解析 json 的一个问题

代码如下：

package main

import (
    "encoding/json"
    "fmt"
)

type MqttClientConfigEntry struct {
    Broker            string `json: "broker"`
    ClientId          string `json: "clientId"`
    CleanSession      bool   `json: "cleanSession"`
    KeepAliveInterval uint32 `json: "keepAliveInterval"`
    Password          string `json: "password"`
    UserName          string `json: "userName"`
    PubTopic          string `json: "pubTopic"`
    SubTopic          string `json: "subTopic"`
}

type MqttClientConfig struct {
    E MqttClientConfigEntry `json: "MqttClient"`
}

const s = `{
  "MqttClient": {
    "broker": "8888888888888888888/",
    "clientId": "11111111111111111",
    "cleanSession": true,
    "keepAliveInterval": 100,
    "password": "2222222222222",
    "userName": "3333333333333333",
    "pubTopic": "9999999999",
    "subTopic": "111111"
  }
}`

func main() {
    var mcc MqttClientConfig
    err := json.Unmarshal([]byte(s), &mcc)
    if err != nil {
        fmt.Println(err)
    } else {
        fmt.Println(mcc)
    }
}

程序的目的是解析一个 json 字符串，返回的 error 为 nil，但 MqttClientConfig 对象没有任何数值填充进来：

输出如下 {{ false 0 }}