Golang add key/value to json file

main.go

package main

import (
  "encoding/json"
  "log"
  "os"
  "sync"
)

type Exclude struct {
	Exclude map[string]string `json:"exclude"`
}


func addToFile(file, key, value string, mu sync.RWMutex) {
  	mu.Lock()
	fileData, _ := os.ReadFile(file)
	excluded := Exclude{}
	unmarshalErr := json.Unmarshal(fileData, &excluded)
	if unmarshalErr != nil {
		log.Fatalf("failed unmarshaling excludeFile %v", excludeFile)
	}
	// add value
	excluded.Exclude[key] = value

	// now Marshal it
	excludedBytes, marshalErr := json.MarshalIndent(excluded, "", "  ")
	if marshalErr != nil {
		log.Fatal("failed marshaling exluded json.")
	}
	writeErr := os.WriteFile(file, excludedBytes, 0666)
	mu.Unlock()
	if writeErr != nil {
		log.Fatal("failed writing to file", err)
	}
	log.Println("done writing to file.")
}

func main() {
	var fileMutex sync.RWMutex
	file := "/home/justin/exclusions.json"
	addToFile(file, "foo", "bar", fileMutex)
}