LibWeb: Implement 'Should response be blocked due to nosniff?' AO

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

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Fetch/Infrastructure/HTTP/Headers.h>
+#include <LibWeb/Fetch/Infrastructure/HTTP/Requests.h>
+#include <LibWeb/Fetch/Infrastructure/HTTP/Responses.h>
+#include <LibWeb/Fetch/Infrastructure/NoSniffBlocking.h>
+
+namespace Web::Fetch::Infrastructure {
+
+// https://fetch.spec.whatwg.org/#determine-nosniff
+ErrorOr<bool> determine_nosniff(HeaderList const& list)
+{
+    // 1. Let values be the result of getting, decoding, and splitting `X-Content-Type-Options` from list.
+    auto values = TRY(list.get_decode_and_split("X-Content-Type-Options"sv.bytes()));
+
+    // 2. If values is null, then return false.
+    if (!values.has_value())
+        return false;
+
+    // 3. If values[0] is an ASCII case-insensitive match for "nosniff", then return true.
+    if (!values->is_empty() && values->at(0).equals_ignoring_case("nosniff"sv))
+        return true;
+
+    // 4. Return false.
+    return false;
+}
+
+// https://fetch.spec.whatwg.org/#should-response-to-request-be-blocked-due-to-nosniff?
+ErrorOr<RequestOrResponseBlocking> should_response_to_request_be_blocked_due_to_nosniff(Response const& response, Request const& request)
+{
+    // 1. If determine nosniff with response’s header list is false, then return allowed.
+    if (!TRY(determine_nosniff(response.header_list())))
+        return RequestOrResponseBlocking::Allowed;
+
+    // 2. Let mimeType be the result of extracting a MIME type from response’s header list.
+    auto mime_type = response.header_list()->extract_mime_type();
+
+    // 3. Let destination be request’s destination.
+    auto const& destination = request.destination();
+
+    // 4. If destination is script-like and mimeType is failure or is not a JavaScript MIME type, then return blocked.
+    if (request.destination_is_script_like() && (!mime_type.has_value() || !mime_type->is_javascript()))
+        return RequestOrResponseBlocking::Blocked;
+
+    // 5. If destination is "style" and mimeType is failure or its essence is not "text/css", then return blocked.
+    if (destination == Request::Destination::Style && (!mime_type.has_value() || mime_type->essence() != "text/css"sv))
+        return RequestOrResponseBlocking::Blocked;
+
+    // 6. Return allowed.
+    return RequestOrResponseBlocking::Allowed;
+}
+
+}