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Source file src/encoding/base32/base32.go

Documentation: encoding/base32

  // 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 (
  	"bytes"
  	"io"
  	"strconv"
  	"strings"
  )
  
  /*
   * 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    string
  	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 {
  	e := new(Encoding)
  	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)
  
  var removeNewlinesMapper = func(r rune) rune {
  	if r == '\r' || r == '\n' {
  		return -1
  	}
  	return r
  }
  
  // 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) {
  	if len(src) == 0 {
  		return
  	}
  
  	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
  		for i := 0; i < 8; i++ {
  			if len(dst) > i {
  				dst[i] = enc.encode[b[i]]
  			}
  		}
  
  		// 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])
  		e.nbuf = 0
  		_, e.err = e.w.Write(e.out[0:8])
  	}
  	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) {
  	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; {
  
  			// We have reached the end and are missing padding
  			if len(src) == 0 && enc.padChar != NoPadding {
  				return n, false, CorruptInputError(olen - len(src) - j)
  			}
  
  			// We have reached the end and are not expecing any padding
  			if len(src) == 0 && enc.padChar == NoPadding {
  				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[4] = dbuf[6]<<5 | dbuf[7]
  			fallthrough
  		case 7:
  			dst[3] = dbuf[4]<<7 | dbuf[5]<<2 | dbuf[6]>>3
  			fallthrough
  		case 5:
  			dst[2] = dbuf[3]<<4 | dbuf[4]>>1
  			fallthrough
  		case 4:
  			dst[1] = dbuf[1]<<6 | dbuf[2]<<1 | dbuf[3]>>4
  			fallthrough
  		case 2:
  			dst[0] = dbuf[0]<<3 | dbuf[1]>>2
  		}
  
  		if !end {
  			dst = dst[5:]
  		}
  
  		switch dlen {
  		case 2:
  			n += 1
  		case 4:
  			n += 2
  		case 5:
  			n += 3
  		case 7:
  			n += 4
  		case 8:
  			n += 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) {
  	src = bytes.Map(removeNewlinesMapper, src)
  	n, _, err = enc.decode(dst, src)
  	return
  }
  
  // DecodeString returns the bytes represented by the base32 string s.
  func (enc *Encoding) DecodeString(s string) ([]byte, error) {
  	s = strings.Map(removeNewlinesMapper, s)
  	dbuf := make([]byte, enc.DecodedLen(len(s)))
  	n, _, err := enc.decode(dbuf, []byte(s))
  	return dbuf[: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) (n int, err error) {
  	for n < min && err == nil {
  		var nn int
  		nn, err = r.Read(buf[n:])
  		n += nn
  	}
  	if n < min && 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)
  	}
  
  	nn, d.err = readEncodedData(d.r, d.buf[d.nbuf:nn], 8-d.nbuf)
  	d.nbuf += nn
  	if d.nbuf < 8 {
  		return 0, d.err
  	}
  
  	// Decode chunk into p, or d.out and then p if p is too small.
  	nr := d.nbuf / 8 * 8
  	nw := d.nbuf / 8 * 5
  	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
  }
  
  func (r *newlineFilteringReader) Read(p []byte) (int, error) {
  	n, err := r.wrapped.Read(p)
  	for n > 0 {
  		offset := 0
  		for i, b := range p[0:n] {
  			if b != '\r' && b != '\n' {
  				if i != offset {
  					p[offset] = b
  				}
  				offset++
  			}
  		}
  		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
  }
  

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