Detect if JSON file has field

Question

My app reads settings from a config file:

file, _ := os.Open("config.json")
config := config.Config{}
err := json.NewDecoder(file).Decode(&config)
if err != nil {
    //handle err
}

My JSON config file looks something like this:

{
    "site" : {
        "url" : "https://example.com"
    },
    "email" : {
        "key" : "abcde"
    }
}

My structs are:

type Site struct {
    Url  string
}

type Email struct {
    Key  string
}

type Config struct {
    Site   Site
    Email  Email
}

I would like the option of removing the email field from the JSON file to indicate that no email account will be used so:

{
    "site" : {
        "url" : "https://example.com"
    }
}

How do I detect if a specific field exists in the JSON file in Go so something on the lines of:

if (Email field found in JSON file) {
    output "You want to receive emails"
} else {
    output "No emails for you!"
}

Answer 1

Change Config to

type Config struct {
  Site   Site
  Email  *Email
}

Use c.Email != nil to test if email is specified as a string value in the JSON file. If c.Email == nil, then email is not specified or null.

playground example