1 // Copyright 2012 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 cookiejar 6 7 // This file implements the Punycode algorithm from RFC 3492. 8 9 import ( 10 "fmt" 11 "strings" 12 "unicode/utf8" 13 ) 14 15 // These parameter values are specified in section 5. 16 // 17 // All computation is done with int32s, so that overflow behavior is identical 18 // regardless of whether int is 32-bit or 64-bit. 19 const ( 20 base int32 = 36 21 damp int32 = 700 22 initialBias int32 = 72 23 initialN int32 = 128 24 skew int32 = 38 25 tmax int32 = 26 26 tmin int32 = 1 27 ) 28 29 // encode encodes a string as specified in section 6.3 and prepends prefix to 30 // the result. 31 // 32 // The "while h < length(input)" line in the specification becomes "for 33 // remaining != 0" in the Go code, because len(s) in Go is in bytes, not runes. 34 func encode(prefix, s string) (string, error) { 35 output := make([]byte, len(prefix), len(prefix)+1+2*len(s)) 36 copy(output, prefix) 37 delta, n, bias := int32(0), initialN, initialBias 38 b, remaining := int32(0), int32(0) 39 for _, r := range s { 40 if r < utf8.RuneSelf { 41 b++ 42 output = append(output, byte(r)) 43 } else { 44 remaining++ 45 } 46 } 47 h := b 48 if b > 0 { 49 output = append(output, '-') 50 } 51 for remaining != 0 { 52 m := int32(0x7fffffff) 53 for _, r := range s { 54 if m > r && r >= n { 55 m = r 56 } 57 } 58 delta += (m - n) * (h + 1) 59 if delta < 0 { 60 return "", fmt.Errorf("cookiejar: invalid label %q", s) 61 } 62 n = m 63 for _, r := range s { 64 if r < n { 65 delta++ 66 if delta < 0 { 67 return "", fmt.Errorf("cookiejar: invalid label %q", s) 68 } 69 continue 70 } 71 if r > n { 72 continue 73 } 74 q := delta 75 for k := base; ; k += base { 76 t := k - bias 77 if t < tmin { 78 t = tmin 79 } else if t > tmax { 80 t = tmax 81 } 82 if q < t { 83 break 84 } 85 output = append(output, encodeDigit(t+(q-t)%(base-t))) 86 q = (q - t) / (base - t) 87 } 88 output = append(output, encodeDigit(q)) 89 bias = adapt(delta, h+1, h == b) 90 delta = 0 91 h++ 92 remaining-- 93 } 94 delta++ 95 n++ 96 } 97 return string(output), nil 98 } 99 100 func encodeDigit(digit int32) byte { 101 switch { 102 case 0 <= digit && digit < 26: 103 return byte(digit + 'a') 104 case 26 <= digit && digit < 36: 105 return byte(digit + ('0' - 26)) 106 } 107 panic("cookiejar: internal error in punycode encoding") 108 } 109 110 // adapt is the bias adaptation function specified in section 6.1. 111 func adapt(delta, numPoints int32, firstTime bool) int32 { 112 if firstTime { 113 delta /= damp 114 } else { 115 delta /= 2 116 } 117 delta += delta / numPoints 118 k := int32(0) 119 for delta > ((base-tmin)*tmax)/2 { 120 delta /= base - tmin 121 k += base 122 } 123 return k + (base-tmin+1)*delta/(delta+skew) 124 } 125 126 // Strictly speaking, the remaining code below deals with IDNA (RFC 5890 and 127 // friends) and not Punycode (RFC 3492) per se. 128 129 // acePrefix is the ASCII Compatible Encoding prefix. 130 const acePrefix = "xn--" 131 132 // toASCII converts a domain or domain label to its ASCII form. For example, 133 // toASCII("bcher.example.com") is "xn--bcher-kva.example.com", and 134 // toASCII("golang") is "golang". 135 func toASCII(s string) (string, error) { 136 if ascii(s) { 137 return s, nil 138 } 139 labels := strings.Split(s, ".") 140 for i, label := range labels { 141 if !ascii(label) { 142 a, err := encode(acePrefix, label) 143 if err != nil { 144 return "", err 145 } 146 labels[i] = a 147 } 148 } 149 return strings.Join(labels, "."), nil 150 } 151 152 func ascii(s string) bool { 153 for i := 0; i < len(s); i++ { 154 if s[i] >= utf8.RuneSelf { 155 return false 156 } 157 } 158 return true 159 } 160
