1 files changed, 166 insertions, 0 deletions
diff --git a/lib/pure/punycode.nim b/lib/pure/punycode.nim
new file mode 100644
index 000000000..4f35de487
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+++ b/lib/pure/punycode.nim
@@ -0,0 +1,166 @@
+
+import strutils
+import unicode
+
+# issue #3045
+
+const
+  Base = 36
+  TMin = 1
+  TMax = 26
+  Skew = 38
+  Damp = 700
+  InitialBias = 72
+  InitialN = 128
+  Delimiter = '-'
+
+type
+  PunyError* = object of Exception
+
+proc decodeDigit(x: char): int {.raises: [PunyError].} =
+  if '0' <= x and x <= '9':
+    result = ord(x) - (ord('0') - 26)
+  elif 'A' <= x and x <= 'Z':
+    result = ord(x) - ord('A')
+  elif 'a' <= x and x <= 'z':
+    result = ord(x) - ord('a')
+  else:
+    raise newException(PunyError, "Bad input")
+
+proc encodeDigit(digit: int): Rune {.raises: [PunyError].} =
+  if 0 <= digit and digit < 26:
+    result = Rune(digit + ord('a'))
+  elif 26 <= digit and digit < 36:
+    result = Rune(digit + (ord('0') - 26))
+  else:
+    raise newException(PunyError, "internal error in punycode encoding")
+
+proc isBasic(c: char): bool = ord(c) < 0x80
+proc isBasic(r: Rune): bool = int(r) < 0x80
+
+proc adapt(delta, numPoints: int, first: bool): int =
+  var d = if first: delta div Damp else: delta div 2
+  d += d div numPoints
+  var k = 0
+  while d > ((Base-TMin)*TMax) div 2:
+    d = d div (Base - TMin)
+    k += Base
+  result = k + (Base - TMin + 1) * d div (d + Skew)
+
+proc encode*(prefix, s: string): string {.raises: [PunyError].} =
+  ## Encode a string that may contain Unicode.
+  ## Prepend `prefix` to the result
+  result = prefix
+  var (d, n, bias) = (0, InitialN, InitialBias)
+  var (b, remaining) = (0, 0)
+  for r in s.runes:
+    if r.isBasic:
+      # basic Ascii character
+      inc b
+      result.add($r)
+    else:
+      # special character
+      inc remaining
+
+  var h = b
+  if b > 0:
+    result.add(Delimiter) # we have some Ascii chars
+  while remaining != 0:
+    var m: int = high(int32)
+    for r in s.runes:
+      if m > int(r) and int(r) >= n:
+        m = int(r)
+    d += (m - n) * (h + 1)
+    if d < 0:
+      raise newException(PunyError, "invalid label " & s)
+    n = m
+    for r in s.runes:
+      if int(r) < n:
+        inc d
+        if d < 0:
+          raise newException(PunyError, "invalid label " & s)
+        continue
+      if int(r) > n:
+        continue
+      var q = d
+      var k = Base
+      while true:
+        var t = k - bias
+        if t < TMin:
+          t = TMin
+        elif t > TMax:
+          t = TMax
+        if q < t:
+          break
+        result.add($encodeDigit(t + (q - t) mod (Base - t)))
+        q = (q - t) div (Base - t)
+        k += Base
+      result.add($encodeDigit(q))
+      bias = adapt(d, h + 1, h == b)
+      d = 0
+      inc h
+      dec remaining
+    inc d
+    inc n
+
+proc encode*(s: string): string {.raises: [PunyError].} =
+  ## Encode a string that may contain Unicode. Prefix is empty.
+  result = encode("", s)
+
+proc decode*(encoded: string): string {.raises: [PunyError].}  =
+  ## Decode a Punycode-encoded string
+  var
+    n = InitialN
+    i = 0
+    bias = InitialBias
+  var d = rfind(encoded, Delimiter)
+  result = ""
+
+  if d > 0:
+    # found Delimiter
+    for j in 0..<d:
+      var c = encoded[j] # char
+      if not c.isBasic:
+        raise newException(PunyError, "Encoded contains a non-basic char")
+      result.add(c) # add the character
+    inc d
+  else:
+    d = 0 # set to first index
+
+  while (d < len(encoded)):
+    var oldi = i
+    var w = 1
+    var k = Base
+    while true:
+      if d == len(encoded):
+        raise newException(PunyError, "Bad input: " & encoded)
+      var c = encoded[d]; inc d
+      var digit = int(decodeDigit(c))
+      if digit > (high(int32) - i) div w:
+        raise newException(PunyError, "Too large a value: " & $digit)
+      i += digit * w
+      var t: int
+      if k <= bias:
+        t = TMin
+      elif k >= bias + TMax:
+        t = TMax
+      else:
+        t = k - bias
+      if digit < t:
+        break
+      w *= Base - t
+      k += Base
+    bias = adapt(i - oldi, runelen(result) + 1, oldi == 0)
+
+    if i div (runelen(result) + 1) > high(int32) - n:
+      raise newException(PunyError, "Value too large")
+
+    n += i div (runelen(result) + 1)
+    i = i mod (runelen(result) + 1)
+    insert(result, $Rune(n), i)
+    inc i
+
+when isMainModule:
+  assert(decode(encode("", "bücher")) == "bücher")
+  assert(decode(encode("münchen")) == "münchen")
+  assert encode("xn--", "münchen") == "xn--mnchen-3ya"