json: cannot unmarshal string into Go value of type MyMap.map-CodePudding

I met problem with marshaling JSON in golang.

I need to unmarshal json object, that I recieve from UDP packets. But I met problem with unmarshaling - it doesn't want to unmarshal properly.

I get "Error with unmarshaling: json: cannot unmarshal string into Go value of type main.MyMap" error. I tested in different ways, but feel stuck on this example - marshaland unmarshal in one line, and still get errors.

    package main

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

type MyMap struct {
    Param map[string]string `json:"packet"`
}

func main() {
    rawJson := []byte(`{
        "packet":{
            "hostname":"host1",
            "pid":"123435",
            "processname":"process",
            "type":"partial"}
        }`)

    data, err := json.Marshal(rawJson)
    if err != nil {
        log.Println("Error with marchal JSON: "   err.Error())
    }

    var unmarshaled MyMap

    err = json.Unmarshal(data, &unmarshaled)
    if err != nil {
        fmt.Printf("Error with unmarshaling: %v", err)
        return
    }

    fmt.Printf("Read a message from %v     %s \n", unmarshaled.Param["pid"], unmarshaled.Param["processname"])
}

If I'm trying to unmarshal JSON, that I received from UDP, the error says

invalid character 'i/x01' looking for beginning of value

I believe I get this kind of error because of my misunderstanding of marshal system. I'd be appreciate if you help me Thanks!

CodePudding user response：

you should change rawjson to string type and change your order code same as:

package main

import (
    "encoding/json"
    "fmt"
)

type MyMap struct {
    Param map[string]string `json:"packet"`
}

func main() {
    rawJson := `{
        "packet":{
            "hostname":"host1",
            "pid":"123435",
            "processname":"process",
            "type":"partial"}
        }`

    struct_instance := MyMap{}
    if er := json.Unmarshal([]byte(rawJson), &struct_instance); er != nil {
        fmt.Println(er)
    }
    fmt.Println(struct_instance)

    json_as_byte, er := json.Marshal(struct_instance)
    if er != nil {
        fmt.Println(er)
    }

    fmt.Println(string(json_as_byte))

}

CodePudding user response：

I did few changes in your code and it's worked very well.

You can run it here: https://go.dev/play/p/jvw9MsVFbHt

type mp map[string]string
type MyMap struct {
    Param mp `json:"packet"`
}

func main() {
    rawJson := []byte(`{
        "packet":{
            "hostname":"host1",
            "pid":"123435",
            "processname":"process",
            "type":"partial"}
        }`)
    data, err := json.Marshal(rawJson)     //Not Required
    if err != nil {
        fmt.Println("Error with marchal JSON: "   err.Error())
    }
    fmt.Println("data ", data)

    var res MyMap

    json.Unmarshal(rawJson, &res)
    fmt.Printf("Read a message from %v     %s \n", res.Param["pid"], res.Param["processname"])
}