LibWeb: Implement more close to spec javascript mime type checking

Previously we would simply check the an input string against a list of
mime type essences, ignoring that the input might not be a valid mime
type or contain parameters.

This patch moves the helpers into the MimeSniff namespace and properly
parses an input string before comparing the essence.

Userland/Libraries/LibWeb/HTML/HTMLScriptElement.cpp

@@ -17,6 +17,7 @@
 #include <LibWeb/HTML/Scripting/ClassicScript.h>
 #include <LibWeb/Infra/CharacterTypes.h>
 #include <LibWeb/Loader/ResourceLoader.h>
+#include <LibWeb/MimeSniff/MimeType.h>
 
 namespace Web::HTML {
 
@@ -108,13 +109,6 @@ void HTMLScriptElement::execute_script()
         dispatch_event(*DOM::Event::create(realm(), HTML::EventNames::load));
 }
 
-// https://mimesniff.spec.whatwg.org/#javascript-mime-type-essence-match
-static bool is_javascript_mime_type_essence_match(String const& string)
-{
-    auto lowercase_string = string.to_lowercase();
-    return lowercase_string.is_one_of("application/ecmascript", "application/javascript", "application/x-ecmascript", "application/x-javascript", "text/ecmascript", "text/javascript", "text/javascript1.0", "text/javascript1.1", "text/javascript1.2", "text/javascript1.3", "text/javascript1.4", "text/javascript1.5", "text/jscript", "text/livescript", "text/x-ecmascript", "text/x-javascript");
-}
-
 // https://html.spec.whatwg.org/multipage/scripting.html#prepare-a-script
 void HTMLScriptElement::prepare_script()
 {
@@ -169,7 +163,7 @@ void HTMLScriptElement::prepare_script()
     }
 
     // Determine the script's type as follows:
-    if (is_javascript_mime_type_essence_match(script_block_type.trim(Infra::ASCII_WHITESPACE))) {
+    if (MimeSniff::is_javascript_mime_type_essence_match(script_block_type.trim(Infra::ASCII_WHITESPACE))) {
         // - If the script block's type string with leading and trailing ASCII whitespace stripped is a JavaScript MIME type essence match, the script's type is "classic".
         m_script_type = ScriptType::Classic;
     } else if (script_block_type.equals_ignoring_case("module"sv)) {

Userland/Libraries/LibWeb/MimeSniff/MimeType.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
  * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2022, networkException <networkexception@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -13,6 +14,16 @@
 
 namespace Web::MimeSniff {
 
+// https://mimesniff.spec.whatwg.org/#javascript-mime-type-essence-match
+bool is_javascript_mime_type_essence_match(String const& string)
+{
+    // NOTE: The mime type parser automatically lowercases the essence.
+    auto type = MimeType::from_string(string);
+    if (!type.has_value())
+        return false;
+    return type->is_javascript();
+}
+
 static bool contains_only_http_quoted_string_token_code_points(StringView string)
 {
     // https://mimesniff.spec.whatwg.org/#http-quoted-string-token-code-point
@@ -221,4 +232,26 @@ void MimeType::set_parameter(String const& name, String const& value)
     m_parameters.set(name, value);
 }
 
+// https://mimesniff.spec.whatwg.org/#javascript-mime-type
+bool MimeType::is_javascript() const
+{
+    return essence().is_one_of(
+        "application/ecmascript"sv,
+        "application/javascript"sv,
+        "application/x-ecmascript"sv,
+        "application/x-javascript"sv,
+        "text/ecmascript"sv,
+        "text/javascript"sv,
+        "text/javascript1.0"sv,
+        "text/javascript1.1"sv,
+        "text/javascript1.2"sv,
+        "text/javascript1.3"sv,
+        "text/javascript1.4"sv,
+        "text/javascript1.5"sv,
+        "text/jscript"sv,
+        "text/livescript"sv,
+        "text/x-ecmascript"sv,
+        "text/x-javascript"sv);
+}
+
 }

Userland/Libraries/LibWeb/MimeSniff/MimeType.h

@@ -12,6 +12,8 @@
 
 namespace Web::MimeSniff {
 
+bool is_javascript_mime_type_essence_match(String const&);
+
 // https://mimesniff.spec.whatwg.org/#mime-type
 class MimeType {
 public:
@@ -24,6 +26,8 @@ public:
     String const& subtype() const { return m_subtype; }
     OrderedHashMap<String, String> const& parameters() const { return m_parameters; }
 
+    bool is_javascript() const;
+
     void set_parameter(String const& name, String const& value);
 
     String essence() const;