Go语言如何序列化以太坊Header结构体 无需遍历字段得到正确JSON输出

问题场景 #

我在Go开发过程中遇到一个此前未接触过的场景，和Stack Overflow上《嵌入带自定义MarshalJSON()方法的结构体的惯用写法》问题场景相似。

测试代码 #

package main

import (
    "context"
    "fmt"
    "os"

    "github.com/ethereum/go-ethereum/ethclient"
)

func main() {
    icpPath, _ := os.LookupEnv("GETH_ICP_PATH")
    
    client, _ := ethclient.Dial(icpPath)
    ctx := context.Background()

    header, _ := client.HeaderByNumber(ctx, nil)
    data, _ := header.MarshalJSON()

    fmt.Println(string(data))
}

运行结果 #

整体序列化输出 #

{"parentHash":"0x0000000000000000000000000000000000000000000000000000000000000000","sha3Uncles":"0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347","miner":"0x0000000000000000000000000000000000000000","stateRoot":"0xd7f8974fb5ac78d9ac099b9ad5018bedc2ce0a72dad1827a1709da30580f0544","transactionsRoot":"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421","receiptsRoot":"0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421","logsBloom":"0x000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","difficulty":"0x400000000","number":"0x0","gasLimit":"0x1388","gasUsed":"0x0","timestamp":"0x0","extraData":"0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa","mixHash":"0x0000000000000000000000000000000000000000000000000000000000000000","nonce":"0x0000000000000042","baseFeePerGas":null,"hash":"0xd4e56740f876aef8c010b86a40d5f56745a118d0906a34e69aec8c0db1cb8fa3"}

单独序列化difficulty字段输出 #

单独执行以下代码序列化difficulty字段：

difficulty, _ := header.Difficulty.MarshalJSON()
fmt.Println(string(difficulty))

得到十进制数值输出：

17179869184

相关类型定义 #

Header是go-ethereum中代表以太坊区块头的结构体，定义如下：

// Header represents a block header in the Ethereum blockchain.
type Header struct {
    ParentHash  common.Hash    `json:"parentHash"       gencodec:"required"`
    UncleHash   common.Hash    `json:"sha3Uncles"       gencodec:"required"`
    Coinbase    common.Address `json:"miner"            gencodec:"required"`
    Root        common.Hash    `json:"stateRoot"        gencodec:"required"`
    TxHash      common.Hash    `json:"transactionsRoot" gencodec:"required"`
    ReceiptHash common.Hash    `json:"receiptsRoot"     gencodec:"required"`
    Bloom       Bloom          `json:"logsBloom"        gencodec:"required"`
    Difficulty  *big.Int       `json:"difficulty"       gencodec:"required"`
    Number      *big.Int       `json:"number"           gencodec:"required"`
    GasLimit    uint64         `json:"gasLimit"         gencodec:"required"`
    GasUsed     uint64         `json:"gasUsed"          gencodec:"required"`
    Time        uint64         `json:"timestamp"        gencodec:"required"`
    Extra       []byte         `json:"extraData"        gencodec:"required"`
    MixDigest   common.Hash    `json:"mixHash"`
    Nonce       BlockNonce     `json:"nonce"`

    // BaseFee was added by EIP-1559 and is ignored in legacy headers.
    BaseFee *big.Int `json:"baseFeePerGas" rlp:"optional"`
}

问题描述 #

无需遍历所有字段，就能将整个Header结构体完整序列化为所有字段数值格式正确的JSON的正确方案是什么？ #

解决方案 #

问题原因 #

出现格式差异的核心原因是：Header结构体本身实现了自定义的MarshalJSON方法（由go-ethereum的gencodec工具自动生成），该实现为了符合以太坊RPC规范，会自动把所有*big.Int类型的字段序列化为带0x前缀的十六进制字符串。而单独调用big.Int的MarshalJSON方法时，走的是标准库big.Int的默认序列化逻辑，输出十进制格式。

最优方案：类型别名绕开自定义序列化 #

Go的类型别名不会继承原类型的方法，因此可以通过定义Header的别名类型，绕开原结构体的自定义MarshalJSON逻辑，直接走标准库的默认序列化规则，自动使用每个字段自身的序列化实现，无需手动遍历处理任何字段。
代码示例：

import (
    "encoding/json"
    "github.com/ethereum/go-ethereum/core/types"
)

// 定义Header类型别名，不会继承原类型的MarshalJSON方法
type CustomHeader types.Header

// 转换后直接序列化
func marshalHeaderCorrectly(header *types.Header) ([]byte, error) {
    ch := CustomHeader(*header)
    return json.Marshal(ch)
}

使用该方案序列化后，difficulty、number、baseFeePerGas等*big.Int类型字段都会输出十进制格式，其余字段的序列化结果和各自类型的默认实现保持一致，完全符合需求。

内容的提问来源于stack exchange，提问作者Kingindanord