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83 lines
3.1 KiB
83 lines
3.1 KiB
// SPDX-License-Identifier: MIT
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pragma solidity >=0.6.0 <0.8.0;
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/**
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* @dev This abstract contract provides a fallback function that delegates all calls to another contract using the EVM
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* instruction `delegatecall`. We refer to the second contract as the _implementation_ behind the proxy, and it has to
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* be specified by overriding the virtual {_implementation} function.
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*
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* Additionally, delegation to the implementation can be triggered manually through the {_fallback} function, or to a
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* different contract through the {_delegate} function.
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*
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* The success and return data of the delegated call will be returned back to the caller of the proxy.
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*/
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abstract contract Proxy {
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/**
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* @dev Delegates the current call to `implementation`.
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*
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* This function does not return to its internall call site, it will return directly to the external caller.
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*/
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function _delegate(address implementation) internal {
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// solhint-disable-next-line no-inline-assembly
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assembly {
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// Copy msg.data. We take full control of memory in this inline assembly
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// block because it will not return to Solidity code. We overwrite the
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// Solidity scratch pad at memory position 0.
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calldatacopy(0, 0, calldatasize())
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// Call the implementation.
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// out and outsize are 0 because we don't know the size yet.
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let result := delegatecall(gas(), implementation, 0, calldatasize(), 0, 0)
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// Copy the returned data.
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returndatacopy(0, 0, returndatasize())
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switch result
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// delegatecall returns 0 on error.
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case 0 { revert(0, returndatasize()) }
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default { return(0, returndatasize()) }
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}
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}
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/**
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* @dev This is a virtual function that should be overriden so it returns the address to which the fallback function
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* and {_fallback} should delegate.
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*/
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function _implementation() internal virtual view returns (address);
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/**
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* @dev Delegates the current call to the address returned by `_implementation()`.
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*
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* This function does not return to its internall call site, it will return directly to the external caller.
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*/
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function _fallback() internal {
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_beforeFallback();
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_delegate(_implementation());
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}
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/**
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* @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if no other
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* function in the contract matches the call data.
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*/
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fallback () external payable {
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_fallback();
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}
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/**
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* @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if call data
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* is empty.
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*/
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receive () external payable {
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_fallback();
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}
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/**
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* @dev Hook that is called before falling back to the implementation. Can happen as part of a manual `_fallback`
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* call, or as part of the Solidity `fallback` or `receive` functions.
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*
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* If overriden should call `super._beforeFallback()`.
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*/
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function _beforeFallback() internal virtual {
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}
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}
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