CODEWITHSUNDEEP
ethereumsoliditysmartcontractsremixerc20
Im retarded but
Im retarded but

Reputation: 15

ERC20 token transfer to smart contract

Hi I've written a simple smart contract to transfer erc20 token from user to smart contract and from smart contract to user. I'm approving it before calling the transferFrom function but the transactions fails. I've tried only calling approve and not calling transferFrom it works. I'm testing on rinkeby testnet.

// SPDX-License-Identifier: MIT
pragma solidity =0.7.6;
pragma abicoder v2;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    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 transferToContract {
    address public _WETH = 0x1f9840a85d5aF5bf1D1762F925BDADdC4201F984;
    IERC20 public WETH = IERC20(_WETH);

    function transferToC (uint amount) public
    {
        WETH.approve(msg.sender,amount);
        WETH.transferFrom(msg.sender,address(this),amount);
    }
    
    function transferFromC(uint amount) public{
        WETH.approve(address(this),amount);
        WETH.transferFrom(address(this),msg.sender,amount);
    }
    
    function getbal() public view returns(uint){
        return WETH.balanceOf(msg.sender);
    }
    
    
}

I'm testing on remix with web3 injected. The error I'm getting is

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending?
execution reverted: Uni::transferFrom: transfer amount exceeds spender allowance { "originalError": { "code": 3, "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000003c556e693a3a7472616e7366657246726f6d3a207472616e7366657220616d6f756e742065786365656473207370656e64657220616c6c6f77616e636500000000", "message": "execution reverted: Uni::transferFrom: transfer amount exceeds spender allowance" } }

Also I have the token in my test wallet on rinkeby testnet and I'm deploying using remix web3 injected.

Upvotes: 0

Views: 5346

Answers (2)

Shubhangi Dargarh
Shubhangi Dargarh

Reputation: 1

I want my contract to accept tokens from external accounts, which has few tokens (can be any, but based on ERC20). So to call the approve function directly I need to create an instance of the token's contract, so how do I create the instance using web3?

Any code piece would help or if you could share link to any document for the same would help too.

Upvotes: 0

Petr Hejda
Petr Hejda

Reputation: 43481

WETH.approve(msg.sender,amount);

This line approves the user to spend your contract's tokens. Not the other way around.

If you want to approve the contract to manipulate the user's tokens, the user needs to execute approve(yourContractAddress, amount) directly on the WETH contract (not through your contract).

I've covered a similar topic in another answer. The TLDR part is also relevant to your question - https://stackoverflow.com/a/67642090/1693192

Upvotes: 2

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