storj/pkg/cfgstruct/bind.go

// Copyright (C) 2018 Storj Labs, Inc.
// See LICENSE for copying information.

package cfgstruct

import (
	"fmt"
	"os"
	"reflect"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// Bind sets flags on a FlagSet that match the configuration struct
// 'config'. This works by traversing the config struct using the 'reflect'
// package.
func Bind(flags FlagSet, config interface{}) {
	ptrtype := reflect.TypeOf(config)
	if ptrtype.Kind() != reflect.Ptr {
		panic(fmt.Sprintf("invalid config type: %#v. "+
			"Expecting pointer to struct.", config))
	}
	bindConfig(flags, "", reflect.ValueOf(config).Elem())
}

var (
	whitespace = regexp.MustCompile(`\s+`)
)

func bindConfig(flags FlagSet, prefix string, val reflect.Value) {
	if val.Kind() != reflect.Struct {
		panic(fmt.Sprintf("invalid config type: %#v. Expecting struct.",
			val.Interface()))
	}
	typ := val.Type()

	for i := 0; i < typ.NumField(); i++ {
		field := typ.Field(i)
		fieldval := val.Field(i)
		flagname := prefix + hyphenate(snakeCase(field.Name))

		switch field.Type.Kind() {
		case reflect.Struct:
			if field.Anonymous {
				bindConfig(flags, prefix, fieldval)
			} else {
				bindConfig(flags, flagname+".", fieldval)
			}
		case reflect.Array, reflect.Slice:
			digits := len(fmt.Sprint(fieldval.Len()))
			for j := 0; j < fieldval.Len(); j++ {
				padding := strings.Repeat("0", digits-len(fmt.Sprint(j)))
				bindConfig(flags, fmt.Sprintf("%s.%s%d.", flagname, padding, j),
					fieldval.Index(j))
			}
		default:
			tag := reflect.StructTag(
				whitespace.ReplaceAllString(string(field.Tag), " "))
			help := tag.Get("help")
			def := tag.Get("default")
			fieldaddr := fieldval.Addr().Interface()
			check := func(err error) {
				if err != nil {
					panic(fmt.Sprintf("invalid default value for %s: %#v", flagname, def))
				}
			}
			switch field.Type {
			case reflect.TypeOf(int(0)):
				val, err := strconv.ParseInt(def, 0, strconv.IntSize)
				check(err)
				flags.IntVar(fieldaddr.(*int), flagname, int(val), help)
			case reflect.TypeOf(int64(0)):
				val, err := strconv.ParseInt(def, 0, 64)
				check(err)
				flags.Int64Var(fieldaddr.(*int64), flagname, val, help)
			case reflect.TypeOf(uint(0)):
				val, err := strconv.ParseUint(def, 0, strconv.IntSize)
				check(err)
				flags.UintVar(fieldaddr.(*uint), flagname, uint(val), help)
			case reflect.TypeOf(uint64(0)):
				val, err := strconv.ParseUint(def, 0, 64)
				check(err)
				flags.Uint64Var(fieldaddr.(*uint64), flagname, val, help)
			case reflect.TypeOf(time.Duration(0)):
				val, err := time.ParseDuration(def)
				check(err)
				flags.DurationVar(fieldaddr.(*time.Duration), flagname, val, help)
			case reflect.TypeOf(float64(0)):
				val, err := strconv.ParseFloat(def, 64)
				check(err)
				flags.Float64Var(fieldaddr.(*float64), flagname, val, help)
			case reflect.TypeOf(string("")):
				flags.StringVar(fieldaddr.(*string), flagname, os.ExpandEnv(def), help)
			case reflect.TypeOf(bool(false)):
				val, err := strconv.ParseBool(def)
				check(err)
				flags.BoolVar(fieldaddr.(*bool), flagname, val, help)
			default:
				panic(fmt.Sprintf("invalid field type: %s", field.Type.String()))
			}
		}
	}
}