LibJS: Implement the AllocateArrayBuffer() AO

This should be used instead of ArrayBuffer::create() in most places, as
it uses OrdinaryCreateFromConstructor to allow for a custom prototype.

The data block (ByteBuffer) is allocated separately and attached
afterwards, if we didn't fail due to OOM.

2 files changed, 32 insertions, 5 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp b/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp
index b2d04c610f..6b57a80f5a 100644
--- a/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp
@@ -1,19 +1,20 @@
 /*
- * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/ArrayBuffer.h>
 #include <LibJS/Runtime/GlobalObject.h>
 
 namespace JS {
 
-ArrayBuffer* ArrayBuffer::create(GlobalObject& global_object, size_t byte_size)
+ArrayBuffer* ArrayBuffer::create(GlobalObject& global_object, size_t byte_length)
 {
-    auto buffer = ByteBuffer::create_zeroed(byte_size);
+    auto buffer = ByteBuffer::create_zeroed(byte_length);
     if (!buffer.has_value()) {
-        global_object.vm().throw_exception<RangeError>(global_object, ErrorType::NotEnoughMemoryToAllocate, byte_size);
+        global_object.vm().throw_exception<RangeError>(global_object, ErrorType::NotEnoughMemoryToAllocate, byte_length);
         return nullptr;
     }
     return global_object.heap().allocate<ArrayBuffer>(global_object, buffer.release_value(), *global_object.array_buffer_prototype());
@@ -48,4 +49,24 @@ void ArrayBuffer::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_detach_key);
 }
 
+// 25.1.2.1 AllocateArrayBuffer ( constructor, byteLength ), https://tc39.es/ecma262/#sec-allocatearraybuffer
+ThrowCompletionOr<ArrayBuffer*> allocate_array_buffer(GlobalObject& global_object, FunctionObject& constructor, size_t byte_length)
+{
+    // 1. Let obj be ? OrdinaryCreateFromConstructor(constructor, "%ArrayBuffer.prototype%", « [[ArrayBufferData]], [[ArrayBufferByteLength]], [[ArrayBufferDetachKey]] »).
+    auto* obj = TRY(ordinary_create_from_constructor<ArrayBuffer>(global_object, constructor, &GlobalObject::array_buffer_prototype, nullptr));
+
+    // 2. Let block be ? CreateByteDataBlock(byteLength).
+    auto block = ByteBuffer::create_zeroed(byte_length);
+    if (!block.has_value())
+        return global_object.vm().throw_completion<RangeError>(global_object, ErrorType::NotEnoughMemoryToAllocate, byte_length);
+
+    // 3. Set obj.[[ArrayBufferData]] to block.
+    obj->set_buffer(move(*block));
+
+    // 4. Set obj.[[ArrayBufferByteLength]] to byteLength.
+
+    // 5. Return obj.
+    return obj;
+}
+
 }
diff --git a/Userland/Libraries/LibJS/Runtime/ArrayBuffer.h b/Userland/Libraries/LibJS/Runtime/ArrayBuffer.h
index 2242a1644a..504e0b59f4 100644
--- a/Userland/Libraries/LibJS/Runtime/ArrayBuffer.h
+++ b/Userland/Libraries/LibJS/Runtime/ArrayBuffer.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -9,6 +9,7 @@
 #include <AK/ByteBuffer.h>
 #include <AK/Function.h>
 #include <AK/Variant.h>
+#include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Object.h>
 
@@ -35,6 +36,9 @@ public:
     ByteBuffer& buffer() { return buffer_impl(); }
     const ByteBuffer& buffer() const { return buffer_impl(); }
 
+    // Used by allocate_array_buffer() to attach the data block after construction
+    void set_buffer(ByteBuffer buffer) { m_buffer = move(buffer); }
+
     Value detach_key() const { return m_detach_key; }
     void set_detach_key(Value detach_key) { m_detach_key = detach_key; }
 
@@ -70,6 +74,8 @@ private:
     Value m_detach_key;
 };
 
+ThrowCompletionOr<ArrayBuffer*> allocate_array_buffer(GlobalObject&, FunctionObject& constructor, size_t byte_length);
+
 // 25.1.2.9 RawBytesToNumeric ( type, rawBytes, isLittleEndian ), https://tc39.es/ecma262/#sec-rawbytestonumeric
 template<typename T>
 static Value raw_bytes_to_numeric(GlobalObject& global_object, ByteBuffer raw_value, bool is_little_endian)