snap to luks

package main

import (
    "encoding/binary"
    "errors"
    "fmt"
    "os"
    "strconv"
)

// ParseRecoveryKey Parse[16]byte interprets the supplied string and returns the corresponding [16]byte. The recovery key is a
// 16-byte number, and the formatted version of this is represented as 8 5-digit zero-extended base-10 numbers (each
// with a range of 00000-65535) which may be separated by an optional '-', eg:
//
// "61665-00531-54469-09783-47273-19035-40077-28287"
//
// The formatted version of the recovery key is designed to be able to be inputted on a numeric keypad.
func ParseRecoveryKey(s string) (out [16]byte, err error) {
    for i := 0; i < 8; i++ {
        if len(s) < 5 {
            return [16]byte{}, errors.New("incorrectly formatted: insufficient characters")
        }
        x, err := strconv.ParseUint(s[0:5], 10, 16) // Base 10 16 bit int
        if err != nil {
            return [16]byte{}, errors.New("incorrectly formatted")
        }
        binary.LittleEndian.PutUint16(out[i*2:], uint16(x))

        // Move to the next 5 digits
        s = s[5:]
        // Permit each set of 5 digits to be separated by an optional '-', but don't allow the formatted key to end or begin with one.
        if len(s) > 1 && s[0] == '-' {
            s = s[1:]
        }
    }

    if len(s) > 0 {
        return [16]byte{}, errors.New("incorrectly formatted: too many characters")
    }

    return
}

func selfTest() bool {
    _, e := ParseRecoveryKey("61665-00531-54469-09783-47273-19035-40077-28287")

    if e != nil {
        return false
    } else {
        return true
    }
}

func main() {
    if !selfTest() {
        fmt.Println("Self-test failed")
        return
    }

    fmt.Println("Please enter your Snap-encoded recovery key below:")
    var recoveryKey string
    _, err := fmt.Scanln(&recoveryKey)
    if err != nil {
        fmt.Println("Failed to read your key!")
    }

    if key, e := ParseRecoveryKey(recoveryKey); e != nil {
        fmt.Printf("Failed to decode recovery key; %s\n", e)
    } else {
        //fmt.Printf("Your recovery key is: ")
        //_, _ = os.Stderr.Write(key[:])
        //fmt.Println()
        fmt.Println("Dumping to ./key.out for your convenience!")

        if err = os.WriteFile("key.out", key[:], 0600); err != nil {
            fmt.Printf("Error writing to key.out: %s", err)
        }
    }
}