New static configuration loading system.

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

pkg/config/flag/flagparser.go

@@ -0,0 +1,108 @@
+package flag
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// Parse parses the command-line flag arguments into a map,
+// using the type information in element to discriminate whether a flag is supposed to be a bool,
+// and other such ambiguities.
+func Parse(args []string, element interface{}) (map[string]string, error) {
+	f := flagSet{
+		flagTypes: getFlagTypes(element),
+		args:      args,
+		values:    make(map[string]string),
+	}
+
+	for {
+		seen, err := f.parseOne()
+		if seen {
+			continue
+		}
+		if err == nil {
+			break
+		}
+		return nil, err
+	}
+	return f.values, nil
+}
+
+type flagSet struct {
+	flagTypes map[string]reflect.Kind
+	args      []string
+	values    map[string]string
+}
+
+func (f *flagSet) parseOne() (bool, error) {
+	if len(f.args) == 0 {
+		return false, nil
+	}
+
+	s := f.args[0]
+	if len(s) < 2 || s[0] != '-' {
+		return false, nil
+	}
+	numMinuses := 1
+	if s[1] == '-' {
+		numMinuses++
+		if len(s) == 2 { // "--" terminates the flags
+			f.args = f.args[1:]
+			return false, nil
+		}
+	}
+
+	name := s[numMinuses:]
+	if len(name) == 0 || name[0] == '-' || name[0] == '=' {
+		return false, fmt.Errorf("bad flag syntax: %s", s)
+	}
+
+	// it's a flag. does it have an argument?
+	f.args = f.args[1:]
+	hasValue := false
+	value := ""
+	for i := 1; i < len(name); i++ { // equals cannot be first
+		if name[i] == '=' {
+			value = name[i+1:]
+			hasValue = true
+			name = name[0:i]
+			break
+		}
+	}
+
+	if hasValue {
+		f.setValue(name, value)
+		return true, nil
+	}
+
+	if f.flagTypes[name] == reflect.Bool || f.flagTypes[name] == reflect.Ptr {
+		f.setValue(name, "true")
+		return true, nil
+	}
+
+	if len(f.args) > 0 {
+		// value is the next arg
+		hasValue = true
+		value, f.args = f.args[0], f.args[1:]
+	}
+
+	if !hasValue {
+		return false, fmt.Errorf("flag needs an argument: -%s", name)
+	}
+
+	f.setValue(name, value)
+	return true, nil
+}
+
+func (f *flagSet) setValue(name string, value string) {
+	n := strings.ToLower("traefik." + name)
+	v, ok := f.values[n]
+
+	if ok && f.flagTypes[name] == reflect.Slice {
+		f.values[n] = v + "," + value
+		return
+	}
+
+	f.values[n] = value
+}