New static configuration loading system.

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

pkg/cli/loader_file.go

@@ -0,0 +1,78 @@
+package cli
+
+import (
+	"io/ioutil"
+	"os"
+	"strings"
+
+	"github.com/containous/traefik/pkg/config/file"
+	"github.com/containous/traefik/pkg/config/flag"
+	"github.com/containous/traefik/pkg/log"
+)
+
+// FileLoader loads a configuration from a file.
+type FileLoader struct {
+	ConfigFileFlag string
+	filename       string
+}
+
+// GetFilename returns the configuration file if any.
+func (f *FileLoader) GetFilename() string {
+	return f.filename
+}
+
+// Load loads the command's configuration from a file either specified with the -traefik.configfile flag, or from default locations.
+func (f *FileLoader) Load(args []string, cmd *Command) (bool, error) {
+	ref, err := flag.Parse(args, cmd.Configuration)
+	if err != nil {
+		_ = PrintHelp(os.Stdout, cmd)
+		return false, err
+	}
+
+	configFileFlag := "traefik.configfile"
+	if f.ConfigFileFlag != "" {
+		configFileFlag = "traefik." + strings.ToLower(f.ConfigFileFlag)
+	}
+
+	configFile, err := loadConfigFiles(ref[configFileFlag], cmd.Configuration)
+	if err != nil {
+		return false, err
+	}
+
+	f.filename = configFile
+
+	if configFile == "" {
+		return false, nil
+	}
+
+	logger := log.WithoutContext()
+	logger.Printf("Configuration loaded from file: %s", configFile)
+
+	content, _ := ioutil.ReadFile(configFile)
+	logger.Debug(string(content))
+
+	return true, nil
+}
+
+// loadConfigFiles tries to decode the given configuration file and all default locations for the configuration file.
+// It stops as soon as decoding one of them is successful.
+func loadConfigFiles(configFile string, element interface{}) (string, error) {
+	finder := Finder{
+		BasePaths:  []string{"/etc/traefik/traefik", "$XDG_CONFIG_HOME/traefik", "$HOME/.config/traefik", "./traefik"},
+		Extensions: []string{"toml", "yaml", "yml"},
+	}
+
+	filePath, err := finder.Find(configFile)
+	if err != nil {
+		return "", err
+	}
+
+	if len(filePath) == 0 {
+		return "", nil
+	}
+
+	if err = file.Decode(filePath, element); err != nil {
+		return "", err
+	}
+	return filePath, nil
+}