Collection of Utility Functions

The utility functions' implementation are found below in the full code section. They are generous in what they accept. Here we'll be showing examples of usage.

Derive the Ethereum public address from a public key:

publicKeyBytes, _ := hex.DecodeString("049a7df67f79246283fdc93af76d4f8cdd62c4886e8cd870944e817dd0b97934fdd7719d0810951e03418205868a5c1b40b192451367f28e0088dd75e15de40c05")
address := util.PublicKeyBytesToAddress(publicKeyBytes)
fmt.Println(address.Hex()) // 0x96216849c49358B10257cb55b28eA603c874b05E

Check if an address is a valid Ethereum address:

valid := util.IsValidAddress("0x323b5d4c32345ced77393b3530b1eed0f346429d")
fmt.Println(valid) // true

Check if an address is a zero address.

zeroed := util.IsZeroAddress("0x0")
fmt.Println(zeroed) // true

Convert a decimal to wei. The second argument is the number of decimals.

wei := util.ToWei(0.02, 18)
fmt.Println(wei) // 20000000000000000

Convert wei to decimals. The second argument is the number of decimals.

wei := new(big.Int)
wei.SetString("20000000000000000", 10)
eth := util.ToDecimal(wei, 18)
fmt.Println(eth) // 0.02

Calculate the gas cost given the gas limit and gas price.

gasLimit := uint64(21000)
gasPrice := new(big.Int)
gasPrice.SetString("2000000000", 10)
gasCost := util.CalcGasCost(gasLimit, gasPrice)
fmt.Println(gasCost) // 42000000000000

Retrieve the R, S, and V values from a signature.

sig := "0x789a80053e4927d0a898db8e065e948f5cf086e32f9ccaa54c1908e22ac430c62621578113ddbb62d509bf6049b8fb544ab06d36f916685a2eb8e57ffadde02301"
r, s, v := util.SigRSV(sig)
fmt.Println(hexutil.Encode(r[:])[2:]) // 789a80053e4927d0a898db8e065e948f5cf086e32f9ccaa54c1908e22ac430c6
fmt.Println(hexutil.Encode(s[:])[2:]) // 2621578113ddbb62d509bf6049b8fb544ab06d36f916685a2eb8e57ffadde023
fmt.Println(v)                        // 28

Full code

util.go

package util

import (
    "math/big"
    "reflect"
    "regexp"
    "strconv"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/hexutil"
    "github.com/shopspring/decimal"
)

// IsValidAddress validate hex address
func IsValidAddress(iaddress interface{}) bool {
    re := regexp.MustCompile("^0x[0-9a-fA-F]{40}$")
    switch v := iaddress.(type) {
    case string:
        return re.MatchString(v)
    case common.Address:
        return re.MatchString(v.Hex())
    default:
        return false
    }
}

// IsZeroAddress validate if it's a 0 address
func IsZeroAddress(iaddress interface{}) bool {
    var address common.Address
    switch v := iaddress.(type) {
    case string:
        address = common.HexToAddress(v)
    case common.Address:
        address = v
    default:
        return false
    }

    zeroAddressBytes := common.FromHex("0x0000000000000000000000000000000000000000")
    addressBytes := address.Bytes()
    return reflect.DeepEqual(addressBytes, zeroAddressBytes)
}

// ToDecimal wei to decimals
func ToDecimal(ivalue interface{}, decimals int) decimal.Decimal {
    value := new(big.Int)
    switch v := ivalue.(type) {
    case string:
        value.SetString(v, 10)
    case *big.Int:
        value = v
    }

    mul := decimal.NewFromFloat(float64(10)).Pow(decimal.NewFromFloat(float64(decimals)))
    num, _ := decimal.NewFromString(value.String())
    result := num.Div(mul)

    return result
}

// ToWei decimals to wei
func ToWei(iamount interface{}, decimals int) *big.Int {
    amount := decimal.NewFromFloat(0)
    switch v := iamount.(type) {
    case string:
        amount, _ = decimal.NewFromString(v)
    case float64:
        amount = decimal.NewFromFloat(v)
    case int64:
        amount = decimal.NewFromFloat(float64(v))
    case decimal.Decimal:
        amount = v
    case *decimal.Decimal:
        amount = *v
    }

    mul := decimal.NewFromFloat(float64(10)).Pow(decimal.NewFromFloat(float64(decimals)))
    result := amount.Mul(mul)

    wei := new(big.Int)
    wei.SetString(result.String(), 10)

    return wei
}

// CalcGasCost calculate gas cost given gas limit (units) and gas price (wei)
func CalcGasCost(gasLimit uint64, gasPrice *big.Int) *big.Int {
    gasLimitBig := big.NewInt(int64(gasLimit))
    return gasLimitBig.Mul(gasLimitBig, gasPrice)
}

// SigRSV signatures R S V returned as arrays
func SigRSV(isig interface{}) ([32]byte, [32]byte, uint8) {
    var sig []byte
    switch v := isig.(type) {
    case []byte:
        sig = v
    case string:
        sig, _ = hexutil.Decode(v)
    }

    sigstr := common.Bytes2Hex(sig)
    rS := sigstr[0:64]
    sS := sigstr[64:128]
    R := [32]byte{}
    S := [32]byte{}
    copy(R[:], common.FromHex(rS))
    copy(S[:], common.FromHex(sS))
    vStr := sigstr[128:130]
    vI, _ := strconv.Atoi(vStr)
    V := uint8(vI + 27)

    return R, S, V
}

test file: util_test.go