LibWeb: Implement encoding sniffing algorithm

This patch implements the HTML specification's "encoding sniffing
algorithm", which is used when no encoding can be obtained from the
Content-Type header (either because it doesn't contain a charset=...)
value or the file has not been opened via HTTP (as with local files).

It also modifies the creator of the HTMLDocumentParser to use the new
HTMLDocumentParser::create_with_uncertain_encoding static method, which
runs the encoding sniffing algorithm before instantiating the parser.

This now allows us to load local HTML pages (or remote pages without a
charset specified in the 'Content-Type' header) with a non-UTF-8
encoding such as 'windows-1252'. This would previously crash the
browser. :^)

1 files changed, 2 insertions, 2 deletions

diff --git a/Userland/Libraries/LibWeb/Loader/FrameLoader.cpp b/Userland/Libraries/LibWeb/Loader/FrameLoader.cpp
index adaba8905e..55a251deee 100644
--- a/Userland/Libraries/LibWeb/Loader/FrameLoader.cpp
+++ b/Userland/Libraries/LibWeb/Loader/FrameLoader.cpp
@@ -113,8 +113,8 @@ bool FrameLoader::parse_document(DOM::Document& document, const ByteBuffer& data
 {
     auto& mime_type = document.content_type();
     if (mime_type == "text/html" || mime_type == "image/svg+xml") {
-        HTML::HTMLDocumentParser parser(document, data, document.encoding_or_default());
-        parser.run(document.url());
+        auto parser = HTML::HTMLDocumentParser::create_with_uncertain_encoding(document, data);
+        parser->run(document.url());
         return true;
     }
     if (mime_type.starts_with("image/"))