libgo/go/encoding/hex/hex.go

   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 hex implements hexadecimal encoding and decoding.
   6 package hex
   7
   8 import (
   9         "bytes"
  10         "errors"
  11         "fmt"
  12         "io"
  13 )
  14
  15 const hextable = "0123456789abcdef"
  16
  17 // EncodedLen returns the length of an encoding of n source bytes.
  18 // Specifically, it returns n * 2.
  19 func EncodedLen(n int) int { return n * 2 }
  20
  21 // Encode encodes src into EncodedLen(len(src))
  22 // bytes of dst. As a convenience, it returns the number
  23 // of bytes written to dst, but this value is always EncodedLen(len(src)).
  24 // Encode implements hexadecimal encoding.
  25 func Encode(dst, src []byte) int {
  26         for i, v := range src {
  27                 dst[i*2] = hextable[v>>4]
  28                 dst[i*2+1] = hextable[v&0x0f]
  29         }
  30
  31         return len(src) * 2
  32 }
  33
  34 // ErrLength results from decoding an odd length slice.
  35 var ErrLength = errors.New("encoding/hex: odd length hex string")
  36
  37 // InvalidByteError values describe errors resulting from an invalid byte in a hex string.
  38 type InvalidByteError byte
  39
  40 func (e InvalidByteError) Error() string {
  41         return fmt.Sprintf("encoding/hex: invalid byte: %#U", rune(e))
  42 }
  43
  44 // DecodedLen returns the length of a decoding of x source bytes.
  45 // Specifically, it returns x / 2.
  46 func DecodedLen(x int) int { return x / 2 }
  47
  48 // Decode decodes src into DecodedLen(len(src)) bytes,
  49 // returning the actual number of bytes written to dst.
  50 //
  51 // Decode expects that src contain only hexadecimal
  52 // characters and that src should have an even length.
  53 func Decode(dst, src []byte) (int, error) {
  54         if len(src)%2 == 1 {
  55                 return 0, ErrLength
  56         }
  57
  58         for i := 0; i < len(src)/2; i++ {
  59                 a, ok := fromHexChar(src[i*2])
  60                 if !ok {
  61                         return 0, InvalidByteError(src[i*2])
  62                 }
  63                 b, ok := fromHexChar(src[i*2+1])
  64                 if !ok {
  65                         return 0, InvalidByteError(src[i*2+1])
  66                 }
  67                 dst[i] = (a << 4) | b
  68         }
  69
  70         return len(src) / 2, nil
  71 }
  72
  73 // fromHexChar converts a hex character into its value and a success flag.
  74 func fromHexChar(c byte) (byte, bool) {
  75         switch {
  76         case '0' <= c && c <= '9':
  77                 return c - '0', true
  78         case 'a' <= c && c <= 'f':
  79                 return c - 'a' + 10, true
  80         case 'A' <= c && c <= 'F':
  81                 return c - 'A' + 10, true
  82         }
  83
  84         return 0, false
  85 }
  86
  87 // EncodeToString returns the hexadecimal encoding of src.
  88 func EncodeToString(src []byte) string {
  89         dst := make([]byte, EncodedLen(len(src)))
  90         Encode(dst, src)
  91         return string(dst)
  92 }
  93
  94 // DecodeString returns the bytes represented by the hexadecimal string s.
  95 func DecodeString(s string) ([]byte, error) {
  96         src := []byte(s)
  97         dst := make([]byte, DecodedLen(len(src)))
  98         _, err := Decode(dst, src)
  99         if err != nil {
 100                 return nil, err
 101         }
 102         return dst, nil
 103 }
 104
 105 // Dump returns a string that contains a hex dump of the given data. The format
 106 // of the hex dump matches the output of `hexdump -C` on the command line.
 107 func Dump(data []byte) string {
 108         var buf bytes.Buffer
 109         dumper := Dumper(&buf)
 110         dumper.Write(data)
 111         dumper.Close()
 112         return buf.String()
 113 }
 114
 115 // Dumper returns a WriteCloser that writes a hex dump of all written data to
 116 // w. The format of the dump matches the output of `hexdump -C` on the command
 117 // line.
 118 func Dumper(w io.Writer) io.WriteCloser {
 119         return &dumper{w: w}
 120 }
 121
 122 type dumper struct {
 123         w          io.Writer
 124         rightChars [18]byte
 125         buf        [14]byte
 126         used       int  // number of bytes in the current line
 127         n          uint // number of bytes, total
 128 }
 129
 130 func toChar(b byte) byte {
 131         if b < 32 || b > 126 {
 132                 return '.'
 133         }
 134         return b
 135 }
 136
 137 func (h *dumper) Write(data []byte) (n int, err error) {
 138         // Output lines look like:
 139         // 00000010  2e 2f 30 31 32 33 34 35  36 37 38 39 3a 3b 3c 3d  |./0123456789:;<=|
 140         // ^ offset                          ^ extra space              ^ ASCII of line.
 141         for i := range data {
 142                 if h.used == 0 {
 143                         // At the beginning of a line we print the current
 144                         // offset in hex.
 145                         h.buf[0] = byte(h.n >> 24)
 146                         h.buf[1] = byte(h.n >> 16)
 147                         h.buf[2] = byte(h.n >> 8)
 148                         h.buf[3] = byte(h.n)
 149                         Encode(h.buf[4:], h.buf[:4])
 150                         h.buf[12] = ' '
 151                         h.buf[13] = ' '
 152                         _, err = h.w.Write(h.buf[4:])
 153                         if err != nil {
 154                                 return
 155                         }
 156                 }
 157                 Encode(h.buf[:], data[i:i+1])
 158                 h.buf[2] = ' '
 159                 l := 3
 160                 if h.used == 7 {
 161                         // There's an additional space after the 8th byte.
 162                         h.buf[3] = ' '
 163                         l = 4
 164                 } else if h.used == 15 {
 165                         // At the end of the line there's an extra space and
 166                         // the bar for the right column.
 167                         h.buf[3] = ' '
 168                         h.buf[4] = '|'
 169                         l = 5
 170                 }
 171                 _, err = h.w.Write(h.buf[:l])
 172                 if err != nil {
 173                         return
 174                 }
 175                 n++
 176                 h.rightChars[h.used] = toChar(data[i])
 177                 h.used++
 178                 h.n++
 179                 if h.used == 16 {
 180                         h.rightChars[16] = '|'
 181                         h.rightChars[17] = '\n'
 182                         _, err = h.w.Write(h.rightChars[:])
 183                         if err != nil {
 184                                 return
 185                         }
 186                         h.used = 0
 187                 }
 188         }
 189         return
 190 }
 191
 192 func (h *dumper) Close() (err error) {
 193         // See the comments in Write() for the details of this format.
 194         if h.used == 0 {
 195                 return
 196         }
 197         h.buf[0] = ' '
 198         h.buf[1] = ' '
 199         h.buf[2] = ' '
 200         h.buf[3] = ' '
 201         h.buf[4] = '|'
 202         nBytes := h.used
 203         for h.used < 16 {
 204                 l := 3
 205                 if h.used == 7 {
 206                         l = 4
 207                 } else if h.used == 15 {
 208                         l = 5
 209                 }
 210                 _, err = h.w.Write(h.buf[:l])
 211                 if err != nil {
 212                         return
 213                 }
 214                 h.used++
 215         }
 216         h.rightChars[nBytes] = '|'
 217         h.rightChars[nBytes+1] = '\n'
 218         _, err = h.w.Write(h.rightChars[:nBytes+2])
 219         return
 220 }