What are the many 0 and 2,1 after the encodeWithSignature result?

Question

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

contract testABI {
    function getEncodePacked(string calldata _func,bytes calldata _data) public pure     returns(bytes memory) {
        return abi.encodePacked(bytes4(keccak256(bytes(_func))), _data);
    }

    function getEncodeWithSignature(string calldata _func,bytes calldata _data) public pure returns(bytes memory) {
        return abi.encodeWithSignature(_func, _data);
    }
}

I'm working on abi.encodePacked and abi.encodeWithSignature.

I want to know what "0000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000000000" means after the result of abi.encodeWithSignature.

Answer 1

That's just the offset of the start of the data and the count of elements in the bytes dynamic 'array' and it's values (which in this case is zero).

Take a look at the docs: https://docs.soliditylang.org/en/v0.8.16/abi-spec.html#use-of-dynamic-types

The 2 is the start offset of the data. 1 is the elements in the bytes array (the only value that is has is an empty byte which is 0x00).

And after 1 we found the value, which is 00, but there many zeros in there, because all those values are padded with zeros to 32 bytes.

For an inmput like this baz(uint32,bool),0x05:

It would result in:

0xcdcd77c0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000010500000000000000000000000000000000000000000000000000000000000000

For baz(uint32,bool),0x0503:

It would be (notice that now there's no 1, but 2 because I sent 2 params. The dynamic data offset is still the same:

0xcdcd77c0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000020503000000000000000000000000000000000000000000000000000000000000