在进行中，什么是json.Unmarshal最大深度？

Question

I'm trying to parse JSON response that looks like this:

{
    "object": "page",
    "entry": [
        {
            "id": 185985174761277,
            "time": 1462333588680,
            "messaging": [
                {
                    "sender": {
                        "id": 1053704801343033
                    },
                    "recipient": {
                        "id": 185985174761277
                    },
                    "timestamp": 1462333588645,
                    "message": {
                        "mid": "mid.1462333588639:d44f4374dfc510c351",
                        "seq": 1948,
                        "text": "Hello World!"
                    }
                }
            ]
        }
    ]
}

I'm using json.Unmarshal and passing the following struct as the interface:

type Message struct {
    Object string
    Entry  []struct {
        Id        int64
        Time      int64
        Messaging []struct {
            Sender struct {
                Id string
            }
            Recipient struct {
                Id string
            }
            Timestamp int64
            Message   struct {
                Mid  string
                Seq  string
                Text string
            }
        }
    }
}

However, json.Unmarshal does not match the JSON Response to any of the structs in Messaging

This function reproduces the issue exactly:

type Message struct {
    Object string
    Entry  []struct {
        Id        int64
        Time      int64
        Messaging []struct {
            Sender struct {
                Id string
            }
            Recipient struct {
                Id string
            }
            Timestamp int64
            Message   struct {
                Mid  string
                Seq  string
                Text string
            }
        }
    }
}
func testStruct() {
    jsonResponse := []byte(`{
    "object": "page",
    "entry": [
        {
            "id": 185985174761277,
            "time": 1462333588680,
            "messaging": [
                {
                    "sender": {
                        "id": 1053704801343033
                    },
                    "recipient": {
                        "id": 185985174761277
                    },
                    "timestamp": 1462333588645,
                    "message": {
                        "mid": "mid.1462333588639:d44f4374dfc510c351",
                        "seq": 1948,
                        "text": "oijsdfoijsdfoij"
                    }
                }
            ]
        }
    ]
}`)
    var m Message
    json.Unmarshal(jsonResponse, &m)
    fmt.Println(string(jsonResponse))
    fmt.Printf("%+v
", m)
}

This is the output:

{Object:page Entry:[{Id:185985174761277 Time:1462333588680 Messaging:[{Sender:{Id:} Recipient:{Id:} Timestamp:0 Message:{Mid: Seq: Text:}}]}]}

and as you can see, all the fields inside the Message struct are not set.

My question is, is there a maximum depth that json.Unmarshal can match? and if there is not, what am I doing wrong?

Answer 1

I don't think there is a maximum depth on json.Unmarshal.

In your code, Seq field in Message field is defined as string, so are Id fields in Sender and Recipient, while in json they are integers. That should be the culprit for the missing fields.