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# Copyright (C) 2022 Stefan Fisk
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
"""
srcset attribute parser
"""
_TAB = '\u0009'
_LF = '\u000A'
_FF = '\u000C'
_CR = '\u000D'
_SPACE = '\u0020'
_COMMA = '\u002C'
_LEFT_PARENTHESIS = '\u0028'
_RIGHT_PARENTHESIS = '\u0029'
_WHITESPACE = {_TAB, _LF, _FF, _CR, _SPACE}
_WHITESPACE_OR_COMMA = _WHITESPACE | {_COMMA}
def parse_srcset(input):
"""
Parse HTML srcset
Based on WhatWG HTML standard § 4.8.4.3.10 Parsing a srcset attribute,
but does not parse or validate descriptors.
https://html.spec.whatwg.org/multipage/images.html#parse-a-srcset-attribute
"""
input_end = len(input)
position = 0
urls = []
while position < input_end:
# 4. Splitting loop: Collect a sequence of code points that are ASCII
# whitespace or U+002C COMMA characters from input given position.
while position < input_end and input[position] in _WHITESPACE_OR_COMMA:
position += 1
# 5. If position is past the end of input, return candidates.
if position >= input_end:
return urls
# 6. Collect a sequence of code points that are not ASCII
# whitespace from input given position, and let that be url.
url_start = position
while position < input_end and input[position] not in _WHITESPACE:
position += 1
url_end = position
# 8, If url ends with U+002C (,), then:
if input[url_end - 1] == _COMMA:
# Remove all trailing U+002C COMMA characters from url.
while url_end > url_start and input[url_end - 1] == _COMMA:
url_end -= 1
else:
# This is a shortened version of 1–4 that simply skips the
# descriptors
while position < input_end:
if input[position] == _LEFT_PARENTHESIS:
# Skip until first closing parenthesis
while (position < input_end and input[position] !=
_RIGHT_PARENTHESIS):
position += 1
elif input[position] == _COMMA:
break
position += 1
# 9-15 is parsing and validation of the descriptors, which we ignore
# If we found an URL
if url_end > url_start:
urls.append(input[url_start:url_end])
return urls
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