[ServiceWorker] Add NULL check of ExecutionContext in FetchBodyStream::readAsync

Source/modules/serviceworkers/FetchBodyStream.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.
 
 #include "config.h"
 #include "modules/serviceworkers/FetchBodyStream.h"
 
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/V8ThrowException.h"
@@ skipping 13 matching lines @@
     fetchBodyStream->suspendIfNeeded();
     return fetchBodyStream.release();
 }
 
 ScriptPromise FetchBodyStream::readAsync(ScriptState* scriptState, ResponseType type)
 {
     if (m_hasRead)
         return ScriptPromise::reject(scriptState, V8ThrowException::createTypeError("Already read", scriptState->isolate()));
 
     m_hasRead = true;
     m_responseType = type;

[yhirano, 2014/09/05 06:17:16]

Can you protect the ExecutionContext by placing a
RefPtrWillBeRawPtr<ExecutionContext> here?
Then we don't have to call scriptState->executionContext() in the latter part.
We need
 - A comment explaining why we need to save the execution context
 - ASSERT(!scriptState->contextIsEmpty())

[haraken, 2014/09/05 06:40:57]

It looks strange to use a protecting pointer for ExecutionContext. Why is it
possible that the ExecutionContext is gone during readAsync()?

 
     ASSERT(!m_resolver);
     m_resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = m_resolver->promise();
 
     FileReaderLoader::ReadType readType = FileReaderLoader::ReadAsText;
 
     switch (type) {
     case ResponseAsArrayBuffer:
         readType = FileReaderLoader::ReadAsArrayBuffer;
@@ skipping 14 matching lines @@
         // FIXME: Implement this.
         ASSERT_NOT_REACHED();
         break;
     case ResponseAsJSON:
     case ResponseAsText:
         break;
     default:
         ASSERT_NOT_REACHED();
     }
 
+    ExecutionContext* executionContext = scriptState->executionContext();
+    if (!executionContext) {
+        m_resolver->reject(V8ThrowException::createTypeError("ExecutionContext terminated", scriptState->isolate()));
+        m_resolver.clear();
+        return promise;
+    }
+
     m_loader = adoptPtr(new FileReaderLoader(readType, this));
-    m_loader->start(scriptState->executionContext(), m_blobDataHandle);
+    m_loader->start(executionContext, m_blobDataHandle);
 
     return promise;
 }
 
 ScriptPromise FetchBodyStream::asArrayBuffer(ScriptState* scriptState)
 {
     return readAsync(scriptState, ResponseAsArrayBuffer);
 }
 
 ScriptPromise FetchBodyStream::asBlob(ScriptState* scriptState)
@@ skipping 97 matching lines @@
 {
     ASSERT(m_resolver);
     if (!m_resolver->executionContext() || m_resolver->executionContext()->activeDOMObjectsAreStopped())
         return;
 
     m_resolver->resolve("");
     m_resolver.clear();
 }
 
 } // namespace blink