WebMessaging: Send transferable ArrayBuffers by copy-and-neuter semantics

third_party/WebKit/Source/bindings/tests/results/core/V8TestObject.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file has been auto-generated by code_generator_v8.py. DO NOT MODIFY!
 
 // clang-format off
 #include "V8TestObject.h"
 
 #include "bindings/core/v8/AnyCallbackFunctionOptionalAnyArg.h"
@@ skipping 49 matching lines @@
 #include "bindings/core/v8/V8TestInterfaceEmpty.h"
 #include "bindings/core/v8/V8TestInterfaceGarbageCollected.h"
 #include "bindings/core/v8/V8TestNode.h"
 #include "bindings/core/v8/V8TestObject.h"
 #include "bindings/core/v8/V8Uint8Array.h"
 #include "bindings/core/v8/V8Window.h"
 #include "bindings/core/v8/V8XPathNSResolver.h"
 #include "bindings/core/v8/VoidCallbackFunction.h"
 #include "core/HTMLNames.h"
 #include "core/dom/ClassCollection.h"
+#include "core/dom/DOMArrayBufferBase.h"
 #include "core/dom/Document.h"
 #include "core/dom/FlexibleArrayBufferView.h"
 #include "core/dom/TagCollection.h"
 #include "core/dom/custom/V0CustomElementProcessingStack.h"
 #include "core/frame/Deprecation.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/UseCounter.h"
 #include "core/html/HTMLCollection.h"
 #include "core/html/HTMLDataListOptionsCollection.h"
 #include "core/html/HTMLFormControlsCollection.h"
@@ skipping 11453 matching lines @@
     TestObjectV8Internal::perWorldBindingsVoidMethodTestInterfaceEmptyArgMethodForMainWorld(info);
 }
 
 static void postMessageImpl(const char* interfaceName, TestObject* instance, const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     ExceptionState exceptionState(info.GetIsolate(), ExceptionState::ExecutionContext, interfaceName, "postMessage");
     if (UNLIKELY(info.Length() < 1)) {
         exceptionState.throwTypeError(ExceptionMessages::notEnoughArguments(1, info.Length()));
         return;
     }
+
     Transferables transferables;
     if (info.Length() > 1) {
         const int transferablesArgIndex = 1;
         if (!SerializedScriptValue::extractTransferables(info.GetIsolate(), info[transferablesArgIndex], transferablesArgIndex, transferables, exceptionState)) {
             return;
         }
     }
-    RefPtr<SerializedScriptValue> message = SerializedScriptValue::serialize(info.GetIsolate(), info[0], &transferables, nullptr, exceptionState);
-    if (exceptionState.hadException())
-        return;
+
+    RefPtr<SerializedScriptValue> message;
+    if (instance->canTransferArrayBuffer()) {
+        // This instance supports sending array buffers by move semantics.
+        message = SerializedScriptValue::serialize(info.GetIsolate(), info[0], &transferables, nullptr, exceptionState);
+        if (exceptionState.hadException())
+            return;
+    } else {
+        // This instance doesn't support sending array buffers by move
+        // semantics. Emulate it by copy-and-neuter semantics that sends array
+        // buffers by copy semantics and then neuters the original array

[haraken, 2016/10/19 09:49:28]

Just to confirm: Your intention is to NOT copy the array buffers (=ignore the
array buffers), right?

[nhiroki, 2016/10/19 12:51:53]

No. My intention is to copy-transfer the array buffers instead of move-transfer.
Conversely, before this CL, we ignored the array buffers marked with
transferable.

[haraken, 2016/10/19 15:40:46]

I'm a bit confused.

You're ignoring the return value of
SerializedScriptValue::transferArrayBufferContents. Doesn't it mean that you're
only neutering the array buffer without copying to the message?

[nhiroki, 2016/10/20 07:44:02]

SerializedScriptValue::serialize() copies the array buffer into the message
before SerializedScriptValue::transferArrayBufferContents() neuters them.

I guess |transferables.arrayBuffers.clear()| at line 11568 could be confusing.
That doesn't mean serialize() ignores ArrayBuffers in info[0], but means
serialize() handles them as regular objects (non-transferable objects) and
copies them into the message instead. I slightly revised the impl comment.

+        // buffers.
+
+        // Clear transferable array buffers so that the serializer can handle
+        // them by copy semantics.
+        ArrayBufferArray transferableArrayBuffers = transferables.arrayBuffers;
+        transferables.arrayBuffers.clear();
+        message = SerializedScriptValue::serialize(info.GetIsolate(), info[0], &transferables, nullptr, exceptionState);
+        if (exceptionState.hadException())
+            return;
+
+        // Neuter the original array buffers on the sender context.
+        SerializedScriptValue::transferArrayBufferContents(info.GetIsolate(), transferableArrayBuffers, exceptionState);
+        if (exceptionState.hadException())
+            return;
+    }
+
     // FIXME: Only pass context/exceptionState if instance really requires it.
     ExecutionContext* context = currentExecutionContext(info.GetIsolate());
     instance->postMessage(context, message.release(), transferables.messagePorts, exceptionState);
 }
 
 static void postMessageMethodCallback(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     postMessageImpl("TestObject", V8TestObject::toImpl(info.Holder()), info);
 }
 
@@ skipping 2509 matching lines @@
     if (!scriptStateInUserScript)
         return false;
 
     ScriptState::Scope scope(scriptState);
     v8::Local<v8::Value> holder = toV8(holderImpl, scriptState->context()->Global(), scriptState->isolate());
     ExceptionState exceptionState(ExceptionState::SetterContext, "enumForPrivateScript", "TestObject", scriptState->context()->Global(), scriptState->isolate());
     return PrivateScriptRunner::runDOMAttributeSetter(scriptState, scriptStateInUserScript, "TestObject", "enumForPrivateScript", holder, v8String(scriptState->isolate(), cppValue));
 }
 
 } // namespace blink