Why my safeTransfer function doesn't work?

Question

I am learning solidity and want to transfer tokens to others in my contract. But something blocked the way. Hope someone to help me. Below is my code:

pragma solidity >= 0.8.0;

contract Test {

    bytes4 private constant SELECTOR = bytes4(keccak256(bytes('transfer(address,uint256)')));

    constructor() {
    }

    function safeTransfer(address token, address to, uint value) public {
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(SELECTOR, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TRANSFER_FAILED');
    }
}

And these are the arguments I pass to safeTransfer in remix on the goerli testnet.

token: 0xB4FBF271143F4FBf7B91A5ded31805e42b2208d6, which is WETH.

And here is the error message.

I do not understand why this fails. I've tried multiple tokens and all of them just failed with the error message TRANSFER_FAILED

I am confident there are enough WETH token on the account I call this function.

Answer 1

When you call the function safeTransfer on contract Test, the Test contract forwards your message and the msg.sender address changes to the Test contract's address. Therefore, the Token expects Test contract to have some tokens available.

You can choose one of the two methods explained below to proceed:

• Send some tokens to the Test contract address.
• Give the Test contract some allowance and change it to call safeTransferFrom to forward your tokens for you.