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Source file src/net/http/cookiejar/punycode.go

Documentation: net/http/cookiejar

  // Copyright 2012 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package cookiejar
  
  // This file implements the Punycode algorithm from RFC 3492.
  
  import (
  	"fmt"
  	"strings"
  	"unicode/utf8"
  )
  
  // These parameter values are specified in section 5.
  //
  // All computation is done with int32s, so that overflow behavior is identical
  // regardless of whether int is 32-bit or 64-bit.
  const (
  	base        int32 = 36
  	damp        int32 = 700
  	initialBias int32 = 72
  	initialN    int32 = 128
  	skew        int32 = 38
  	tmax        int32 = 26
  	tmin        int32 = 1
  )
  
  // encode encodes a string as specified in section 6.3 and prepends prefix to
  // the result.
  //
  // The "while h < length(input)" line in the specification becomes "for
  // remaining != 0" in the Go code, because len(s) in Go is in bytes, not runes.
  func encode(prefix, s string) (string, error) {
  	output := make([]byte, len(prefix), len(prefix)+1+2*len(s))
  	copy(output, prefix)
  	delta, n, bias := int32(0), initialN, initialBias
  	b, remaining := int32(0), int32(0)
  	for _, r := range s {
  		if r < utf8.RuneSelf {
  			b++
  			output = append(output, byte(r))
  		} else {
  			remaining++
  		}
  	}
  	h := b
  	if b > 0 {
  		output = append(output, '-')
  	}
  	for remaining != 0 {
  		m := int32(0x7fffffff)
  		for _, r := range s {
  			if m > r && r >= n {
  				m = r
  			}
  		}
  		delta += (m - n) * (h + 1)
  		if delta < 0 {
  			return "", fmt.Errorf("cookiejar: invalid label %q", s)
  		}
  		n = m
  		for _, r := range s {
  			if r < n {
  				delta++
  				if delta < 0 {
  					return "", fmt.Errorf("cookiejar: invalid label %q", s)
  				}
  				continue
  			}
  			if r > n {
  				continue
  			}
  			q := delta
  			for k := base; ; k += base {
  				t := k - bias
  				if t < tmin {
  					t = tmin
  				} else if t > tmax {
  					t = tmax
  				}
  				if q < t {
  					break
  				}
  				output = append(output, encodeDigit(t+(q-t)%(base-t)))
  				q = (q - t) / (base - t)
  			}
  			output = append(output, encodeDigit(q))
  			bias = adapt(delta, h+1, h == b)
  			delta = 0
  			h++
  			remaining--
  		}
  		delta++
  		n++
  	}
  	return string(output), nil
  }
  
  func encodeDigit(digit int32) byte {
  	switch {
  	case 0 <= digit && digit < 26:
  		return byte(digit + 'a')
  	case 26 <= digit && digit < 36:
  		return byte(digit + ('0' - 26))
  	}
  	panic("cookiejar: internal error in punycode encoding")
  }
  
  // adapt is the bias adaptation function specified in section 6.1.
  func adapt(delta, numPoints int32, firstTime bool) int32 {
  	if firstTime {
  		delta /= damp
  	} else {
  		delta /= 2
  	}
  	delta += delta / numPoints
  	k := int32(0)
  	for delta > ((base-tmin)*tmax)/2 {
  		delta /= base - tmin
  		k += base
  	}
  	return k + (base-tmin+1)*delta/(delta+skew)
  }
  
  // Strictly speaking, the remaining code below deals with IDNA (RFC 5890 and
  // friends) and not Punycode (RFC 3492) per se.
  
  // acePrefix is the ASCII Compatible Encoding prefix.
  const acePrefix = "xn--"
  
  // toASCII converts a domain or domain label to its ASCII form. For example,
  // toASCII("bücher.example.com") is "xn--bcher-kva.example.com", and
  // toASCII("golang") is "golang".
  func toASCII(s string) (string, error) {
  	if ascii(s) {
  		return s, nil
  	}
  	labels := strings.Split(s, ".")
  	for i, label := range labels {
  		if !ascii(label) {
  			a, err := encode(acePrefix, label)
  			if err != nil {
  				return "", err
  			}
  			labels[i] = a
  		}
  	}
  	return strings.Join(labels, "."), nil
  }
  
  func ascii(s string) bool {
  	for i := 0; i < len(s); i++ {
  		if s[i] >= utf8.RuneSelf {
  			return false
  		}
  	}
  	return true
  }
  

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