After fallback atived, who is msg.sender and what the msg.data

Smart Contracts
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1

I read on internet ,after call a non exist founction in contract , that fallback will be actived. address app is a empty contract . address token is busd contract .
address app = 0x85a389C274c62F5108E662F017C04FE22d574483 ;
address token= 0x55d398326f99059fF775485246999027B3197955;
address sender appoved 1 busd to empty contract app already now i call from
app.call(abi.encodeWithSignature("transferFrom(address sender, address recipient, uint256 amount)", sender, recipient,amount));
due to app is empty , so the fallback will be actived , and msg.sender is contract app. and msg.data istransferFrom(address sender, address recipient, uint256 amount) then going to call another
token.call(abi.encodeWithSignature("transferFrom(address sender, address recipient, uint256 amount)", sender, recipient,amount));
at this monment : msg.sender should be address app, msg.data is still "transferFrom(address sender, address recipient, uint256 amount)" and sender already appoved 1 busd to the address app. so it should be working well
here is the full code

pragma solidity ^0.8;

interface IERC20  {
    function totalSupply() external view returns (uint256);

    function balanceOf(address account) external view returns (uint256);

    function transfer(address recipient, uint256 amount)
        external
        returns (bool);

    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}
contract callnmblq {
      address app = 0x85a389C274c62F5108E662F017C04FE22d574437 ;
      address token= 0x55d398326f99059fF775485246999027B3197955;
    
    
    function transferFrom( address sender, address recipient, uint256 amount) external   {
        bool success;
         (success, ) =app.call(abi.encodeWithSignature("transferFrom(address sender, address recipient, uint256 amount)", sender, recipient,amount));
         require(success,"fall to transferFrom");
         (success, ) =token.call(abi.encodeWithSignature("transferFrom(address sender, address recipient, uint256 amount)", sender, recipient,amount));
         require(success,"fall to transferFrom");
    }
    
   
        


    }

help to check the logic.if i understand well at the seconder call msg.sender and msg.data. help to understand after fallback active , how to continue contract. help how to make this transferFrom working . by the way the feedback is gas limited

transact to callnmblq.transferFrom errored: Internal JSON-RPC error.
{
  "code": 3,
  "message": "execution reverted: fall to transferFrom",
  "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001466616c6c20746f207472616e7366657246726f6d000000000000000000000000"
}
2

Hello @Dbz,

The description of the problem is not very clear, but I'm assuming you want the code you shared to work when calling the transferFrom function.

In that case, I can see there's a problem with how you're encoding the call.

Instead of transferFrom(address sender, address recipient, uint256 amount), try with transferFrom(address, address, uint256), since according to the function selector specification from Solidity states the following:

Parameter types are split by a single comma — no spaces are used

Note they also don't include the name of the parameter.

Also, make sure to test this with a valid fork of the chain you're targeting, otherwise, the addresses you're using won't have deployed code on local.

3

Instead of abi.encodeWithSignature consider using the safer abi.encodeCall. See Solidity By Example. Keep in mind that it was added in 0.8.11 so you need a version more recent than that.