[BlobAsync] Disk support for blob storage

storage/browser/blob/blob_slice.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 STORAGE_BROWSER_BLOB_BLOB_SLICE_H_
+#define STORAGE_BROWSER_BLOB_BLOB_SLICE_H_
+
+#include <stddef.h>
+
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "storage/browser/blob/internal_blob_data.h"
+#include "storage/browser/blob/shareable_blob_data_item.h"
+
+namespace storage {
+
+class BlobSlice {
+ public:
+  BlobSlice();
+  BlobSlice(const InternalBlobData& source,
+            uint64_t offset,
+            uint64_t size,
+            bool done_building);
+  BlobSlice(BlobSlice&&);
+  ~BlobSlice();
+
+  bool done_building() { return done_building_; }
+
+  size_t copying_memory_size() { return copying_memory_size_; }
+
+  // If our first item is a new memory item, where we are a slice of the item
+  // in the original blob. See first_item_slice_offset() and first_item_index().
+  bool has_sliced_first_memory_item() { return has_sliced_first_memory_item_; }

[michaeln, 2016/07/07 20:05:21]

the names of these members confused me at first, the term 'slice' is being
applied to two different things
- the whole class is a 'slice' of a blob
- partial copies of source items are also being called a 'slice'

+  // If our last item is a new memory item, where we are a slice of the item
+  // in the original blob.
+  bool has_sliced_last_memory_item() { return has_sliced_last_memory_item_; }
+
+  size_t first_item_slice_offset() { return first_item_slice_offset_; }
+  size_t first_item_index() { return first_item_index_; }
+  size_t last_item_index() { return last_item_index_; }
+
+  const std::vector<scoped_refptr<ShareableBlobDataItem>>& items() {
+    return items_;
+  }
+
+ private:
+  void BinarySearch(const InternalBlobData& source_blob,
+                    uint64_t blob_offset,
+                    size_t* item_index,
+                    uint64_t* offset_in_item);
+
+  size_t copying_memory_size_ = 0;
+  bool done_building_ = true;
+
+  bool has_sliced_first_memory_item_ = false;
+  bool has_sliced_last_memory_item_ = false;
+  size_t first_item_slice_offset_ = 0;
+  size_t first_item_index_ = 0;
+  size_t last_item_index_ = 0;
+
+  std::vector<scoped_refptr<ShareableBlobDataItem>> items_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlobSlice);
+};
+
+}  // namespace storage
+#endif  // STORAGE_BROWSER_BLOB_BLOB_SLICE_H_