How to generate calldata for a function

Question

I have got as far as generating the method ID for the function:

function transfer(address src, address dst, uint256 amount);

The method ID would be:

bytes4(keccak256("transfer(address,address,uint256)")) // 0xbeabacc8

How do I pass the function variables (on-chain) along with the method ID to a function:

function execute(address _target, bytes _data)

Where _data is the calldata of the transfer function.

Answer 1

You can execute the call the following way (members of addresses, abi.encode*, low-level calls):

Example 1: Call using already calculated function signature (this answers your question)

---

bytes memory transferPayload = abi.encodeWithSelector(bytes4(0xbeabacc8), param1, param2, param3);
bytes memory executePayload = abi.encodeWithSignature("execute(address,bytes)", transferContractAdr, transferPayload);
(bool success, bytes memory returnData) = address(executeContractAdr).call(executePayload);
require(success, "low-level call of function execute failed [transfer(address,address,uint256), param1, param2, param3]");

Example 2: Call function and let Solidity automatically calculate the function signature

---

Just replace

bytes memory transferPayload = abi.encodeWithSelector(bytes4(0xbeabacc8), param1, param2, param3);

with

bytes memory transferPayload = abi.encodeWithSignature("transfer(address,address,uint256)", param1, param2, param3);

---

note 1: Please consider which call (call, callcode, delegatecall, staticcall) will be appropriate for your scenario

note 2: Replace the require statement with an appropriate try-catch block

note 3: If you call a function in the same contract, you can use address(this)

Answer 2

For on-chain transactions, you can use abi.encodeWithSelector. This article has a ton of great information about it.

In your case, you can do the following:

bytes4 methodSig = 0xbeabacc8;
address addressOne = address(0);
address addressTwo = address(1);
uint256 uintOne = 2;
abi.encodeWithSelector(
    methodSig,   
    addressOne,
    addressTwo,
    uintOne
);

See the official Solidity docs for more info.

Answer 3

Example 3: Use an interface and let Solidity handle the encodings for you

---

interface IExecute {
    function execute(address _target, bytes calldata _data) external;
}

bytes memory transferPayload = abi.encodeWithSignature(
    "transfer(address,address,uint256)",
    from, to, amount
);

IExecute(executeContractAddress).execute(
    transferContractAddress,
    transferPayload
);

Or even better, (this may not apply if you have specific logic in your execute function)

Example 4: Skip the execute contract altogether and create a direct interface

---

interface ITransfer {
    function transfer(address src, address dst, uint256 amount) external;
}

ITransfer(transferContractAddress).transfer(from, to, amount);