Gracefully handle FileReader() read operations when in a detached state.

Source/core/fileapi/FileReader.cpp

 /*
  * Copyright (C) 2010 Google Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 62 matching lines @@
 // excessive IPC congestion. We limit this to 100 per thread to throttle the
 // requests (the value is arbitrarily chosen).
 static const size_t kMaxOutstandingRequestsPerThread = 100;
 static const double progressNotificationIntervalMS = 50;
 
 class FileReader::ThrottlingController FINAL : public NoBaseWillBeGarbageCollectedFinalized<FileReader::ThrottlingController>, public WillBeHeapSupplement<LocalFrame>, public WillBeHeapSupplement<WorkerClients> {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(FileReader::ThrottlingController);
 public:
     static ThrottlingController* from(ExecutionContext* context)
     {
+        if (!context)
+            return 0;
+
         if (context->isDocument()) {
             Document* document = toDocument(context);
             if (!document->frame())
                 return 0;
 
             ThrottlingController* controller = static_cast<ThrottlingController*>(WillBeHeapSupplement<LocalFrame>::from(document->frame(), supplementName()));
             if (controller)
                 return controller;
 
             controller = new ThrottlingController();
@@ skipping 185 matching lines @@
     if (m_state == LOADING) {
         exceptionState.throwDOMException(InvalidStateError, "The object is already busy reading Blobs.");
         return;
     }
 
     if (blob->hasBeenClosed()) {
         exceptionState.throwDOMException(InvalidStateError, String(blob->isFile() ? "File" : "Blob") + " has been closed.");
         return;
     }
 
+    if (!throttlingController()) {
+        exceptionState.throwDOMException(NotSupportedError, "Reading from a Document-detached FileReader is not supported.");

[kinuko, 2014/07/17 15:22:24]

I don't have strong opinion, but AbortError might sound more common in these
cases?

+        return;
+    }
+
     // "Snapshot" the Blob data rather than the Blob itself as ongoing
     // read operations should not be affected if close() is called on
     // the Blob being read.
     m_blobDataHandle = blob->blobDataHandle();
     m_blobType = blob->type();
     m_readType = type;
     m_state = LOADING;
     m_loadingState = LoadingStatePending;
     m_error = nullptr;
     throttlingController()->pushReader(this);
@@ skipping 87 matching lines @@
     // since any of the events could call abort(), which internally checks
     // if we're still loading (therefore we need abort process) or not.
     m_loadingState = LoadingStateNone;
 
     fireEvent(EventTypeNames::progress);
 
     ASSERT(m_state != DONE);
     m_state = DONE;
 
     // Unregister the reader.
     ThrottlingController::FinishReaderType finalStep = throttlingController()->removeReader(this);

[kinuko, 2014/07/17 15:22:24]

I assume these loader client methods are called while execution context is alive
(is it guaranteed?)

[sof, 2014/07/17 15:42:44]

Good question; my assumption was that a valid ExecutionContext implied that the
LocalFrame would stay around. But that sounds far fetched, will go over it again
tomorrow.

[sof, 2014/07/17 22:12:01]

kinuko-san, thanks for raising the lifetime question (and I really shouldn't
bother you when you're OOO; will try not to :) ).

I've rephrased how the FileReader accesses its throttling controller, leaving it
to its implementation to safely handle the details of whether or not the
underlying supplement instance is available.

 
     fireEvent(EventTypeNames::load);
     fireEvent(EventTypeNames::loadend);
 
     // All possible events have fired and we're done, no more pending activity.
     throttlingController()->finishReader(this, finalStep);
 }
 
 void FileReader::didFail(FileError::ErrorCode errorCode)
 {
@@ skipping 49 matching lines @@
     return m_loader->stringResult();
 }
 
 void FileReader::trace(Visitor* visitor)
 {
     visitor->trace(m_error);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace WebCore