src/pkg/encoding/base64/base64.go - go - Git at Google

 // Copyright 2009 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 base64 implements base64 encoding as specified by RFC 4648.
 package base64

 import (
 	"io"
 	"os"
 	"strconv"
 )

 /*
  * Encodings
  */

 // An Encoding is a radix 64 encoding/decoding scheme, defined by a
 // 64-character alphabet.  The most common encoding is the "base64"
 // encoding defined in RFC 4648 and used in MIME (RFC 2045) and PEM
 // (RFC 1421).  RFC 4648 also defines an alternate encoding, which is
 // the standard encoding with - and _ substituted for + and /.
 type Encoding struct {
 	encode    string
 	decodeMap [256]byte
 }

 const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
 const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"

 // NewEncoding returns a new Encoding defined by the given alphabet,
 // which must be a 64-byte string.
 func NewEncoding(encoder string) *Encoding {
 	e := new(Encoding)
 	e.encode = encoder
 	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 base64 encoding, as defined in
 // RFC 4648.
 var StdEncoding = NewEncoding(encodeStd)

 // URLEncoding is the alternate base64 encoding defined in RFC 4648.
 // It is typically used in URLs and file names.
 var URLEncoding = NewEncoding(encodeURL)

 /*
  * Encoder
  */

 // Encode encodes src using the encoding enc, writing
 // EncodedLen(len(src)) bytes to dst.
 //
 // The encoding pads the output to a multiple of 4 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 {
 		dst[0] = 0
 		dst[1] = 0
 		dst[2] = 0
 		dst[3] = 0

 		// Unpack 4x 6-bit source blocks into a 4 byte
 		// destination quantum
 		switch len(src) {
 		default:
 			dst[3] |= src[2] & 0x3F
 			dst[2] |= src[2] >> 6
 			fallthrough
 		case 2:
 			dst[2] |= (src[1] << 2) & 0x3F
 			dst[1] |= src[1] >> 4
 			fallthrough
 		case 1:
 			dst[1] |= (src[0] << 4) & 0x3F
 			dst[0] |= src[0] >> 2
 		}

 		// Encode 6-bit blocks using the base64 alphabet
 		for j := 0; j < 4; j++ {
 			dst[j] = enc.encode[dst[j]]
 		}

 		// Pad the final quantum
 		if len(src) < 3 {
 			dst[3] = '='
 			if len(src) < 2 {
 				dst[2] = '='
 			}
 			break
 		}

 		src = src[3:]
 		dst = dst[4:]
 	}
 }

 // EncodeToString returns the base64 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  os.Error
 	enc  *Encoding
 	w    io.Writer
 	buf  [3]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 os.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 < 3; i++ {
 			e.buf[e.nbuf] = p[i]
 			e.nbuf++
 		}
 		n += i
 		p = p[i:]
 		if e.nbuf < 3 {
 			return
 		}
 		e.enc.Encode(e.out[0:], e.buf[0:])
 		if _, e.err = e.w.Write(e.out[0:4]); e.err != nil {
 			return n, e.err
 		}
 		e.nbuf = 0
 	}

 	// Large interior chunks.
 	for len(p) >= 3 {
 		nn := len(e.out) / 4 * 3
 		if nn > len(p) {
 			nn = len(p)
 		}
 		nn -= nn % 3
 		if nn > 0 {
 			e.enc.Encode(e.out[0:], p[0:nn])
 			if _, e.err = e.w.Write(e.out[0 : nn/3*4]); 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() os.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[0:4])
 	}
 	return e.err
 }

 // NewEncoder returns a new base64 stream encoder.  Data written to
 // the returned writer will be encoded using enc and then written to w.
 // Base64 encodings operate in 4-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 base64 encoding
 // of an input buffer of length n.
 func (enc *Encoding) EncodedLen(n int) int { return (n + 2) / 3 * 4 }

 /*
  * Decoder
  */

 type CorruptInputError int64

 func (e CorruptInputError) String() string {
 	return "illegal base64 data at input byte " + strconv.Itoa64(int64(e))
 }

 // 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.  decode also assumes len(src)%4==0,
 // since it is meant for internal use.
 func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err os.Error) {
 	for i := 0; i < len(src)/4 && !end; i++ {
 		// Decode quantum using the base64 alphabet
 		var dbuf [4]byte
 		dlen := 4

 	dbufloop:
 		for j := 0; j < 4; j++ {
 			in := src[i*4+j]
 			if in == '=' && j >= 2 && i == len(src)/4-1 {
 				// We've reached the end and there's
 				// padding
 				if src[i*4+3] != '=' {
 					return n, false, CorruptInputError(i*4 + 2)
 				}
 				dlen = j
 				end = true
 				break dbufloop
 			}
 			dbuf[j] = enc.decodeMap[in]
 			if dbuf[j] == 0xFF {
 				return n, false, CorruptInputError(i*4 + j)
 			}
 		}

 		// Pack 4x 6-bit source blocks into 3 byte destination
 		// quantum
 		switch dlen {
 		case 4:
 			dst[i*3+2] = dbuf[2]<<6 | dbuf[3]
 			fallthrough
 		case 3:
 			dst[i*3+1] = dbuf[1]<<4 | dbuf[2]>>2
 			fallthrough
 		case 2:
 			dst[i*3+0] = dbuf[0]<<2 | dbuf[1]>>4
 		}
 		n += dlen - 1
 	}

 	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 base64 data, it will return the
 // number of bytes successfully written and CorruptInputError.
 func (enc *Encoding) Decode(dst, src []byte) (n int, err os.Error) {
 	if len(src)%4 != 0 {
 		return 0, CorruptInputError(len(src) / 4 * 4)
 	}

 	n, _, err = enc.decode(dst, src)
 	return
 }

 // DecodeString returns the bytes represented by the base64 string s.
 func (enc *Encoding) DecodeString(s string) ([]byte, os.Error) {
 	dbuf := make([]byte, enc.DecodedLen(len(s)))
 	n, err := enc.Decode(dbuf, []byte(s))
 	return dbuf[:n], err
 }

 type decoder struct {
 	err    os.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 / 4 * 3]byte
 }

 func (d *decoder) Read(p []byte) (n int, err os.Error) {
 	if d.err != nil {
 		return 0, d.err
 	}

 	// Use leftover decoded output from last read.
 	if len(d.out) > 0 {
 		n = copy(p, d.out)
 		d.out = d.out[n:]
 		return n, nil
 	}

 	// Read a chunk.
 	nn := len(p) / 3 * 4
 	if nn < 4 {
 		nn = 4
 	}
 	if nn > len(d.buf) {
 		nn = len(d.buf)
 	}
 	nn, d.err = io.ReadAtLeast(d.r, d.buf[d.nbuf:nn], 4-d.nbuf)
 	d.nbuf += nn
 	if d.nbuf < 4 {
 		return 0, d.err
 	}

 	// Decode chunk into p, or d.out and then p if p is too small.
 	nr := d.nbuf / 4 * 4
 	nw := d.nbuf / 4 * 3
 	if nw > len(p) {
 		nw, d.end, d.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, d.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 d.err == nil {
 		d.err = err
 	}
 	return n, d.err
 }

 // NewDecoder constructs a new base64 stream decoder.
 func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
 	return &decoder{enc: enc, r: r}
 }

 // DecodedLen returns the maximum length in bytes of the decoded data
 // corresponding to n bytes of base64-encoded data.
 func (enc *Encoding) DecodedLen(n int) int { return n / 4 * 3 }
	// Copyright 2009 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 base64 implements base64 encoding as specified by RFC 4648.
	package base64

	import (
	"io"
	"os"
	"strconv"
	)

	/*
	* Encodings
	*/

	// An Encoding is a radix 64 encoding/decoding scheme, defined by a
	// 64-character alphabet. The most common encoding is the "base64"
	// encoding defined in RFC 4648 and used in MIME (RFC 2045) and PEM
	// (RFC 1421). RFC 4648 also defines an alternate encoding, which is
	// the standard encoding with - and _ substituted for + and /.
	type Encoding struct {
	encode string
	decodeMap [256]byte
	}

	const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
	const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"

	// NewEncoding returns a new Encoding defined by the given alphabet,
	// which must be a 64-byte string.
	func NewEncoding(encoder string) *Encoding {
	e := new(Encoding)
	e.encode = encoder
	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 base64 encoding, as defined in
	// RFC 4648.
	var StdEncoding = NewEncoding(encodeStd)

	// URLEncoding is the alternate base64 encoding defined in RFC 4648.
	// It is typically used in URLs and file names.
	var URLEncoding = NewEncoding(encodeURL)

	/*
	* Encoder
	*/

	// Encode encodes src using the encoding enc, writing
	// EncodedLen(len(src)) bytes to dst.
	//
	// The encoding pads the output to a multiple of 4 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 {
	dst[0] = 0
	dst[1] = 0
	dst[2] = 0
	dst[3] = 0

	// Unpack 4x 6-bit source blocks into a 4 byte
	// destination quantum
	switch len(src) {
	default:
	dst[3] \|= src[2] & 0x3F
	dst[2] \|= src[2] >> 6
	fallthrough
	case 2:
	dst[2] \|= (src[1] << 2) & 0x3F
	dst[1] \|= src[1] >> 4
	fallthrough
	case 1:
	dst[1] \|= (src[0] << 4) & 0x3F
	dst[0] \|= src[0] >> 2
	}

	// Encode 6-bit blocks using the base64 alphabet
	for j := 0; j < 4; j++ {
	dst[j] = enc.encode[dst[j]]
	}

	// Pad the final quantum
	if len(src) < 3 {
	dst[3] = '='
	if len(src) < 2 {
	dst[2] = '='
	}
	break
	}

	src = src[3:]
	dst = dst[4:]
	}
	}

	// EncodeToString returns the base64 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 os.Error
	enc *Encoding
	w io.Writer
	buf [3]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 os.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 < 3; i++ {
	e.buf[e.nbuf] = p[i]
	e.nbuf++
	}
	n += i
	p = p[i:]
	if e.nbuf < 3 {
	return
	}
	e.enc.Encode(e.out[0:], e.buf[0:])
	if _, e.err = e.w.Write(e.out[0:4]); e.err != nil {
	return n, e.err
	}
	e.nbuf = 0
	}

	// Large interior chunks.
	for len(p) >= 3 {
	nn := len(e.out) / 4 * 3
	if nn > len(p) {
	nn = len(p)
	}
	nn -= nn % 3
	if nn > 0 {
	e.enc.Encode(e.out[0:], p[0:nn])
	if _, e.err = e.w.Write(e.out[0 : nn/3*4]); 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() os.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[0:4])
	}
	return e.err
	}

	// NewEncoder returns a new base64 stream encoder. Data written to
	// the returned writer will be encoded using enc and then written to w.
	// Base64 encodings operate in 4-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 base64 encoding
	// of an input buffer of length n.
	func (enc Encoding) EncodedLen(n int) int { return (n + 2) / 3 4 }

	/*
	* Decoder
	*/

	type CorruptInputError int64

	func (e CorruptInputError) String() string {
	return "illegal base64 data at input byte " + strconv.Itoa64(int64(e))
	}

	// 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. decode also assumes len(src)%4==0,
	// since it is meant for internal use.
	func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err os.Error) {
	for i := 0; i < len(src)/4 && !end; i++ {
	// Decode quantum using the base64 alphabet
	var dbuf [4]byte
	dlen := 4

	dbufloop:
	for j := 0; j < 4; j++ {
	in := src[i*4+j]
	if in == '=' && j >= 2 && i == len(src)/4-1 {
	// We've reached the end and there's
	// padding
	if src[i*4+3] != '=' {
	return n, false, CorruptInputError(i*4 + 2)
	}
	dlen = j
	end = true
	break dbufloop
	}
	dbuf[j] = enc.decodeMap[in]
	if dbuf[j] == 0xFF {
	return n, false, CorruptInputError(i*4 + j)
	}
	}

	// Pack 4x 6-bit source blocks into 3 byte destination
	// quantum
	switch dlen {
	case 4:
	dst[i*3+2] = dbuf[2]<<6 \| dbuf[3]
	fallthrough
	case 3:
	dst[i*3+1] = dbuf[1]<<4 \| dbuf[2]>>2
	fallthrough
	case 2:
	dst[i*3+0] = dbuf[0]<<2 \| dbuf[1]>>4
	}
	n += dlen - 1
	}

	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 base64 data, it will return the
	// number of bytes successfully written and CorruptInputError.
	func (enc *Encoding) Decode(dst, src []byte) (n int, err os.Error) {
	if len(src)%4 != 0 {
	return 0, CorruptInputError(len(src) / 4 * 4)
	}

	n, _, err = enc.decode(dst, src)
	return
	}

	// DecodeString returns the bytes represented by the base64 string s.
	func (enc *Encoding) DecodeString(s string) ([]byte, os.Error) {
	dbuf := make([]byte, enc.DecodedLen(len(s)))
	n, err := enc.Decode(dbuf, []byte(s))
	return dbuf[:n], err
	}

	type decoder struct {
	err os.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 / 4 * 3]byte
	}

	func (d *decoder) Read(p []byte) (n int, err os.Error) {
	if d.err != nil {
	return 0, d.err
	}

	// Use leftover decoded output from last read.
	if len(d.out) > 0 {
	n = copy(p, d.out)
	d.out = d.out[n:]
	return n, nil
	}

	// Read a chunk.
	nn := len(p) / 3 * 4
	if nn < 4 {
	nn = 4
	}
	if nn > len(d.buf) {
	nn = len(d.buf)
	}
	nn, d.err = io.ReadAtLeast(d.r, d.buf[d.nbuf:nn], 4-d.nbuf)
	d.nbuf += nn
	if d.nbuf < 4 {
	return 0, d.err
	}

	// Decode chunk into p, or d.out and then p if p is too small.
	nr := d.nbuf / 4 * 4
	nw := d.nbuf / 4 * 3
	if nw > len(p) {
	nw, d.end, d.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, d.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 d.err == nil {
	d.err = err
	}
	return n, d.err
	}

	// NewDecoder constructs a new base64 stream decoder.
	func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
	return &decoder{enc: enc, r: r}
	}

	// DecodedLen returns the maximum length in bytes of the decoded data
	// corresponding to n bytes of base64-encoded data.
	func (enc Encoding) DecodedLen(n int) int { return n / 4 3 }