How Do I Parse a JSON file into a struct with Go

I'm trying to configure my Go program by creating a JSON file and parsing it into a struct:

var settings struct {
    serverMode bool
    sourceDir  string
    targetDir  string
}

func main() {

    // then config file settings

    configFile, err := os.Open("config.json")
    if err != nil {
        printError("opening config file", err.Error())
    }

    jsonParser := json.NewDecoder(configFile)
    if err = jsonParser.Decode(&settings); err != nil {
        printError("parsing config file", err.Error())
    }

    fmt.Printf("%v %s %s", settings.serverMode, settings.sourceDir, settings.targetDir)
    return
}

The config.json file:

{
    "serverMode": true,
    "sourceDir": ".",
    "targetDir": "."
}

The Program compiles and runs without any errors, but the print statement outputs:

false  

(false and two empty strings)

I've also tried with json.Unmarshal(..) but had the same result.

How do I parse the JSON in a way that fills the struct values?