Add methods for creating V8 extras-based ReadableStreams from C++

third_party/WebKit/Source/core/streams/ReadableStreamController.h

+// Copyright 2016 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.
+
+#ifndef ReadableStreamController_h
+#define ReadableStreamController_h
+
+#include "bindings/core/v8/ScopedPersistent.h"
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/ToV8.h"
+#include "bindings/core/v8/V8ScriptRunner.h"
+#include "core/CoreExport.h"
+#include "platform/heap/Handle.h"
+#include "wtf/RefPtr.h"
+#include <v8.h>
+
+namespace blink {
+
+class CORE_EXPORT ReadableStreamController final : public GarbageCollectedFinalized<ReadableStreamController> {
+public:
+    DEFINE_INLINE_TRACE() {}
+
+    explicit ReadableStreamController(ScriptValue stream)
+        : m_scriptState(stream.scriptState())
+        , m_stream(stream.isolate(), stream.v8Value())
+    {
+        m_stream.setWeak(&m_stream, ReadableStreamController::streamWeakCallback);
+    }
+
+    // Users of the ReadableStreamController can call this to note that the stream has been canceled and thus they
+    // don't anticipate using the ReadableStreamController anymore. (close/desiredSize/enqueue/error will become no-ops
+    // afterward.)
+    void noteHasBeenCanceled()
+    {
+        m_stream.clear();
+    }
+
+    bool isActive() const
+    {
+        return !m_stream.isEmpty();
+    }
+
+    void close()
+    {
+        ScriptState* scriptState = m_scriptState.get();
+        ScriptState::Scope scope(scriptState);
+        v8::Isolate* isolate = scriptState->isolate();
+
+        v8::Local<v8::Value> stream = m_stream.newLocal(isolate);
+        if (stream.IsEmpty())
+            return;
+
+        v8::Local<v8::Value> args[] = { stream };
+        V8ScriptRunner::callExtraOrCrash(scriptState, "CloseReadableStream", args);
+
+        m_stream.clear();
+    }
+
+    double desiredSize() const
+    {
+        ScriptState* scriptState = m_scriptState.get();

[haraken, 2016/02/05 04:56:54]

How is it guaranteed that scriptState->contextIsValid is true (i.e., the
execution context has not yet stopped) when the desiredSize is called?

[haraken, 2016/02/05 05:30:08]

If it's not obvious, I'd prefer just inserting:

  if (!m_scriptState->contextIsValid())
    return 0;

But let's wait for yhirano's thoughts.

[yhirano, 2016/02/05 06:57:08]

Inserting early return statements is OK. I'm also OK with just writing comments
so that close / desiredSize / enqueue / error must not be called when the
ScriptState is invalid.

I agree with domenic's following comment

+        ScriptState::Scope scope(scriptState);
+        v8::Isolate* isolate = scriptState->isolate();
+
+        v8::Local<v8::Value> stream = m_stream.newLocal(isolate);
+        if (stream.IsEmpty())
+            return 0;
+
+        v8::Local<v8::Value> args[] = { stream };
+        v8::Local<v8::Value> result = V8ScriptRunner::callExtraOrCrash(scriptState, "GetReadableStreamDesiredSize", args);
+
+        return result.As<v8::Number>()->Value();
+    }
+
+    template <typename ChunkType>
+    void enqueue(ChunkType chunk) const
+    {
+        ScriptState* scriptState = m_scriptState.get();
+        ScriptState::Scope scope(scriptState);
+        v8::Isolate* isolate = scriptState->isolate();
+
+        v8::Local<v8::Value> stream = m_stream.newLocal(isolate);
+        if (stream.IsEmpty())
+            return;
+
+        v8::Local<v8::Value> jsChunk = toV8(chunk, scriptState);
+        v8::Local<v8::Value> args[] = { stream, jsChunk };
+        V8ScriptRunner::callExtraOrCrash(scriptState, "EnqueueInReadableStream", args);
+    }
+
+    template <typename ErrorType>
+    void error(ErrorType error)
+    {
+        ScriptState* scriptState = m_scriptState.get();
+        ScriptState::Scope scope(scriptState);
+        v8::Isolate* isolate = scriptState->isolate();
+
+        v8::Local<v8::Value> stream = m_stream.newLocal(isolate);
+        if (stream.IsEmpty())
+            return;
+
+        v8::Local<v8::Value> jsError = toV8(error, scriptState);
+        v8::Local<v8::Value> args[] = { stream, jsError };
+        V8ScriptRunner::callExtraOrCrash(scriptState, "ErrorReadableStream", args);
+
+        m_stream.clear();
+    }
+
+private:
+    static void streamWeakCallback(const v8::WeakCallbackInfo<ScopedPersistent<v8::Value>>& weakInfo)
+    {
+        weakInfo.GetParameter()->clear();
+    }
+
+    ScopedPersistent<v8::Value> m_stream;
+    RefPtr<ScriptState> m_scriptState;
+};
+
+} // namespace blink
+
+#endif // ReadableStreamController_h