Raw transaction data in Go

Question

I would like to generate raw transactions in golang without any go binding and I'm wondering if there is library to dynamically encode my argument parameter using go?

https://github.com/ethereum/wiki/wiki/Ethereum-Contract-ABI

Using this resource it look like it would be a huge amount of work to dynamically encode each param manually for every type of data available.

Is there a way to do this?

Again I'm not looking for Ethereum Go bindings since i need to return the raw unsigned transaction data.

Answer 1

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
}

Answer 2

One place to start from would be NewTransaction() in transaction.go. This is part of the types package.

// NewTransaction creates a new transaction with the given properties.
func NewTransaction(nonce int64, to *Address, amount, gasLimit, gasPrice *BigInt, data []byte) *Transaction {
    return &Transaction{types.NewTransaction(uint64(nonce), to.address, amount.bigint, gasLimit.bigint, gasPrice.bigint, data)}
}

There are countless places in the code which have examples of how to test the function, with or without the step that performs the signing.