard as reentrancy_guard;
    #[ink(storage)]    #[import(reentrancy_guard)]    pub struct Contracts {        reentrancy_guard: reentrancy_guard::Data,
        // others    }

To use reentrancy guard, we can use a marco to check, it like the modifier in solidity:

        #[ink(message)]        #[metis_lang::reentrancy_guard]        pub fn function_can_not_reentrancy(&mut self) {            // logics        }