Golang: Marshal & Unmarshal partially known / dynamic JSON. Using structs (type safe).

json.go

// To stop json.Marshal from using HTMLEscape and adding trailing newline, see:
// https://github.com/SCP002/jsonexraw

package main

import (
	"fmt"

	json "github.com/yaegashi/jsonex.go/v1"
)

type TopStruct struct {
	TopKnownKey      int                    `json:"topKnownKey"`
	NestedKnownArray []NestedStruct         `json:"nestedKnownArray"`
	ExcludedKnownKey int                    `json:"-"`               // Field sample for internal needs, excluded from JSON processing.
	Unknown          map[string]interface{} `json:"-" jsonex:"true"` // All unknown fields go here.
}

type NestedStruct struct {
	NestedKnownKey   int                    `json:"nestedKnownKey"`
	ExcludedKnownKey int                    `json:"-"`               // Field sample for internal needs, excluded from JSON processing.
	Unknown          map[string]interface{} `json:"-" jsonex:"true"` // All unknown fields go here.
}

func main() {
	const input string = `
	{
		"topKnownKey": 1,
		"topUnknownKey": 2,
		"nestedKnownArray": [
		  {
			"nestedKnownKey": 3,
			"nestedUnknownKey": 4
		  },
		  {
			"nestedKnownKey": 5,
			"nestedUnknownKey": 6
		  }
		],
		"nestedUnknownArray": [
		  {
			"nestedKnownKey": 7,
			"nestedUnknownKey": 8
		  }
		]
	  }
	`

	// Decode.
	ts := TopStruct{}
	err := json.Unmarshal([]byte(input), &ts)
	if err != nil {
		panic(err)
	}

	// Modify.
	ts.TopKnownKey = 100
	ts.ExcludedKnownKey = 200
	ts.NestedKnownArray[0].NestedKnownKey = 300
	ts.NestedKnownArray[0].ExcludedKnownKey = 400

	// Encode.
	out, err := json.MarshalIndent(&ts, "", "  ")
	if err != nil {
		panic(err)
	}

	// Print output.
	fmt.Print(string(out))
}