LibWeb: Implement "Resolve a Blob URL"

Which performs a lookup to find a blob (if any) corresponding to the
given blob URL.

Userland/Libraries/LibWeb/FileAPI/BlobURLStore.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
  * Copyright (c) 2024, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2024, Shannon Booth <shannon@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -106,4 +107,20 @@ void run_unloading_cleanup_steps(JS::NonnullGCPtr<DOM::Document> document)
     });
 }
 
+// https://w3c.github.io/FileAPI/#blob-url-resolve
+Optional<BlobURLEntry> resolve_a_blob_url(URL::URL const& url)
+{
+    // 1. Assert: url’s scheme is "blob".
+    VERIFY(url.scheme() == "blob"sv);
+
+    // 2. Let store be the user agent’s blob URL store.
+    auto& store = blob_url_store();
+
+    // 3. Let url string be the result of serializing url with the exclude fragment flag set.
+    auto url_string = MUST(String::from_byte_string(url.serialize(URL::ExcludeFragment::Yes)));
+
+    // 4. If store[url string] exists, return store[url string]; otherwise return failure.
+    return store.get(url_string);
+}
+
 }

Userland/Libraries/LibWeb/FileAPI/BlobURLStore.h

@@ -10,6 +10,7 @@
 #include <AK/String.h>
 #include <LibJS/Heap/GCPtr.h>
 #include <LibJS/Heap/Handle.h>
+#include <LibURL/Forward.h>
 #include <LibWeb/Forward.h>
 
 namespace Web::FileAPI {
@@ -27,6 +28,7 @@ BlobURLStore& blob_url_store();
 ErrorOr<String> generate_new_blob_url();
 ErrorOr<String> add_entry_to_blob_url_store(JS::NonnullGCPtr<Blob> object);
 ErrorOr<void> remove_entry_from_blob_url_store(StringView url);
+Optional<BlobURLEntry> resolve_a_blob_url(URL::URL const&);
 
 void run_unloading_cleanup_steps(JS::NonnullGCPtr<DOM::Document>);