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/*
* Copyright (C) 2022 Square, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package okhttp3.internal.idn
import okio.Buffer
/**
* An [RFC 3492] punycode decoder for converting ASCII to Unicode domain name labels. This is
* intended for use in Internationalized Domain Names (IDNs).
*
* This class contains a Kotlin implementation of the pseudocode specified by RFC 3492. It includes
* direct translation of the pseudocode presented there.
*
* Partner this class with [Stringprep] to implement IDNA [RFC 3490].
*
* [RFC 3490]: https://datatracker.ietf.org/doc/html/rfc3490
* [RFC 3492]: https://datatracker.ietf.org/doc/html/rfc3492
*/
object Punycode {
private const val base = 36
private const val tmin = 1
private const val tmax = 26
private const val skew = 38
private const val damp = 700
private const val initial_bias = 72
private const val initial_n = 0x80
/**
* Converts a punycode-encoded domain name with `.`-separated labels into a human-readable
* Internationalized Domain Name.
*/
fun decode(string: String): String {
var pos = 0
val limit = string.length
val result = Buffer()
while (pos < limit) {
var dot = string.indexOf('.', startIndex = pos)
if (dot == -1) dot = limit
if (!decodeLabel(string, pos, dot, result)) {
// If we couldn't decode the label, emit it without decoding.
result.writeUtf8(string, pos, dot)
}
if (dot < limit) {
result.writeByte('.'.code)
pos = dot + 1
} else {
break
}
}
return result.readUtf8()
}
/**
* Converts a single label from Punycode to Unicode.
*
* @return true if the range of [string] from [pos] to [limit] was valid and decoded successfully.
* Otherwise, the decode failed.
*/
private fun decodeLabel(
string: String,
pos: Int,
limit: Int,
result: Buffer
): Boolean {
if (!string.regionMatches(pos, "xn--", 0, 4, ignoreCase = true)) {
result.writeUtf8(string, pos, limit)
return true
}
var pos = pos + 4 // 'xn--'.size.
// We'd prefer to operate directly on `result` but it doesn't offer insertCodePoint(), only
// appendCodePoint(). The Punycode algorithm processes code points in increasing code-point
// order, not in increasing index order.
val codePoints = mutableListOf()
// consume all code points before the last delimiter (if there is one)
// and copy them to output, fail on any non-basic code point
val lastDelimiter = string.lastIndexOf('-', limit)
if (lastDelimiter >= pos) {
while (pos < lastDelimiter) {
when (val codePoint = string[pos++]) {
in 'a'..'z', in 'A'..'Z', in '0'..'9', '-' -> {
codePoints += codePoint.code
}
else -> return false // Malformed.
}
}
pos++ // Consume '-'.
}
var n = initial_n
var i = 0
var bias = initial_bias
while (pos < limit) {
val oldi = i
var w = 1
for (k in base until Int.MAX_VALUE step base) {
if (pos == limit) return false // Malformed.
val c = string[pos++]
val digit = when (c) {
in 'a'..'z' -> c - 'a'
in 'A'..'Z' -> c - 'A'
in '0'..'9' -> c - '0' + 26
else -> return false // Malformed.
}
val deltaI = digit * w
if (i > Int.MAX_VALUE - deltaI) return false // Prevent overflow.
i += deltaI
val t = when {
k <= bias -> tmin
k >= bias + tmax -> tmax
else -> k - bias
}
if (digit < t) break
val scaleW = base - t
if (w > Int.MAX_VALUE / scaleW) return false // Prevent overflow.
w *= scaleW
}
bias = adapt(i - oldi, codePoints.size + 1, oldi == 0)
val deltaN = i / (codePoints.size + 1)
if (n > Int.MAX_VALUE - deltaN) return false // Prevent overflow.
n += deltaN
i %= (codePoints.size + 1)
if (n > 0x10ffff) return false // Not a valid code point.
codePoints.add(i, n)
i++
}
for (codePoint in codePoints) {
result.writeUtf8CodePoint(codePoint)
}
return true
}
/** Returns a new bias. */
private fun adapt(delta: Int, numpoints: Int, first: Boolean): Int {
var delta = when {
first -> delta / damp
else -> delta / 2
}
delta += (delta / numpoints)
var k = 0
while (delta > ((base - tmin) * tmax) / 2) {
delta /= (base - tmin)
k += base
}
return k + (((base - tmin + 1) * delta) / (delta + skew))
}
}
