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###############################################################################
##
## Copyright 2011 Tavendo GmbH
##
## Note:
##
## This code is a Python implementation of the algorithm
##
## "Flexible and Economical UTF-8 Decoder"
##
## by Bjoern Hoehrmann
##
## bjoern@hoehrmann.de
## http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
##
## 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.
##
###############################################################################
class Utf8Validator:
"""
Incremental UTF-8 validator with constant memory consumption (minimal state).
Implements the algorithm "Flexible and Economical UTF-8 Decoder" by
Bjoern Hoehrmann (http://bjoern.hoehrmann.de/utf-8/decoder/dfa/).
"""
## DFA transitions
UTF8VALIDATOR_DFA = [
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, # 00..1f
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, # 20..3f
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, # 40..5f
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, # 60..7f
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9, # 80..9f
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, # a0..bf
8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, # c0..df
0xa,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x4,0x3,0x3, # e0..ef
0xb,0x6,0x6,0x6,0x5,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8, # f0..ff
0x0,0x1,0x2,0x3,0x5,0x8,0x7,0x1,0x1,0x1,0x4,0x6,0x1,0x1,0x1,0x1, # s0..s0
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,1,1, # s1..s2
1,2,1,1,1,1,1,2,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1, # s3..s4
1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,3,1,3,1,1,1,1,1,1, # s5..s6
1,3,1,1,1,1,1,3,1,3,1,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1, # s7..s8
]
UTF8_ACCEPT = 0
UTF8_REJECT = 1
def __init__(self):
self.reset()
def decode(self, b):
"""
Eat one UTF-8 octet, and validate on the fly.
Returns UTF8_ACCEPT when enough octets have been consumed, in which case
self.codepoint contains the decoded Unicode code point.
Returns UTF8_REJECT when invalid UTF-8 was encountered.
Returns some other positive integer when more octets need to be eaten.
"""
type = Utf8Validator.UTF8VALIDATOR_DFA[b]
if self.state != Utf8Validator.UTF8_ACCEPT:
self.codepoint = (b & 0x3f) | (self.codepoint << 6)
else:
self.codepoint = (0xff >> type) & b
self.state = Utf8Validator.UTF8VALIDATOR_DFA[256 + self.state * 16 + type]
return self.state
def reset(self):
"""
Reset validator to start new incremental UTF-8 decode/validation.
"""
self.state = Utf8Validator.UTF8_ACCEPT
self.codepoint = 0
self.i = 0
def validate(self, ba):
"""
Incrementally validate a chunk of bytes provided as string.
Will return a quad (valid?, endsOnCodePoint?, currentIndex, totalIndex).
As soon as an octet is encountered which renders the octet sequence
invalid, a quad with valid? == False is returned. currentIndex returns
the index within the currently consumed chunk, and totalIndex the
index within the total consumed sequence that was the point of bail out.
When valid? == True, currentIndex will be len(ba) and totalIndex the
total amount of consumed bytes.
"""
l = len(ba)
for i in xrange(l):
## optimized version of decode(), since we are not interested in actual code points
self.state = Utf8Validator.UTF8VALIDATOR_DFA[256 + (self.state << 4) + Utf8Validator.UTF8VALIDATOR_DFA[ord(ba[i])]]
if self.state == Utf8Validator.UTF8_REJECT:
self.i += i
return False, False, i, self.i
self.i += l
return True, self.state == Utf8Validator.UTF8_ACCEPT, l, self.i
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