LibWeb: Make extract_header_list_values differentiate parsing failures

Previously, parsing failures and the header not existing made
extract_header_list_values return an empty Optional, making it
impossible to differentiate between the two.

Required for implementing CORS-preflight, where parsing failures for
the headers makes it fail, but not having them doesn't make it fail in
all cases.

Userland/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Headers.cpp

@@ -685,11 +685,11 @@ ErrorOr<Optional<Vector<ByteBuffer>>> extract_header_values(Header const& header
 }
 
 // https://fetch.spec.whatwg.org/#extract-header-list-values
-ErrorOr<Optional<Vector<ByteBuffer>>> extract_header_list_values(ReadonlyBytes name, HeaderList const& list)
+ErrorOr<Variant<Vector<ByteBuffer>, ExtractHeaderParseFailure, Empty>> extract_header_list_values(ReadonlyBytes name, HeaderList const& list)
 {
     // 1. If list does not contain name, then return null.
     if (!list.contains(name))
-        return Optional<Vector<ByteBuffer>> {};
+        return Empty {};
 
     // FIXME: 2. If the ABNF for name allows a single header and list contains more than one, then return failure.
     // NOTE: If different error handling is needed, extract the desired header first.
@@ -706,10 +706,8 @@ ErrorOr<Optional<Vector<ByteBuffer>>> extract_header_list_values(ReadonlyBytes n
         auto extract = TRY(extract_header_values(header));
 
         // 2. If extract is failure, then return failure.
-        // FIXME: Currently we treat the null return above and failure return as the same thing,
-        //        ErrorOr already signals OOM to the caller.
         if (!extract.has_value())
-            return Optional<Vector<ByteBuffer>> {};
+            return ExtractHeaderParseFailure {};
 
         // 3. Append each value in extract, in order, to values.
         values.extend(extract.release_value());

Userland/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Headers.h

@@ -59,6 +59,9 @@ struct RangeHeaderValue {
     Optional<u64> end;
 };
 
+struct ExtractHeaderParseFailure {
+};
+
 [[nodiscard]] ErrorOr<Optional<Vector<DeprecatedString>>> get_decode_and_split_header_value(ReadonlyBytes);
 [[nodiscard]] ErrorOr<OrderedHashTable<ByteBuffer>> convert_header_names_to_a_sorted_lowercase_set(Span<ReadonlyBytes>);
 [[nodiscard]] bool is_header_name(ReadonlyBytes);
@@ -76,7 +79,7 @@ struct RangeHeaderValue {
 [[nodiscard]] bool is_forbidden_response_header_name(ReadonlyBytes);
 [[nodiscard]] bool is_request_body_header_name(ReadonlyBytes);
 [[nodiscard]] ErrorOr<Optional<Vector<ByteBuffer>>> extract_header_values(Header const&);
-[[nodiscard]] ErrorOr<Optional<Vector<ByteBuffer>>> extract_header_list_values(ReadonlyBytes, HeaderList const&);
+[[nodiscard]] ErrorOr<Variant<Vector<ByteBuffer>, ExtractHeaderParseFailure, Empty>> extract_header_list_values(ReadonlyBytes, HeaderList const&);
 [[nodiscard]] Optional<RangeHeaderValue> parse_single_range_header_value(ReadonlyBytes);
 [[nodiscard]] ErrorOr<ByteBuffer> default_user_agent_value();
 

Userland/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Responses.cpp

@@ -104,13 +104,17 @@ ErrorOr<Optional<AK::URL>> Response::location_url(Optional<DeprecatedString> con
         return Optional<AK::URL> {};
 
     // 2. Let location be the result of extracting header list values given `Location` and response’s header list.
-    auto location_values = TRY(extract_header_list_values("Location"sv.bytes(), m_header_list));
-    if (!location_values.has_value() || location_values->size() != 1)
+    auto location_values_or_failure = TRY(extract_header_list_values("Location"sv.bytes(), m_header_list));
+    if (location_values_or_failure.has<Infrastructure::ExtractHeaderParseFailure>() || location_values_or_failure.has<Empty>())
+        return Optional<AK::URL> {};
+
+    auto const& location_values = location_values_or_failure.get<Vector<ByteBuffer>>();
+    if (location_values.size() != 1)
         return Optional<AK::URL> {};
 
     // 3. If location is a header value, then set location to the result of parsing location with response’s URL.
     auto base_url = *url();
-    auto location = AK::URLParser::parse(location_values->first(), &base_url);
+    auto location = AK::URLParser::parse(location_values.first(), &base_url);
     if (!location.is_valid())
         return Error::from_string_view("Invalid 'Location' header URL"sv);