Parse http json request based on a field in json

I want to decode an incoming JSON payload of a POST request using the Decode() function from encoding/json

However, I have a case where the body of the JSON can be different for the same http request. I want to differentiate this body based on a field embedded in the JSON. How can I extract this singular field in Go? For instance, I want the following logic-

type BaseObj struct {
        Version string
}

type v1Object struct {
        BaseObj
        Name string
}

type v2Object struct {
        BaseObj
        Name string
        Address string
}

// Somehow extract the 'version' from JSON (req.Body)
if version == "v1" {
        var data v1Object
        json.NewDecoder(req.Body).Decode(&data)
} else {
        var data v2Object
        json.NewDecoder(req.Body).Decode(&data)
}

How can I get the 'version' field embedded in the body?

Thanks for your help!

There are 2 ways to solve this issue:

Solution 1: Core Library Way

By only using the core library, you may do this:

<!--language:golang-->

import (
    "bytes"
    "ioutil"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {

    // read body content first to reuse
    type protoData struct {
        Version string `json:"version"`
    }
    proto := protoData{}
    content, err := ioutil.ReadAll(req.Body)
    json.NewDecoder(bytes.NewBuffer(content)).Decode(&proto)

    // version switch
    if proto.Version == "v1" {
            var data v1Object
            json.NewDecoder(bytes.NewBuffer(content)).Decode(&data)
            // ... do something with data
    } else {
            var data v2Object
            json.NewDecoder(bytes.NewBuffer(content)).Decode(&data)
            // ... do something with data
    }

}

Solution 2: lzjson Way

I've written a silly library, lzjson, to make the code cleaner.

<!--language:golang-->

import (
    "net/http"

    "github/go-restit/lzjson"
)

func handler(w http.ResponseWriter, r *http.Request) {
    jsonBody := lzjson.Decode(r.Body)
    version := jsonBody.Get("version").String()
    if version == "v1" {
        var data v1Object
        jsonBody.Unmarshal(&data)
        // ... do something with data
    } else {
        var data v2Object
        jsonBody.Unmarshal(&data)
        // ... do something with data
    }
}

type BaseObj struct {
        Version string
}

type v1Object struct {
        BaseObj
        Name string
}

type v2Object struct {
        BaseObj
        Name string
        Address string
}

var response map[string]string


json.Unmarshal(req.Body, &response)

if response["version"] == "v1" {
        var data v1Object
        json.NewDecoder(req.Body).Decode(&data)
} else {
        var data v2Object
        json.NewDecoder(req.Body).Decode(&data)

total solution is not good but this is the way you could use data