如何判断golang的解组json接口{}类型？

Question

I want to judge json type,but it always return "I don't know about type map[string]interface {}!",How to resolve it.

=========================================================================

type getRemoteCardInfo struct {
  Code int
  Msg  string
  Data []*remoteCardInfo
 }
type remoteCardInfo struct {
 Sn            string
 RemoteCardIp  string
 RemoteCardMac string
}
func Get_json_data(url string) (interface{}, error) {
    client := &http.Client{}
    req, err := http.NewRequest("GET", url, nil)
    req.Header.Add("X-MYCMDB-Auth-Token", "sPf98SMBWzOZJEJB8KWltbJyKvFYPauu")
    if err != nil {
         return nil, err
    }
    resp, _ := client.Do(req)
    if resp.StatusCode != http.StatusOK {
    resp.Body.Close()
    return nil, fmt.Errorf("query failed: %s", resp.Status)
    }
    var result interface{}
    body, err := ioutil.ReadAll(resp.Body)
    if err := json.Unmarshal(body, &result); err != nil {
        log.Fatalf("JSON unmarshaling failed: %s", err)
    }
    resp.Body.Close()
    fmt.Println(result)
    return result, nil
    }
 func main() {
       jsondata, err := Get_json_data(DHCPURL)
       if err != nil {
         log.Fatal(err)
       }
       switch v := jsondata.(type) {
       case getRemoteCardInfo:
          fmt.Println("aaaa")
       default:
          fmt.Printf("I don't know about type %T!
", v)
       }

Answer 1

The go JSON unmarshaler doesn't know about types, as you can tell by the fact that it stores the result into an interface{} value:

func Unmarshal(data []byte, v interface{}) error
// "v" can be any type -------^

So it's up to you to use the unmarshaler to populate your structure and determine if the result is valid or not.

In your example it looks like you're trying to unmarshal a remoteCardInfo from an HTTP response. To do this you should unmarshal into an empty remoteCardInfo struct and determine if the required fields were populated.

For example, suppose you expect a JSON document like so:

{
  "sn": "123",
  "ip": "0.0.0.0",
  "mac": "ff:ff:ff:ff:ff:ff"
}

Then you should define your "remoteCardInfo" struct as below:

type remoteCardInfo struct {
  Sn            string `json:"sn"`
  RemoteCardIp  string `json:"ip"`
  RemoteCardMac string `json:"mac"`
}

And then unmarshal and validate it like so:

func getRemoteCardInfo(bs []byte) (*remoteCardInfo, error) {
  rci := remoteCardInfo{}
  err := json.Unmarshal(bs, &rci)
  if err != nil {
    return nil, err
  }
  // Validate the expected fields
  if rci.Sn == "" {
    return nil, fmt.Errorf(`missing "sn"`)
  }
  if rci.RemoteCardIp == "" {
    return nil, fmt.Errorf(`missing "ip"`)
  }
  if rci.RemoteCardMac == "" {
    return nil, fmt.Errorf(`missing "mac"`)
  }
  return &rci, nil
}

Of course, you can validate the fields any way you like but the main thing to remember is that the unmarshaler only does the job of ensuring that the input byte array is a valid JSON document and populates the fields from the document into the fields defined by the value.

It cannot tell you what "type" of object the JSON document represents.