libgo/go/golang_org/x/net/idna/punycode.go

   1 // Code generated by running "go run gen.go -core" in golang.org/x/text. DO NOT EDIT.
   2
   3 // Copyright 2016 The Go Authors. All rights reserved.
   4 // Use of this source code is governed by a BSD-style
   5 // license that can be found in the LICENSE file.
   6
   7 package idna
   8
   9 // This file implements the Punycode algorithm from RFC 3492.
  10
  11 import (
  12         "math"
  13         "strings"
  14         "unicode/utf8"
  15 )
  16
  17 // These parameter values are specified in section 5.
  18 //
  19 // All computation is done with int32s, so that overflow behavior is identical
  20 // regardless of whether int is 32-bit or 64-bit.
  21 const (
  22         base        int32 = 36
  23         damp        int32 = 700
  24         initialBias int32 = 72
  25         initialN    int32 = 128
  26         skew        int32 = 38
  27         tmax        int32 = 26
  28         tmin        int32 = 1
  29 )
  30
  31 func punyError(s string) error { return &labelError{s, "A3"} }
  32
  33 // decode decodes a string as specified in section 6.2.
  34 func decode(encoded string) (string, error) {
  35         if encoded == "" {
  36                 return "", nil
  37         }
  38         pos := 1 + strings.LastIndex(encoded, "-")
  39         if pos == 1 {
  40                 return "", punyError(encoded)
  41         }
  42         if pos == len(encoded) {
  43                 return encoded[:len(encoded)-1], nil
  44         }
  45         output := make([]rune, 0, len(encoded))
  46         if pos != 0 {
  47                 for _, r := range encoded[:pos-1] {
  48                         output = append(output, r)
  49                 }
  50         }
  51         i, n, bias := int32(0), initialN, initialBias
  52         for pos < len(encoded) {
  53                 oldI, w := i, int32(1)
  54                 for k := base; ; k += base {
  55                         if pos == len(encoded) {
  56                                 return "", punyError(encoded)
  57                         }
  58                         digit, ok := decodeDigit(encoded[pos])
  59                         if !ok {
  60                                 return "", punyError(encoded)
  61                         }
  62                         pos++
  63                         i += digit * w
  64                         if i < 0 {
  65                                 return "", punyError(encoded)
  66                         }
  67                         t := k - bias
  68                         if t < tmin {
  69                                 t = tmin
  70                         } else if t > tmax {
  71                                 t = tmax
  72                         }
  73                         if digit < t {
  74                                 break
  75                         }
  76                         w *= base - t
  77                         if w >= math.MaxInt32/base {
  78                                 return "", punyError(encoded)
  79                         }
  80                 }
  81                 x := int32(len(output) + 1)
  82                 bias = adapt(i-oldI, x, oldI == 0)
  83                 n += i / x
  84                 i %= x
  85                 if n > utf8.MaxRune || len(output) >= 1024 {
  86                         return "", punyError(encoded)
  87                 }
  88                 output = append(output, 0)
  89                 copy(output[i+1:], output[i:])
  90                 output[i] = n
  91                 i++
  92         }
  93         return string(output), nil
  94 }
  95
  96 // encode encodes a string as specified in section 6.3 and prepends prefix to
  97 // the result.
  98 //
  99 // The "while h < length(input)" line in the specification becomes "for
 100 // remaining != 0" in the Go code, because len(s) in Go is in bytes, not runes.
 101 func encode(prefix, s string) (string, error) {
 102         output := make([]byte, len(prefix), len(prefix)+1+2*len(s))
 103         copy(output, prefix)
 104         delta, n, bias := int32(0), initialN, initialBias
 105         b, remaining := int32(0), int32(0)
 106         for _, r := range s {
 107                 if r < 0x80 {
 108                         b++
 109                         output = append(output, byte(r))
 110                 } else {
 111                         remaining++
 112                 }
 113         }
 114         h := b
 115         if b > 0 {
 116                 output = append(output, '-')
 117         }
 118         for remaining != 0 {
 119                 m := int32(0x7fffffff)
 120                 for _, r := range s {
 121                         if m > r && r >= n {
 122                                 m = r
 123                         }
 124                 }
 125                 delta += (m - n) * (h + 1)
 126                 if delta < 0 {
 127                         return "", punyError(s)
 128                 }
 129                 n = m
 130                 for _, r := range s {
 131                         if r < n {
 132                                 delta++
 133                                 if delta < 0 {
 134                                         return "", punyError(s)
 135                                 }
 136                                 continue
 137                         }
 138                         if r > n {
 139                                 continue
 140                         }
 141                         q := delta
 142                         for k := base; ; k += base {
 143                                 t := k - bias
 144                                 if t < tmin {
 145                                         t = tmin
 146                                 } else if t > tmax {
 147                                         t = tmax
 148                                 }
 149                                 if q < t {
 150                                         break
 151                                 }
 152                                 output = append(output, encodeDigit(t+(q-t)%(base-t)))
 153                                 q = (q - t) / (base - t)
 154                         }
 155                         output = append(output, encodeDigit(q))
 156                         bias = adapt(delta, h+1, h == b)
 157                         delta = 0
 158                         h++
 159                         remaining--
 160                 }
 161                 delta++
 162                 n++
 163         }
 164         return string(output), nil
 165 }
 166
 167 func decodeDigit(x byte) (digit int32, ok bool) {
 168         switch {
 169         case '0' <= x && x <= '9':
 170                 return int32(x - ('0' - 26)), true
 171         case 'A' <= x && x <= 'Z':
 172                 return int32(x - 'A'), true
 173         case 'a' <= x && x <= 'z':
 174                 return int32(x - 'a'), true
 175         }
 176         return 0, false
 177 }
 178
 179 func encodeDigit(digit int32) byte {
 180         switch {
 181         case 0 <= digit && digit < 26:
 182                 return byte(digit + 'a')
 183         case 26 <= digit && digit < 36:
 184                 return byte(digit + ('0' - 26))
 185         }
 186         panic("idna: internal error in punycode encoding")
 187 }
 188
 189 // adapt is the bias adaptation function specified in section 6.1.
 190 func adapt(delta, numPoints int32, firstTime bool) int32 {
 191         if firstTime {
 192                 delta /= damp
 193         } else {
 194                 delta /= 2
 195         }
 196         delta += delta / numPoints
 197         k := int32(0)
 198         for delta > ((base-tmin)*tmax)/2 {
 199                 delta /= base - tmin
 200                 k += base
 201         }
 202         return k + (base-tmin+1)*delta/(delta+skew)
 203 }