Blobs: Catching browser-process created Blobs in extension code.

extensions/browser/blob_holder.h

+// 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.
+
+#ifndef EXTENSIONS_BROWSER_BLOB_HOLDER_H_
+#define EXTENSIONS_BROWSER_BLOB_HOLDER_H_
+
+#include <map>
+
+#include "base/memory/linked_ptr.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/supports_user_data.h"
+
+namespace content {
+class BlobHandle;
+class RenderProcessHost;
+}
+
+namespace extensions {
+
+class ExtensionMessageFilter;
+
+// Used for holding onto Blobs created into the browser process until a
+// renderer takes over ownership. This class operates on the UI thread.
+class BlobHolder : public base::SupportsUserData::Data {
+ public:
+  // Will create the BlobHolder if it doesn't already exist.
+  static BlobHolder* FromRenderProcessHost(
+      content::RenderProcessHost* render_process_host);
+
+  virtual ~BlobHolder();
+
+  // Causes BlobHolder to take ownership of |blob|.
+  void HoldBlobReference(scoped_ptr<content::BlobHandle> blob);
+
+ private:
+  typedef std::multimap<std::string, linked_ptr<content::BlobHandle> >

[Yoyo Zhou, 2014/05/23 22:14:00]

Why is this a multimap rather than a map? If uuids are the keys, shouldn't they
be unique?

[michaeln, 2014/05/23 23:49:42]

i can answer that, blobHandle != blob, there can be many blobHandles referring
to the same blob, the blob stays around until all handles to it are gone.

[tommycli, 2014/05/23 23:52:47]

content::BlobHandle is copyable and roughly serves as a refcounting. There can
be multiple handles to the same Blob with a single UUID.

+      BlobHandleMultimap;
+
+  explicit BlobHolder(content::RenderProcessHost* render_process_host);
+
+  // BlobHolder will drop a blob handle for each element in blob_uuids.
+  // If caller wishes to drop multiple references to the same blob,
+  // |blob_uuids| may contain duplicate UUIDs.
+  void DropBlobs(const std::vector<std::string>& blob_uuids);
+  friend class ExtensionMessageFilter;
+
+  bool ContainsBlobHandle(content::BlobHandle* handle) const;
+
+  // A reference to the owner of this class.
+  content::RenderProcessHost* render_process_host_;
+
+  BlobHandleMultimap held_blobs_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlobHolder);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_BLOB_HOLDER_H_