Security

This document is better viewed at https://docs.openzeppelin.com/contracts/api/security

These contracts aim to cover common security practices.

  • ReentrancyGuard: A modifier that can prevent reentrancy during certain functions.

  • Pausable: A common emergency response mechanism that can pause functionality while a remediation is pending.

For an overview on reentrancy and the possible mechanisms to prevent it, read our article Reentrancy After Istanbul.

Contracts

ReentrancyGuard 

import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

Contract module that helps prevent reentrant calls to a function.

Inheriting from ReentrancyGuard will make the nonReentrant modifier available, which can be applied to functions to make sure there are no nested (reentrant) calls to them.

Note that because there is a single nonReentrant guard, functions marked as nonReentrant may not call one another. This can be worked around by making those functions private, and then adding external nonReentrant entry points to them.

If you would like to learn more about reentrancy and alternative ways to protect against it, check out our blog post Reentrancy After Istanbul.
Modifiers
Functions

nonReentrant() modifier

Prevents a contract from calling itself, directly or indirectly. Calling a nonReentrant function from another nonReentrant function is not supported. It is possible to prevent this from happening by making the nonReentrant function external, and making it call a private function that does the actual work.

constructor() internal

_reentrancyGuardEntered() → bool internal

Returns true if the reentrancy guard is currently set to "entered", which indicates there is a nonReentrant function in the call stack.

Pausable 

import "@openzeppelin/contracts/security/Pausable.sol";

Contract module which allows children to implement an emergency stop mechanism that can be triggered by an authorized account.

This module is used through inheritance. It will make available the modifiers whenNotPaused and whenPaused, which can be applied to the functions of your contract. Note that they will not be pausable by simply including this module, only once the modifiers are put in place.

Modifiers
Functions
Events

whenNotPaused() modifier

Modifier to make a function callable only when the contract is not paused.

Requirements:

  • The contract must not be paused.

whenPaused() modifier

Modifier to make a function callable only when the contract is paused.

Requirements:

  • The contract must be paused.

constructor() internal

Initializes the contract in unpaused state.

paused() → bool public

Returns true if the contract is paused, and false otherwise.

_requireNotPaused() internal

Throws if the contract is paused.

_requirePaused() internal

Throws if the contract is not paused.

_pause() internal

Triggers stopped state.

Requirements:

  • The contract must not be paused.

_unpause() internal

Returns to normal state.

Requirements:

  • The contract must be paused.

Paused(address account) event

Emitted when the pause is triggered by account.

Unpaused(address account) event

Emitted when the pause is lifted by account.

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