506 lines
12 KiB
Go
506 lines
12 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package base32 implements base32 encoding as specified by RFC 4648.
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package base32
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import (
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"io"
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"strconv"
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)
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/*
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* Encodings
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*/
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// An Encoding is a radix 32 encoding/decoding scheme, defined by a
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// 32-character alphabet. The most common is the "base32" encoding
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// introduced for SASL GSSAPI and standardized in RFC 4648.
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// The alternate "base32hex" encoding is used in DNSSEC.
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type Encoding struct {
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encode string
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decodeMap [256]byte
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padChar rune
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}
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// Alphabet returns the Base32 alphabet used
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func (enc *Encoding) Alphabet() string {
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return enc.encode
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}
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const (
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StdPadding rune = '='
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NoPadding rune = -1
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)
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const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
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const encodeHex = "0123456789ABCDEFGHIJKLMNOPQRSTUV"
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// NewEncoding returns a new Encoding defined by the given alphabet,
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// which must be a 32-byte string.
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func NewEncoding(encoder string) *Encoding {
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e := new(Encoding)
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e.padChar = StdPadding
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e.encode = encoder
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for i := 0; i < len(e.decodeMap); i++ {
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e.decodeMap[i] = 0xFF
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}
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for i := 0; i < len(encoder); i++ {
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e.decodeMap[encoder[i]] = byte(i)
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}
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return e
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}
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// NewEncoding returns a new case insensitive Encoding defined by the
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// given alphabet, which must be a 32-byte string.
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func NewEncodingCI(encoder string) *Encoding {
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e := new(Encoding)
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e.padChar = StdPadding
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e.encode = encoder
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for i := 0; i < len(e.decodeMap); i++ {
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e.decodeMap[i] = 0xFF
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}
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for i := 0; i < len(encoder); i++ {
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e.decodeMap[asciiToLower(encoder[i])] = byte(i)
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e.decodeMap[asciiToUpper(encoder[i])] = byte(i)
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}
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return e
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}
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func asciiToLower(c byte) byte {
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if c >= 'A' && c <= 'Z' {
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return c + 32
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}
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return c
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}
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func asciiToUpper(c byte) byte {
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if c >= 'a' && c <= 'z' {
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return c - 32
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}
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return c
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}
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// WithPadding creates a new encoding identical to enc except
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// with a specified padding character, or NoPadding to disable padding.
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func (enc Encoding) WithPadding(padding rune) *Encoding {
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enc.padChar = padding
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return &enc
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}
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// StdEncoding is the standard base32 encoding, as defined in
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// RFC 4648.
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var StdEncoding = NewEncodingCI(encodeStd)
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// HexEncoding is the ``Extended Hex Alphabet'' defined in RFC 4648.
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// It is typically used in DNS.
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var HexEncoding = NewEncodingCI(encodeHex)
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var RawStdEncoding = NewEncodingCI(encodeStd).WithPadding(NoPadding)
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var RawHexEncoding = NewEncodingCI(encodeHex).WithPadding(NoPadding)
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/*
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* Encoder
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*/
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// Encode encodes src using the encoding enc, writing
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// EncodedLen(len(src)) bytes to dst.
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//
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// The encoding pads the output to a multiple of 8 bytes,
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// so Encode is not appropriate for use on individual blocks
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// of a large data stream. Use NewEncoder() instead.
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func (enc *Encoding) Encode(dst, src []byte) {
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if len(src) == 0 {
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return
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}
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for len(src) > 0 {
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var carry byte
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// Unpack 8x 5-bit source blocks into a 5 byte
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// destination quantum
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switch len(src) {
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default:
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dst[7] = enc.encode[src[4]&0x1F]
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carry = src[4] >> 5
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fallthrough
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case 4:
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dst[6] = enc.encode[carry|(src[3]<<3)&0x1F]
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dst[5] = enc.encode[(src[3]>>2)&0x1F]
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carry = src[3] >> 7
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fallthrough
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case 3:
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dst[4] = enc.encode[carry|(src[2]<<1)&0x1F]
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carry = (src[2] >> 4) & 0x1F
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fallthrough
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case 2:
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dst[3] = enc.encode[carry|(src[1]<<4)&0x1F]
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dst[2] = enc.encode[(src[1]>>1)&0x1F]
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carry = (src[1] >> 6) & 0x1F
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fallthrough
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case 1:
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dst[1] = enc.encode[carry|(src[0]<<2)&0x1F]
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dst[0] = enc.encode[src[0]>>3]
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}
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// Pad the final quantum
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if len(src) < 5 {
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if enc.padChar != NoPadding {
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dst[7] = byte(enc.padChar)
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if len(src) < 4 {
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dst[6] = byte(enc.padChar)
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dst[5] = byte(enc.padChar)
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if len(src) < 3 {
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dst[4] = byte(enc.padChar)
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if len(src) < 2 {
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dst[3] = byte(enc.padChar)
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dst[2] = byte(enc.padChar)
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}
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}
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}
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}
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break
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}
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src = src[5:]
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dst = dst[8:]
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}
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}
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// EncodeToString returns the base32 encoding of src.
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func (enc *Encoding) EncodeToString(src []byte) string {
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buf := make([]byte, enc.EncodedLen(len(src)))
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enc.Encode(buf, src)
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return string(buf)
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}
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type encoder struct {
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err error
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enc *Encoding
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w io.Writer
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buf [5]byte // buffered data waiting to be encoded
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nbuf int // number of bytes in buf
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out [1024]byte // output buffer
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}
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func (e *encoder) Write(p []byte) (n int, err error) {
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if e.err != nil {
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return 0, e.err
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}
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// Leading fringe.
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if e.nbuf > 0 {
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var i int
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for i = 0; i < len(p) && e.nbuf < 5; i++ {
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e.buf[e.nbuf] = p[i]
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e.nbuf++
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}
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n += i
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p = p[i:]
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if e.nbuf < 5 {
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return
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}
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e.enc.Encode(e.out[0:], e.buf[0:])
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if _, e.err = e.w.Write(e.out[0:8]); e.err != nil {
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return n, e.err
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}
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e.nbuf = 0
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}
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// Large interior chunks.
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for len(p) >= 5 {
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nn := len(e.out) / 8 * 5
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if nn > len(p) {
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nn = len(p)
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nn -= nn % 5
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}
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e.enc.Encode(e.out[0:], p[0:nn])
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if _, e.err = e.w.Write(e.out[0 : nn/5*8]); e.err != nil {
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return n, e.err
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}
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n += nn
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p = p[nn:]
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}
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// Trailing fringe.
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for i := 0; i < len(p); i++ {
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e.buf[i] = p[i]
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}
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e.nbuf = len(p)
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n += len(p)
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return
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}
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// Close flushes any pending output from the encoder.
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// It is an error to call Write after calling Close.
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func (e *encoder) Close() error {
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// If there's anything left in the buffer, flush it out
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if e.err == nil && e.nbuf > 0 {
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e.enc.Encode(e.out[0:], e.buf[0:e.nbuf])
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e.nbuf = 0
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_, e.err = e.w.Write(e.out[0:8])
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}
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return e.err
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}
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// NewEncoder returns a new base32 stream encoder. Data written to
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// the returned writer will be encoded using enc and then written to w.
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// Base32 encodings operate in 5-byte blocks; when finished
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// writing, the caller must Close the returned encoder to flush any
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// partially written blocks.
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func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser {
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return &encoder{enc: enc, w: w}
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}
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// EncodedLen returns the length in bytes of the base32 encoding
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// of an input buffer of length n.
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func (enc *Encoding) EncodedLen(n int) int {
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if enc.padChar == NoPadding {
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return (n*8 + 4) / 5 // minimum # chars at 5 bits per char
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}
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return (n + 4) / 5 * 8
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}
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/*
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* Decoder
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*/
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type CorruptInputError int64
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func (e CorruptInputError) Error() string {
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return "illegal base32 data at input byte " + strconv.FormatInt(int64(e), 10)
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}
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// decode is like Decode but returns an additional 'end' value, which
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// indicates if end-of-message padding was encountered and thus any
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// additional data is an error. This method assumes that src has been
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// stripped of all supported whitespace ('\r' and '\n').
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func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
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olen := len(src)
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for len(src) > 0 && !end {
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// Decode quantum using the base32 alphabet
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var dbuf [8]byte
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dlen := 8
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for j := 0; j < 8; {
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if len(src) == 0 {
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if enc.padChar != NoPadding {
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return n, false, CorruptInputError(olen - len(src) - j)
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}
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dlen = j
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break
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}
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in := src[0]
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src = src[1:]
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if in == byte(enc.padChar) && j >= 2 && len(src) < 8 {
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if enc.padChar == NoPadding {
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return n, false, CorruptInputError(olen)
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}
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// We've reached the end and there's padding
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if len(src)+j < 8-1 {
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// not enough padding
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return n, false, CorruptInputError(olen)
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}
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for k := 0; k < 8-1-j; k++ {
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if len(src) > k && src[k] != byte(enc.padChar) {
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// incorrect padding
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return n, false, CorruptInputError(olen - len(src) + k - 1)
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}
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}
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dlen, end = j, true
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// 7, 5 and 2 are not valid padding lengths, and so 1, 3 and 6 are not
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// valid dlen values. See RFC 4648 Section 6 "Base 32 Encoding" listing
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// the five valid padding lengths, and Section 9 "Illustrations and
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// Examples" for an illustration for how the 1st, 3rd and 6th base32
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// src bytes do not yield enough information to decode a dst byte.
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if dlen == 1 || dlen == 3 || dlen == 6 {
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return n, false, CorruptInputError(olen - len(src) - 1)
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}
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break
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}
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dbuf[j] = enc.decodeMap[in]
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if dbuf[j] == 0xFF {
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return n, false, CorruptInputError(olen - len(src) - 1)
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}
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j++
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}
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// Pack 8x 5-bit source blocks into 5 byte destination
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// quantum
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switch dlen {
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case 8:
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dst[4] = dbuf[6]<<5 | dbuf[7]
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fallthrough
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case 7:
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dst[3] = dbuf[4]<<7 | dbuf[5]<<2 | dbuf[6]>>3
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fallthrough
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case 5:
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dst[2] = dbuf[3]<<4 | dbuf[4]>>1
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fallthrough
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case 4:
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dst[1] = dbuf[1]<<6 | dbuf[2]<<1 | dbuf[3]>>4
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fallthrough
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case 2:
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dst[0] = dbuf[0]<<3 | dbuf[1]>>2
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}
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if len(dst) > 5 {
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dst = dst[5:]
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}
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switch dlen {
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case 2:
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n += 1
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case 4:
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n += 2
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case 5:
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n += 3
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case 7:
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n += 4
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case 8:
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n += 5
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}
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}
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return n, end, nil
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}
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// Decode decodes src using the encoding enc. It writes at most
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// DecodedLen(len(src)) bytes to dst and returns the number of bytes
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// written. If src contains invalid base32 data, it will return the
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// number of bytes successfully written and CorruptInputError.
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// New line characters (\r and \n) are ignored.
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func (enc *Encoding) Decode(dst, s []byte) (n int, err error) {
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// FIXME: if dst is the same as s use decodeInPlace
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stripped := make([]byte, 0, len(s))
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for _, c := range s {
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if c != '\r' && c != '\n' {
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stripped = append(stripped, c)
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}
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}
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n, _, err = enc.decode(dst, stripped)
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return
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}
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func (enc *Encoding) decodeInPlace(strb []byte) (n int, err error) {
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off := 0
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for _, b := range strb {
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if b == '\n' || b == '\r' {
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continue
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}
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strb[off] = b
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off++
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}
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n, _, err = enc.decode(strb, strb[:off])
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return
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}
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// DecodeString returns the bytes represented by the base32 string s.
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func (enc *Encoding) DecodeString(s string) ([]byte, error) {
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strb := []byte(s)
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n, err := enc.decodeInPlace(strb)
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if err != nil {
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return nil, err
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}
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return strb[:n], nil
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}
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type decoder struct {
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err error
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enc *Encoding
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r io.Reader
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end bool // saw end of message
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buf [1024]byte // leftover input
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nbuf int
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out []byte // leftover decoded output
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outbuf [1024 / 8 * 5]byte
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}
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func (d *decoder) Read(p []byte) (n int, err error) {
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if d.err != nil {
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return 0, d.err
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}
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// Use leftover decoded output from last read.
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if len(d.out) > 0 {
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n = copy(p, d.out)
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d.out = d.out[n:]
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return n, nil
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}
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// Read a chunk.
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nn := len(p) / 5 * 8
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if nn < 8 {
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nn = 8
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}
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if nn > len(d.buf) {
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nn = len(d.buf)
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}
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nn, d.err = io.ReadAtLeast(d.r, d.buf[d.nbuf:nn], 8-d.nbuf)
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d.nbuf += nn
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if d.nbuf < 8 {
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return 0, d.err
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}
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// Decode chunk into p, or d.out and then p if p is too small.
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nr := d.nbuf / 8 * 8
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nw := d.nbuf / 8 * 5
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if nw > len(p) {
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nw, d.end, d.err = d.enc.decode(d.outbuf[0:], d.buf[0:nr])
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d.out = d.outbuf[0:nw]
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n = copy(p, d.out)
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d.out = d.out[n:]
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} else {
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n, d.end, d.err = d.enc.decode(p, d.buf[0:nr])
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}
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d.nbuf -= nr
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for i := 0; i < d.nbuf; i++ {
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d.buf[i] = d.buf[i+nr]
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}
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if d.err == nil {
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d.err = err
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}
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return n, d.err
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}
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type newlineFilteringReader struct {
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wrapped io.Reader
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}
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func (r *newlineFilteringReader) Read(p []byte) (int, error) {
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n, err := r.wrapped.Read(p)
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for n > 0 {
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offset := 0
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for i, b := range p[0:n] {
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if b != '\r' && b != '\n' {
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if i != offset {
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p[offset] = b
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}
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offset++
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}
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}
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if offset > 0 {
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return offset, err
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}
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// Previous buffer entirely whitespace, read again
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n, err = r.wrapped.Read(p)
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}
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return n, err
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}
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// NewDecoder constructs a new base32 stream decoder.
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func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
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return &decoder{enc: enc, r: &newlineFilteringReader{r}}
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}
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// DecodedLen returns the maximum length in bytes of the decoded data
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// corresponding to n bytes of base32-encoded data.
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func (enc *Encoding) DecodedLen(n int) int {
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if enc.padChar == NoPadding {
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return (n*5 + 7) / 8
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}
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return n / 8 * 5
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}
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