github.com/rsc/tmp@v0.0.0-20240517235954-6deaab19748b/git85/git.go (about) 1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package git85 implements the radix 85 data encoding 6 // used in the Git version control system. 7 package git85 8 9 import ( 10 "bytes" 11 "io" 12 "strconv" 13 ) 14 15 type CorruptInputError int64 16 17 func (e CorruptInputError) Error() string { 18 return "illegal git85 data at input byte " + strconv.FormatInt(int64(e), 10) 19 } 20 21 const encode = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~" 22 23 // The decodings are 1+ the actual value, so that the 24 // default zero value can be used to mean "not valid". 25 var decode = [256]uint8{ 26 '0': 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 27 'A': 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 28 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 29 'a': 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 30 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 31 '!': 63, 32 '#': 64, 65, 66, 67, 33 '(': 68, 69, 70, 71, 34 '-': 72, 35 ';': 73, 36 '<': 74, 75, 76, 77, 37 '@': 78, 38 '^': 79, 80, 81, 39 '{': 82, 83, 84, 85, 40 } 41 42 // Encode encodes src into EncodedLen(len(src)) 43 // bytes of dst. As a convenience, it returns the number 44 // of bytes written to dst, but this value is always EncodedLen(len(src)). 45 // Encode implements the radix 85 encoding used in the 46 // Git version control tool. 47 // 48 // The encoding splits src into chunks of at most 52 bytes 49 // and encodes each chunk on its own line. 50 func Encode(dst, src []byte) int { 51 ndst := 0 52 for len(src) > 0 { 53 n := len(src) 54 if n > 52 { 55 n = 52 56 } 57 if n <= 27 { 58 dst[ndst] = byte('A' + n - 1) 59 } else { 60 dst[ndst] = byte('a' + n - 26 - 1) 61 } 62 ndst++ 63 for i := 0; i < n; i += 4 { 64 var v uint32 65 for j := 0; j < 4 && i+j < n; j++ { 66 v |= uint32(src[i+j]) << uint(24-j*8) 67 } 68 for j := 4; j >= 0; j-- { 69 dst[ndst+j] = encode[v%85] 70 v /= 85 71 } 72 ndst += 5 73 } 74 dst[ndst] = '\n' 75 ndst++ 76 src = src[n:] 77 } 78 return ndst 79 } 80 81 // EncodedLen returns the length of an encoding of n source bytes. 82 func EncodedLen(n int) int { 83 if n == 0 { 84 return 0 85 } 86 // 5 bytes per 4 bytes of input, rounded up. 87 // 2 extra bytes for each line of 52 src bytes, rounded up. 88 return (n+3)/4*5 + (n+51)/52*2 89 } 90 91 var newline = []byte{'\n'} 92 93 // Decode decodes src into at most MaxDecodedLen(len(src)) 94 // bytes, returning the actual number of bytes written to dst. 95 // 96 // If Decode encounters invalid input, it returns a CorruptInputError. 97 // 98 func Decode(dst, src []byte) (n int, err error) { 99 ndst := 0 100 nsrc := 0 101 for nsrc < len(src) { 102 var l int 103 switch ch := int(src[nsrc]); { 104 case 'A' <= ch && ch <= 'Z': 105 l = ch - 'A' + 1 106 case 'a' <= ch && ch <= 'z': 107 l = ch - 'a' + 26 + 1 108 default: 109 return ndst, CorruptInputError(nsrc) 110 } 111 if nsrc+1+l > len(src) { 112 return ndst, CorruptInputError(nsrc) 113 } 114 el := (l + 3) / 4 * 5 // encoded len 115 if nsrc+1+el+1 > len(src) || src[nsrc+1+el] != '\n' { 116 return ndst, CorruptInputError(nsrc) 117 } 118 line := src[nsrc+1 : nsrc+1+el] 119 for i := 0; i < el; i += 5 { 120 var v uint32 121 for j := 0; j < 5; j++ { 122 ch := decode[line[i+j]] 123 if ch == 0 { 124 return ndst, CorruptInputError(nsrc + 1 + i + j) 125 } 126 v = v*85 + uint32(ch-1) 127 } 128 for j := 0; j < 4; j++ { 129 dst[ndst] = byte(v >> 24) 130 v <<= 8 131 ndst++ 132 } 133 } 134 // Last fragment may have run too far (but there was room in dst). 135 // Back up. 136 if l%4 != 0 { 137 ndst -= 4 - l%4 138 } 139 nsrc += 1 + el + 1 140 } 141 return ndst, nil 142 } 143 144 func MaxDecodedLen(n int) int { return n / 5 * 4 } 145 146 // NewEncoder returns a new Git base85 stream encoder. Data written to 147 // the returned writer will be encoded and then written to w. 148 // The Git encoding operates on 52-byte blocks; when finished 149 // writing, the caller must Close the returned encoder to flush any 150 // partially written blocks. 151 func NewEncoder(w io.Writer) io.WriteCloser { return &encoder{w: w} } 152 153 type encoder struct { 154 w io.Writer 155 err error 156 buf [52]byte 157 nbuf int 158 out [1024]byte 159 nout int 160 } 161 162 func (e *encoder) Write(p []byte) (n int, err error) { 163 if e.err != nil { 164 return 0, e.err 165 } 166 167 // Leading fringe. 168 if e.nbuf > 0 { 169 var i int 170 for i = 0; i < len(p) && e.nbuf < 52; i++ { 171 e.buf[e.nbuf] = p[i] 172 e.nbuf++ 173 } 174 n += i 175 p = p[i:] 176 if e.nbuf < 52 { 177 return 178 } 179 nout := Encode(e.out[0:], e.buf[0:]) 180 if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil { 181 return n, e.err 182 } 183 e.nbuf = 0 184 } 185 186 // Large interior chunks. 187 for len(p) >= 52 { 188 nn := len(e.out) / (1 + 52/4*5 + 1) * 52 189 if nn > len(p) { 190 nn = len(p) / 52 * 52 191 } 192 if nn > 0 { 193 nout := Encode(e.out[0:], p[0:nn]) 194 if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil { 195 return n, e.err 196 } 197 } 198 n += nn 199 p = p[nn:] 200 } 201 202 // Trailing fringe. 203 for i := 0; i < len(p); i++ { 204 e.buf[i] = p[i] 205 } 206 e.nbuf = len(p) 207 n += len(p) 208 return 209 } 210 211 func (e *encoder) Close() error { 212 // If there's anything left in the buffer, flush it out 213 if e.err == nil && e.nbuf > 0 { 214 nout := Encode(e.out[0:], e.buf[0:e.nbuf]) 215 e.nbuf = 0 216 _, e.err = e.w.Write(e.out[0:nout]) 217 } 218 return e.err 219 } 220 221 // NewDecoder returns a new Git base85 stream decoder. 222 func NewDecoder(r io.Reader) io.Reader { return &decoder{r: r} } 223 224 type decoder struct { 225 r io.Reader 226 err error 227 readErr error 228 buf [1024]byte 229 nbuf int 230 out []byte 231 outbuf [1024]byte 232 off int64 233 } 234 235 func (d *decoder) Read(p []byte) (n int, err error) { 236 if len(p) == 0 { 237 return 0, nil 238 } 239 240 for { 241 // Copy leftover output from last decode. 242 if len(d.out) > 0 { 243 n = copy(p, d.out) 244 d.out = d.out[n:] 245 return 246 } 247 248 // Out of decoded output. Check errors. 249 if d.err != nil { 250 return 0, d.err 251 } 252 if d.readErr != nil { 253 d.err = d.readErr 254 return 0, d.err 255 } 256 257 // Read and decode more input. 258 var nn int 259 nn, d.readErr = d.r.Read(d.buf[d.nbuf:]) 260 d.nbuf += nn 261 262 // Send complete lines to Decode. 263 nl := bytes.LastIndex(d.buf[0:d.nbuf], newline) 264 if nl < 0 { 265 continue 266 } 267 nn, d.err = Decode(d.outbuf[0:], d.buf[0:nl+1]) 268 if e, ok := d.err.(CorruptInputError); ok { 269 d.err = CorruptInputError(int64(e) + d.off) 270 } 271 d.out = d.outbuf[0:nn] 272 d.nbuf = copy(d.buf[0:], d.buf[nl+1:d.nbuf]) 273 d.off += int64(nl + 1) 274 } 275 panic("unreachable") 276 }