src/encoding/base32/base32.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package base32 implements base32 encoding as specified by RFC 4648.
 package base32

 import (
 	"io"
 	"strconv"
 )

 /*
  * Encodings
  */

 // An Encoding is a radix 32 encoding/decoding scheme, defined by a
 // 32-character alphabet. The most common is the "base32" encoding
 // introduced for SASL GSSAPI and standardized in RFC 4648.
 // The alternate "base32hex" encoding is used in DNSSEC.
 type Encoding struct {
 	encode    [32]byte
 	decodeMap [256]byte
 	padChar   rune
 }

 const (
 	StdPadding rune = '=' // Standard padding character
 	NoPadding  rune = -1  // No padding
 )

 const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
 const encodeHex = "0123456789ABCDEFGHIJKLMNOPQRSTUV"

 // NewEncoding returns a new Encoding defined by the given alphabet,
 // which must be a 32-byte string.
 func NewEncoding(encoder string) *Encoding {
 	if len(encoder) != 32 {
 		panic("encoding alphabet is not 32-bytes long")
 	}

 	e := new(Encoding)
 	copy(e.encode[:], encoder)
 	e.padChar = StdPadding

 	for i := 0; i < len(e.decodeMap); i++ {
 		e.decodeMap[i] = 0xFF
 	}
 	for i := 0; i < len(encoder); i++ {
 		e.decodeMap[encoder[i]] = byte(i)
 	}
 	return e
 }

 // StdEncoding is the standard base32 encoding, as defined in
 // RFC 4648.
 var StdEncoding = NewEncoding(encodeStd)

 // HexEncoding is the ``Extended Hex Alphabet'' defined in RFC 4648.
 // It is typically used in DNS.
 var HexEncoding = NewEncoding(encodeHex)

 // WithPadding creates a new encoding identical to enc except
 // with a specified padding character, or NoPadding to disable padding.
 // The padding character must not be '\r' or '\n', must not
 // be contained in the encoding's alphabet and must be a rune equal or
 // below '\xff'.
 func (enc Encoding) WithPadding(padding rune) *Encoding {
 	if padding == '\r' || padding == '\n' || padding > 0xff {
 		panic("invalid padding")
 	}

 	for i := 0; i < len(enc.encode); i++ {
 		if rune(enc.encode[i]) == padding {
 			panic("padding contained in alphabet")
 		}
 	}

 	enc.padChar = padding
 	return &enc
 }

 /*
  * Encoder
  */

 // Encode encodes src using the encoding enc, writing
 // EncodedLen(len(src)) bytes to dst.
 //
 // The encoding pads the output to a multiple of 8 bytes,
 // so Encode is not appropriate for use on individual blocks
 // of a large data stream. Use NewEncoder() instead.
 func (enc *Encoding) Encode(dst, src []byte) {
 	for len(src) > 0 {
 		var b [8]byte

 		// Unpack 8x 5-bit source blocks into a 5 byte
 		// destination quantum
 		switch len(src) {
 		default:
 			b[7] = src[4] & 0x1F
 			b[6] = src[4] >> 5
 			fallthrough
 		case 4:
 			b[6] |= (src[3] << 3) & 0x1F
 			b[5] = (src[3] >> 2) & 0x1F
 			b[4] = src[3] >> 7
 			fallthrough
 		case 3:
 			b[4] |= (src[2] << 1) & 0x1F
 			b[3] = (src[2] >> 4) & 0x1F
 			fallthrough
 		case 2:
 			b[3] |= (src[1] << 4) & 0x1F
 			b[2] = (src[1] >> 1) & 0x1F
 			b[1] = (src[1] >> 6) & 0x1F
 			fallthrough
 		case 1:
 			b[1] |= (src[0] << 2) & 0x1F
 			b[0] = src[0] >> 3
 		}

 		// Encode 5-bit blocks using the base32 alphabet
 		size := len(dst)
 		if size >= 8 {
 			// Common case, unrolled for extra performance
 			dst[0] = enc.encode[b[0]&31]
 			dst[1] = enc.encode[b[1]&31]
 			dst[2] = enc.encode[b[2]&31]
 			dst[3] = enc.encode[b[3]&31]
 			dst[4] = enc.encode[b[4]&31]
 			dst[5] = enc.encode[b[5]&31]
 			dst[6] = enc.encode[b[6]&31]
 			dst[7] = enc.encode[b[7]&31]
 		} else {
 			for i := 0; i < size; i++ {
 				dst[i] = enc.encode[b[i]&31]
 			}
 		}

 		// Pad the final quantum
 		if len(src) < 5 {
 			if enc.padChar == NoPadding {
 				break
 			}

 			dst[7] = byte(enc.padChar)
 			if len(src) < 4 {
 				dst[6] = byte(enc.padChar)
 				dst[5] = byte(enc.padChar)
 				if len(src) < 3 {
 					dst[4] = byte(enc.padChar)
 					if len(src) < 2 {
 						dst[3] = byte(enc.padChar)
 						dst[2] = byte(enc.padChar)
 					}
 				}
 			}

 			break
 		}

 		src = src[5:]
 		dst = dst[8:]
 	}
 }

 // EncodeToString returns the base32 encoding of src.
 func (enc *Encoding) EncodeToString(src []byte) string {
 	buf := make([]byte, enc.EncodedLen(len(src)))
 	enc.Encode(buf, src)
 	return string(buf)
 }

 type encoder struct {
 	err  error
 	enc  *Encoding
 	w    io.Writer
 	buf  [5]byte    // buffered data waiting to be encoded
 	nbuf int        // number of bytes in buf
 	out  [1024]byte // output buffer
 }

 func (e *encoder) Write(p []byte) (n int, err error) {
 	if e.err != nil {
 		return 0, e.err
 	}

 	// Leading fringe.
 	if e.nbuf > 0 {
 		var i int
 		for i = 0; i < len(p) && e.nbuf < 5; i++ {
 			e.buf[e.nbuf] = p[i]
 			e.nbuf++
 		}
 		n += i
 		p = p[i:]
 		if e.nbuf < 5 {
 			return
 		}
 		e.enc.Encode(e.out[0:], e.buf[0:])
 		if _, e.err = e.w.Write(e.out[0:8]); e.err != nil {
 			return n, e.err
 		}
 		e.nbuf = 0
 	}

 	// Large interior chunks.
 	for len(p) >= 5 {
 		nn := len(e.out) / 8 * 5
 		if nn > len(p) {
 			nn = len(p)
 			nn -= nn % 5
 		}
 		e.enc.Encode(e.out[0:], p[0:nn])
 		if _, e.err = e.w.Write(e.out[0 : nn/5*8]); e.err != nil {
 			return n, e.err
 		}
 		n += nn
 		p = p[nn:]
 	}

 	// Trailing fringe.
 	for i := 0; i < len(p); i++ {
 		e.buf[i] = p[i]
 	}
 	e.nbuf = len(p)
 	n += len(p)
 	return
 }

 // Close flushes any pending output from the encoder.
 // It is an error to call Write after calling Close.
 func (e *encoder) Close() error {
 	// If there's anything left in the buffer, flush it out
 	if e.err == nil && e.nbuf > 0 {
 		e.enc.Encode(e.out[0:], e.buf[0:e.nbuf])
 		encodedLen := e.enc.EncodedLen(e.nbuf)
 		e.nbuf = 0
 		_, e.err = e.w.Write(e.out[0:encodedLen])
 	}
 	return e.err
 }

 // NewEncoder returns a new base32 stream encoder. Data written to
 // the returned writer will be encoded using enc and then written to w.
 // Base32 encodings operate in 5-byte blocks; when finished
 // writing, the caller must Close the returned encoder to flush any
 // partially written blocks.
 func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser {
 	return &encoder{enc: enc, w: w}
 }

 // EncodedLen returns the length in bytes of the base32 encoding
 // of an input buffer of length n.
 func (enc *Encoding) EncodedLen(n int) int {
 	if enc.padChar == NoPadding {
 		return (n*8 + 4) / 5
 	}
 	return (n + 4) / 5 * 8
 }

 /*
  * Decoder
  */

 type CorruptInputError int64

 func (e CorruptInputError) Error() string {
 	return "illegal base32 data at input byte " + strconv.FormatInt(int64(e), 10)
 }

 // decode is like Decode but returns an additional 'end' value, which
 // indicates if end-of-message padding was encountered and thus any
 // additional data is an error. This method assumes that src has been
 // stripped of all supported whitespace ('\r' and '\n').
 func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
 	// Lift the nil check outside of the loop.
 	_ = enc.decodeMap

 	dsti := 0
 	olen := len(src)

 	for len(src) > 0 && !end {
 		// Decode quantum using the base32 alphabet
 		var dbuf [8]byte
 		dlen := 8

 		for j := 0; j < 8; {

 			if len(src) == 0 {
 				if enc.padChar != NoPadding {
 					// We have reached the end and are missing padding
 					return n, false, CorruptInputError(olen - len(src) - j)
 				}
 				// We have reached the end and are not expecting any padding
 				dlen, end = j, true
 				break
 			}
 			in := src[0]
 			src = src[1:]
 			if in == byte(enc.padChar) && j >= 2 && len(src) < 8 {
 				// We've reached the end and there's padding
 				if len(src)+j < 8-1 {
 					// not enough padding
 					return n, false, CorruptInputError(olen)
 				}
 				for k := 0; k < 8-1-j; k++ {
 					if len(src) > k && src[k] != byte(enc.padChar) {
 						// incorrect padding
 						return n, false, CorruptInputError(olen - len(src) + k - 1)
 					}
 				}
 				dlen, end = j, true
 				// 7, 5 and 2 are not valid padding lengths, and so 1, 3 and 6 are not
 				// valid dlen values. See RFC 4648 Section 6 "Base 32 Encoding" listing
 				// the five valid padding lengths, and Section 9 "Illustrations and
 				// Examples" for an illustration for how the 1st, 3rd and 6th base32
 				// src bytes do not yield enough information to decode a dst byte.
 				if dlen == 1 || dlen == 3 || dlen == 6 {
 					return n, false, CorruptInputError(olen - len(src) - 1)
 				}
 				break
 			}
 			dbuf[j] = enc.decodeMap[in]
 			if dbuf[j] == 0xFF {
 				return n, false, CorruptInputError(olen - len(src) - 1)
 			}
 			j++
 		}

 		// Pack 8x 5-bit source blocks into 5 byte destination
 		// quantum
 		switch dlen {
 		case 8:
 			dst[dsti+4] = dbuf[6]<<5 | dbuf[7]
 			n++
 			fallthrough
 		case 7:
 			dst[dsti+3] = dbuf[4]<<7 | dbuf[5]<<2 | dbuf[6]>>3
 			n++
 			fallthrough
 		case 5:
 			dst[dsti+2] = dbuf[3]<<4 | dbuf[4]>>1
 			n++
 			fallthrough
 		case 4:
 			dst[dsti+1] = dbuf[1]<<6 | dbuf[2]<<1 | dbuf[3]>>4
 			n++
 			fallthrough
 		case 2:
 			dst[dsti+0] = dbuf[0]<<3 | dbuf[1]>>2
 			n++
 		}
 		dsti += 5
 	}
 	return n, end, nil
 }

 // Decode decodes src using the encoding enc. It writes at most
 // DecodedLen(len(src)) bytes to dst and returns the number of bytes
 // written. If src contains invalid base32 data, it will return the
 // number of bytes successfully written and CorruptInputError.
 // New line characters (\r and \n) are ignored.
 func (enc *Encoding) Decode(dst, src []byte) (n int, err error) {
 	buf := make([]byte, len(src))
 	l := stripNewlines(buf, src)
 	n, _, err = enc.decode(dst, buf[:l])
 	return
 }

 // DecodeString returns the bytes represented by the base32 string s.
 func (enc *Encoding) DecodeString(s string) ([]byte, error) {
 	buf := []byte(s)
 	l := stripNewlines(buf, buf)
 	n, _, err := enc.decode(buf, buf[:l])
 	return buf[:n], err
 }

 type decoder struct {
 	err    error
 	enc    *Encoding
 	r      io.Reader
 	end    bool       // saw end of message
 	buf    [1024]byte // leftover input
 	nbuf   int
 	out    []byte // leftover decoded output
 	outbuf [1024 / 8 * 5]byte
 }

 func readEncodedData(r io.Reader, buf []byte, min int, expectsPadding bool) (n int, err error) {
 	for n < min && err == nil {
 		var nn int
 		nn, err = r.Read(buf[n:])
 		n += nn
 	}
 	// data was read, less than min bytes could be read
 	if n < min && n > 0 && err == io.EOF {
 		err = io.ErrUnexpectedEOF
 	}
 	// no data was read, the buffer already contains some data
 	// when padding is disabled this is not an error, as the message can be of
 	// any length
 	if expectsPadding && min < 8 && n == 0 && err == io.EOF {
 		err = io.ErrUnexpectedEOF
 	}
 	return
 }

 func (d *decoder) Read(p []byte) (n int, err error) {
 	// Use leftover decoded output from last read.
 	if len(d.out) > 0 {
 		n = copy(p, d.out)
 		d.out = d.out[n:]
 		if len(d.out) == 0 {
 			return n, d.err
 		}
 		return n, nil
 	}

 	if d.err != nil {
 		return 0, d.err
 	}

 	// Read a chunk.
 	nn := len(p) / 5 * 8
 	if nn < 8 {
 		nn = 8
 	}
 	if nn > len(d.buf) {
 		nn = len(d.buf)
 	}

 	// Minimum amount of bytes that needs to be read each cycle
 	var min int
 	var expectsPadding bool
 	if d.enc.padChar == NoPadding {
 		min = 1
 		expectsPadding = false
 	} else {
 		min = 8 - d.nbuf
 		expectsPadding = true
 	}

 	nn, d.err = readEncodedData(d.r, d.buf[d.nbuf:nn], min, expectsPadding)
 	d.nbuf += nn
 	if d.nbuf < min {
 		return 0, d.err
 	}

 	// Decode chunk into p, or d.out and then p if p is too small.
 	var nr int
 	if d.enc.padChar == NoPadding {
 		nr = d.nbuf
 	} else {
 		nr = d.nbuf / 8 * 8
 	}
 	nw := d.enc.DecodedLen(d.nbuf)

 	if nw > len(p) {
 		nw, d.end, err = d.enc.decode(d.outbuf[0:], d.buf[0:nr])
 		d.out = d.outbuf[0:nw]
 		n = copy(p, d.out)
 		d.out = d.out[n:]
 	} else {
 		n, d.end, err = d.enc.decode(p, d.buf[0:nr])
 	}
 	d.nbuf -= nr
 	for i := 0; i < d.nbuf; i++ {
 		d.buf[i] = d.buf[i+nr]
 	}

 	if err != nil && (d.err == nil || d.err == io.EOF) {
 		d.err = err
 	}

 	if len(d.out) > 0 {
 		// We cannot return all the decoded bytes to the caller in this
 		// invocation of Read, so we return a nil error to ensure that Read
 		// will be called again.  The error stored in d.err, if any, will be
 		// returned with the last set of decoded bytes.
 		return n, nil
 	}

 	return n, d.err
 }

 type newlineFilteringReader struct {
 	wrapped io.Reader
 }

 // stripNewlines removes newline characters and returns the number
 // of non-newline characters copied to dst.
 func stripNewlines(dst, src []byte) int {
 	offset := 0
 	for _, b := range src {
 		if b == '\r' || b == '\n' {
 			continue
 		}
 		dst[offset] = b
 		offset++
 	}
 	return offset
 }

 func (r *newlineFilteringReader) Read(p []byte) (int, error) {
 	n, err := r.wrapped.Read(p)
 	for n > 0 {
 		s := p[0:n]
 		offset := stripNewlines(s, s)
 		if err != nil || offset > 0 {
 			return offset, err
 		}
 		// Previous buffer entirely whitespace, read again
 		n, err = r.wrapped.Read(p)
 	}
 	return n, err
 }

 // NewDecoder constructs a new base32 stream decoder.
 func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
 	return &decoder{enc: enc, r: &newlineFilteringReader{r}}
 }

 // DecodedLen returns the maximum length in bytes of the decoded data
 // corresponding to n bytes of base32-encoded data.
 func (enc *Encoding) DecodedLen(n int) int {
 	if enc.padChar == NoPadding {
 		return n * 5 / 8
 	}

 	return n / 8 * 5
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package base32 implements base32 encoding as specified by RFC 4648.
	package base32

	import (
	"io"
	"strconv"
	)

	/*
	* Encodings
	*/

	// An Encoding is a radix 32 encoding/decoding scheme, defined by a
	// 32-character alphabet. The most common is the "base32" encoding
	// introduced for SASL GSSAPI and standardized in RFC 4648.
	// The alternate "base32hex" encoding is used in DNSSEC.
	type Encoding struct {
	encode [32]byte
	decodeMap [256]byte
	padChar rune
	}

	const (
	StdPadding rune = '=' // Standard padding character
	NoPadding rune = -1 // No padding
	)

	const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
	const encodeHex = "0123456789ABCDEFGHIJKLMNOPQRSTUV"

	// NewEncoding returns a new Encoding defined by the given alphabet,
	// which must be a 32-byte string.
	func NewEncoding(encoder string) *Encoding {
	if len(encoder) != 32 {
	panic("encoding alphabet is not 32-bytes long")
	}

	e := new(Encoding)
	copy(e.encode[:], encoder)
	e.padChar = StdPadding

	for i := 0; i < len(e.decodeMap); i++ {
	e.decodeMap[i] = 0xFF
	}
	for i := 0; i < len(encoder); i++ {
	e.decodeMap[encoder[i]] = byte(i)
	}
	return e
	}

	// StdEncoding is the standard base32 encoding, as defined in
	// RFC 4648.
	var StdEncoding = NewEncoding(encodeStd)

	// HexEncoding is the ``Extended Hex Alphabet'' defined in RFC 4648.
	// It is typically used in DNS.
	var HexEncoding = NewEncoding(encodeHex)

	// WithPadding creates a new encoding identical to enc except
	// with a specified padding character, or NoPadding to disable padding.
	// The padding character must not be '\r' or '\n', must not
	// be contained in the encoding's alphabet and must be a rune equal or
	// below '\xff'.
	func (enc Encoding) WithPadding(padding rune) *Encoding {
	if padding == '\r' \|\| padding == '\n' \|\| padding > 0xff {
	panic("invalid padding")
	}

	for i := 0; i < len(enc.encode); i++ {
	if rune(enc.encode[i]) == padding {
	panic("padding contained in alphabet")
	}
	}

	enc.padChar = padding
	return &enc
	}

	/*
	* Encoder
	*/

	// Encode encodes src using the encoding enc, writing
	// EncodedLen(len(src)) bytes to dst.
	//
	// The encoding pads the output to a multiple of 8 bytes,
	// so Encode is not appropriate for use on individual blocks
	// of a large data stream. Use NewEncoder() instead.
	func (enc *Encoding) Encode(dst, src []byte) {
	for len(src) > 0 {
	var b [8]byte

	// Unpack 8x 5-bit source blocks into a 5 byte
	// destination quantum
	switch len(src) {
	default:
	b[7] = src[4] & 0x1F
	b[6] = src[4] >> 5
	fallthrough
	case 4:
	b[6] \|= (src[3] << 3) & 0x1F
	b[5] = (src[3] >> 2) & 0x1F
	b[4] = src[3] >> 7
	fallthrough
	case 3:
	b[4] \|= (src[2] << 1) & 0x1F
	b[3] = (src[2] >> 4) & 0x1F
	fallthrough
	case 2:
	b[3] \|= (src[1] << 4) & 0x1F
	b[2] = (src[1] >> 1) & 0x1F
	b[1] = (src[1] >> 6) & 0x1F
	fallthrough
	case 1:
	b[1] \|= (src[0] << 2) & 0x1F
	b[0] = src[0] >> 3
	}

	// Encode 5-bit blocks using the base32 alphabet
	size := len(dst)
	if size >= 8 {
	// Common case, unrolled for extra performance
	dst[0] = enc.encode[b[0]&31]
	dst[1] = enc.encode[b[1]&31]
	dst[2] = enc.encode[b[2]&31]
	dst[3] = enc.encode[b[3]&31]
	dst[4] = enc.encode[b[4]&31]
	dst[5] = enc.encode[b[5]&31]
	dst[6] = enc.encode[b[6]&31]
	dst[7] = enc.encode[b[7]&31]
	} else {
	for i := 0; i < size; i++ {
	dst[i] = enc.encode[b[i]&31]
	}
	}

	// Pad the final quantum
	if len(src) < 5 {
	if enc.padChar == NoPadding {
	break
	}

	dst[7] = byte(enc.padChar)
	if len(src) < 4 {
	dst[6] = byte(enc.padChar)
	dst[5] = byte(enc.padChar)
	if len(src) < 3 {
	dst[4] = byte(enc.padChar)
	if len(src) < 2 {
	dst[3] = byte(enc.padChar)
	dst[2] = byte(enc.padChar)
	}
	}
	}

	break
	}

	src = src[5:]
	dst = dst[8:]
	}
	}

	// EncodeToString returns the base32 encoding of src.
	func (enc *Encoding) EncodeToString(src []byte) string {
	buf := make([]byte, enc.EncodedLen(len(src)))
	enc.Encode(buf, src)
	return string(buf)
	}

	type encoder struct {
	err error
	enc *Encoding
	w io.Writer
	buf [5]byte // buffered data waiting to be encoded
	nbuf int // number of bytes in buf
	out [1024]byte // output buffer
	}

	func (e *encoder) Write(p []byte) (n int, err error) {
	if e.err != nil {
	return 0, e.err
	}

	// Leading fringe.
	if e.nbuf > 0 {
	var i int
	for i = 0; i < len(p) && e.nbuf < 5; i++ {
	e.buf[e.nbuf] = p[i]
	e.nbuf++
	}
	n += i
	p = p[i:]
	if e.nbuf < 5 {
	return
	}
	e.enc.Encode(e.out[0:], e.buf[0:])
	if _, e.err = e.w.Write(e.out[0:8]); e.err != nil {
	return n, e.err
	}
	e.nbuf = 0
	}

	// Large interior chunks.
	for len(p) >= 5 {
	nn := len(e.out) / 8 * 5
	if nn > len(p) {
	nn = len(p)
	nn -= nn % 5
	}
	e.enc.Encode(e.out[0:], p[0:nn])
	if _, e.err = e.w.Write(e.out[0 : nn/5*8]); e.err != nil {
	return n, e.err
	}
	n += nn
	p = p[nn:]
	}

	// Trailing fringe.
	for i := 0; i < len(p); i++ {
	e.buf[i] = p[i]
	}
	e.nbuf = len(p)
	n += len(p)
	return
	}

	// Close flushes any pending output from the encoder.
	// It is an error to call Write after calling Close.
	func (e *encoder) Close() error {
	// If there's anything left in the buffer, flush it out
	if e.err == nil && e.nbuf > 0 {
	e.enc.Encode(e.out[0:], e.buf[0:e.nbuf])
	encodedLen := e.enc.EncodedLen(e.nbuf)
	e.nbuf = 0
	_, e.err = e.w.Write(e.out[0:encodedLen])
	}
	return e.err
	}

	// NewEncoder returns a new base32 stream encoder. Data written to
	// the returned writer will be encoded using enc and then written to w.
	// Base32 encodings operate in 5-byte blocks; when finished
	// writing, the caller must Close the returned encoder to flush any
	// partially written blocks.
	func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser {
	return &encoder{enc: enc, w: w}
	}

	// EncodedLen returns the length in bytes of the base32 encoding
	// of an input buffer of length n.
	func (enc *Encoding) EncodedLen(n int) int {
	if enc.padChar == NoPadding {
	return (n*8 + 4) / 5
	}
	return (n + 4) / 5 * 8
	}

	/*
	* Decoder
	*/

	type CorruptInputError int64

	func (e CorruptInputError) Error() string {
	return "illegal base32 data at input byte " + strconv.FormatInt(int64(e), 10)
	}

	// decode is like Decode but returns an additional 'end' value, which
	// indicates if end-of-message padding was encountered and thus any
	// additional data is an error. This method assumes that src has been
	// stripped of all supported whitespace ('\r' and '\n').
	func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
	// Lift the nil check outside of the loop.
	_ = enc.decodeMap

	dsti := 0
	olen := len(src)

	for len(src) > 0 && !end {
	// Decode quantum using the base32 alphabet
	var dbuf [8]byte
	dlen := 8

	for j := 0; j < 8; {

	if len(src) == 0 {
	if enc.padChar != NoPadding {
	// We have reached the end and are missing padding
	return n, false, CorruptInputError(olen - len(src) - j)
	}
	// We have reached the end and are not expecting any padding
	dlen, end = j, true
	break
	}
	in := src[0]
	src = src[1:]
	if in == byte(enc.padChar) && j >= 2 && len(src) < 8 {
	// We've reached the end and there's padding
	if len(src)+j < 8-1 {
	// not enough padding
	return n, false, CorruptInputError(olen)
	}
	for k := 0; k < 8-1-j; k++ {
	if len(src) > k && src[k] != byte(enc.padChar) {
	// incorrect padding
	return n, false, CorruptInputError(olen - len(src) + k - 1)
	}
	}
	dlen, end = j, true
	// 7, 5 and 2 are not valid padding lengths, and so 1, 3 and 6 are not
	// valid dlen values. See RFC 4648 Section 6 "Base 32 Encoding" listing
	// the five valid padding lengths, and Section 9 "Illustrations and
	// Examples" for an illustration for how the 1st, 3rd and 6th base32
	// src bytes do not yield enough information to decode a dst byte.
	if dlen == 1 \|\| dlen == 3 \|\| dlen == 6 {
	return n, false, CorruptInputError(olen - len(src) - 1)
	}
	break
	}
	dbuf[j] = enc.decodeMap[in]
	if dbuf[j] == 0xFF {
	return n, false, CorruptInputError(olen - len(src) - 1)
	}
	j++
	}

	// Pack 8x 5-bit source blocks into 5 byte destination
	// quantum
	switch dlen {
	case 8:
	dst[dsti+4] = dbuf[6]<<5 \| dbuf[7]
	n++
	fallthrough
	case 7:
	dst[dsti+3] = dbuf[4]<<7 \| dbuf[5]<<2 \| dbuf[6]>>3
	n++
	fallthrough
	case 5:
	dst[dsti+2] = dbuf[3]<<4 \| dbuf[4]>>1
	n++
	fallthrough
	case 4:
	dst[dsti+1] = dbuf[1]<<6 \| dbuf[2]<<1 \| dbuf[3]>>4
	n++
	fallthrough
	case 2:
	dst[dsti+0] = dbuf[0]<<3 \| dbuf[1]>>2
	n++
	}
	dsti += 5
	}
	return n, end, nil
	}

	// Decode decodes src using the encoding enc. It writes at most
	// DecodedLen(len(src)) bytes to dst and returns the number of bytes
	// written. If src contains invalid base32 data, it will return the
	// number of bytes successfully written and CorruptInputError.
	// New line characters (\r and \n) are ignored.
	func (enc *Encoding) Decode(dst, src []byte) (n int, err error) {
	buf := make([]byte, len(src))
	l := stripNewlines(buf, src)
	n, _, err = enc.decode(dst, buf[:l])
	return
	}

	// DecodeString returns the bytes represented by the base32 string s.
	func (enc *Encoding) DecodeString(s string) ([]byte, error) {
	buf := []byte(s)
	l := stripNewlines(buf, buf)
	n, _, err := enc.decode(buf, buf[:l])
	return buf[:n], err
	}

	type decoder struct {
	err error
	enc *Encoding
	r io.Reader
	end bool // saw end of message
	buf [1024]byte // leftover input
	nbuf int
	out []byte // leftover decoded output
	outbuf [1024 / 8 * 5]byte
	}

	func readEncodedData(r io.Reader, buf []byte, min int, expectsPadding bool) (n int, err error) {
	for n < min && err == nil {
	var nn int
	nn, err = r.Read(buf[n:])
	n += nn
	}
	// data was read, less than min bytes could be read
	if n < min && n > 0 && err == io.EOF {
	err = io.ErrUnexpectedEOF
	}
	// no data was read, the buffer already contains some data
	// when padding is disabled this is not an error, as the message can be of
	// any length
	if expectsPadding && min < 8 && n == 0 && err == io.EOF {
	err = io.ErrUnexpectedEOF
	}
	return
	}

	func (d *decoder) Read(p []byte) (n int, err error) {
	// Use leftover decoded output from last read.
	if len(d.out) > 0 {
	n = copy(p, d.out)
	d.out = d.out[n:]
	if len(d.out) == 0 {
	return n, d.err
	}
	return n, nil
	}

	if d.err != nil {
	return 0, d.err
	}

	// Read a chunk.
	nn := len(p) / 5 * 8
	if nn < 8 {
	nn = 8
	}
	if nn > len(d.buf) {
	nn = len(d.buf)
	}

	// Minimum amount of bytes that needs to be read each cycle
	var min int
	var expectsPadding bool
	if d.enc.padChar == NoPadding {
	min = 1
	expectsPadding = false
	} else {
	min = 8 - d.nbuf
	expectsPadding = true
	}

	nn, d.err = readEncodedData(d.r, d.buf[d.nbuf:nn], min, expectsPadding)
	d.nbuf += nn
	if d.nbuf < min {
	return 0, d.err
	}

	// Decode chunk into p, or d.out and then p if p is too small.
	var nr int
	if d.enc.padChar == NoPadding {
	nr = d.nbuf
	} else {
	nr = d.nbuf / 8 * 8
	}
	nw := d.enc.DecodedLen(d.nbuf)

	if nw > len(p) {
	nw, d.end, err = d.enc.decode(d.outbuf[0:], d.buf[0:nr])
	d.out = d.outbuf[0:nw]
	n = copy(p, d.out)
	d.out = d.out[n:]
	} else {
	n, d.end, err = d.enc.decode(p, d.buf[0:nr])
	}
	d.nbuf -= nr
	for i := 0; i < d.nbuf; i++ {
	d.buf[i] = d.buf[i+nr]
	}

	if err != nil && (d.err == nil \|\| d.err == io.EOF) {
	d.err = err
	}

	if len(d.out) > 0 {
	// We cannot return all the decoded bytes to the caller in this
	// invocation of Read, so we return a nil error to ensure that Read
	// will be called again. The error stored in d.err, if any, will be
	// returned with the last set of decoded bytes.
	return n, nil
	}

	return n, d.err
	}

	type newlineFilteringReader struct {
	wrapped io.Reader
	}

	// stripNewlines removes newline characters and returns the number
	// of non-newline characters copied to dst.
	func stripNewlines(dst, src []byte) int {
	offset := 0
	for _, b := range src {
	if b == '\r' \|\| b == '\n' {
	continue
	}
	dst[offset] = b
	offset++
	}
	return offset
	}

	func (r *newlineFilteringReader) Read(p []byte) (int, error) {
	n, err := r.wrapped.Read(p)
	for n > 0 {
	s := p[0:n]
	offset := stripNewlines(s, s)
	if err != nil \|\| offset > 0 {
	return offset, err
	}
	// Previous buffer entirely whitespace, read again
	n, err = r.wrapped.Read(p)
	}
	return n, err
	}

	// NewDecoder constructs a new base32 stream decoder.
	func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
	return &decoder{enc: enc, r: &newlineFilteringReader{r}}
	}

	// DecodedLen returns the maximum length in bytes of the decoded data
	// corresponding to n bytes of base32-encoded data.
	func (enc *Encoding) DecodedLen(n int) int {
	if enc.padChar == NoPadding {
	return n * 5 / 8
	}

	return n / 8 * 5
	}