PermFromString.go

// http://play.golang.org/p/cvSYnYce0I
package main

import "fmt"
import "os"

func main() {
	perm, err := PermFromString("0777")
	if err != nil {
		panic(err)
	}
	fmt.Println(perm & os.ModeType)
	fmt.Println(perm & os.ModePerm)
	
	perm, err = formatToOSFileMode("0777")
	fmt.Println(perm & os.ModeType)
	fmt.Println(perm & os.ModePerm)
}


func formatToOSFileMode(testString string) (perm os.FileMode, err error) {
    var r int64
    r, err = strconv.ParseInt(testString, 8, 32)
    if err == nil {
        perm = os.FileMode(r)
    }
    return
}

func PermFromString(perm_str string) (perm os.FileMode, err error) {
	err = nil
	if len(perm_str) != 4 {
		err = fmt.Errorf("too long")
	}
	perm = perm | (os.ModeType & (os.FileMode(perm_str[0] - 48)))
	for i, c := range perm_str[1:] {
		if c < 48 || c > 55 {
			err = fmt.Errorf("out of range")
		}
		//fmt.Println(c-48)
		if i == 0 {
			perm = os.ModePerm & (os.FileMode(c - 48))
		}
		perm = (perm << uint32(i+1)) | (os.ModePerm & (os.FileMode(c - 48)))
	}
	return
}