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Source file src/vendor/golang.org/x/net/idna/punycode.go

Documentation: vendor/golang.org/x/net/idna

     1  // Code generated by running "go generate" 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  }
   204  

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