// 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"
"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
}
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.
// 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")
}
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.
func (enc Encoding) WithPadding(padding rune) *Encoding {
enc.padChar = padding
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)
// URLEncoding 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
}
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)
}
// decode is like Decode but returns an additional 'end' value, which
// indicates if end-of-message padding or a partial quantum was encountered
// and thus any additional data is an error.
func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
si := 0
// skip over newlines
for si < len(src) && (src[si] == '\n' || src[si] == '\r') {
si++
}
for si < len(src) && !end {
// Decode quantum using the base64 alphabet
var dbuf [4]byte
dinc, dlen := 3, 4
for j := range dbuf {
if len(src) == si {
if enc.padChar != NoPadding || j < 2 {
return n, false, CorruptInputError(si - j)
}
dinc, dlen, end = j-1, j, true
break
}
in := src[si]
si++
// skip over newlines
for si < len(src) && (src[si] == '\n' || src[si] == '\r') {
si++
}
if rune(in) == enc.padChar {
// We've reached the end and there's padding
switch j {
case 0, 1:
// incorrect padding
return n, false, CorruptInputError(si - 1)
case 2:
// "==" is expected, the first "=" is already consumed.
if si == len(src) {
// not enough padding
return n, false, CorruptInputError(len(src))
}
if rune(src[si]) != enc.padChar {
// incorrect padding
return n, false, 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)
}
dinc, dlen, end = 3, j, true
break
}
dbuf[j] = enc.decodeMap[in]
if dbuf[j] == 0xFF {
return n, false, CorruptInputError(si - 1)
}
}
// Convert 4x 6bit source bytes into 3 bytes
val := uint(dbuf[0])<<18 | uint(dbuf[1])<<12 | uint(dbuf[2])<<6 | uint(dbuf[3])
switch dlen {
case 4:
dst[2] = byte(val >> 0)
fallthrough
case 3:
dst[1] = byte(val >> 8)
fallthrough
case 2:
dst[0] = byte(val >> 16)
}
dst = dst[dinc:]
n += dlen - 1
}
return n, end, 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) {
n, _, err = enc.decode(dst, src)
return
}
// 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
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 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
}
// This code assumes that d.r strips supported whitespace ('\r' and '\n').
// 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.err != nil || 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[:], d.buf[:nr])
d.out = d.outbuf[:nw]
n = copy(p, d.out)
d.out = d.out[n:]
} else {
n, d.end, d.err = d.enc.decode(p, d.buf[: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
}
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 + 7) / 8
}
// Padded base64 should always be a multiple of 4 characters in length.
return n / 4 * 3
}