Using JSON Config in Go

In this article, we’re going to see how we can use json files an config for out Go applications.

First of all, we have to define struct, to load our config.
Example,

type Config struct {
 Database struct {
  Host     string `json:"host"`
  Password string `json:"password"`
  User     string `json:"user"`
  Port     int    `json:"port"`
 } `json:"database"`
 Token string `json:"token"`
}

This struct can load, following json

{
    "database": {
        "host": "localhost",
        "password": "12345"
         "user": "user",
    },
 "token": "super_secret_token"
}

Now let’s see how we can load this.

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As we know, Go will assign zero values of respective types if value is not given. Hence, we will create an value of our Config type, and add any default values if we want.

In our example, we’re assigning defualt value 5432 for port field.

config := Config{
  Database: struct {
   Host     string `json:"host"`
   Password string `json:"password"`
   User     string `json:"user"`
   Port     int    `json:"port"`
  }{
   Port: 5432,
  },
 }

Now, we just have to open a file, and decode the content into the struct.

configFile, err := os.Open(homeDir + "/.config/your_config.json")
defer configFile.Close()
if err != nil {
  log.Fatal(err)
}
jsonParser := json.NewDecoder(configFile)
jsonParser.Decode(&config)

We’re done!

Full code:

type Config struct {
 Database struct {
  Host     string `json:"host"`
  Password string `json:"password"`
  User     string `json:"user"`
  Port     int    `json:"port"`
 } `json:"database"`
 Token string `json:"token"`
}

func GetConfig() Config {
 config := Config{
  Database: struct {
   Host     string `json:"host"`
   Password string `json:"password"`
   User     string `json:"user"`
   Port     int    `json:"port"`
  }{
   Port: 5432,
  },
 }

 homeDir, err := os.UserHomeDir()
 if err != nil {
  log.Fatal(err)
 }

 configFile, err := os.Open(homeDir + "/.config/your_config.json")
 defer configFile.Close()
 if err != nil {
  log.Fatal(err)
 }
 jsonParser := json.NewDecoder(configFile)
 jsonParser.Decode(&config)
 return config
}