Cannot get readable integer from nethereum decoded input data

Question

I'm having trouble with converting solidity's uint256 to readable c# object.

public Transaction DecodeInputData(Transaction tx)
    {

        EthApiContractService ethApi = new EthApiContractService(null);
        var contract = ethApi.GetContract(Abi.Replace(@"\", string.Empty), Address);

        var transfer = contract.GetFunction("transfer");
        var decodedTx = transfer.DecodeInput(tx.input);

        tx.to = (string)decodedTx[0].Result;
        tx.value = "0x" + ((BigInteger)decodedTx[1].Result).ToString("x");

        return tx;
    }

Example Tx: https://etherscan.io/tx/0x622760ad1a0ead8d16641d5888b8c36cb67be5369556f8887499f4ad3e3d1c3d

We must able to convert decodedTx[1].Result variable ( its: {53809663494440740791636285293469688360281260987263635605451211260198698423701}) to 83218945020000000000.

We converting this value to hex to compatibility. But the hex i get is; "0x76f730b400000000000000000000000000000000000000000000000482e51595"

I am using Nethereum library with .net core 2.1

You aren't hashing anything. You're formatting a number using the hexadecimal form. Why do you assume the hex string you got is wrong? If you don't want the hex representation of a BigInteger, what *do* you want? — Panagiotis Kanavos, Mar 22 '19 at 08:29
Sorry its must be hex not hash. Edited. I am converting to hex to compatibility with ether process. But when i parse hex, i cannot get the right big integer value. — whatTheCase, Mar 22 '19 at 10:22
The right value is the one that was used to create that string. To get it, use `BigInteger.Parse()` with that string. It has nothing to do with Ethereum. Post code that actually reproduces the problem. It shouldn't be more than 3 lines: `var i=new BigInteger(.....); var hex=i.ToString("x"); var i2=BigInteger.Parse(hex);`. I suspect you'll find that the numbers are equal though — Panagiotis Kanavos, Mar 22 '19 at 10:29
What does the phrase `We must able to convert decodedTx[1].Result variable` mean? What are those numbers and why should one produce the other? This has nothing to do with hexadecimal representation. Thos eare two arbitrary numbers — Panagiotis Kanavos, Mar 22 '19 at 10:31

Juan Blanco · Accepted Answer · 2021-05-22T14:12:10.747

You are trying to decode the smart contract function parameters of a transaction. The smart contract is an ERC20 smart contract, and the function is the Transfer method.

To do so you need to do the following.

Create your Function message in this is scenario the Transfer Function.
Retrieve the transaction
Using the FunctionMessage extension method DecodeTransaction, decode the values of the original Transaction input.

using Nethereum.Web3;
using Nethereum.ABI.FunctionEncoding.Attributes;
using Nethereum.Contracts.CQS;
using Nethereum.Util;
using Nethereum.Web3.Accounts;
using Nethereum.Hex.HexConvertors.Extensions;
using Nethereum.Contracts;
using Nethereum.Contracts.Extensions;
using System;
using System.Numerics;
using System.Threading;
using System.Threading.Tasks;


public class GetStartedSmartContracts
{

    [Function("transfer", "bool")]
    public class TransferFunction : FunctionMessage
    {
        [Parameter("address", "_to", 1)]
        public string To { get; set; }

        [Parameter("uint256", "_value", 2)]
        public BigInteger TokenAmount { get; set; }
    }

    public static async Task Main()
    {

        var url = "https://mainnet.infura.io";
        var web3 = new Web3(url);
                var txn = await web3.Eth.Transactions.GetTransactionByHash.SendRequestAsync("0x622760ad1a0ead8d16641d5888b8c36cb67be5369556f8887499f4ad3e3d1c3d");

        var transfer = new TransferFunction().DecodeTransaction(txn);
                Console.WriteLine(transfer.TokenAmount);
                //BAT has 18 decimal places the same as Wei
                Console.WriteLine(Web3.Convert.FromWei(transfer.TokenAmount));
    }
}

You can test this in the http://playground.nethereum.com

Or you can also do, if want to check what function is:

var functionCallDecoder = new FunctionCallDecoder();

        if(functionCallDecoder.IsDataForFunction(ABITypedRegistry.GetFunctionABI<TransferFunction>().Sha3Signature, txn.Input)) {
            
                var transfer = new TransferFunction().DecodeInput(txn.Input);
                Console.WriteLine(Web3.Convert.FromWei(transfer.TokenAmount));
                Console.WriteLine(transfer.To);
        }

Is it possible to decode the input data WITHOUT first knowing which function it is first? If you know which contract it was sent and you have the complete ABI, is it possible? I want to know which method name was called given only the Transaction input data. — user1142433, May 21 '21 at 19:27

Cannot get readable integer from nethereum decoded input data

1 Answers1