213 lines
4.4 KiB
Go
213 lines
4.4 KiB
Go
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package dns
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import (
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"bytes"
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"unicode"
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)
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// See http://tools.ietf.org/html/rfc3492
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// Implementation idea from RFC itself and from from IDNA::Punycode created by
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// Tatsuhiko Miyagawa <miyagawa@bulknews.net> in 2002
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const (
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_MIN = '\u0001'
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_MAX = '\u001a' // 26
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_SKEW = '\u0026' // 38
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_DAMP = '\u02BC' // 700
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_BASE = '\u0024' // 36
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_BIAS = '\u0048' // 72
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_N = '\u0080' // 128
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Delimiter = '-'
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Prefix = "xn--"
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)
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func IdnToASCII(string) string {
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return ""
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}
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func IdnFromASCII(string) string {
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return ""
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}
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// digit_value convert single byte into meaningful value that's used to calculate decoded unicode character.
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func digit_value(code rune) rune {
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switch {
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case code >= 'A' && code <= 'Z':
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return code - 'A'
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case code >= 'a' && code <= 'z':
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return code - 'a'
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case code >= '0' && code <= '9':
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return code - '0' + 26
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}
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panic("never happens")
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}
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// code_point finds BASE36 byte (a-z0-9) based on calculated number.
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func code_point(digit rune) rune {
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switch {
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case digit >= 0 && digit <= 25:
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return digit + 'a'
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case digit >= 26 && digit <= 36:
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return digit - 26 + '0'
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}
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panic("never happens")
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}
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// adapt calculates next bias to be used for next iteration delta
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func adapt_bias(delta rune, numpoints rune, firsttime bool) rune {
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if firsttime {
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delta /= _DAMP
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} else {
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delta /= 2
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}
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var k rune
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for delta = delta + delta/numpoints; delta > (_BASE-_MIN)*_MAX/2; k += _BASE {
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if _BASE <= _MIN {
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panic("1")
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}
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delta /= _BASE - _MIN
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}
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return k + ((_BASE-_MIN+1)*delta)/(delta+_SKEW)
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}
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// next finds minimal rune (one with lowest codepoint value) that should be equal or above boundary.
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func next(b []rune, boundary rune) rune {
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if len(b) == 0 {
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panic("invalid set of runes to determine next one")
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}
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m := b[0]
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for _, x := range b[1:] {
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if x >= boundary && (m < boundary || x < m) {
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m = x
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}
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}
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return m
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}
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// PrepRune should do actions recommended by stringprep (RFC3491) for each unicode char. TODO(asergeyev): work on actual implementation, currently just lowercases Unicode chars.
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func PrepRune(r rune) rune {
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if unicode.IsUpper(r) {
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r = unicode.ToLower(r)
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}
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return r
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}
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// tfunc is a function that helps calculate each character weight
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func tfunc(k, bias rune) rune {
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switch {
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case k <= bias:
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return _MIN
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case k >= bias+_MAX:
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return _MAX
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}
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return k - bias
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}
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// encode_punycode transforms Unicode input bytes (that represent DNS label) into punycode bytestream
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func encode_punycode(input []byte) []byte {
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n, delta, bias := _N, rune(0), _BIAS
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b := bytes.Runes(input)
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for i := range b {
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b[i] = PrepRune(b[i])
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}
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basic := make([]byte, 0, len(b))
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for _, ltr := range b {
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if ltr <= 0x7f {
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basic = append(basic, byte(ltr))
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}
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}
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basiclen := rune(len(basic))
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fulllen := rune(len(b))
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if basiclen == fulllen {
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return basic
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}
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var out bytes.Buffer
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out.WriteString(Prefix)
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if basiclen > 0 {
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out.Write(basic)
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out.WriteByte(Delimiter)
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}
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for h := basiclen; h < fulllen; n, delta = n+1, delta+1 {
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next := next(b, n)
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s := &bytes.Buffer{}
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s.WriteRune(next)
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delta, n = delta+(next-n)*(h+1), next
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for _, ltr := range b {
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if ltr < n {
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delta++
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}
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if ltr == n {
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q := delta
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for k := _BASE; ; k += _BASE {
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t := tfunc(k, bias)
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if q < t {
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break
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}
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cp := t + ((q - t) % (_BASE - t))
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out.WriteRune(code_point(cp))
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q = (q - t) / (_BASE - t)
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}
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out.WriteRune(code_point(q))
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bias = adapt_bias(delta, h+1, h == basiclen)
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h, delta = h+1, 0
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}
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}
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}
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return out.Bytes()
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}
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// encode_punycode transforms punycode input bytes (that represent DNS label) into Unicode bytestream
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func decode_punycode(b []byte) []byte {
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n, bias := _N, _BIAS
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if !bytes.HasPrefix(b, []byte(Prefix)) {
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return b
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}
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out := make([]rune, 0, len(b))
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b = b[len(Prefix):]
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pos := bytes.Index(b, []byte{Delimiter})
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if pos >= 0 {
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out = append(out, bytes.Runes(b[:pos])...)
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b = b[pos+1:] // trim source string
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}
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for i := rune(0); len(b) > 0; i++ {
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oldi, w, ch := i, rune(1), byte(0)
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for k := _BASE; ; k += _BASE {
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ch, b = b[0], b[1:]
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digit := digit_value(rune(ch))
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i += digit * w
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t := tfunc(k, bias)
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if digit < t {
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break
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}
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w *= _BASE - t
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}
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ln := rune(len(out) + 1)
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bias = adapt_bias(i-oldi, ln, oldi == 0)
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n += i / ln
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i = i % ln
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// insert
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out = append(out, 0)
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copy(out[i+1:], out[i:])
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out[i] = n
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}
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var ret bytes.Buffer
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for _, r := range out {
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ret.WriteRune(r)
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}
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return ret.Bytes()
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}
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