Test different standard location for config file

If no path is given in the environment variable CORE_CONFIGFILE, different
standard locations will be probed:
- os.UserConfigDir() + /datarhei-core/config.js
- os.UserHomeDir() + /.config/datarhei-core/config.js
- ./config/config.js
If the config.js doesn't exist in any of these locations, it will be
assumed at ./config/config.js

app/api/api.go

@@ -229,6 +229,8 @@ func (a *api) Reload() error {
 
 	logger.Info().WithFields(logfields).Log("")
 
+	logger.Info().WithField("path", a.config.path).Log("Read config file")
+
 	configlogger := logger.WithComponent("Config")
 	cfg.Messages(func(level string, v configvars.Variable, message string) {
 		configlogger = configlogger.WithFields(log.Fields{

config/store/json.go

@@ -118,6 +118,10 @@ func (c *jsonStore) load(cfg *config.Config) error {
 		return err
 	}
 
+	if len(jsondata) == 0 {
+		return nil
+	}
+
 	data, err := migrate(jsondata)
 	if err != nil {
 		return err

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"os"
 	"os/signal"
+	"path"
 
 	"github.com/datarhei/core/v16/app/api"
 	"github.com/datarhei/core/v16/log"
@@ -13,7 +14,9 @@ import (
 func main() {
 	logger := log.New("Core").WithOutput(log.NewConsoleWriter(os.Stderr, log.Lwarn, true))
 
-	app, err := api.New(os.Getenv("CORE_CONFIGFILE"), os.Stderr)
+	configfile := findConfigfile()
+
+	app, err := api.New(configfile, os.Stderr)
 	if err != nil {
 		logger.Error().WithError(err).Log("Failed to create new API")
 		os.Exit(1)
@@ -54,3 +57,51 @@ func main() {
 	// Stop the app
 	app.Destroy()
 }
+
+// findConfigfie returns the path to the config file. If no path is given
+// in the environment variable CORE_CONFIGFILE, different standard location
+// will be probed:
+// - os.UserConfigDir() + /datarhei-core/config.js
+// - os.UserHomeDir() + /.config/datarhei-core/config.js
+// - ./config/config.js
+// If the config doesn't exist in none of these locations, it will be assumed
+// at ./config/config.js
+func findConfigfile() string {
+	configfile := os.Getenv("CORE_CONFIGFILE")
+	if len(configfile) != 0 {
+		return configfile
+	}
+
+	locations := []string{}
+
+	if dir, err := os.UserConfigDir(); err == nil {
+		locations = append(locations, dir+"/datarhei-core/config.js")
+	}
+
+	if dir, err := os.UserHomeDir(); err == nil {
+		locations = append(locations, dir+"/.config/datarhei-core/config.js")
+	}
+
+	locations = append(locations, "./config/config.js")
+
+	for _, path := range locations {
+		info, err := os.Stat(path)
+		if err != nil {
+			continue
+		}
+
+		if info.IsDir() {
+			continue
+		}
+
+		configfile = path
+	}
+
+	if len(configfile) == 0 {
+		configfile = "./config/config.js"
+	}
+
+	os.MkdirAll(path.Dir(configfile), 0740)
+
+	return configfile
+}