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SafeERC20.sol
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SafeERC20.sol
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// Inspired by AdEx (https://github.com/AdExNetwork/adex-protocol-eth/blob/b9df617829661a7518ee10f4cb6c4108659dd6d5/contracts/libs/SafeERC20.sol)
// and 0x (https://github.com/0xProject/0x-monorepo/blob/737d1dc54d72872e24abce5a1dbe1b66d35fa21a/contracts/protocol/contracts/protocol/AssetProxy/ERC20Proxy.sol#L143)
pragma solidity ^0.4.24;
import "../lib/token/ERC20.sol";
library SafeERC20 {
// Before 0.5, solidity has a mismatch between `address.transfer()` and `token.transfer()`:
// https://github.com/ethereum/solidity/issues/3544
bytes4 private constant TRANSFER_SELECTOR = 0xa9059cbb;
string private constant ERROR_TOKEN_BALANCE_REVERTED = "SAFE_ERC_20_BALANCE_REVERTED";
string private constant ERROR_TOKEN_ALLOWANCE_REVERTED = "SAFE_ERC_20_ALLOWANCE_REVERTED";
function invokeAndCheckSuccess(address _addr, bytes memory _calldata)
private
returns (bool)
{
bool ret;
assembly {
let ptr := mload(0x40) // free memory pointer
let success := call(
gas, // forward all gas
_addr, // address
0, // no value
add(_calldata, 0x20), // calldata start
mload(_calldata), // calldata length
ptr, // write output over free memory
0x20 // uint256 return
)
if gt(success, 0) {
// Check number of bytes returned from last function call
switch returndatasize
// No bytes returned: assume success
case 0 {
ret := 1
}
// 32 bytes returned: check if non-zero
case 0x20 {
// Only return success if returned data was true
// Already have output in ptr
ret := eq(mload(ptr), 1)
}
// Not sure what was returned: don't mark as success
default { }
}
}
return ret;
}
function staticInvoke(address _addr, bytes memory _calldata)
private
view
returns (bool, uint256)
{
bool success;
uint256 ret;
assembly {
let ptr := mload(0x40) // free memory pointer
success := staticcall(
gas, // forward all gas
_addr, // address
add(_calldata, 0x20), // calldata start
mload(_calldata), // calldata length
ptr, // write output over free memory
0x20 // uint256 return
)
if gt(success, 0) {
ret := mload(ptr)
}
}
return (success, ret);
}
/**
* @dev Same as a standards-compliant ERC20.transfer() that never reverts (returns false).
* Note that this makes an external call to the token.
*/
function safeTransfer(ERC20 _token, address _to, uint256 _amount) internal returns (bool) {
bytes memory transferCallData = abi.encodeWithSelector(
TRANSFER_SELECTOR,
_to,
_amount
);
return invokeAndCheckSuccess(_token, transferCallData);
}
/**
* @dev Same as a standards-compliant ERC20.transferFrom() that never reverts (returns false).
* Note that this makes an external call to the token.
*/
function safeTransferFrom(ERC20 _token, address _from, address _to, uint256 _amount) internal returns (bool) {
bytes memory transferFromCallData = abi.encodeWithSelector(
_token.transferFrom.selector,
_from,
_to,
_amount
);
return invokeAndCheckSuccess(_token, transferFromCallData);
}
/**
* @dev Same as a standards-compliant ERC20.approve() that never reverts (returns false).
* Note that this makes an external call to the token.
*/
function safeApprove(ERC20 _token, address _spender, uint256 _amount) internal returns (bool) {
bytes memory approveCallData = abi.encodeWithSelector(
_token.approve.selector,
_spender,
_amount
);
return invokeAndCheckSuccess(_token, approveCallData);
}
/**
* @dev Static call into ERC20.balanceOf().
* Reverts if the call fails for some reason (should never fail).
*/
function staticBalanceOf(ERC20 _token, address _owner) internal view returns (uint256) {
bytes memory balanceOfCallData = abi.encodeWithSelector(
_token.balanceOf.selector,
_owner
);
(bool success, uint256 tokenBalance) = staticInvoke(_token, balanceOfCallData);
require(success, ERROR_TOKEN_BALANCE_REVERTED);
return tokenBalance;
}
/**
* @dev Static call into ERC20.allowance().
* Reverts if the call fails for some reason (should never fail).
*/
function staticAllowance(ERC20 _token, address _owner, address _spender) internal view returns (uint256) {
bytes memory allowanceCallData = abi.encodeWithSelector(
_token.allowance.selector,
_owner,
_spender
);
(bool success, uint256 allowance) = staticInvoke(_token, allowanceCallData);
require(success, ERROR_TOKEN_ALLOWANCE_REVERTED);
return allowance;
}
/**
* @dev Static call into ERC20.totalSupply().
* Reverts if the call fails for some reason (should never fail).
*/
function staticTotalSupply(ERC20 _token) internal view returns (uint256) {
bytes memory totalSupplyCallData = abi.encodeWithSelector(_token.totalSupply.selector);
(bool success, uint256 totalSupply) = staticInvoke(_token, totalSupplyCallData);
require(success, ERROR_TOKEN_ALLOWANCE_REVERTED);
return totalSupply;
}
}