traefik/vendor/github.com/tv42/zbase32/zbase32.go
2017-03-09 13:13:02 +01:00

222 lines
5.8 KiB
Go

// Package zbase32 implements the z-base-32 encoding as specified in
// http://philzimmermann.com/docs/human-oriented-base-32-encoding.txt
//
// Note that this is NOT RFC 4648, for that see encoding/base32.
// z-base-32 is a variant that aims to be more human-friendly, and in
// some circumstances shorter.
//
// Bits
//
// When the amount of input is not a full number of bytes, encoding
// the data can lead to an unnecessary, non-information-carrying,
// trailing character in the encoded data. This package provides
// 'Bits' variants of the functions that can avoid outputting this
// unnecessary trailing character. For example, encoding a 20-bit
// message:
//
// EncodeToString([]byte{0x10, 0x11, 0x10}) == "nyety"
// EncodeBitsToString([]byte{0x10, 0x11, 0x10}, 20) == "nyet"
//
// Decoding such a message requires also using the 'Bits' variant
// function.
package zbase32
import (
"errors"
"strconv"
)
const alphabet = "ybndrfg8ejkmcpqxot1uwisza345h769"
var decodeMap [256]byte
func init() {
for i := 0; i < len(decodeMap); i++ {
decodeMap[i] = 0xFF
}
for i := 0; i < len(alphabet); i++ {
decodeMap[alphabet[i]] = byte(i)
}
}
// CorruptInputError means that the byte at this offset was not a valid
// z-base-32 encoding byte.
type CorruptInputError int64
func (e CorruptInputError) Error() string {
return "illegal z-base-32 data at input byte " + strconv.FormatInt(int64(e), 10)
}
// EncodedLen returns the maximum length in bytes of the z-base-32
// encoding of an input buffer of length n.
func EncodedLen(n int) int {
return (n + 4) / 5 * 8
}
// DecodedLen returns the maximum length in bytes of the decoded data
// corresponding to n bytes of z-base-32-encoded data.
func DecodedLen(n int) int {
return (n + 7) / 8 * 5
}
func encode(dst, src []byte, bits int) int {
off := 0
for i := 0; i < bits || (bits < 0 && len(src) > 0); i += 5 {
b0 := src[0]
b1 := byte(0)
if len(src) > 1 {
b1 = src[1]
}
char := byte(0)
offset := uint(i % 8)
if offset < 4 {
char = b0 & (31 << (3 - offset)) >> (3 - offset)
} else {
char = b0 & (31 >> (offset - 3)) << (offset - 3)
char |= b1 & (255 << (11 - offset)) >> (11 - offset)
}
// If src is longer than necessary, mask trailing bits to zero
if bits >= 0 && i+5 > bits {
char &= 255 << uint((i+5)-bits)
}
dst[off] = alphabet[char]
off++
if offset > 2 {
src = src[1:]
}
}
return off
}
// EncodeBits encodes the specified number of bits of src. It writes at
// most EncodedLen(len(src)) bytes to dst and returns the number of
// bytes written.
//
// EncodeBits is not appropriate for use on individual blocks of a
// large data stream.
func EncodeBits(dst, src []byte, bits int) int {
if bits < 0 {
return 0
}
return encode(dst, src, bits)
}
// Encode encodes src. It writes at most EncodedLen(len(src)) bytes to
// dst and returns the number of bytes written.
//
// Encode is not appropriate for use on individual blocks of a large
// data stream.
func Encode(dst, src []byte) int {
return encode(dst, src, -1)
}
// EncodeToString returns the z-base-32 encoding of src.
func EncodeToString(src []byte) string {
dst := make([]byte, EncodedLen(len(src)))
n := Encode(dst, src)
return string(dst[:n])
}
// EncodeBitsToString returns the z-base-32 encoding of the specified
// number of bits of src.
func EncodeBitsToString(src []byte, bits int) string {
dst := make([]byte, EncodedLen(len(src)))
n := EncodeBits(dst, src, bits)
return string(dst[:n])
}
func decode(dst, src []byte, bits int) (int, error) {
olen := len(src)
off := 0
for len(src) > 0 {
// Decode quantum using the z-base-32 alphabet
var dbuf [8]byte
j := 0
for ; j < 8; j++ {
if len(src) == 0 {
break
}
in := src[0]
src = src[1:]
dbuf[j] = decodeMap[in]
if dbuf[j] == 0xFF {
return off, CorruptInputError(olen - len(src) - 1)
}
}
// 8x 5-bit source blocks, 5 byte destination quantum
dst[off+0] = dbuf[0]<<3 | dbuf[1]>>2
dst[off+1] = dbuf[1]<<6 | dbuf[2]<<1 | dbuf[3]>>4
dst[off+2] = dbuf[3]<<4 | dbuf[4]>>1
dst[off+3] = dbuf[4]<<7 | dbuf[5]<<2 | dbuf[6]>>3
dst[off+4] = dbuf[6]<<5 | dbuf[7]
// bits < 0 means as many bits as there are in src
if bits < 0 {
var lookup = []int{0, 1, 1, 2, 2, 3, 4, 4, 5}
off += lookup[j]
continue
}
bitsInBlock := bits
if bitsInBlock > 40 {
bitsInBlock = 40
}
off += (bitsInBlock + 7) / 8
bits -= 40
}
return off, nil
}
// DecodeBits decodes the specified number of bits of z-base-32
// encoded data from src. It writes at most DecodedLen(len(src)) bytes
// to dst and returns the number of bytes written.
//
// If src contains invalid z-base-32 data, it will return the number
// of bytes successfully written and CorruptInputError.
func DecodeBits(dst, src []byte, bits int) (int, error) {
if bits < 0 {
return 0, errors.New("cannot decode a negative bit count")
}
return decode(dst, src, bits)
}
// Decode decodes z-base-32 encoded data from src. It writes at most
// DecodedLen(len(src)) bytes to dst and returns the number of bytes
// written.
//
// If src contains invalid z-base-32 data, it will return the number
// of bytes successfully written and CorruptInputError.
func Decode(dst, src []byte) (int, error) {
return decode(dst, src, -1)
}
func decodeString(s string, bits int) ([]byte, error) {
dst := make([]byte, DecodedLen(len(s)))
n, err := decode(dst, []byte(s), bits)
if err != nil {
return nil, err
}
return dst[:n], nil
}
// DecodeBitsString returns the bytes represented by the z-base-32
// string s containing the specified number of bits.
func DecodeBitsString(s string, bits int) ([]byte, error) {
if bits < 0 {
return nil, errors.New("cannot decode a negative bit count")
}
return decodeString(s, bits)
}
// DecodeString returns the bytes represented by the z-base-32 string
// s.
func DecodeString(s string) ([]byte, error) {
return decodeString(s, -1)
}