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

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

Index: third_party/WebKit/Source/bindings/tests/results/core/V8TestObject.cpp
diff --git a/third_party/WebKit/Source/bindings/tests/results/core/V8TestObject.cpp b/third_party/WebKit/Source/bindings/tests/results/core/V8TestObject.cpp
index a1ac418547a4cff6bd0e2e372237eaf1386184b3..2c72c353341f2e15d6847539947d82c69574f066 100644
--- a/third_party/WebKit/Source/bindings/tests/results/core/V8TestObject.cpp
+++ b/third_party/WebKit/Source/bindings/tests/results/core/V8TestObject.cpp
@@ -67,6 +67,7 @@
 #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"
@@ -11540,6 +11541,7 @@ static void postMessageImpl(const char* interfaceName, TestObject* instance, con
         exceptionState.throwTypeError(ExceptionMessages::notEnoughArguments(1, info.Length()));
         return;
     }
+
     Transferables transferables;
     if (info.Length() > 1) {
         const int transferablesArgIndex = 1;
@@ -11547,9 +11549,33 @@ static void postMessageImpl(const char* interfaceName, TestObject* instance, con
             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);