In one of the smart contracts for this project, the following function is used to replace _msgSender() and I'm wondering what it does and why it is used. At the end, the comment suggests "This is used instead of msg.sender as transactions won't be sent by the original token owner, but by OpenSea." I'm wondering what the exact meaning is. Thanks.
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
abstract contract ContextMixin {
function msgSender() internal view returns (address payable sender)
{
if (msg.sender == address(this)) {
bytes memory array = msg.data;
uint256 index = msg.data.length;
assembly {
// Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
sender := and(
mload(add(array, index)),
0xffffffffffffffffffffffffffffffffffffffff
)
}
} else {
sender = payable(msg.sender);
}
return sender;
}
}
/**
* This is used instead of msg.sender as transactions won't be sent by the original token owner, but by OpenSea.
*/
function _msgSender()
internal
override
view
returns (address sender)
{
return ContextMixin.msgSender();
}