Go-Ethereum – How to Decode Raw Transaction Inputs in Golang

go-ethereumgolangraw-transaction

When making a contract transaction using go-ethereum (golang) how can I decode the transaction inputs.

Specifically
Given a tx.Data []byte , the contract's contractABI abi.ABI and the method that is being called its methodID string how can I decode tx.Data from hexadecimal to go types ?

I've tried doing abi.Methods[methodID].Inputs.Arguments.UnpackValues(tx.Data) but this always results in an empty slice of values.

Code:

func decodeTxParams(abi abi.ABI, method string, data []byte) ([]interface{}, error) {
    txParams, err := abi.Methods[method].Inputs.UnpackValues(data)
    if err != nil {
        return []interface{}{}, err
    }
    return txParams, nil
}

caller:

func (b *backend) SendTransaction(ctx context.Context, tx *types.Transaction) error {
    err := b.Client.SendTransaction(ctx, tx)
    if err != nil {
        return err
    }

    // update local nonce
    msg, err := tx.AsMessage(types.HomesteadSigner{})
    if err != nil {
        return err
    }
    sender := msg.From()
    b.nonceManager.Lock(sender)
    b.nonceManager.Update(sender, tx.Nonce())
    b.nonceManager.Unlock(sender)

    data := msg.Data()
    method, ok := b.methods[string(data[:4])]
    if !ok {
        method = "unknown"
    }

        txParams, err := decodeTxParams(b.abiMap[string(data[:4])], string(data[:4]), data[4:])

    if err != nil {
        return err
    }

    if err != nil {
        glog.Infof("\n%vEth Transaction%v\n\nInvoking transaction: \"%v\".  \nTransaction Failed: %v\n\n%v\n", strings.Repeat("*", 30), strings.Repeat("*", 30), method, err, strings.Repeat("*", 75))
        return err
    }

    glog.Infof("\n%vEth Transaction%v\n\nInvoking transaction: \"%v\".  Hash: \"%v\". \n\n%v\n", strings.Repeat("*", 30), strings.Repeat("*", 30), method, tx.Hash().String(), strings.Repeat("*", 75))

    return nil
}

Best Answer

func decodeTxParams(abi abi.ABI, v map[string]interface{}, data []byte) (map[string]interface{}, error) {
    m, err := abi.MethodById(data[:4])
    if err != nil {
        return map[string]interface{}{}, err
    }
    if err := m.Inputs.UnpackIntoMap(v, data[4:]); err != nil {
        return map[string]interface{}{}, err
    }
    return v, nil
}

Related Solutions

[Ethereum] Raw transaction data in Go

The go-ethereum package provides a common.LeftPadBytes function for left padding values for solidity. You'd use this to pad to 32 bytes which is the word size the EVM uses.

Here's a full example of how to manually construct the transaction data for transferring an ERC-20 token which should give you an good idea (from the Ethereum Development with Go book).

package main

import (
    "context"
    "crypto/ecdsa"
    "fmt"
    "log"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/hexutil"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/crypto/sha3"
    "github.com/ethereum/go-ethereum/ethclient"
)

func main() {
    client, err := ethclient.Dial("https://rinkeby.infura.io")
    if err != nil {
        log.Fatal(err)
    }

    privateKey, err := crypto.HexToECDSA("fad9c8855b740a0b7ed4c221dbad0f33a83a49cad6b3fe8d5817ac83d38b6a19")
    if err != nil {
        log.Fatal(err)
    }

    publicKey := privateKey.Public()
    publicKeyECDSA, ok := publicKey.(*ecdsa.PublicKey)
    if !ok {
        log.Fatal("error casting public key to ECDSA")
    }

    fromAddress := crypto.PubkeyToAddress(*publicKeyECDSA)
    nonce, err := client.PendingNonceAt(context.Background(), fromAddress)
    if err != nil {
        log.Fatal(err)
    }

    value := big.NewInt(0)      // in wei (0 eth)
    gasLimit := uint64(2000000) // in units
    gasPrice, err := client.SuggestGasPrice(context.Background())
    if err != nil {
        log.Fatal(err)
    }

    toAddress := common.HexToAddress("0x4592d8f8d7b001e72cb26a73e4fa1806a51ac79d")
    tokenAddress := common.HexToAddress("0x28b149020d2152179873ec60bed6bf7cd705775d")

    transferFnSignature := []byte("transfer(address,uint256)")
    hash := sha3.NewKeccak256()
    hash.Write(transferFnSignature)
    methodID := hash.Sum(nil)[:4]
    fmt.Println(hexutil.Encode(methodID)) // 0xa9059cbb

    paddedAddress := common.LeftPadBytes(toAddress.Bytes(), 32)
    fmt.Println(hexutil.Encode(paddedAddress)) // 0x0000000000000000000000004592d8f8d7b001e72cb26a73e4fa1806a51ac79d

    amount := new(big.Int)
    amount.SetString("1000000000000000000000", 10) // 1000 tokens
    paddedAmount := common.LeftPadBytes(amount.Bytes(), 32)
    fmt.Println(hexutil.Encode(paddedAmount)) // 0x00000000000000000000000000000000000000000000003635c9adc5dea00000

    var data []byte
    data = append(data, methodID...)
    data = append(data, paddedAddress...)
    data = append(data, paddedAmount...)

    tx := types.NewTransaction(nonce, tokenAddress, value, gasLimit, gasPrice, data)
    signedTx, err := types.SignTx(tx, types.HomesteadSigner{}, privateKey)
    if err != nil {
        log.Fatal(err)
    }

    err = client.SendTransaction(context.Background(), signedTx)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("tx sent: %s", signedTx.Hash().Hex()) // tx sent: 0xa56316b637a94c4cc0331c73ef26389d6c097506d581073f927275e7a6ece0bc
}

[Ethereum] How to decode input data with ABI using golang

took me a bit of time to figure out that myAbi.Unpack(...) unpacks output of a method or event. In your case (and mine) we want to unpack the inputs. Here is a working code sample

// example of transaction input data
txInput := "0xa5142faa00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000003"

// load contract ABI
abi, err := abi.JSON(strings.NewReader(myContractAbi))
if err != nil {
    log.Fatal(err)
}

// decode txInput method signature
decodedSig, err := hex.DecodeString(txInput[2:10])
if err != nil {
    log.Fatal(err)
}

// recover Method from signature and ABI
method, err := abi.MethodById(decodedSig)
if err != nil {
    log.Fatal(err)
}

// decode txInput Payload
decodedData, err := hex.DecodeString(txInput[10:])
if err != nil {
    log.Fatal(err)
}

// create strut that matches input names to unpack
// for example my function takes 2 inputs, with names "Name1" and "Name2" and of type uint256 (solidity)
type FunctionInputs struct {
    Name1 *big.Int // *big.Int for uint256 for example
    Name2 *big.Int
}

var data FunctionInputs

// unpack method inputs
err = method.Inputs.Unpack(&data, decodedData)
if err != nil {
    log.Fatal(err)
}

fmt.Println(data)

Best Answer

Related Solutions

[Ethereum] Raw transaction data in Go

[Ethereum] How to decode input data with ABI using golang

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