Open Zeppelin is a smart contract library in the Solidity programming language for the Ethereum blockchain. The library provides functions for performing common ERC-20 token operations in a safe and secure manner.
The library is a collection of utility functions that implement various ERC-20 token operations, such as transfer, approve, and increase/decrease allowance.
It imports three other smart contract libraries, IERC20.sol, IERC20Permit.sol, and Address.sol, which define the standard ERC-20 token interface, a permit extension for ERC-20 tokens, and address manipulation functions, respectively.
The main functions are:
safeTransfer() function, which transfers a specified amount of tokens from the contract's address to another address.
safeTransferFrom() function, which transfers a specified amount of tokens from one address to another address.
safeApprove() function, which approves a specified spender to transfer tokens from the contract's address.
safeIncreaseAllowance() function, which increases the approved amount of tokens for a specified spender.
safeDecreaseAllowance() function, which decreases the approved amount of tokens for a specified spender.
safePermit() function, which performs a permit operation on a token with the IERC20Permit extension.
All of these functions are declared as internal, meaning they can be called only within the same contract or by derived contracts. The library also contains a private function _callOptionalReturn(), which is used by the other functions to perform low-level contract calls and check the return value.