Create blobs from Disk Cache entries.

storage/browser/blob/blob_data_item.h

 // Copyright (c) 2015 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 STORAGE_BROWSER_BLOB_BLOB_DATA_ITEM_H_
 #define STORAGE_BROWSER_BLOB_BLOB_DATA_ITEM_H_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
+#include "net/disk_cache/disk_cache.h"
 #include "storage/browser/blob/shareable_file_reference.h"
 #include "storage/browser/storage_browser_export.h"
 #include "storage/common/data_element.h"
 
 namespace storage {
 class BlobDataBuilder;
 class BlobStorageContext;
 
-// Ref counted blob item.  This class owns the backing data of the blob item.
-// The backing data is immutable, and cannot change after creation.
-// The purpose of this class is to allow the resource to stick around in the
-// snapshot even after the resource was swapped in the blob (either to disk or
-// to memory) by the BlobStorageContext.
+// Ref counted blob item. This class owns the backing data of the blob item. The
+// backing data is immutable, and cannot change after creation. The purpose of
+// this class is to allow the resource to stick around in the snapshot even
+// after the resource was swapped in the blob (either to disk or to memory) by
+// the BlobStorageContext.
 class STORAGE_EXPORT BlobDataItem : public base::RefCounted<BlobDataItem> {
  public:
   DataElement::Type type() const { return item_->type(); }
   const char* bytes() const { return item_->bytes(); }
   const base::FilePath& path() const { return item_->path(); }
   const GURL& filesystem_url() const { return item_->filesystem_url(); }
   const std::string& blob_uuid() const { return item_->blob_uuid(); }
   const base::Time& expected_modification_time() const {
     return item_->expected_modification_time();
   }
   const DataElement& data_element() const { return *item_; }
   const DataElement* data_element_ptr() const { return item_.get(); }
 
-  uint64 GetOffset() const { return item_->offset(); }
-  uint64 GetLength() const { return item_->length(); }
+  const disk_cache::ScopedEntryPtr& disk_cache_entry() const {
+    return disk_cache_entry_;
+  }
+  int disk_cache_stream_index() const { return disk_cache_stream_index_; }
+
+  uint64 GetLength() const;
+  uint64 GetOffset() const;
 
  private:
+  // The ExtraData class owns data for the lifetime of this BlobDataItem. It is
+  // used to ensure that required data for backing the blob has a lifetime of at
+  // least the life of the blob.
+  class ExtraData {
+   public:
+    virtual ~ExtraData() {}
+  };

[dmurph, 2015/05/29 19:13:43]

Hm, what about

// The DataHandle class is used to persist resources that are needed for
// reading this blob data item. This object will stay around while any
// reads are pending event if
// * All blobs with this item are deleted, or
// * The item is swapped for a different backed version (mem-to-disk or reverse)
// In these cases the item will be destructed after all pending reads are
// complete.
class DataHandle {


and we can also remove the ShareableFileReference class variable and replace it
with a private class that extends DataHandle as well.

[gavinp, 2015/06/04 18:40:00]

Done. I avoided an extra layer of indirection in the case of the
ShareableFileHandle by just making it a descendent of DataHandle, as well.

+
   friend class BlobDataBuilder;
   friend class BlobStorageContext;
   friend class base::RefCounted<BlobDataItem>;
 
   BlobDataItem(scoped_ptr<DataElement> item);
   BlobDataItem(scoped_ptr<DataElement> item,
-               scoped_refptr<ShareableFileReference> file_handle);
+               const scoped_refptr<ShareableFileReference>& file_handle);
+  BlobDataItem(scoped_ptr<DataElement> item,
+               scoped_ptr<ExtraData> extra_data,
+               disk_cache::ScopedEntryPtr disk_cache_entry_,
+               int disk_cache_stream_index_);
   virtual ~BlobDataItem();
 
   scoped_ptr<DataElement> item_;
   scoped_refptr<ShareableFileReference> file_handle_;
+  scoped_ptr<ExtraData> extra_data_;
+
+  disk_cache::ScopedEntryPtr disk_cache_entry_;  // For TYPE_DISK_CACHE_ENTRY.
+  int disk_cache_stream_index_;  // For TYPE_DISK_CACHE_ENTRY.
 };
 
 #if defined(UNIT_TEST)
 inline bool operator==(const BlobDataItem& a, const BlobDataItem& b) {
-  return a.data_element() == b.data_element();
+  return a.disk_cache_entry() == b.disk_cache_entry() &&
+         a.data_element() == b.data_element();
 }
 
 inline bool operator!=(const BlobDataItem& a, const BlobDataItem& b) {
   return !(a == b);
 }
 #endif  // defined(UNIT_TEST)
 
 }  // namespace storage
 
 #endif  // STORAGE_BROWSER_BLOB_BLOB_DATA_ITEM_H_