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 (
	
	
	
)
* 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 ( string) *Encoding {
	if len() != 64 {
		panic("encoding alphabet is not 64-bytes long")
	}
	for  := 0;  < len(); ++ {
		if [] == '\n' || [] == '\r' {
			panic("encoding alphabet contains newline character")
		}
	}

	 := new(Encoding)
	.padChar = StdPadding
	copy(.encode[:], )

	for  := 0;  < len(.decodeMap); ++ {
		.decodeMap[] = 0xFF
	}
	for  := 0;  < len(); ++ {
		.decodeMap[[]] = byte()
	}
	return 
}
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 ( Encoding) ( rune) *Encoding {
	if  == '\r' ||  == '\n' ||  > 0xff {
		panic("invalid padding")
	}

	for  := 0;  < len(.encode); ++ {
		if rune(.encode[]) ==  {
			panic("padding contained in alphabet")
		}
	}

	.padChar = 
	return &
}
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 ( Encoding) () *Encoding {
	.strict = true
	return &
}
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 ( *Encoding) (,  []byte) {
	if len() == 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.
	_ = .encode

	,  := 0, 0
	 := (len() / 3) * 3
Convert 3x 8bit source bytes into 4 bytes
		 := uint([+0])<<16 | uint([+1])<<8 | uint([+2])

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

		 += 3
		 += 4
	}

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

	[+0] = .encode[>>18&0x3F]
	[+1] = .encode[>>12&0x3F]

	switch  {
	case 2:
		[+2] = .encode[>>6&0x3F]
		if .padChar != NoPadding {
			[+3] = byte(.padChar)
		}
	case 1:
		if .padChar != NoPadding {
			[+2] = byte(.padChar)
			[+3] = byte(.padChar)
		}
	}
}
EncodeToString returns the base64 encoding of src.
func ( *Encoding) ( []byte) string {
	 := make([]byte, .EncodedLen(len()))
	.Encode(, )
	return string()
}

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 ( *encoder) ( []byte) ( int,  error) {
	if .err != nil {
		return 0, .err
	}
Leading fringe.
	if .nbuf > 0 {
		var  int
		for  = 0;  < len() && .nbuf < 3; ++ {
			.buf[.nbuf] = []
			.nbuf++
		}
		 += 
		 = [:]
		if .nbuf < 3 {
			return
		}
		.enc.Encode(.out[:], .buf[:])
		if _, .err = .w.Write(.out[:4]); .err != nil {
			return , .err
		}
		.nbuf = 0
	}
Large interior chunks.
	for len() >= 3 {
		 := len(.out) / 4 * 3
		if  > len() {
			 = len()
			 -=  % 3
		}
		.enc.Encode(.out[:], [:])
		if _, .err = .w.Write(.out[0 : /3*4]); .err != nil {
			return , .err
		}
		 += 
		 = [:]
	}
Trailing fringe.
	for  := 0;  < len(); ++ {
		.buf[] = []
	}
	.nbuf = len()
	 += len()
	return
}
Close flushes any pending output from the encoder. It is an error to call Write after calling Close.
If there's anything left in the buffer, flush it out
	if .err == nil && .nbuf > 0 {
		.enc.Encode(.out[:], .buf[:.nbuf])
		_, .err = .w.Write(.out[:.enc.EncodedLen(.nbuf)])
		.nbuf = 0
	}
	return .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 ( *Encoding,  io.Writer) io.WriteCloser {
	return &encoder{enc: , w: }
}
EncodedLen returns the length in bytes of the base64 encoding of an input buffer of length n.
func ( *Encoding) ( int) int {
	if .padChar == NoPadding {
		return (*8 + 5) / 6 // minimum # chars at 6 bits per char
	}
	return ( + 2) / 3 * 4 // minimum # 4-char quanta, 3 bytes each
}
* Decoder 

type CorruptInputError int64

func ( CorruptInputError) () string {
	return "illegal base64 data at input byte " + strconv.FormatInt(int64(), 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.
Decode quantum using the base64 alphabet
	var  [4]byte
	 := 4
Lift the nil check outside of the loop.
	_ = .decodeMap

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

		 := .decodeMap[]
		if  != 0xff {
			[] = 
			continue
		}

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

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

			++
		}
skip over newlines
		for  < len() && ([] == '\n' || [] == '\r') {
			++
		}
trailing garbage
			 = CorruptInputError()
		}
		 = 
		break
	}
Convert 4x 6bit source bytes into 3 bytes
	 := uint([0])<<18 | uint([1])<<12 | uint([2])<<6 | uint([3])
	[2], [1], [0] = byte(>>0), byte(>>8), byte(>>16)
	switch  {
	case 4:
		[2] = [2]
		[2] = 0
		fallthrough
	case 3:
		[1] = [1]
		if .strict && [2] != 0 {
			return , 0, CorruptInputError( - 1)
		}
		[1] = 0
		fallthrough
	case 2:
		[0] = [0]
		if .strict && ([1] != 0 || [2] != 0) {
			return , 0, CorruptInputError( - 2)
		}
	}

	return ,  - 1, 
}
DecodeString returns the bytes represented by the base64 string s.
func ( *Encoding) ( string) ([]byte, error) {
	 := make([]byte, .DecodedLen(len()))
	,  := .Decode(, []byte())
	return [:], 
}

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

	if .err != nil {
		return 0, .err
	}
This code assumes that d.r strips supported whitespace ('\r' and '\n').
Refill buffer.
	for .nbuf < 4 && .readErr == nil {
		 := len() / 3 * 4
		if  < 4 {
			 = 4
		}
		if  > len(.buf) {
			 = len(.buf)
		}
		, .readErr = .r.Read(.buf[.nbuf:])
		.nbuf += 
	}

	if .nbuf < 4 {
Decode final fragment, without padding.
			var  int
			, .err = .enc.Decode(.outbuf[:], .buf[:.nbuf])
			.nbuf = 0
			.out = .outbuf[:]
			 = copy(, .out)
			.out = .out[:]
			if  > 0 || len() == 0 && len(.out) > 0 {
				return , nil
			}
			if .err != nil {
				return 0, .err
			}
		}
		.err = .readErr
		if .err == io.EOF && .nbuf > 0 {
			.err = io.ErrUnexpectedEOF
		}
		return 0, .err
	}
Decode chunk into p, or d.out and then p if p is too small.
	 := .nbuf / 4 * 4
	 := .nbuf / 4 * 3
	if  > len() {
		, .err = .enc.Decode(.outbuf[:], .buf[:])
		.out = .outbuf[:]
		 = copy(, .out)
		.out = .out[:]
	} else {
		, .err = .enc.Decode(, .buf[:])
	}
	.nbuf -= 
	copy(.buf[:.nbuf], .buf[:])
	return , .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 ( *Encoding) (,  []byte) ( int,  error) {
	if len() == 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.
	_ = .decodeMap

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

	for len()- >= 4 && len()- >= 4 {
		 := [ : +4]
		if ,  := assemble32(
			.decodeMap[[0]],
			.decodeMap[[1]],
			.decodeMap[[2]],
			.decodeMap[[3]],
		);  {
			binary.BigEndian.PutUint32([:], )
			 += 3
			 += 4
		} else {
			var  int
			, ,  = .decodeQuantum([:], , )
			 += 
			if  != nil {
				return , 
			}
		}
	}

	for  < len() {
		var  int
		, ,  = .decodeQuantum([:], , )
		 += 
		if  != nil {
			return , 
		}
	}
	return , 
}
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.
Check that all the digits are valid. If any of them was 0xff, their bitwise OR will be 0xff.
	if ||| == 0xff {
		return 0, false
	}
	return uint32()<<26 |
			uint32()<<20 |
			uint32()<<14 |
			uint32()<<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.
Check that all the digits are valid. If any of them was 0xff, their bitwise OR will be 0xff.
	if ||||||| == 0xff {
		return 0, false
	}
	return uint64()<<58 |
			uint64()<<52 |
			uint64()<<46 |
			uint64()<<40 |
			uint64()<<34 |
			uint64()<<28 |
			uint64()<<22 |
			uint64()<<16,
		true
}

type newlineFilteringReader struct {
	wrapped io.Reader
}

func ( *newlineFilteringReader) ( []byte) (int, error) {
	,  := .wrapped.Read()
	for  > 0 {
		 := 0
		for ,  := range [:] {
			if  != '\r' &&  != '\n' {
				if  !=  {
					[] = 
				}
				++
			}
		}
		if  > 0 {
			return ,
Previous buffer entirely whitespace, read again
		,  = .wrapped.Read()
	}
	return , 
}
NewDecoder constructs a new base64 stream decoder.
func ( *Encoding,  io.Reader) io.Reader {
	return &decoder{enc: , r: &newlineFilteringReader{}}
}
DecodedLen returns the maximum length in bytes of the decoded data corresponding to n bytes of base64-encoded data.
func ( *Encoding) ( int) int {
Unpadded data may end with partial block of 2-3 characters.
		return  * 6 / 8
Padded base64 should always be a multiple of 4 characters in length.
	return  / 4 * 3