1+ // SPDX-License-Identifier: MIT
2+
3+ pragma solidity >= 0.7.0 < 0.8.0 ;
4+
5+ import "./IERC20.sol " ;
6+ import "./SafeMath.sol " ;
7+ import "./Address.sol " ;
8+
9+ /**
10+ * @title SafeERC20
11+ * @dev Wrappers around ERC20 operations that throw on failure (when the token
12+ * contract returns false). Tokens that return no value (and instead revert or
13+ * throw on failure) are also supported, non-reverting calls are assumed to be
14+ * successful.
15+ * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
16+ * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
17+ */
18+ library SafeERC20 {
19+ using SafeMath for uint256 ;
20+ using Address for address ;
21+
22+ function safeTransfer (IERC20 token , address to , uint256 value ) internal {
23+ _callOptionalReturn (token, abi.encodeWithSelector (token.transfer.selector , to, value));
24+ }
25+
26+ function safeTransferFrom (IERC20 token , address from , address to , uint256 value ) internal {
27+ _callOptionalReturn (token, abi.encodeWithSelector (token.transferFrom.selector , from, to, value));
28+ }
29+
30+ function safeApprove (IERC20 token , address spender , uint256 value ) internal {
31+ // safeApprove should only be called when setting an initial allowance,
32+ // or when resetting it to zero. To increase and decrease it, use
33+ // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
34+ // solhint-disable-next-line max-line-length
35+ require ((value == 0 ) || (token.allowance (address (this ), spender) == 0 ),
36+ "SafeERC20: approve from non-zero to non-zero allowance "
37+ );
38+ _callOptionalReturn (token, abi.encodeWithSelector (token.approve.selector , spender, value));
39+ }
40+
41+ function safeIncreaseAllowance (IERC20 token , address spender , uint256 value ) internal {
42+ uint256 newAllowance = token.allowance (address (this ), spender).add (value);
43+ _callOptionalReturn (token, abi.encodeWithSelector (token.approve.selector , spender, newAllowance));
44+ }
45+
46+ function safeDecreaseAllowance (IERC20 token , address spender , uint256 value ) internal {
47+ uint256 newAllowance = token.allowance (address (this ), spender).sub (value, "SafeERC20: decreased allowance below zero " );
48+ _callOptionalReturn (token, abi.encodeWithSelector (token.approve.selector , spender, newAllowance));
49+ }
50+
51+ /**
52+ * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
53+ * on the return value: the return value is optional (but if data is returned, it must not be false).
54+ * @param token The token targeted by the call.
55+ * @param data The call data (encoded using abi.encode or one of its variants).
56+ */
57+ function _callOptionalReturn (IERC20 token , bytes memory data ) private {
58+ // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
59+ // we're implementing it ourselves.
60+
61+ // A Solidity high level call has three parts:
62+ // 1. The target address is checked to verify it contains contract code
63+ // 2. The call itself is made, and success asserted
64+ // 3. The return value is decoded, which in turn checks the size of the returned data.
65+ // solhint-disable-next-line max-line-length
66+ require (address (token).isContract (), "SafeERC20: call to non-contract " );
67+
68+ // solhint-disable-next-line avoid-low-level-calls
69+ (bool success , bytes memory returndata ) = address (token).call (data);
70+ require (success, "SafeERC20: low-level call failed " );
71+
72+ if (returndata.length > 0 ) { // Return data is optional
73+ // solhint-disable-next-line max-line-length
74+ require (abi.decode (returndata, (bool )), "SafeERC20: ERC20 operation did not succeed " );
75+ }
76+ }
77+ }
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