LibJS: Implement the CloneArrayBuffer AO

Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp

@@ -73,4 +73,30 @@ ThrowCompletionOr<ArrayBuffer*> allocate_array_buffer(GlobalObject& global_objec
     return obj;
 }
 
+// 25.1.2.4 CloneArrayBuffer ( srcBuffer, srcByteOffset, srcLength, cloneConstructor ), https://tc39.es/ecma262/#sec-clonearraybuffer
+ThrowCompletionOr<ArrayBuffer*> clone_array_buffer(GlobalObject& global_object, ArrayBuffer& source_buffer, size_t source_byte_offset, size_t source_length, FunctionObject& clone_constructor)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Let targetBuffer be ? AllocateArrayBuffer(cloneConstructor, srcLength).
+    auto* target_buffer = TRY(allocate_array_buffer(global_object, clone_constructor, source_length));
+
+    // 2. If IsDetachedBuffer(srcBuffer) is true, throw a TypeError exception.
+    if (source_buffer.is_detached())
+        return vm.throw_completion<TypeError>(global_object, ErrorType::DetachedArrayBuffer);
+
+    // 3. Let srcBlock be srcBuffer.[[ArrayBufferData]].
+    auto& source_block = source_buffer.buffer();
+
+    // 4. Let targetBlock be targetBuffer.[[ArrayBufferData]].
+    auto& target_block = target_buffer->buffer();
+
+    // 5. Perform CopyDataBlockBytes(targetBlock, 0, srcBlock, srcByteOffset, srcLength).
+    // FIXME: This is only correct for ArrayBuffers, once SharedArrayBuffer is implemented, the AO has to be implemented
+    target_block.overwrite(0, source_block.offset_pointer(source_byte_offset), source_length);
+
+    // 6. Return targetBuffer.
+    return target_buffer;
+}
+
 }