使用golang JSON解码PubNub消息

Question

I've been trying to parse this JSON message from PubNub without any luck:

type PubNubMessage struct {
    body []string
}

[[{"text":"hey"}],"1231212412423235","channelName"]
json: cannot unmarshal array into Go value of type main.PubNubMessage

Does anyone have an idea on how to decode such complex types in golang?

Answer 1

The short answer is that you cannot directly unmarshal a JSON array of non-homogenous types (per your example) into a golang struct.

The long answer is that you should define an (m *PubNubMessage) UnmarshalJSON([]byte) error method for your PubNubMessage type which unmarshals the JSON string into an interface{} and then uses type assertions to ensure the expected format and populates the structure.

For example:

type TextMessage struct {
  Text string
}

type PubNubMessage struct {
  Messages []TextMessage
  Id       string
  Channel  string
}

func (pnm *PubNubMessage) UnmarshalJSON(bs []byte) error {
  var arr []interface{}
  err := json.Unmarshal(bs, &arr)
  if err != nil {
    return err
  }
  messages := arr[0].([]interface{}) // TODO: proper type check.
  pnm.Messages = make([]TextMessage, len(messages))
  for i, m := range messages {
    pnm.Messages[i].Text = m.(map[string]interface{})["text"].(string) // TODO: proper type check.
  }
  pnm.Id = arr[1].(string) // TODO: proper type check.
  pnm.Channel = arr[2].(string) // TODO: proper type check.
  return nil
}

  // ...
  jsonStr := `[[{"text":"hey"},{"text":"ok"}],"1231212412423235","channelName"]`
  message := PubNubMessage{}
  err := json.Unmarshal([]byte(jsonStr), &message)