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