src/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 (
 	"encoding/binary"
 	"io"
 	"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    [64]byte
 	decodeMap [256]byte
 	padChar   rune
 	strict    bool
 }

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

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

 // NewEncoding returns a new padded Encoding defined by the given alphabet,
 // which must be a 64-byte string that does not contain the padding character
 // or CR / LF ('\r', '\n').
 // The resulting Encoding uses the default padding character ('='),
 // which may be changed or disabled via WithPadding.
 func NewEncoding(encoder string) *Encoding {
 	if len(encoder) != 64 {
 		panic("encoding alphabet is not 64-bytes long")
 	}
 	for i := 0; i < len(encoder); i++ {
 		if encoder[i] == '\n' || encoder[i] == '\r' {
 			panic("encoding alphabet contains newline character")
 		}
 	}

 	e := new(Encoding)
 	e.padChar = StdPadding
 	copy(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
 }

 // 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
 }

 // Strict creates a new encoding identical to enc except with
 // strict decoding enabled. In this mode, the decoder requires that
 // trailing padding bits are zero, as described in RFC 4648 section 3.5.
 //
 // Note that the input is still malleable, as new line characters
 // (CR and LF) are still ignored.
 func (enc Encoding) Strict() *Encoding {
 	enc.strict = true
 	return &enc
 }

 // 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)

 // RawStdEncoding is the standard raw, unpadded base64 encoding,
 // as defined in RFC 4648 section 3.2.
 // This is the same as StdEncoding but omits padding characters.
 var RawStdEncoding = StdEncoding.WithPadding(NoPadding)

 // RawURLEncoding is the unpadded alternate base64 encoding defined in RFC 4648.
 // It is typically used in URLs and file names.
 // This is the same as URLEncoding but omits padding characters.
 var RawURLEncoding = URLEncoding.WithPadding(NoPadding)

 /*
  * 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
 	}
 	// enc is a pointer receiver, so the use of enc.encode within the hot
 	// loop below means a nil check at every operation. Lift that nil check
 	// outside of the loop to speed up the encoder.
 	_ = enc.encode

 	di, si := 0, 0
 	n := (len(src) / 3) * 3
 	for si < n {
 		// Convert 3x 8bit source bytes into 4 bytes
 		val := uint(src[si+0])<<16 | uint(src[si+1])<<8 | uint(src[si+2])

 		dst[di+0] = enc.encode[val>>18&0x3F]
 		dst[di+1] = enc.encode[val>>12&0x3F]
 		dst[di+2] = enc.encode[val>>6&0x3F]
 		dst[di+3] = enc.encode[val&0x3F]

 		si += 3
 		di += 4
 	}

 	remain := len(src) - si
 	if remain == 0 {
 		return
 	}
 	// Add the remaining small block
 	val := uint(src[si+0]) << 16
 	if remain == 2 {
 		val |= uint(src[si+1]) << 8
 	}

 	dst[di+0] = enc.encode[val>>18&0x3F]
 	dst[di+1] = enc.encode[val>>12&0x3F]

 	switch remain {
 	case 2:
 		dst[di+2] = enc.encode[val>>6&0x3F]
 		if enc.padChar != NoPadding {
 			dst[di+3] = byte(enc.padChar)
 		}
 	case 1:
 		if enc.padChar != NoPadding {
 			dst[di+2] = byte(enc.padChar)
 			dst[di+3] = byte(enc.padChar)
 		}
 	}
 }

 // 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  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 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[:], e.buf[:])
 		if _, e.err = e.w.Write(e.out[: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
 		}
 		e.enc.Encode(e.out[:], p[: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() error {
 	// If there's anything left in the buffer, flush it out
 	if e.err == nil && e.nbuf > 0 {
 		e.enc.Encode(e.out[:], e.buf[:e.nbuf])
 		_, e.err = e.w.Write(e.out[:e.enc.EncodedLen(e.nbuf)])
 		e.nbuf = 0
 	}
 	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 {
 	if enc.padChar == NoPadding {
 		return (n*8 + 5) / 6 // minimum # chars at 6 bits per char
 	}
 	return (n + 2) / 3 * 4 // minimum # 4-char quanta, 3 bytes each
 }

 /*
  * Decoder
  */

 type CorruptInputError int64

 func (e CorruptInputError) Error() string {
 	return "illegal base64 data at input byte " + strconv.FormatInt(int64(e), 10)
 }

 // decodeQuantum decodes up to 4 base64 bytes. The received parameters are
 // the destination buffer dst, the source buffer src and an index in the
 // source buffer si.
 // It returns the number of bytes read from src, the number of bytes written
 // to dst, and an error, if any.
 func (enc *Encoding) decodeQuantum(dst, src []byte, si int) (nsi, n int, err error) {
 	// Decode quantum using the base64 alphabet
 	var dbuf [4]byte
 	dlen := 4

 	// Lift the nil check outside of the loop.
 	_ = enc.decodeMap

 	for j := 0; j < len(dbuf); j++ {
 		if len(src) == si {
 			switch {
 			case j == 0:
 				return si, 0, nil
 			case j == 1, enc.padChar != NoPadding:
 				return si, 0, CorruptInputError(si - j)
 			}
 			dlen = j
 			break
 		}
 		in := src[si]
 		si++

 		out := enc.decodeMap[in]
 		if out != 0xff {
 			dbuf[j] = out
 			continue
 		}

 		if in == '\n' || in == '\r' {
 			j--
 			continue
 		}

 		if rune(in) != enc.padChar {
 			return si, 0, CorruptInputError(si - 1)
 		}

 		// We've reached the end and there's padding
 		switch j {
 		case 0, 1:
 			// incorrect padding
 			return si, 0, CorruptInputError(si - 1)
 		case 2:
 			// "==" is expected, the first "=" is already consumed.
 			// skip over newlines
 			for si < len(src) && (src[si] == '\n' || src[si] == '\r') {
 				si++
 			}
 			if si == len(src) {
 				// not enough padding
 				return si, 0, CorruptInputError(len(src))
 			}
 			if rune(src[si]) != enc.padChar {
 				// incorrect padding
 				return si, 0, CorruptInputError(si - 1)
 			}

 			si++
 		}

 		// skip over newlines
 		for si < len(src) && (src[si] == '\n' || src[si] == '\r') {
 			si++
 		}
 		if si < len(src) {
 			// trailing garbage
 			err = CorruptInputError(si)
 		}
 		dlen = j
 		break
 	}

 	// Convert 4x 6bit source bytes into 3 bytes
 	val := uint(dbuf[0])<<18 | uint(dbuf[1])<<12 | uint(dbuf[2])<<6 | uint(dbuf[3])
 	dbuf[2], dbuf[1], dbuf[0] = byte(val>>0), byte(val>>8), byte(val>>16)
 	switch dlen {
 	case 4:
 		dst[2] = dbuf[2]
 		dbuf[2] = 0
 		fallthrough
 	case 3:
 		dst[1] = dbuf[1]
 		if enc.strict && dbuf[2] != 0 {
 			return si, 0, CorruptInputError(si - 1)
 		}
 		dbuf[1] = 0
 		fallthrough
 	case 2:
 		dst[0] = dbuf[0]
 		if enc.strict && (dbuf[1] != 0 || dbuf[2] != 0) {
 			return si, 0, CorruptInputError(si - 2)
 		}
 	}

 	return si, dlen - 1, err
 }

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

 type decoder struct {
 	err     error
 	readErr error // error from r.Read
 	enc     *Encoding
 	r       io.Reader
 	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 error) {
 	// 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
 	}

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

 	// This code assumes that d.r strips supported whitespace ('\r' and '\n').

 	// Refill buffer.
 	for d.nbuf < 4 && d.readErr == nil {
 		nn := len(p) / 3 * 4
 		if nn < 4 {
 			nn = 4
 		}
 		if nn > len(d.buf) {
 			nn = len(d.buf)
 		}
 		nn, d.readErr = d.r.Read(d.buf[d.nbuf:nn])
 		d.nbuf += nn
 	}

 	if d.nbuf < 4 {
 		if d.enc.padChar == NoPadding && d.nbuf > 0 {
 			// Decode final fragment, without padding.
 			var nw int
 			nw, d.err = d.enc.Decode(d.outbuf[:], d.buf[:d.nbuf])
 			d.nbuf = 0
 			d.out = d.outbuf[:nw]
 			n = copy(p, d.out)
 			d.out = d.out[n:]
 			if n > 0 || len(p) == 0 && len(d.out) > 0 {
 				return n, nil
 			}
 			if d.err != nil {
 				return 0, d.err
 			}
 		}
 		d.err = d.readErr
 		if d.err == io.EOF && d.nbuf > 0 {
 			d.err = io.ErrUnexpectedEOF
 		}
 		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.err = d.enc.Decode(d.outbuf[:], d.buf[:nr])
 		d.out = d.outbuf[:nw]
 		n = copy(p, d.out)
 		d.out = d.out[n:]
 	} else {
 		n, d.err = d.enc.Decode(p, d.buf[:nr])
 	}
 	d.nbuf -= nr
 	copy(d.buf[:d.nbuf], d.buf[nr:])
 	return n, d.err
 }

 // 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.
 // New line characters (\r and \n) are ignored.
 func (enc *Encoding) Decode(dst, src []byte) (n int, err error) {
 	if len(src) == 0 {
 		return 0, nil
 	}

 	// Lift the nil check outside of the loop. enc.decodeMap is directly
 	// used later in this function, to let the compiler know that the
 	// receiver can't be nil.
 	_ = enc.decodeMap

 	si := 0
 	for strconv.IntSize >= 64 && len(src)-si >= 8 && len(dst)-n >= 8 {
 		src2 := src[si : si+8]
 		if dn, ok := assemble64(
 			enc.decodeMap[src2[0]],
 			enc.decodeMap[src2[1]],
 			enc.decodeMap[src2[2]],
 			enc.decodeMap[src2[3]],
 			enc.decodeMap[src2[4]],
 			enc.decodeMap[src2[5]],
 			enc.decodeMap[src2[6]],
 			enc.decodeMap[src2[7]],
 		); ok {
 			binary.BigEndian.PutUint64(dst[n:], dn)
 			n += 6
 			si += 8
 		} else {
 			var ninc int
 			si, ninc, err = enc.decodeQuantum(dst[n:], src, si)
 			n += ninc
 			if err != nil {
 				return n, err
 			}
 		}
 	}

 	for len(src)-si >= 4 && len(dst)-n >= 4 {
 		src2 := src[si : si+4]
 		if dn, ok := assemble32(
 			enc.decodeMap[src2[0]],
 			enc.decodeMap[src2[1]],
 			enc.decodeMap[src2[2]],
 			enc.decodeMap[src2[3]],
 		); ok {
 			binary.BigEndian.PutUint32(dst[n:], dn)
 			n += 3
 			si += 4
 		} else {
 			var ninc int
 			si, ninc, err = enc.decodeQuantum(dst[n:], src, si)
 			n += ninc
 			if err != nil {
 				return n, err
 			}
 		}
 	}

 	for si < len(src) {
 		var ninc int
 		si, ninc, err = enc.decodeQuantum(dst[n:], src, si)
 		n += ninc
 		if err != nil {
 			return n, err
 		}
 	}
 	return n, err
 }

 // assemble32 assembles 4 base64 digits into 3 bytes.
 // Each digit comes from the decode map, and will be 0xff
 // if it came from an invalid character.
 func assemble32(n1, n2, n3, n4 byte) (dn uint32, ok bool) {
 	// Check that all the digits are valid. If any of them was 0xff, their
 	// bitwise OR will be 0xff.
 	if n1|n2|n3|n4 == 0xff {
 		return 0, false
 	}
 	return uint32(n1)<<26 |
 			uint32(n2)<<20 |
 			uint32(n3)<<14 |
 			uint32(n4)<<8,
 		true
 }

 // assemble64 assembles 8 base64 digits into 6 bytes.
 // Each digit comes from the decode map, and will be 0xff
 // if it came from an invalid character.
 func assemble64(n1, n2, n3, n4, n5, n6, n7, n8 byte) (dn uint64, ok bool) {
 	// Check that all the digits are valid. If any of them was 0xff, their
 	// bitwise OR will be 0xff.
 	if n1|n2|n3|n4|n5|n6|n7|n8 == 0xff {
 		return 0, false
 	}
 	return uint64(n1)<<58 |
 			uint64(n2)<<52 |
 			uint64(n3)<<46 |
 			uint64(n4)<<40 |
 			uint64(n5)<<34 |
 			uint64(n6)<<28 |
 			uint64(n7)<<22 |
 			uint64(n8)<<16,
 		true
 }

 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[:n] {
 			if b != '\r' && b != '\n' {
 				if i != offset {
 					p[offset] = b
 				}
 				offset++
 			}
 		}
 		if offset > 0 {
 			return offset, err
 		}
 		// Previous buffer entirely whitespace, read again
 		n, err = r.wrapped.Read(p)
 	}
 	return n, err
 }

 // NewDecoder constructs a new base64 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 base64-encoded data.
 func (enc *Encoding) DecodedLen(n int) int {
 	if enc.padChar == NoPadding {
 		// Unpadded data may end with partial block of 2-3 characters.
 		return n * 6 / 8
 	}
 	// Padded base64 should always be a multiple of 4 characters in length.
 	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 (
	"encoding/binary"
	"io"
	"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 [64]byte
	decodeMap [256]byte
	padChar rune
	strict bool
	}

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

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

	// NewEncoding returns a new padded Encoding defined by the given alphabet,
	// which must be a 64-byte string that does not contain the padding character
	// or CR / LF ('\r', '\n').
	// The resulting Encoding uses the default padding character ('='),
	// which may be changed or disabled via WithPadding.
	func NewEncoding(encoder string) *Encoding {
	if len(encoder) != 64 {
	panic("encoding alphabet is not 64-bytes long")
	}
	for i := 0; i < len(encoder); i++ {
	if encoder[i] == '\n' \|\| encoder[i] == '\r' {
	panic("encoding alphabet contains newline character")
	}
	}

	e := new(Encoding)
	e.padChar = StdPadding
	copy(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
	}

	// 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
	}

	// Strict creates a new encoding identical to enc except with
	// strict decoding enabled. In this mode, the decoder requires that
	// trailing padding bits are zero, as described in RFC 4648 section 3.5.
	//
	// Note that the input is still malleable, as new line characters
	// (CR and LF) are still ignored.
	func (enc Encoding) Strict() *Encoding {
	enc.strict = true
	return &enc
	}

	// 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)

	// RawStdEncoding is the standard raw, unpadded base64 encoding,
	// as defined in RFC 4648 section 3.2.
	// This is the same as StdEncoding but omits padding characters.
	var RawStdEncoding = StdEncoding.WithPadding(NoPadding)

	// RawURLEncoding is the unpadded alternate base64 encoding defined in RFC 4648.
	// It is typically used in URLs and file names.
	// This is the same as URLEncoding but omits padding characters.
	var RawURLEncoding = URLEncoding.WithPadding(NoPadding)

	/*
	* 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
	}
	// enc is a pointer receiver, so the use of enc.encode within the hot
	// loop below means a nil check at every operation. Lift that nil check
	// outside of the loop to speed up the encoder.
	_ = enc.encode

	di, si := 0, 0
	n := (len(src) / 3) * 3
	for si < n {
	// Convert 3x 8bit source bytes into 4 bytes
	val := uint(src[si+0])<<16 \| uint(src[si+1])<<8 \| uint(src[si+2])

	dst[di+0] = enc.encode[val>>18&0x3F]
	dst[di+1] = enc.encode[val>>12&0x3F]
	dst[di+2] = enc.encode[val>>6&0x3F]
	dst[di+3] = enc.encode[val&0x3F]

	si += 3
	di += 4
	}

	remain := len(src) - si
	if remain == 0 {
	return
	}
	// Add the remaining small block
	val := uint(src[si+0]) << 16
	if remain == 2 {
	val \|= uint(src[si+1]) << 8
	}

	dst[di+0] = enc.encode[val>>18&0x3F]
	dst[di+1] = enc.encode[val>>12&0x3F]

	switch remain {
	case 2:
	dst[di+2] = enc.encode[val>>6&0x3F]
	if enc.padChar != NoPadding {
	dst[di+3] = byte(enc.padChar)
	}
	case 1:
	if enc.padChar != NoPadding {
	dst[di+2] = byte(enc.padChar)
	dst[di+3] = byte(enc.padChar)
	}
	}
	}

	// 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 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 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[:], e.buf[:])
	if _, e.err = e.w.Write(e.out[: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
	}
	e.enc.Encode(e.out[:], p[: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() error {
	// If there's anything left in the buffer, flush it out
	if e.err == nil && e.nbuf > 0 {
	e.enc.Encode(e.out[:], e.buf[:e.nbuf])
	_, e.err = e.w.Write(e.out[:e.enc.EncodedLen(e.nbuf)])
	e.nbuf = 0
	}
	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 {
	if enc.padChar == NoPadding {
	return (n*8 + 5) / 6 // minimum # chars at 6 bits per char
	}
	return (n + 2) / 3 * 4 // minimum # 4-char quanta, 3 bytes each
	}

	/*
	* Decoder
	*/

	type CorruptInputError int64

	func (e CorruptInputError) Error() string {
	return "illegal base64 data at input byte " + strconv.FormatInt(int64(e), 10)
	}

	// decodeQuantum decodes up to 4 base64 bytes. The received parameters are
	// the destination buffer dst, the source buffer src and an index in the
	// source buffer si.
	// It returns the number of bytes read from src, the number of bytes written
	// to dst, and an error, if any.
	func (enc *Encoding) decodeQuantum(dst, src []byte, si int) (nsi, n int, err error) {
	// Decode quantum using the base64 alphabet
	var dbuf [4]byte
	dlen := 4

	// Lift the nil check outside of the loop.
	_ = enc.decodeMap

	for j := 0; j < len(dbuf); j++ {
	if len(src) == si {
	switch {
	case j == 0:
	return si, 0, nil
	case j == 1, enc.padChar != NoPadding:
	return si, 0, CorruptInputError(si - j)
	}
	dlen = j
	break
	}
	in := src[si]
	si++

	out := enc.decodeMap[in]
	if out != 0xff {
	dbuf[j] = out
	continue
	}

	if in == '\n' \|\| in == '\r' {
	j--
	continue
	}

	if rune(in) != enc.padChar {
	return si, 0, CorruptInputError(si - 1)
	}

	// We've reached the end and there's padding
	switch j {
	case 0, 1:
	// incorrect padding
	return si, 0, CorruptInputError(si - 1)
	case 2:
	// "==" is expected, the first "=" is already consumed.
	// skip over newlines
	for si < len(src) && (src[si] == '\n' \|\| src[si] == '\r') {
	si++
	}
	if si == len(src) {
	// not enough padding
	return si, 0, CorruptInputError(len(src))
	}
	if rune(src[si]) != enc.padChar {
	// incorrect padding
	return si, 0, CorruptInputError(si - 1)
	}

	si++
	}

	// skip over newlines
	for si < len(src) && (src[si] == '\n' \|\| src[si] == '\r') {
	si++
	}
	if si < len(src) {
	// trailing garbage
	err = CorruptInputError(si)
	}
	dlen = j
	break
	}

	// Convert 4x 6bit source bytes into 3 bytes
	val := uint(dbuf[0])<<18 \| uint(dbuf[1])<<12 \| uint(dbuf[2])<<6 \| uint(dbuf[3])
	dbuf[2], dbuf[1], dbuf[0] = byte(val>>0), byte(val>>8), byte(val>>16)
	switch dlen {
	case 4:
	dst[2] = dbuf[2]
	dbuf[2] = 0
	fallthrough
	case 3:
	dst[1] = dbuf[1]
	if enc.strict && dbuf[2] != 0 {
	return si, 0, CorruptInputError(si - 1)
	}
	dbuf[1] = 0
	fallthrough
	case 2:
	dst[0] = dbuf[0]
	if enc.strict && (dbuf[1] != 0 \|\| dbuf[2] != 0) {
	return si, 0, CorruptInputError(si - 2)
	}
	}

	return si, dlen - 1, err
	}

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

	type decoder struct {
	err error
	readErr error // error from r.Read
	enc *Encoding
	r io.Reader
	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 error) {
	// 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
	}

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

	// This code assumes that d.r strips supported whitespace ('\r' and '\n').

	// Refill buffer.
	for d.nbuf < 4 && d.readErr == nil {
	nn := len(p) / 3 * 4
	if nn < 4 {
	nn = 4
	}
	if nn > len(d.buf) {
	nn = len(d.buf)
	}
	nn, d.readErr = d.r.Read(d.buf[d.nbuf:nn])
	d.nbuf += nn
	}

	if d.nbuf < 4 {
	if d.enc.padChar == NoPadding && d.nbuf > 0 {
	// Decode final fragment, without padding.
	var nw int
	nw, d.err = d.enc.Decode(d.outbuf[:], d.buf[:d.nbuf])
	d.nbuf = 0
	d.out = d.outbuf[:nw]
	n = copy(p, d.out)
	d.out = d.out[n:]
	if n > 0 \|\| len(p) == 0 && len(d.out) > 0 {
	return n, nil
	}
	if d.err != nil {
	return 0, d.err
	}
	}
	d.err = d.readErr
	if d.err == io.EOF && d.nbuf > 0 {
	d.err = io.ErrUnexpectedEOF
	}
	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.err = d.enc.Decode(d.outbuf[:], d.buf[:nr])
	d.out = d.outbuf[:nw]
	n = copy(p, d.out)
	d.out = d.out[n:]
	} else {
	n, d.err = d.enc.Decode(p, d.buf[:nr])
	}
	d.nbuf -= nr
	copy(d.buf[:d.nbuf], d.buf[nr:])
	return n, d.err
	}

	// 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.
	// New line characters (\r and \n) are ignored.
	func (enc *Encoding) Decode(dst, src []byte) (n int, err error) {
	if len(src) == 0 {
	return 0, nil
	}

	// Lift the nil check outside of the loop. enc.decodeMap is directly
	// used later in this function, to let the compiler know that the
	// receiver can't be nil.
	_ = enc.decodeMap

	si := 0
	for strconv.IntSize >= 64 && len(src)-si >= 8 && len(dst)-n >= 8 {
	src2 := src[si : si+8]
	if dn, ok := assemble64(
	enc.decodeMap[src2[0]],
	enc.decodeMap[src2[1]],
	enc.decodeMap[src2[2]],
	enc.decodeMap[src2[3]],
	enc.decodeMap[src2[4]],
	enc.decodeMap[src2[5]],
	enc.decodeMap[src2[6]],
	enc.decodeMap[src2[7]],
	); ok {
	binary.BigEndian.PutUint64(dst[n:], dn)
	n += 6
	si += 8
	} else {
	var ninc int
	si, ninc, err = enc.decodeQuantum(dst[n:], src, si)
	n += ninc
	if err != nil {
	return n, err
	}
	}
	}

	for len(src)-si >= 4 && len(dst)-n >= 4 {
	src2 := src[si : si+4]
	if dn, ok := assemble32(
	enc.decodeMap[src2[0]],
	enc.decodeMap[src2[1]],
	enc.decodeMap[src2[2]],
	enc.decodeMap[src2[3]],
	); ok {
	binary.BigEndian.PutUint32(dst[n:], dn)
	n += 3
	si += 4
	} else {
	var ninc int
	si, ninc, err = enc.decodeQuantum(dst[n:], src, si)
	n += ninc
	if err != nil {
	return n, err
	}
	}
	}

	for si < len(src) {
	var ninc int
	si, ninc, err = enc.decodeQuantum(dst[n:], src, si)
	n += ninc
	if err != nil {
	return n, err
	}
	}
	return n, err
	}

	// assemble32 assembles 4 base64 digits into 3 bytes.
	// Each digit comes from the decode map, and will be 0xff
	// if it came from an invalid character.
	func assemble32(n1, n2, n3, n4 byte) (dn uint32, ok bool) {
	// Check that all the digits are valid. If any of them was 0xff, their
	// bitwise OR will be 0xff.
	if n1\|n2\|n3\|n4 == 0xff {
	return 0, false
	}
	return uint32(n1)<<26 \|
	uint32(n2)<<20 \|
	uint32(n3)<<14 \|
	uint32(n4)<<8,
	true
	}

	// assemble64 assembles 8 base64 digits into 6 bytes.
	// Each digit comes from the decode map, and will be 0xff
	// if it came from an invalid character.
	func assemble64(n1, n2, n3, n4, n5, n6, n7, n8 byte) (dn uint64, ok bool) {
	// Check that all the digits are valid. If any of them was 0xff, their
	// bitwise OR will be 0xff.
	if n1\|n2\|n3\|n4\|n5\|n6\|n7\|n8 == 0xff {
	return 0, false
	}
	return uint64(n1)<<58 \|
	uint64(n2)<<52 \|
	uint64(n3)<<46 \|
	uint64(n4)<<40 \|
	uint64(n5)<<34 \|
	uint64(n6)<<28 \|
	uint64(n7)<<22 \|
	uint64(n8)<<16,
	true
	}

	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[:n] {
	if b != '\r' && b != '\n' {
	if i != offset {
	p[offset] = b
	}
	offset++
	}
	}
	if offset > 0 {
	return offset, err
	}
	// Previous buffer entirely whitespace, read again
	n, err = r.wrapped.Read(p)
	}
	return n, err
	}

	// NewDecoder constructs a new base64 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 base64-encoded data.
	func (enc *Encoding) DecodedLen(n int) int {
	if enc.padChar == NoPadding {
	// Unpadded data may end with partial block of 2-3 characters.
	return n * 6 / 8
	}
	// Padded base64 should always be a multiple of 4 characters in length.
	return n / 4 * 3
	}