Fix: list decode代码中将nil过滤掉的问题

[apache]

Fix: list decode代码中将nil过滤掉的问题

[wongoo]

@gaoxinge yes，list should support nil item，u can submit a pr with unit test about it. thanks!

[wongoo]

@gaoxinge slice support nil element only if the type of element is pointer, which must be verified when decoding. The following is a test to append nil to slice:

func TestSliceAppendNil(t *testing.T) {
	type Msg struct {
		Text string
	}
	a := Msg{Text: "a"}
	c := Msg{Text: "c"}

	var list []*Msg

	list = append(list, &a)
	list = append(list, nil) // append nil
	list = append(list, &c)

	assert.Equal(t, 3, len(list))
	assert.Equal(t, "a", list[0].Text)
	assert.Nil(t, list[1])
	assert.Equal(t, "c", list[2].Text)

	var list2 []*Msg
	v := reflect.ValueOf(list)
	vv := reflect.ValueOf(list2)

	for i := 0; i < v.Len(); i++ {
		vv = reflect.Append(vv, v.Index(i)) // support append nil value
	}
	list2 = vv.Interface().([]*Msg)

	assert.Equal(t, 3, len(list2))
	assert.Equal(t, "a", list2[0].Text)
	assert.Nil(t, list2[1])
	assert.Equal(t, "c", list2[2].Text)
}

[gaoxinge]

@wongoo Yes, if the slice hold a concrete type (Msg or *Msg), we should consinder to verify whether the type of element is a pointer when adding a nil. However, we use a abstract type (Interface{}) in list.go , which can hold anything, including nil.

• https://github.com/dubbogo/hessian2/blob/38ccc67445df598f0ef12020f00f6b45c6bb3470/list.go#L176
• https://github.com/dubbogo/hessian2/blob/38ccc67445df598f0ef12020f00f6b45c6bb3470/list.go#L228

[wongoo]

@gaoxinge yes, currently it ignore the list type and uses []interface{} to accept elements, and u can submit a pr for it .

While in the future, may be we can refactor to define the exact type of slice. see another implement
https://github.com/vogo/gohessian/blob/228bdae7a821ce53f4512694969325e7d60bc264/list.go#L194

[gaoxinge]

@wongoo You are very right! Although []interface{}{} is a dynamic type slice, we can't use reflect.Append to append a interface{}(nil) (or reflect.ValueOf(nil)) to the slice. So the code below

https://github.com/dubbogo/hessian2/blob/eb9857f7fae12289cad801c2914fb0b5cffbff33/list.go#L181-L195

will throw a runtime error at line 191 if variable it is nil.

So I raise a question, and maybe we can use this answer to work around this.