Parse Error from Converting Json String to Struct

Question

i cannot parse the json value i am sending a playground link Any idea about that? here is the link and codes

https://play.golang.org/p/qhZpS_-618s

package main

import (
    "encoding/json"
    "fmt"
    //mapstructure "github.com/mitchellh/mapstructure"

)

type presence struct{
    id string 
    m_type string 
    deny string 
}
type jsonHandler struct {
    name string 
    dat map[string]interface{}

}   

func main() {
    s := `["Presence",{"id":"905356870666@c.us","type":"unavailable","deny":true}]`
    data := jsonHandler{}
    json.Unmarshal([]byte(s), &data)
    fmt.Printf("Operation: %s", data.name)


}

Output : Operation: Program exited.

Answer 1

Go Playground Link: https://play.golang.org/p/qe0jyFVNTH1

Few Problem are present in this:

1. Json Package can't refer the Unexported Structure Elements.So please use Deny instead of deny in the following snippet.This is applicable to all variables declared inside the structure

2. The json fields tag are incorrect. eg.mapstructure:"id" should be json:"id"

3. The json to be parsed contains two distinct elements i.e string "Presence" and nested json object.It can't be parsed as a single element.It is better to declare "Presence" as a key and nested json as the value.

4. The deny variable should be bool rather than string

Answer 2

Try with this one: https://play.golang.com/p/UICf_uNNFdC

I've commented a lot in order to enhance code readability. Be sure to handle error properly and remove debug print.

package main

import (
    "encoding/json"
    "log"
    "strings"
)

type Presence struct {
    Presence string
    ID       string `json:"id"`
    Type     string `json:"type"`
    Deny     bool   `json:"deny"`
}

type JsonHandler struct {
    Name string   `json:"name"`
    Dat  Presence `json:"dat"`
}

func main() {
    var (
        // Used for unmarshal a given json
        packedData []json.RawMessage
        err        error
        // Data that does not have a related json key
        name []byte
        // Used for extract the raw data that will be unmarshalled into the Presence struct
        temp []byte
        // Nested json
        jsonPresence Presence
        handler      JsonHandler
    )

    s := `["Presence",{"id":"905356870666@c.us","type":"unavailable","deny":true}]`

    log.Println("Dealing with -> " + s)

    // Unmarshall into a raw json message
    err = json.Unmarshal([]byte(s), &packedData)
    if err != nil {
        panic(err)
    }

    // Extract the presence
    log.Println("Presence: ", string(packedData[0]))
    // Extract the nested json
    log.Println("Packed: ", string(packedData[1]))

    // NOTE: 0 refers to the first value of the JSON
    name, err = packedData[0].MarshalJSON()
    if err != nil {
        panic(err)
    }
    log.Println("Value that does not have a key: " + string(name))
    handler.Name = strings.Replace(string(name), "\"", "", -1)

    // NOTE: 1 refers to the second value of the JSON, the entire JSON
    // Unmarshal the nested Json into byte
    temp, err = packedData[1].MarshalJSON()
    if err != nil {
        panic(err)
    }

    // Unmarshal the raw byte into the struct
    err = json.Unmarshal(temp, &jsonPresence)
    if err != nil {
        panic(err)
    }

    log.Println("ID:", jsonPresence.ID)
    log.Println("Type:", jsonPresence.Type)
    log.Println("Deny:", jsonPresence.Deny)

    handler.Dat = jsonPresence

    log.Println("Data unmarshalled: ", handler)
}

Answer 3

Wow,solved problem by adding only these codes

Here Go Lang Link : https://play.golang.org/p/doHNWK58Cae

func (n *JsonHandler) UnmarshalJSON(buf []byte) error {
    tmp := []interface{}{&n.Name, &n.Dat}
    wantLen := len(tmp)
    if err := json.Unmarshal(buf, &tmp); err != nil {
        return err
    }
    if g, e := len(tmp), wantLen; g != e {
        return fmt.Errorf("wrong number of fields in Notification: %d != %d", g, e)
    }
    return nil
}