63 lines
2.5 KiB
Solidity
63 lines
2.5 KiB
Solidity
// SPDX-License-Identifier: MIT
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pragma solidity ^0.6.0;
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/**
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* @dev Contract module that helps prevent reentrant calls to a function.
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*
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* Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
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* available, which can be applied to functions to make sure there are no nested
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* (reentrant) calls to them.
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*
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* Note that because there is a single `nonReentrant` guard, functions marked as
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* `nonReentrant` may not call one another. This can be worked around by making
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* those functions `private`, and then adding `external` `nonReentrant` entry
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* points to them.
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*
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* TIP: If you would like to learn more about reentrancy and alternative ways
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* to protect against it, check out our blog post
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* https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
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*/
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contract ReentrancyGuard {
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// Booleans are more expensive than uint256 or any type that takes up a full
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// word because each write operation emits an extra SLOAD to first read the
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// slot's contents, replace the bits taken up by the boolean, and then write
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// back. This is the compiler's defense against contract upgrades and
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// pointer aliasing, and it cannot be disabled.
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// The values being non-zero value makes deployment a bit more expensive,
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// but in exchange the refund on every call to nonReentrant will be lower in
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// amount. Since refunds are capped to a percentage of the total
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// transaction's gas, it is best to keep them low in cases like this one, to
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// increase the likelihood of the full refund coming into effect.
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uint256 private constant _NOT_ENTERED = 1;
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uint256 private constant _ENTERED = 2;
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uint256 private _status;
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constructor () internal {
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_status = _NOT_ENTERED;
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}
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/**
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* @dev Prevents a contract from calling itself, directly or indirectly.
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* Calling a `nonReentrant` function from another `nonReentrant`
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* function is not supported. It is possible to prevent this from happening
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* by making the `nonReentrant` function external, and make it call a
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* `private` function that does the actual work.
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*/
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modifier nonReentrant() {
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// On the first call to nonReentrant, _notEntered will be true
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require(_status != _ENTERED, "ReentrancyGuard: reentrant call");
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// Any calls to nonReentrant after this point will fail
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_status = _ENTERED;
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_;
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// By storing the original value once again, a refund is triggered (see
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// https://eips.ethereum.org/EIPS/eip-2200)
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_status = _NOT_ENTERED;
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}
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}
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