LibWeb: Use ISO-8859-1 decoder for "isomorphic decode"

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -8,6 +8,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include "LibTextCodec/Decoder.h"
 #include <AK/CharacterTypes.h>
 #include <AK/Debug.h>
 #include <AK/GenericLexer.h>
@@ -347,7 +348,9 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Document>> Document::create_and_initialize(
     // 16. If navigationParams's response has a `Refresh` header, then:
     if (auto maybe_refresh = navigation_params.response->header_list()->get("Refresh"sv.bytes()); maybe_refresh.has_value()) {
         // 1. Let value be the isomorphic decoding of the value of the header.
-        auto const& value = maybe_refresh.value();
+        auto decoder = TextCodec::decoder_for_exact_name("ISO-8859-1"sv);
+        VERIFY(decoder.has_value());
+        auto value = MUST(decoder->to_utf8(StringView { maybe_refresh.value() }));
 
         // 2. Run the shared declarative refresh steps with document and value.
         document->shared_declarative_refresh_steps(value, nullptr);

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

@@ -128,7 +128,9 @@ Optional<Vector<String>> get_decode_and_split_header_value(ReadonlyBytes value)
     // To get, decode, and split a header value value, run these steps:
 
     // 1. Let input be the result of isomorphic decoding value.
-    auto input = StringView { value };
+    auto decoder = TextCodec::decoder_for_exact_name("ISO-8859-1"sv);
+    VERIFY(decoder.has_value());
+    auto input = MUST(decoder->to_utf8(StringView { value }));
 
     // 2. Let position be a position variable for input, initially pointing at the start of input.
     auto lexer = GenericLexer { input };
@@ -523,7 +525,10 @@ bool is_cors_safelisted_request_header(Header const& header)
             return false;
 
         // 2. Let mimeType be the result of parsing the result of isomorphic decoding value.
-        auto mime_type = MimeSniff::MimeType::parse(StringView { value });
+        auto decoder = TextCodec::decoder_for_exact_name("ISO-8859-1"sv);
+        VERIFY(decoder.has_value());
+        auto decoded = MUST(decoder->to_utf8(StringView { value }));
+        auto mime_type = MimeSniff::MimeType::parse(decoded);
 
         // 3. If mimeType is failure, then return false.
         if (!mime_type.has_value())
@@ -726,6 +731,7 @@ bool is_forbidden_request_header(Header const& header)
         auto parsed_values = get_decode_and_split_header_value(header.value);
 
         // 2. For each method of parsedValues: if the isomorphic encoding of method is a forbidden method, then return true.
+        // Note: The values returned from get_decode_and_split_header_value have already been decoded.
         if (parsed_values.has_value() && any_of(*parsed_values, [](auto method) { return is_forbidden_method(method.bytes()); }))
             return true;
     }
@@ -826,10 +832,12 @@ Variant<Vector<ByteBuffer>, ExtractHeaderParseFailure, Empty> extract_header_lis
 Optional<RangeHeaderValue> parse_single_range_header_value(ReadonlyBytes value)
 {
     // 1. Let data be the isomorphic decoding of value.
-    auto data = StringView { value };
+    auto decoder = TextCodec::decoder_for_exact_name("ISO-8859-1"sv);
+    VERIFY(decoder.has_value());
+    auto data = MUST(decoder->to_utf8(StringView { value }));
 
     // 2. If data does not start with "bytes=", then return failure.
-    if (!data.starts_with("bytes="sv))
+    if (!data.starts_with_bytes("bytes="sv))
         return {};
 
     // 3. Let position be a position variable for data, initially pointing at the 6th code point of data.

Userland/Libraries/LibWeb/Fetch/Infrastructure/URL.cpp

@@ -6,6 +6,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include "LibTextCodec/Decoder.h"
 #include <AK/Base64.h>
 #include <LibURL/URL.h>
 #include <LibWeb/Fetch/Infrastructure/URL.h>
@@ -75,7 +76,9 @@ ErrorOr<DataURL> process_data_url(URL::URL const& data_url)
         trimmed_substring_view = trimmed_substring_view.trim(" "sv, TrimMode::Right);
         if (trimmed_substring_view.ends_with(';')) {
             // 1. Let stringBody be the isomorphic decode of body.
-            auto string_body = StringView(body);
+            auto decoder = TextCodec::decoder_for_exact_name("ISO-8859-1"sv);
+            VERIFY(decoder.has_value());
+            auto string_body = MUST(decoder->to_utf8(StringView { body }));
 
             // 2. Set body to the forgiving-base64 decode of stringBody.
             // 3. If body is failure, then return failure.