Go: Nested Struct Marshall & UnMarshall

The journey of “struct to json” -> “json to struct”

Mapping your model object to the response JSON from an API or reading from an input file is a common scenario while building a distributed application using Go.

Let’s take an example to understand: We have a nested JSON sample response as input in our application. Input consists of an encrypted message and key. If you look closely encryption mechanism is Caesar cipher.

{
    "sampleInput": {
        "input": {
            "encryptedMessage": "F KFRTZX JCUQTWJW TSHJ XFNI, YMFY YMJ JCYWFTWINSFWD NX NS BMFY BJ IT, STY BMT BJ FWJ. LT JCUQTWJ!",
            "key": 5
        }
    }
}

Let us construct the model hierarchy for this input.

type input struct {
 EncryptedMessage string `json:"encryptedMessage"`
 Key              int    `json:"key"`
}
type sampleInput struct {
 Input input `json:"input"`
}
type sample struct {
 SampleInput sampleInput `json:"sampleInput"`
}

In this case, I am considering inputs from a local file.

Let’s UnMarshall it (using “encoding/json” module)

file, _ := ioutil.ReadFile("input-nested.json")
var data sample
 err := json.Unmarshal([]byte(file), &data)
 if err != nil {
  fmt.Println("error:", err)
 }
fmt.Println(data)