""" Codec for the Punycode encoding, as specified in RFC 3492
Written by Martin v. Löwis.
"""
import codecs
##################### Encoding #####################################
def segregate(str):
"""3.1 Basic code point segregation"""
base = bytearray()
extended = set()
for c in str:
if ord(c) < 128:
base.append(ord(c))
else:
extended.add(c)
extended = sorted(extended)
return bytes(base), extended
def selective_len(str, max):
"""Return the length of str, considering only characters below max."""
res = 0
for c in str:
if ord(c) < max:
res += 1
return res
def selective_find(str, char, index, pos):
"""Return a pair (index, pos), indicating the next occurrence of
char in str. index is the position of the character considering
only ordinals up to and including char, and pos is the position in
the full string. index/pos is the starting position in the full
string."""
l = len(str)
while 1:
pos += 1
if pos == l:
return (-1, -1)
c = str[pos]
if c == char:
return index+1, pos
elif c < char:
index += 1
def insertion_unsort(str, extended):
"""3.2 Insertion unsort coding"""
oldchar = 0x80
result = []
oldindex = -1
for c in extended:
index = pos = -1
char = ord(c)
curlen = selective_len(str, char)
delta = (curlen+1) * (char - oldchar)
while 1:
index,pos = selective_find(str,c,index,pos)
if index == -1:
break
delta += index - oldindex
result.append(delta-1)
oldindex = index
delta = 0
oldchar = char
return result
def T(j, bias):
# Punycode parameters: tmin = 1, tmax = 26, base = 36
res = 36 * (j + 1) - bias
if res < 1: return 1
if res > 26: return 26
return res
digits = b"abcdefghijklmnopqrstuvwxyz0123456789"
def generate_generalized_integer(N, bias):
"""3.3 Generalized variable-length integers"""
result = bytearray()
j = 0
while 1:
t = T(j, bias)
if N < t:
result.append(digits[N])
return bytes(result)
result.append(digits[t + ((N - t) % (36 - t))])
N = (N - t) // (36 - t)
j += 1
def adapt(delta, first, numchars):
if first:
delta //= 700
else:
delta //= 2
delta += delta // numchars
# ((base - tmin) * tmax) // 2 == 455
divisions = 0
while delta > 455:
delta = delta // 35 # base - tmin
divisions += 36
bias = divisions + (36 * delta // (delta + 38))
return bias
def generate_integers(baselen, deltas):
"""3.4 Bias adaptation"""
# Punycode parameters: initial bias = 72, damp = 700, skew = 38
result = bytearray()
bias = 72
for points, delta in enumerate(deltas):
s = generate_generalized_integer(delta, bias)
result.extend(s)
bias = adapt(delta, points==0, baselen+points+1)
return bytes(result)
def punycode_encode(text):
base, extended = segregate(text)
deltas = insertion_unsort(text, extended)
extended = generate_integers(len(base), deltas)
if base:
return base + b"-" + extended
return extended
##################### Decoding #####################################
def decode_generalized_number(extended, extpos, bias, errors):
"""3.3 Generalized variable-length integers"""
result = 0
w = 1
j = 0
while 1:
try:
char = extended[extpos]
except IndexError:
if errors == "strict":
raise UnicodeDecodeError("punycode", extended, extpos, extpos+1,
"incomplete punycode string")
return extpos + 1, None
extpos += 1
if 0x41 <= char <= 0x5A: # A-Z
digit = char - 0x41
elif 0x30 <= char <= 0x39:
digit = char - 22 # 0x30-26
elif errors == "strict":
raise UnicodeDecodeError("punycode", extended, extpos-1, extpos,
f"Invalid extended code point '{extended[extpos-1]}'")
else:
return extpos, None
t = T(j, bias)
result += digit * w
if digit < t:
return extpos, result
w = w * (36 - t)
j += 1
def insertion_sort(base, extended, errors):
"""3.2 Insertion sort coding"""
# This function raises UnicodeDecodeError with position in the extended.
# Caller should add the offset.
char = 0x80
pos = -1
bias = 72
extpos = 0
while extpos < len(extended):
newpos, delta = decode_generalized_number(extended, extpos,
bias, errors)
if delta is None:
# There was an error in decoding. We can't continue because
# synchronization is lost.
return base
pos += delta+1
char += pos // (len(base) + 1)
if char > 0x10FFFF:
if errors == "strict":
raise UnicodeDecodeError(
"punycode", extended, pos-1, pos,
f"Invalid character U+{char:x}")
char = ord('?')
pos = pos % (len(base) + 1)
base = base[:pos] + chr(char) + base[pos:]
bias = adapt(delta, (extpos == 0), len(base))
extpos = newpos
return base
def punycode_decode(text, errors):
if isinstance(text, str):
text = text.encode("ascii")
if isinstance(text, memoryview):
text = bytes(text)
pos = text.rfind(b"-")
if pos == -1:
base = ""
extended = text.upper()
else:
try:
base = str(text[:pos], "ascii", errors)
except UnicodeDecodeError as exc:
raise UnicodeDecodeError("ascii", text, exc.start, exc.end,
exc.reason) from None
extended = text[pos+1:].upper()
try:
return insertion_sort(base, extended, errors)
except UnicodeDecodeError as exc:
offset = pos + 1
raise UnicodeDecodeError("punycode", text,
offset+exc.start, offset+exc.end,
exc.reason) from None
### Codec APIs
class Codec(codecs.Codec):
def encode(self, input, errors='strict'):
res = punycode_encode(input)
return res, len(input)
def decode(self, input, errors='strict'):
if errors not in ('strict', 'replace', 'ignore'):
raise UnicodeError(f"Unsupported error handling: {errors}")
res = punycode_decode(input, errors)
return res, len(input)
class IncrementalEncoder(codecs.IncrementalEncoder):
def encode(self, input, final=False):
return punycode_encode(input)
class IncrementalDecoder(codecs.IncrementalDecoder):
def decode(self, input, final=False):
if self.errors not in ('strict', 'replace', 'ignore'):
raise UnicodeError(f"Unsupported error handling: {self.errors}")
return punycode_decode(input, self.errors)
class StreamWriter(Codec,codecs.StreamWriter):
pass
class StreamReader(Codec,codecs.StreamReader):
pass
### encodings module API
def getregentry():
return codecs.CodecInfo(
name='punycode',
encode=Codec().encode,
decode=Codec().decode,
incrementalencoder=IncrementalEncoder,
incrementaldecoder=IncrementalDecoder,
streamwriter=StreamWriter,
streamreader=StreamReader,
)
Codebase Browser
cpython