// 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.
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 {
if dn, ok := assemble64(
enc.decodeMap[src[si+0]],
enc.decodeMap[src[si+1]],
enc.decodeMap[src[si+2]],
enc.decodeMap[src[si+3]],
enc.decodeMap[src[si+4]],
enc.decodeMap[src[si+5]],
enc.decodeMap[src[si+6]],
enc.decodeMap[src[si+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 {
if dn, ok := assemble32(
enc.decodeMap[src[si+0]],
enc.decodeMap[src[si+1]],
enc.decodeMap[src[si+2]],
enc.decodeMap[src[si+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
}
|
