354 lines
8.2 KiB
Go
354 lines
8.2 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package base64 implements base64 encoding as specified by RFC 4648.
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package base64
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import (
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"io"
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"strconv"
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)
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/*
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* Encodings
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*/
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// An Encoding is a radix 64 encoding/decoding scheme, defined by a
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// 64-character alphabet. The most common encoding is the "base64"
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// encoding defined in RFC 4648 and used in MIME (RFC 2045) and PEM
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// (RFC 1421). RFC 4648 also defines an alternate encoding, which is
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// the standard encoding with - and _ substituted for + and /.
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type Encoding struct {
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encode string
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decodeMap [256]byte
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}
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const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
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const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
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// NewEncoding returns a new Encoding defined by the given alphabet,
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// which must be a 64-byte string.
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func NewEncoding(encoder string) *Encoding {
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e := new(Encoding)
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e.encode = encoder
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for i := 0; i < len(e.decodeMap); i++ {
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e.decodeMap[i] = 0xFF
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}
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for i := 0; i < len(encoder); i++ {
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e.decodeMap[encoder[i]] = byte(i)
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}
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return e
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}
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// StdEncoding is the standard base64 encoding, as defined in
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// RFC 4648.
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var StdEncoding = NewEncoding(encodeStd)
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// URLEncoding is the alternate base64 encoding defined in RFC 4648.
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// It is typically used in URLs and file names.
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var URLEncoding = NewEncoding(encodeURL)
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/*
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* Encoder
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*/
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// Encode encodes src using the encoding enc, writing
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// EncodedLen(len(src)) bytes to dst.
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//
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// The encoding pads the output to a multiple of 4 bytes,
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// so Encode is not appropriate for use on individual blocks
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// of a large data stream. Use NewEncoder() instead.
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func (enc *Encoding) Encode(dst, src []byte) {
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if len(src) == 0 {
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return
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}
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for len(src) > 0 {
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dst[0] = 0
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dst[1] = 0
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dst[2] = 0
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dst[3] = 0
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// Unpack 4x 6-bit source blocks into a 4 byte
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// destination quantum
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switch len(src) {
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default:
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dst[3] |= src[2] & 0x3F
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dst[2] |= src[2] >> 6
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fallthrough
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case 2:
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dst[2] |= (src[1] << 2) & 0x3F
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dst[1] |= src[1] >> 4
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fallthrough
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case 1:
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dst[1] |= (src[0] << 4) & 0x3F
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dst[0] |= src[0] >> 2
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}
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// Encode 6-bit blocks using the base64 alphabet
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for j := 0; j < 4; j++ {
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dst[j] = enc.encode[dst[j]]
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}
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// Pad the final quantum
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if len(src) < 3 {
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dst[3] = '='
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if len(src) < 2 {
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dst[2] = '='
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}
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break
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}
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src = src[3:]
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dst = dst[4:]
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}
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}
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// EncodeToString returns the base64 encoding of src.
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func (enc *Encoding) EncodeToString(src []byte) string {
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buf := make([]byte, enc.EncodedLen(len(src)))
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enc.Encode(buf, src)
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return string(buf)
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}
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type encoder struct {
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err error
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enc *Encoding
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w io.Writer
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buf [3]byte // buffered data waiting to be encoded
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nbuf int // number of bytes in buf
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out [1024]byte // output buffer
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}
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func (e *encoder) Write(p []byte) (n int, err error) {
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if e.err != nil {
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return 0, e.err
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}
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// Leading fringe.
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if e.nbuf > 0 {
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var i int
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for i = 0; i < len(p) && e.nbuf < 3; i++ {
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e.buf[e.nbuf] = p[i]
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e.nbuf++
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}
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n += i
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p = p[i:]
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if e.nbuf < 3 {
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return
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}
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e.enc.Encode(e.out[0:], e.buf[0:])
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if _, e.err = e.w.Write(e.out[0:4]); e.err != nil {
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return n, e.err
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}
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e.nbuf = 0
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}
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// Large interior chunks.
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for len(p) >= 3 {
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nn := len(e.out) / 4 * 3
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if nn > len(p) {
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nn = len(p)
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}
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nn -= nn % 3
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if nn > 0 {
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e.enc.Encode(e.out[0:], p[0:nn])
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if _, e.err = e.w.Write(e.out[0 : nn/3*4]); e.err != nil {
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return n, e.err
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}
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}
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n += nn
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p = p[nn:]
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}
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// Trailing fringe.
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for i := 0; i < len(p); i++ {
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e.buf[i] = p[i]
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}
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e.nbuf = len(p)
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n += len(p)
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return
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}
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// Close flushes any pending output from the encoder.
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// It is an error to call Write after calling Close.
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func (e *encoder) Close() error {
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// If there's anything left in the buffer, flush it out
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if e.err == nil && e.nbuf > 0 {
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e.enc.Encode(e.out[0:], e.buf[0:e.nbuf])
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e.nbuf = 0
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_, e.err = e.w.Write(e.out[0:4])
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}
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return e.err
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}
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// NewEncoder returns a new base64 stream encoder. Data written to
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// the returned writer will be encoded using enc and then written to w.
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// Base64 encodings operate in 4-byte blocks; when finished
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// writing, the caller must Close the returned encoder to flush any
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// partially written blocks.
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func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser {
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return &encoder{enc: enc, w: w}
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}
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// EncodedLen returns the length in bytes of the base64 encoding
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// of an input buffer of length n.
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func (enc *Encoding) EncodedLen(n int) int { return (n + 2) / 3 * 4 }
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/*
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* Decoder
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*/
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type CorruptInputError int64
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func (e CorruptInputError) Error() string {
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return "illegal base64 data at input byte " + strconv.FormatInt(int64(e), 10)
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}
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// decode is like Decode but returns an additional 'end' value, which
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// indicates if end-of-message padding was encountered and thus any
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// additional data is an error.
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func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
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osrc := src
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for len(src) > 0 && !end {
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// Decode quantum using the base64 alphabet
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var dbuf [4]byte
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dlen := 4
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for j := 0; j < 4; {
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if len(src) == 0 {
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return n, false, CorruptInputError(len(osrc) - len(src) - j)
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}
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in := src[0]
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src = src[1:]
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if in == '\r' || in == '\n' {
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// Ignore this character.
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continue
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}
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if in == '=' && j >= 2 && len(src) < 4 {
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// We've reached the end and there's
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// padding
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if len(src) == 0 && j == 2 {
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// not enough padding
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return n, false, CorruptInputError(len(osrc))
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}
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if len(src) > 0 && src[0] != '=' {
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// incorrect padding
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return n, false, CorruptInputError(len(osrc) - len(src) - 1)
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}
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dlen = j
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end = true
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break
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}
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dbuf[j] = enc.decodeMap[in]
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if dbuf[j] == 0xFF {
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return n, false, CorruptInputError(len(osrc) - len(src) - 1)
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}
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j++
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}
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// Pack 4x 6-bit source blocks into 3 byte destination
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// quantum
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switch dlen {
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case 4:
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dst[2] = dbuf[2]<<6 | dbuf[3]
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fallthrough
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case 3:
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dst[1] = dbuf[1]<<4 | dbuf[2]>>2
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fallthrough
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case 2:
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dst[0] = dbuf[0]<<2 | dbuf[1]>>4
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}
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dst = dst[3:]
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n += dlen - 1
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}
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return n, end, nil
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}
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// Decode decodes src using the encoding enc. It writes at most
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// DecodedLen(len(src)) bytes to dst and returns the number of bytes
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// written. If src contains invalid base64 data, it will return the
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// number of bytes successfully written and CorruptInputError.
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// New line characters (\r and \n) are ignored.
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func (enc *Encoding) Decode(dst, src []byte) (n int, err error) {
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n, _, err = enc.decode(dst, src)
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return
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}
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// DecodeString returns the bytes represented by the base64 string s.
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func (enc *Encoding) DecodeString(s string) ([]byte, error) {
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dbuf := make([]byte, enc.DecodedLen(len(s)))
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n, err := enc.Decode(dbuf, []byte(s))
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return dbuf[:n], err
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}
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type decoder struct {
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err error
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enc *Encoding
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r io.Reader
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end bool // saw end of message
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buf [1024]byte // leftover input
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nbuf int
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out []byte // leftover decoded output
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outbuf [1024 / 4 * 3]byte
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}
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func (d *decoder) Read(p []byte) (n int, err error) {
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if d.err != nil {
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return 0, d.err
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}
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// Use leftover decoded output from last read.
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if len(d.out) > 0 {
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n = copy(p, d.out)
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d.out = d.out[n:]
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return n, nil
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}
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// Read a chunk.
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nn := len(p) / 3 * 4
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if nn < 4 {
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nn = 4
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}
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if nn > len(d.buf) {
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nn = len(d.buf)
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}
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nn, d.err = io.ReadAtLeast(d.r, d.buf[d.nbuf:nn], 4-d.nbuf)
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d.nbuf += nn
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if d.err != nil || d.nbuf < 4 {
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return 0, d.err
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}
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// Decode chunk into p, or d.out and then p if p is too small.
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nr := d.nbuf / 4 * 4
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nw := d.nbuf / 4 * 3
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if nw > len(p) {
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nw, d.end, d.err = d.enc.decode(d.outbuf[0:], d.buf[0:nr])
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d.out = d.outbuf[0:nw]
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n = copy(p, d.out)
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d.out = d.out[n:]
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} else {
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n, d.end, d.err = d.enc.decode(p, d.buf[0:nr])
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}
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d.nbuf -= nr
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for i := 0; i < d.nbuf; i++ {
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d.buf[i] = d.buf[i+nr]
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}
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if d.err == nil {
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d.err = err
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}
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return n, d.err
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}
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// NewDecoder constructs a new base64 stream decoder.
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func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
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return &decoder{enc: enc, r: r}
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}
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// DecodedLen returns the maximum length in bytes of the decoded data
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// corresponding to n bytes of base64-encoded data.
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func (enc *Encoding) DecodedLen(n int) int { return n / 4 * 3 }
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