Malformed URL with a [ or ] character breaks conversion

[edugonza]

I have an html that contains a malformed link with a ] character:

<p><a hfref="http://sample.com] ">My link</a>

When converting to PDF, I get the following error:

weasyprint/__init__.py:257: in write_pdf
    self.render(font_config, counter_style, **options)
weasyprint/__init__.py:214: in render
    return Document._render(self, font_config, counter_style, options)
weasyprint/document.py:262: in _render
    [Page(page_box) for page_box in page_boxes],
weasyprint/document.py:262: in <listcomp>
    [Page(page_box) for page_box in page_boxes],
weasyprint/document.py:76: in __init__
    gather_anchors(
weasyprint/anchors.py:119: in gather_anchors
    gather_anchors(child, anchors, links, bookmarks, inputs, matrix)
weasyprint/anchors.py:119: in gather_anchors
    gather_anchors(child, anchors, links, bookmarks, inputs, matrix)
weasyprint/anchors.py:119: in gather_anchors
    gather_anchors(child, anchors, links, bookmarks, inputs, matrix)
weasyprint/anchors.py:119: in gather_anchors
    gather_anchors(child, anchors, links, bookmarks, inputs, matrix)
weasyprint/anchors.py:119: in gather_anchors
    gather_anchors(child, anchors, links, bookmarks, inputs, matrix)
weasyprint/anchors.py:83: in gather_anchors
    link = box.style['link']
weasyprint/css/__init__.py:792: in __missing__
    value = COMPUTER_FUNCTIONS[key](self, key, value)
weasyprint/css/computed_values.py:563: in link
    return get_link_attribute(style.element, value, style.base_url)
weasyprint/urls.py:154: in get_link_attribute
    parsed = urlsplit(uri)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

url = '', scheme = 'https', allow_fragments = True

    def urlsplit(url, scheme='', allow_fragments=True):
        """Parse a URL into 5 components:
        <scheme>://<netloc>/<path>?<query>#<fragment>
        Return a 5-tuple: (scheme, netloc, path, query, fragment).
        Note that we don't break the components up in smaller bits
        (e.g. netloc is a single string) and we don't expand % escapes."""
        url, scheme, _coerce_result = _coerce_args(url, scheme)
        url = _remove_unsafe_bytes_from_url(url)
        scheme = _remove_unsafe_bytes_from_url(scheme)
        allow_fragments = bool(allow_fragments)
        key = url, scheme, allow_fragments, type(url), type(scheme)
        cached = _parse_cache.get(key, None)
        if cached:
            return _coerce_result(cached)
        if len(_parse_cache) >= MAX_CACHE_SIZE: # avoid runaway growth
            clear_cache()
        netloc = query = fragment = ''
        i = url.find(':')
        if i > 0:
            if url[:i] == 'http': # optimize the common case
                url = url[i+1:]
                if url[:2] == '//':
                    netloc, url = _splitnetloc(url, 2)
                    if (('[' in netloc and ']' not in netloc) or
                            (']' in netloc and '[' not in netloc)):
                        raise ValueError("Invalid IPv6 URL")
                if allow_fragments and '#' in url:
                    url, fragment = url.split('#', 1)
                if '?' in url:
                    url, query = url.split('?', 1)
                _checknetloc(netloc)
                v = SplitResult('http', netloc, url, query, fragment)
                _parse_cache[key] = v
                return _coerce_result(v)
            for c in url[:i]:
                if c not in scheme_chars:
                    break
            else:
                # make sure "url" is not actually a port number (in which case
                # "scheme" is really part of the path)
                rest = url[i+1:]
                if not rest or any(c not in '0123456789' for c in rest):
                    # not a port number
                    scheme, url = url[:i].lower(), rest
    
        if url[:2] == '//':
            netloc, url = _splitnetloc(url, 2)
            if (('[' in netloc and ']' not in netloc) or
                    (']' in netloc and '[' not in netloc)):
>               raise ValueError("Invalid IPv6 URL")
E               ValueError: Invalid IPv6 URL

/usr/local/lib/python3.8/urllib/parse.py:474: ValueError

This causes the conversion to fail because it thinks that it's a malformed IPv6 URL.

I think that the library should still generate a file with the original URL, even if it is malformed, and possibly print a warning to the console.