golang 实现 ETH 交易离线签名（冷签）

import (
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/rlp"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/common/hexutil"
)
const (
    GAS_LIMIT         = 21000
    GAS_PRICE         = 500000000000
)
tx := types.NewTransaction(nonce, common.HexToAddress(toAddress), value, GAS_LIMIT, big.NewInt(GAS_PRICE), nil)

func SignTransaction(tx *types.Transaction, privateKeyStr string) (string, error) {
    privateKey, err := StringToPrivateKey(privateKeyStr)
    if err != nil {
        return "", err
    }
    signTx, err := types.SignTx(tx, types.NewEIP155Signer(big.NewInt(4)), privateKey)
    //signTx, err := types.SignTx(tx, types.HomesteadSigner{}, privateKey)
    if err != nil {
        return "", nil
    }

    b, err := rlp.EncodeToBytes(signTx)
    if err != nil {
        return "", err
    }
    return hex.EncodeToString(b), nil
}

func StringToPrivateKey(privateKeyStr string) (*ecdsa.PrivateKey, error) {
    privateKeyByte, err := hexutil.Decode(privateKeyStr)
    if err != nil {
        return nil, err
    }
    privateKey, err := crypto.ToECDSA(privateKeyByte)
    if err != nil {
        return nil, err
    }
    return privateKey, nil
}

func KeystoreToPrivateKey(keystoreContent []byte, password string) (*ecdsa.PrivateKey, error) {
    unlockedKey, err := keystore.DecryptKey(keystoreContent, password)
    if err != nil {
        return nil, err
    }
    return unlockedKey.PrivateKey, nil
}