LibWeb: Implement "get a copy of the bytes held by the buffer source"

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/5e06d5e9e58
Pull-request: https://github.com/SerenityOS/serenity/pull/11249

Userland/Libraries/LibWeb/Bindings/IDLAbstractOperations.cpp

@@ -1,12 +1,17 @@
 /*
  * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/ByteBuffer.h>
 #include <AK/NumericLimits.h>
 #include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/ArrayBuffer.h>
+#include <LibJS/Runtime/DataView.h>
 #include <LibJS/Runtime/PropertyKey.h>
+#include <LibJS/Runtime/TypedArray.h>
 #include <LibWeb/Bindings/IDLAbstractOperations.h>
 
 namespace Web::Bindings::IDL {
@@ -50,4 +55,72 @@ bool is_an_array_index(JS::GlobalObject& global_object, JS::PropertyKey const& p
     return true;
 }
 
+// https://webidl.spec.whatwg.org/#dfn-get-buffer-source-copy
+Optional<ByteBuffer> get_buffer_source_copy(JS::Object const& buffer_source)
+{
+    // 1. Let esBufferSource be the result of converting bufferSource to an ECMAScript value.
+
+    // 2. Let esArrayBuffer be esBufferSource.
+    JS::ArrayBuffer* es_array_buffer;
+
+    // 3. Let offset be 0.
+    u32 offset = 0;
+
+    // 4. Let length be 0.
+    u32 length = 0;
+
+    // 5. If esBufferSource has a [[ViewedArrayBuffer]] internal slot, then:
+    if (is<JS::TypedArrayBase>(buffer_source)) {
+        auto const& es_buffer_source = static_cast<JS::TypedArrayBase const&>(buffer_source);
+
+        // 1. Set esArrayBuffer to esBufferSource.[[ViewedArrayBuffer]].
+        es_array_buffer = es_buffer_source.viewed_array_buffer();
+
+        // 2. Set offset to esBufferSource.[[ByteOffset]].
+        offset = es_buffer_source.byte_offset();
+
+        // 3. Set length to esBufferSource.[[ByteLength]].
+        length = es_buffer_source.byte_length();
+    } else if (is<JS::DataView>(buffer_source)) {
+        auto const& es_buffer_source = static_cast<JS::DataView const&>(buffer_source);
+
+        // 1. Set esArrayBuffer to esBufferSource.[[ViewedArrayBuffer]].
+        es_array_buffer = es_buffer_source.viewed_array_buffer();
+
+        // 2. Set offset to esBufferSource.[[ByteOffset]].
+        offset = es_buffer_source.byte_offset();
+
+        // 3. Set length to esBufferSource.[[ByteLength]].
+        length = es_buffer_source.byte_length();
+    }
+    // 6. Otherwise:
+    else {
+        // 1. Assert: esBufferSource is an ArrayBuffer or SharedArrayBuffer object.
+        auto const& es_buffer_source = static_cast<JS::ArrayBuffer const&>(buffer_source);
+        es_array_buffer = &const_cast<JS ::ArrayBuffer&>(es_buffer_source);
+
+        // 2. Set length to esBufferSource.[[ArrayBufferByteLength]].
+        length = es_buffer_source.byte_length();
+    }
+
+    // 7. If ! IsDetachedBuffer(esArrayBuffer) is true, then return the empty byte sequence.
+    if (es_array_buffer->is_detached())
+        return {};
+
+    // 8. Let bytes be a new byte sequence of length equal to length.
+    auto bytes = ByteBuffer::create_zeroed(length);
+    if (!bytes.has_value())
+        return {};
+
+    // 9. For i in the range offset to offset + length − 1, inclusive, set bytes[i − offset] to ! GetValueFromBuffer(esArrayBuffer, i, Uint8, true, Unordered).
+    for (u64 i = offset; i <= offset + length - 1; ++i) {
+        auto value = es_array_buffer->get_value<u8>(i, true, JS::ArrayBuffer::Unordered);
+        dbgln("value at i = {} is {}", i, value);
+        (*bytes)[i - offset] = (u8)value.as_u32();
+    }
+
+    // 10. Return bytes.
+    return bytes;
+}
+
 }

Userland/Libraries/LibWeb/Bindings/IDLAbstractOperations.h

@@ -1,15 +1,18 @@
 /*
  * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #pragma once
 
+#include <AK/Forward.h>
 #include <LibJS/Forward.h>
 
 namespace Web::Bindings::IDL {
 
 bool is_an_array_index(JS::GlobalObject&, JS::PropertyKey const&);
+Optional<ByteBuffer> get_buffer_source_copy(JS::Object const& buffer_source);
 
 }