[BlobAsync] Disk support for blob storage

storage/browser/blob/blob_slice.cc

+// 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.
+
+#include "storage/browser/blob/blob_slice.h"
+
+#include <algorithm>
+
+#include "storage/browser/blob/blob_data_builder.h"
+#include "storage/browser/blob/blob_data_item.h"
+#include "storage/browser/blob/internal_blob_data.h"
+#include "storage/browser/blob/shareable_blob_data_item.h"
+
+namespace storage {
+
+BlobSlice::BlobSlice(const InternalBlobData& source,
+                     uint64_t slice_offset,
+                     uint64_t slice_size) {
+  const auto& source_items = source.items();
+  const auto& offsets = source.offsets();
+  LOG(ERROR) << "doing a slice at " << slice_offset << " with size "
+             << slice_size;
+  DCHECK_LE(slice_offset + slice_size, source.total_size());
+  size_t item_index =
+      std::upper_bound(offsets.begin(), offsets.end(), slice_offset) -
+      offsets.begin();
+  uint64_t item_offset =
+      item_index == 0 ? slice_offset : slice_offset - offsets[item_index - 1];
+  size_t num_items = source_items.size();
+
+  size_t first_item_index = item_index;
+  copying_memory_size = 0;
+
+  // Read starting from 'first_item_index' and 'item_offset'.
+  for (uint64_t total_sliced = 0;
+       item_index < num_items && total_sliced < slice_size; item_index++) {
+    const scoped_refptr<BlobDataItem>& source_item =
+        source_items[item_index]->item();
+    uint64_t source_length = source_item->length();
+    DCHECK_NE(source_length, std::numeric_limits<uint64_t>::max());
+    DCHECK_NE(source_length, 0ull);
+
+    uint64_t read_size =
+        std::min(source_length - item_offset, slice_size - total_sliced);
+    total_sliced += read_size;
+
+    if (read_size == source_length) {
+      // We can share the entire item.
+      LOG(ERROR) << "we can share";
+      dest_items.push_back(source_items[item_index]);
+      continue;
+    }
+
+    scoped_refptr<BlobDataItem> data_item;
+    switch (source_item->type()) {
+      case DataElement::TYPE_BYTES_DESCRIPTION:
+      case DataElement::TYPE_BYTES: {
+        if (item_index == first_item_index) {
+          first_item_slice_offset = item_offset;
+          first_source_item = source_items[item_index];
+        } else {
+          last_source_item = source_items[item_index];
+        }
+        LOG(ERROR) << "we're slicing a bytes item!";
+        copying_memory_size += read_size;
+        // Since we don't have quota yet for memory, we create temporary items

[michaeln, 2016/08/15 22:44:42]

terminilogy nit: "unpopulated" might be a good term to use consistently for
incomplete byte and file items

+        // for this data. When our blob is finished constructing, all dependent
+        // blobs are done, and we have enough memory quota, we'll copy the data
+        // over.
+        std::unique_ptr<DataElement> element(new DataElement());
+        element->SetToBytesDescription(base::checked_cast<size_t>(read_size));
+        data_item = new BlobDataItem(std::move(element));
+        break;
+      }
+      case DataElement::TYPE_FILE: {
+        std::unique_ptr<DataElement> element(new DataElement());
+        element->SetToFilePathRange(
+            source_item->path(), source_item->offset() + item_offset, read_size,
+            source_item->expected_modification_time());
+        data_item =
+            new BlobDataItem(std::move(element), source_item->data_handle_);
+
+        if (source_item->path().value() ==
+            std::string(BlobDataBuilder::kAppendFutureFileTemporaryFileName)) {
+          // Since we don't have file path / reference for our future file, we
+          // create another file item with this temporary file name. When our
+          // blob is finished constructing, all dependent blobs are done, and we
+          // can copy the handle over.
+          LOG(ERROR) << "we're slicing a temp file item!";
+          if (item_index == first_item_index) {
+            first_item_slice_offset = item_offset;
+            first_source_item = source_items[item_index];
+          } else {
+            last_source_item = source_items[item_index];
+          }
+        }
+        break;
+      }
+      case DataElement::TYPE_FILE_FILESYSTEM: {
+        std::unique_ptr<DataElement> element(new DataElement());
+        element->SetToFileSystemUrlRange(
+            source_item->filesystem_url(), source_item->offset() + item_offset,
+            read_size, source_item->expected_modification_time());
+        data_item = new BlobDataItem(std::move(element));
+        break;
+      }
+      case DataElement::TYPE_DISK_CACHE_ENTRY: {
+        std::unique_ptr<DataElement> element(new DataElement());
+        element->SetToDiskCacheEntryRange(source_item->offset() + item_offset,
+                                          read_size);
+        data_item =
+            new BlobDataItem(std::move(element), source_item->data_handle_,
+                             source_item->disk_cache_entry(),
+                             source_item->disk_cache_stream_index(),
+                             source_item->disk_cache_side_stream_index());
+        break;
+      }
+      case DataElement::TYPE_BLOB:
+      case DataElement::TYPE_UNKNOWN:
+        CHECK(false) << "Illegal blob item type: " << source_item->type();
+    }
+    dest_items.push_back(new ShareableBlobDataItem(std::move(data_item)));
+    item_offset = 0;
+  }
+}
+
+BlobSlice::~BlobSlice() {}
+
+}  // namespace storage