JSON in Go

Internal

• Go Code Examples
• Go Package encoding/json
• JSON

TODO

TO PROCESS:

• https://www.digitalocean.com/community/tutorials/how-to-use-struct-tags-in-go
• https://golang.cafe/blog/golang-json-marshal-example.html
• Reading into an array of custom structs:

var ratings []model.RatingEvent
if err := json.NewDecoder(f).Decode(&ratings); err != nil {
    return nil, err
}

Overview

Struct tags can be used in the JAML serialization/deserialization process.

JSON Marshalling Go → JSON

JSON marshalling means generating a JSON representation from a Go object. It is done with json.Marshal(). The result is a byte array. To convert the byte array to a string, see:

Go Integers | Conversion between bytes and strings

Struct Marshalling

By default, only fields that start with capital letters are marshaled. The fields that start with lower caps are invisible to the marshaling process.

type Item struct {
  Color string
  Size int
  Options []string
}

i := Item{Color: "blue", Size: 5, Options: []string{"brake", "acceleration", "lights"}}

ba, err := json.Marshal(i) // pass the value

fmt.Println(string(ba))

JSON Unmarshalling JSON → Go

Unmarshalling into Struct

With a Byte Slice

type Item struct {
  Color string
  Size int
  Options []string
}

s := "{\"Color\":\"blue\",\"Size\":5,\"Options\":[\"brake\",\"acceleration\",\"lights\"]}"
ba := []byte(s)
var i Item

err := json.Unmarshal(ba, &i) // pass the pointer

fmt.Printf("%+v\n", i)

With a Reader

Using a Reader:

var req *http.Request = ...
reader := req.Body // body implements Reader
jsonDecoder := json.NewDecoder(reader)
var s SomeStruct
if e := jsonDecoder.Decode(&s); e != nil {
  // ...
}
fmt.Printf("%+v\n", s)

This only works if the HTTP requests has a "Content-Type: application/json" header, otherwise the decoding fails with an EOF error. Also see:

net/http | Reading the Request Body