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// 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 git85 implements the radix 85 data encoding
// used in the Git version control system.
package git85
import (
"bytes"
"io"
"os"
"strconv"
)
type CorruptInputError int64
func (e CorruptInputError) String() string {
return "illegal git85 data at input byte " + strconv.Itoa64(int64(e))
}
const encode = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~"
// The decodings are 1+ the actual value, so that the
// default zero value can be used to mean "not valid".
var decode = [256]uint8{
'0': 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
'A': 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
'a': 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,
'!': 63,
'#': 64, 65, 66, 67,
'(': 68, 69, 70, 71,
'-': 72,
';': 73,
'<': 74, 75, 76, 77,
'@': 78,
'^': 79, 80, 81,
'{': 82, 83, 84, 85,
}
// Encode encodes src into EncodedLen(len(src))
// bytes of dst. As a convenience, it returns the number
// of bytes written to dst, but this value is always EncodedLen(len(src)).
// Encode implements the radix 85 encoding used in the
// Git version control tool.
//
// The encoding splits src into chunks of at most 52 bytes
// and encodes each chunk on its own line.
func Encode(dst, src []byte) int {
ndst := 0
for len(src) > 0 {
n := len(src)
if n > 52 {
n = 52
}
if n <= 27 {
dst[ndst] = byte('A' + n - 1)
} else {
dst[ndst] = byte('a' + n - 26 - 1)
}
ndst++
for i := 0; i < n; i += 4 {
var v uint32
for j := 0; j < 4 && i+j < n; j++ {
v |= uint32(src[i+j]) << uint(24-j*8)
}
for j := 4; j >= 0; j-- {
dst[ndst+j] = encode[v%85]
v /= 85
}
ndst += 5
}
dst[ndst] = '\n'
ndst++
src = src[n:]
}
return ndst
}
// EncodedLen returns the length of an encoding of n source bytes.
func EncodedLen(n int) int {
if n == 0 {
return 0
}
// 5 bytes per 4 bytes of input, rounded up.
// 2 extra bytes for each line of 52 src bytes, rounded up.
return (n+3)/4*5 + (n+51)/52*2
}
var newline = []byte{'\n'}
// Decode decodes src into at most MaxDecodedLen(len(src))
// bytes, returning the actual number of bytes written to dst.
//
// If Decode encounters invalid input, it returns a CorruptInputError.
//
func Decode(dst, src []byte) (n int, err os.Error) {
ndst := 0
nsrc := 0
for nsrc < len(src) {
var l int
switch ch := int(src[nsrc]); {
case 'A' <= ch && ch <= 'Z':
l = ch - 'A' + 1
case 'a' <= ch && ch <= 'z':
l = ch - 'a' + 26 + 1
default:
return ndst, CorruptInputError(nsrc)
}
if nsrc+1+l > len(src) {
return ndst, CorruptInputError(nsrc)
}
el := (l + 3) / 4 * 5 // encoded len
if nsrc+1+el+1 > len(src) || src[nsrc+1+el] != '\n' {
return ndst, CorruptInputError(nsrc)
}
line := src[nsrc+1 : nsrc+1+el]
for i := 0; i < el; i += 5 {
var v uint32
for j := 0; j < 5; j++ {
ch := decode[line[i+j]]
if ch == 0 {
return ndst, CorruptInputError(nsrc + 1 + i + j)
}
v = v*85 + uint32(ch-1)
}
for j := 0; j < 4; j++ {
dst[ndst] = byte(v >> 24)
v <<= 8
ndst++
}
}
// Last fragment may have run too far (but there was room in dst).
// Back up.
if l%4 != 0 {
ndst -= 4 - l%4
}
nsrc += 1 + el + 1
}
return ndst, nil
}
func MaxDecodedLen(n int) int { return n / 5 * 4 }
// NewEncoder returns a new Git base85 stream encoder. Data written to
// the returned writer will be encoded and then written to w.
// The Git encoding operates on 52-byte blocks; when finished
// writing, the caller must Close the returned encoder to flush any
// partially written blocks.
func NewEncoder(w io.Writer) io.WriteCloser { return &encoder{w: w} }
type encoder struct {
w io.Writer
err os.Error
buf [52]byte
nbuf int
out [1024]byte
nout int
}
func (e *encoder) Write(p []byte) (n int, err os.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 < 52; i++ {
e.buf[e.nbuf] = p[i]
e.nbuf++
}
n += i
p = p[i:]
if e.nbuf < 52 {
return
}
nout := Encode(e.out[0:], e.buf[0:])
if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
return n, e.err
}
e.nbuf = 0
}
// Large interior chunks.
for len(p) >= 52 {
nn := len(e.out) / (1 + 52/4*5 + 1) * 52
if nn > len(p) {
nn = len(p) / 52 * 52
}
if nn > 0 {
nout := Encode(e.out[0:], p[0:nn])
if _, e.err = e.w.Write(e.out[0:nout]); 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
}
func (e *encoder) Close() os.Error {
// If there's anything left in the buffer, flush it out
if e.err == nil && e.nbuf > 0 {
nout := Encode(e.out[0:], e.buf[0:e.nbuf])
e.nbuf = 0
_, e.err = e.w.Write(e.out[0:nout])
}
return e.err
}
// NewDecoder returns a new Git base85 stream decoder.
func NewDecoder(r io.Reader) io.Reader { return &decoder{r: r} }
type decoder struct {
r io.Reader
err os.Error
readErr os.Error
buf [1024]byte
nbuf int
out []byte
outbuf [1024]byte
off int64
}
func (d *decoder) Read(p []byte) (n int, err os.Error) {
if len(p) == 0 {
return 0, nil
}
for {
// Copy leftover output from last decode.
if len(d.out) > 0 {
n = copy(p, d.out)
d.out = d.out[n:]
return
}
// Out of decoded output. Check errors.
if d.err != nil {
return 0, d.err
}
if d.readErr != nil {
d.err = d.readErr
return 0, d.err
}
// Read and decode more input.
var nn int
nn, d.readErr = d.r.Read(d.buf[d.nbuf:])
d.nbuf += nn
// Send complete lines to Decode.
nl := bytes.LastIndex(d.buf[0:d.nbuf], newline)
if nl < 0 {
continue
}
nn, d.err = Decode(d.outbuf[0:], d.buf[0:nl+1])
if e, ok := d.err.(CorruptInputError); ok {
d.err = CorruptInputError(int64(e) + d.off)
}
d.out = d.outbuf[0:nn]
d.nbuf = copy(d.buf[0:], d.buf[nl+1:d.nbuf])
d.off += int64(nl + 1)
}
panic("unreachable")
}