解决 golang 实现json序列化调用原生序列化stack溢出问题

1. 问题描述

实现json序列化接口后调用原生序列化方法会造成代码死循环而导致stack溢出

代码如下

type test struct{
}

func (t test) MarshalJSON() ([]byte, error){
   return json.Marshal(t) // stack over
}

2. 问题分析

json.Marshal核心代码中包含会调用对象实现的MarshalJSON方法

核心代码如下

type Marshaler interface {
	MarshalJSON() ([]byte, error)
}


// newTypeEncoder constructs an encoderFunc for a type.
// The returned encoder only checks CanAddr when allowAddr is true.
func newTypeEncoder(t reflect.Type, allowAddr bool) encoderFunc {
	// If we have a non-pointer value whose type implements
	// Marshaler with a value receiver, then we're better off taking
	// the address of the value - otherwise we end up with an
	// allocation as we cast the value to an interface.
	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(marshalerType) {
		return newCondAddrEncoder(addrMarshalerEncoder, newTypeEncoder(t, false))
	}
	if t.Implements(marshalerType) { 
		return marshalerEncoder
	}
	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(textMarshalerType) {
		return newCondAddrEncoder(addrTextMarshalerEncoder, newTypeEncoder(t, false))
	}
	if t.Implements(textMarshalerType) {
		return textMarshalerEncoder
	}
    // 省略 ...
}

func marshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
	if v.Kind() == reflect.Pointer && v.IsNil() {
		e.WriteString("null")
		return
	}
	m, ok := v.Interface().(Marshaler)
	if !ok {
		e.WriteString("null")
		return
	}
	b, err := m.MarshalJSON() // 调用自身，循环核心问题
	if err == nil {
		// copy JSON into buffer, checking validity.
		err = compact(&e.Buffer, b, opts.escapeHTML)
	}
	if err != nil {
		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})
	}
}

3.解决方案

1. 真实现自身序列化 MarshalJSON() ([]byte, error) 方法
2. 打断json.MashalJson循环条件，即m, ok := v.Interface().(Marshaler) 不成立

代码如下

type test struct {
}

//方案1
func (t test) MarshalJSON() ([]byte, error) {
	return []byte("{}")
}

//方案2
func (t test) MarshalJSON() ([]byte, error) {
	type x test
	return json.Marshal(x(t))
}

func main() {
	t := test{}
	type x test
	marshalerType := reflect.TypeOf((*json.Marshaler)(nil)).Elem()
	println(reflect.TypeOf(t).Implements(marshalerType)) // true
	println(reflect.TypeOf(x(t)).Implements(marshalerType)) //false
}