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