data-uri-to-svg.py

#!/usr/bin/env python

"""
Replace data: URIs for SVGs in CSS files with URIs pointing to the extracted
SVG file.

This allows us to avoid adding the data: scheme to our Content Security Policy,
because it is insecure.

See https://github.com/fedora-infra/noggin/issues/333

If you update the CSS file, you need to run this script on it again.
"""

import argparse
import os
import re
from urllib.parse import unquote


DATA_URI_RE = re.compile(r"url\(\"data:image/svg\+xml,([^\"]+)\"\)")


def parse_args():
    parser = argparse.ArgumentParser()
    parser.add_argument("css_file", metavar="css-file", nargs="+")
    args = parser.parse_args()
    return args


class Replacer:
    def __init__(self, filename):
        self.filename = filename
        self.directory = os.path.dirname(filename)
        self.svgs = []
        self.replacements = 0

    @property
    def target_filename(self):
        return os.path.splitext(self.filename)[0] + ".nodata.css"

    def _get_svg(self, match):
        svg = match.group(1)
        try:
            svg_index = self.svgs.index(svg)
        except ValueError:
            svg_index = len(self.svgs)
            self.svgs.append(svg)
        with open(os.path.join(self.directory, f"{svg_index}.svg"), "w") as svg_file:
            svg_file.write(unquote(svg))
        self.replacements += 1
        return f"url(\"{svg_index}.svg\")"

    def run(self):
        with open(self.filename) as css_file:
            with open(self.target_filename, "w") as new_css_file:
                new_css_file.write(
                    "/* This file has been generated by data-uri-to-svg.py */\n\n"
                )
                for line in css_file:
                    new_css_file.write(DATA_URI_RE.sub(self._get_svg, line))
        print(
            f"Replaced {self.replacements} data URIs with {len(self.svgs)} "
            f"SVG files in {self.target_filename}."
        )


def main():
    args = parse_args()
    for css_file in args.css_file:
        Replacer(css_file).run()


if __name__ == "__main__":
    main()