Revert of [Blob] BlobReader class & tests, and removal of all redundant reading.

storage/browser/blob/blob_url_request_job.cc

Index: storage/browser/blob/blob_url_request_job.cc
diff --git a/storage/browser/blob/blob_url_request_job.cc b/storage/browser/blob/blob_url_request_job.cc
index 6ec2fe57ae7ca706b53171c9d8e1f8a24f1d3d3f..f42902004e3b6d570b7be4ceda04f1919efe972e 100644
--- a/storage/browser/blob/blob_url_request_job.cc
+++ b/storage/browser/blob/blob_url_request_job.cc
@@ -31,8 +31,6 @@
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_error_job.h"
 #include "net/url_request/url_request_status.h"
-#include "storage/browser/blob/blob_data_handle.h"
-#include "storage/browser/blob/blob_reader.h"
 #include "storage/browser/fileapi/file_stream_reader.h"
 #include "storage/browser/fileapi/file_system_context.h"
 #include "storage/browser/fileapi/file_system_url.h"
@@ -40,24 +38,41 @@
 
 namespace storage {
 
+namespace {
+
+bool IsFileType(DataElement::Type type) {
+  switch (type) {
+    case DataElement::TYPE_FILE:
+    case DataElement::TYPE_FILE_FILESYSTEM:
+      return true;
+    default:
+      return false;
+  }
+}
+
+}  // namespace
+
 BlobURLRequestJob::BlobURLRequestJob(
     net::URLRequest* request,
     net::NetworkDelegate* network_delegate,
-    BlobDataHandle* blob_handle,
-    FileSystemContext* file_system_context,
+    scoped_ptr<BlobDataSnapshot> blob_data,
+    storage::FileSystemContext* file_system_context,
     base::SingleThreadTaskRunner* file_task_runner)
     : net::URLRequestJob(request, network_delegate),
+      blob_data_(blob_data.Pass()),
+      file_system_context_(file_system_context),
+      file_task_runner_(file_task_runner),
+      total_size_(0),
+      remaining_bytes_(0),
+      pending_get_file_info_count_(0),
+      current_item_index_(0),
+      current_item_offset_(0),
       error_(false),
       byte_range_set_(false),
       weak_factory_(this) {
   TRACE_EVENT_ASYNC_BEGIN1("Blob", "BlobRequest", this, "uuid",
-                           blob_handle ? blob_handle->uuid() : "NotFound");
-  DCHECK(file_task_runner);
-  if (blob_handle) {
-    blob_handle_.reset(new BlobDataHandle(*blob_handle));
-    blob_reader_ =
-        blob_handle_->CreateReader(file_system_context, file_task_runner);
-  }
+                           blob_data_ ? blob_data_->uuid() : "NotFound");
+  DCHECK(file_task_runner_.get());
 }
 
 void BlobURLRequestJob::Start() {
@@ -68,9 +83,8 @@
 }
 
 void BlobURLRequestJob::Kill() {
-  if (blob_reader_) {
-    blob_reader_->Kill();
-  }
+  DeleteCurrentFileReader();
+
   net::URLRequestJob::Kill();
   weak_factory_.InvalidateWeakPtrs();
 }
@@ -78,10 +92,9 @@
 bool BlobURLRequestJob::ReadRawData(net::IOBuffer* dest,
                                     int dest_size,
                                     int* bytes_read) {
-  TRACE_EVENT_ASYNC_BEGIN1("Blob", "BlobRequest::ReadRawData", this, "uuid",
-                           blob_handle_ ? blob_handle_->uuid() : "NotFound");
   DCHECK_NE(dest_size, 0);
   DCHECK(bytes_read);
+  DCHECK_GE(remaining_bytes_, 0);
 
   // Bail out immediately if we encounter an error.
   if (error_) {
@@ -89,27 +102,21 @@
     return true;
   }
 
-  BlobReader::Status read_status =
-      blob_reader_->Read(dest, dest_size, bytes_read,
-                         base::Bind(&BlobURLRequestJob::DidReadRawData,
-                                    weak_factory_.GetWeakPtr()));
-
-  switch (read_status) {
-    case BlobReader::Status::NET_ERROR:
-      NotifyFailure(blob_reader_->net_error());
-      TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest::ReadRawData", this, "uuid",
-                             blob_handle_ ? blob_handle_->uuid() : "NotFound");
-      return false;
-    case BlobReader::Status::IO_PENDING:
-      SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
-      return false;
-    case BlobReader::Status::DONE:
-      TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest::ReadRawData", this, "uuid",
-                             blob_handle_ ? blob_handle_->uuid() : "NotFound");
-      return true;
-  }
-  NOTREACHED();
-  return true;
+  if (remaining_bytes_ < dest_size)
+    dest_size = static_cast<int>(remaining_bytes_);
+
+  // If we should copy zero bytes because |remaining_bytes_| is zero, short
+  // circuit here.
+  if (!dest_size) {
+    *bytes_read = 0;
+    return true;
+  }
+
+  // Keep track of the buffer.
+  DCHECK(!read_buf_.get());
+  read_buf_ = new net::DrainableIOBuffer(dest, dest_size);
+
+  return ReadLoop(bytes_read);
 }
 
 bool BlobURLRequestJob::GetMimeType(std::string* mime_type) const {
@@ -152,11 +159,13 @@
 }
 
 BlobURLRequestJob::~BlobURLRequestJob() {
+  STLDeleteValues(&index_to_reader_);
   TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest", this, "uuid",
-                         blob_handle_ ? blob_handle_->uuid() : "NotFound");
+                         blob_data_ ? blob_data_->uuid() : "NotFound");
 }
 
 void BlobURLRequestJob::DidStart() {
+  current_file_chunk_number_ = 0;
   error_ = false;
 
   // We only support GET request per the spec.
@@ -166,79 +175,379 @@
   }
 
   // If the blob data is not present, bail out.
-  if (!blob_handle_) {
+  if (!blob_data_) {
     NotifyFailure(net::ERR_FILE_NOT_FOUND);
     return;
   }
 
+  CountSize();
+}
+
+bool BlobURLRequestJob::AddItemLength(size_t index, int64 item_length) {
+  if (item_length > kint64max - total_size_) {
+    TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest::CountSize", this, "uuid",
+                           blob_data_->uuid());
+    NotifyFailure(net::ERR_FAILED);
+    return false;
+  }
+
+  // Cache the size and add it to the total size.
+  DCHECK_LT(index, item_length_list_.size());
+  item_length_list_[index] = item_length;
+  total_size_ += item_length;
+  return true;
+}
+
+bool BlobURLRequestJob::CountSize() {
   TRACE_EVENT_ASYNC_BEGIN1("Blob", "BlobRequest::CountSize", this, "uuid",
-                           blob_handle_->uuid());
-  BlobReader::Status size_status = blob_reader_->CalculateSize(base::Bind(
-      &BlobURLRequestJob::DidCalculateSize, weak_factory_.GetWeakPtr()));
-  switch (size_status) {
-    case BlobReader::Status::NET_ERROR:
-      NotifyFailure(blob_reader_->net_error());
-      return;
-    case BlobReader::Status::IO_PENDING:
-      SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
-      return;
-    case BlobReader::Status::DONE:
-      DidCalculateSize(net::OK);
-      return;
-  }
-}
-
-void BlobURLRequestJob::DidCalculateSize(int result) {
+                           blob_data_->uuid());
+  pending_get_file_info_count_ = 0;
+  total_size_ = 0;
+  const auto& items = blob_data_->items();
+  item_length_list_.resize(items.size());
+
+  for (size_t i = 0; i < items.size(); ++i) {
+    const BlobDataItem& item = *items.at(i);
+    if (IsFileType(item.type())) {
+      ++pending_get_file_info_count_;
+      storage::FileStreamReader* const reader = GetFileStreamReader(i);
+      if (!reader) {
+        NotifyFailure(net::ERR_FAILED);
+        return false;
+      }
+      if (!reader->GetLength(
+              base::Bind(&BlobURLRequestJob::DidGetFileItemLength,
+                         weak_factory_.GetWeakPtr(), i))) {
+        NotifyFailure(net::ERR_FILE_NOT_FOUND);
+        return false;
+      }
+      continue;
+    }
+
+    if (!AddItemLength(i, item.length()))
+      return false;
+  }
+
+  if (pending_get_file_info_count_ == 0)
+    DidCountSize(net::OK);
+
+  return true;
+}
+
+void BlobURLRequestJob::DidCountSize(int error) {
+  DCHECK(!error_);
   TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest::CountSize", this, "uuid",
-                         blob_handle_->uuid());
-  // Clear the IO_PENDING status
+                         blob_data_->uuid());
+
+  // If an error occured, bail out.
+  if (error != net::OK) {
+    NotifyFailure(error);
+    return;
+  }
+
+  // Apply the range requirement.
+  if (!byte_range_.ComputeBounds(total_size_)) {
+    NotifyFailure(net::ERR_REQUEST_RANGE_NOT_SATISFIABLE);
+    return;
+  }
+
+  remaining_bytes_ = base::checked_cast<int64>(
+      byte_range_.last_byte_position() - byte_range_.first_byte_position() + 1);
+  DCHECK_GE(remaining_bytes_, 0);
+
+  // Do the seek at the beginning of the request.
+  if (byte_range_.first_byte_position())
+    Seek(byte_range_.first_byte_position());
+
+  NotifySuccess();
+}
+
+void BlobURLRequestJob::DidGetFileItemLength(size_t index, int64 result) {
+  // Do nothing if we have encountered an error.
+  if (error_)
+    return;
+
+  if (result == net::ERR_UPLOAD_FILE_CHANGED) {
+    NotifyFailure(net::ERR_FILE_NOT_FOUND);
+    return;
+  } else if (result < 0) {
+    NotifyFailure(result);
+    return;
+  }
+
+  const auto& items = blob_data_->items();
+  DCHECK_LT(index, items.size());
+  const BlobDataItem& item = *items.at(index);
+  DCHECK(IsFileType(item.type()));
+
+  uint64 file_length = result;
+  uint64 item_offset = item.offset();
+  uint64 item_length = item.length();
+
+  if (item_offset > file_length) {
+    NotifyFailure(net::ERR_FILE_NOT_FOUND);
+    return;
+  }
+
+  uint64 max_length = file_length - item_offset;
+
+  // If item length is undefined, then we need to use the file size being
+  // resolved in the real time.
+  if (item_length == std::numeric_limits<uint64>::max()) {
+    item_length = max_length;
+  } else if (item_length > max_length) {
+    NotifyFailure(net::ERR_FILE_NOT_FOUND);
+    return;
+  }
+
+  if (!AddItemLength(index, item_length))
+    return;
+
+  if (--pending_get_file_info_count_ == 0)
+    DidCountSize(net::OK);
+}
+
+void BlobURLRequestJob::Seek(int64 offset) {
+  // Skip the initial items that are not in the range.
+  const auto& items = blob_data_->items();
+  for (current_item_index_ = 0;
+       current_item_index_ < items.size() &&
+           offset >= item_length_list_[current_item_index_];
+       ++current_item_index_) {
+    offset -= item_length_list_[current_item_index_];
+  }
+
+  // Set the offset that need to jump to for the first item in the range.
+  current_item_offset_ = offset;
+
+  if (offset == 0)
+    return;
+
+  // Adjust the offset of the first stream if it is of file type.
+  const BlobDataItem& item = *items.at(current_item_index_);
+  if (IsFileType(item.type())) {
+    DeleteCurrentFileReader();
+    CreateFileStreamReader(current_item_index_, offset);
+  }
+}
+
+bool BlobURLRequestJob::ReadItem() {
+  // Are we done with reading all the blob data?
+  if (remaining_bytes_ == 0)
+    return true;
+
+  const auto& items = blob_data_->items();
+  // If we get to the last item but still expect something to read, bail out
+  // since something is wrong.
+  if (current_item_index_ >= items.size()) {
+    NotifyFailure(net::ERR_FAILED);
+    return false;
+  }
+
+  // Compute the bytes to read for current item.
+  int bytes_to_read = ComputeBytesToRead();
+
+  // If nothing to read for current item, advance to next item.
+  if (bytes_to_read == 0) {
+    AdvanceItem();
+    return true;
+  }
+
+  // Do the reading.
+  const BlobDataItem& item = *items.at(current_item_index_);
+  if (item.type() == DataElement::TYPE_BYTES)
+    return ReadBytesItem(item, bytes_to_read);
+  if (item.type() == DataElement::TYPE_DISK_CACHE_ENTRY)
+    return ReadDiskCacheEntryItem(item, bytes_to_read);
+  if (!IsFileType(item.type())) {
+    NOTREACHED();
+    return false;
+  }
+  storage::FileStreamReader* const reader =
+      GetFileStreamReader(current_item_index_);
+  if (!reader) {
+    NotifyFailure(net::ERR_FAILED);
+    return false;
+  }
+
+  return ReadFileItem(reader, bytes_to_read);
+}
+
+void BlobURLRequestJob::AdvanceItem() {
+  // Close the file if the current item is a file.
+  DeleteCurrentFileReader();
+
+  // Advance to the next item.
+  current_item_index_++;
+  current_item_offset_ = 0;
+}
+
+void BlobURLRequestJob::AdvanceBytesRead(int result) {
+  DCHECK_GT(result, 0);
+
+  // Do we finish reading the current item?
+  current_item_offset_ += result;
+  if (current_item_offset_ == item_length_list_[current_item_index_])
+    AdvanceItem();
+
+  // Subtract the remaining bytes.
+  remaining_bytes_ -= result;
+  DCHECK_GE(remaining_bytes_, 0);
+
+  // Adjust the read buffer.
+  read_buf_->DidConsume(result);
+  DCHECK_GE(read_buf_->BytesRemaining(), 0);
+}
+
+bool BlobURLRequestJob::ReadBytesItem(const BlobDataItem& item,
+                                      int bytes_to_read) {
+  TRACE_EVENT1("Blob", "BlobRequest::ReadBytesItem", "uuid",
+               blob_data_->uuid());
+  DCHECK_GE(read_buf_->BytesRemaining(), bytes_to_read);
+
+  memcpy(read_buf_->data(),
+         item.bytes() + item.offset() + current_item_offset_,
+         bytes_to_read);
+
+  AdvanceBytesRead(bytes_to_read);
+  return true;
+}
+
+bool BlobURLRequestJob::ReadFileItem(FileStreamReader* reader,
+                                     int bytes_to_read) {
+  DCHECK(!GetStatus().is_io_pending())
+      << "Can't begin IO while another IO operation is pending.";
+  DCHECK_GE(read_buf_->BytesRemaining(), bytes_to_read);
+  DCHECK(reader);
+  int chunk_number = current_file_chunk_number_++;
+  TRACE_EVENT_ASYNC_BEGIN1("Blob", "BlobRequest::ReadFileItem", this, "uuid",
+                           blob_data_->uuid());
+  const int result =
+      reader->Read(read_buf_.get(), bytes_to_read,
+                   base::Bind(&BlobURLRequestJob::DidReadFile,
+                              weak_factory_.GetWeakPtr(), chunk_number));
+  if (result >= 0) {
+    AdvanceBytesRead(result);
+    return true;
+  }
+  if (result == net::ERR_IO_PENDING)
+    SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
+  else
+    NotifyFailure(result);
+  return false;
+}
+
+void BlobURLRequestJob::DidReadFile(int chunk_number, int result) {
+  DCHECK(GetStatus().is_io_pending())
+      << "Asynchronous IO completed while IO wasn't pending?";
+  TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest::ReadFileItem", this, "uuid",
+                         blob_data_->uuid());
+  if (result <= 0) {
+    NotifyFailure(result);
+    return;
+  }
+  SetStatus(net::URLRequestStatus());  // Clear the IO_PENDING status
+
+  AdvanceBytesRead(result);
+
+  // Otherwise, continue the reading.
+  int bytes_read = 0;
+  if (ReadLoop(&bytes_read))
+    NotifyReadComplete(bytes_read);
+}
+
+void BlobURLRequestJob::DeleteCurrentFileReader() {
+  IndexToReaderMap::iterator found = index_to_reader_.find(current_item_index_);
+  if (found != index_to_reader_.end() && found->second) {
+    delete found->second;
+    index_to_reader_.erase(found);
+  }
+}
+
+bool BlobURLRequestJob::ReadDiskCacheEntryItem(const BlobDataItem& item,
+                                               int bytes_to_read) {
+  DCHECK(!GetStatus().is_io_pending())
+      << "Can't begin IO while another IO operation is pending.";
+  DCHECK_GE(read_buf_->BytesRemaining(), bytes_to_read);
+
+  const int result = item.disk_cache_entry()->ReadData(
+      item.disk_cache_stream_index(), current_item_offset_, read_buf_.get(),
+      bytes_to_read, base::Bind(&BlobURLRequestJob::DidReadDiskCacheEntry,
+                                weak_factory_.GetWeakPtr()));
+  if (result >= 0) {
+    AdvanceBytesRead(result);
+    return true;
+  }
+  if (result == net::ERR_IO_PENDING)
+    SetStatus(net::URLRequestStatus(net::URLRequestStatus::IO_PENDING, 0));
+  else
+    NotifyFailure(result);
+  return false;
+}
+
+void BlobURLRequestJob::DidReadDiskCacheEntry(int result) {
+  DCHECK(GetStatus().is_io_pending())
+      << "Asynchronous IO completed while IO wasn't pending?";
+  if (result <= 0) {
+    NotifyFailure(result);
+    return;
+  }
   SetStatus(net::URLRequestStatus());
 
-  if (result != net::OK) {
-    NotifyFailure(result);
-    return;
-  }
-
-  // Apply the range requirement.
-  if (!byte_range_.ComputeBounds(blob_reader_->total_size())) {
-    NotifyFailure(net::ERR_REQUEST_RANGE_NOT_SATISFIABLE);
-    return;
-  }
-
-  DCHECK_LE(byte_range_.first_byte_position(),
-            byte_range_.last_byte_position() + 1);
-  uint64_t length = base::checked_cast<uint64_t>(
-      byte_range_.last_byte_position() - byte_range_.first_byte_position() + 1);
-
-  if (byte_range_set_)
-    blob_reader_->SetReadRange(byte_range_.first_byte_position(), length);
-
+  AdvanceBytesRead(result);
+
+  int bytes_read = 0;
+  if (ReadLoop(&bytes_read))
+    NotifyReadComplete(bytes_read);
+}
+
+int BlobURLRequestJob::BytesReadCompleted() {
+  int bytes_read = read_buf_->BytesConsumed();
+  read_buf_ = NULL;
+  return bytes_read;
+}
+
+int BlobURLRequestJob::ComputeBytesToRead() const {
+  int64 current_item_length = item_length_list_[current_item_index_];
+
+  int64 item_remaining = current_item_length - current_item_offset_;
+  int64 buf_remaining = read_buf_->BytesRemaining();
+  int64 max_remaining = std::numeric_limits<int>::max();
+
+  int64 min = std::min(std::min(std::min(item_remaining,
+                                         buf_remaining),
+                                         remaining_bytes_),
+                                         max_remaining);
+
+  return static_cast<int>(min);
+}
+
+bool BlobURLRequestJob::ReadLoop(int* bytes_read) {
+  // Read until we encounter an error or could not get the data immediately.
+  while (remaining_bytes_ > 0 && read_buf_->BytesRemaining() > 0) {
+    if (!ReadItem())
+      return false;
+  }
+
+  *bytes_read = BytesReadCompleted();
+  return true;
+}
+
+void BlobURLRequestJob::NotifySuccess() {
   net::HttpStatusCode status_code = net::HTTP_OK;
   if (byte_range_set_ && byte_range_.IsValid())
     status_code = net::HTTP_PARTIAL_CONTENT;
   HeadersCompleted(status_code);
 }
 
-void BlobURLRequestJob::DidReadRawData(int result) {
-  TRACE_EVENT_ASYNC_END1("Blob", "BlobRequest::ReadRawData", this, "uuid",
-                         blob_handle_ ? blob_handle_->uuid() : "NotFound");
-  if (result < 0) {
-    NotifyFailure(result);
-    return;
-  }
-  // Clear the IO_PENDING status
-  SetStatus(net::URLRequestStatus());
-  NotifyReadComplete(result);
-}
-
 void BlobURLRequestJob::NotifyFailure(int error_code) {
   error_ = true;
 
   // If we already return the headers on success, we can't change the headers
   // now. Instead, we just error out.
   if (response_info_) {
-    NotifyDone(
-        net::URLRequestStatus(net::URLRequestStatus::FAILED, error_code));
+    NotifyDone(net::URLRequestStatus(net::URLRequestStatus::FAILED,
+                                     error_code));
     return;
   }
 
@@ -273,14 +582,10 @@
   status.append("\0\0", 2);
   net::HttpResponseHeaders* headers = new net::HttpResponseHeaders(status);
 
-  set_expected_content_size(0);
-
   if (status_code == net::HTTP_OK || status_code == net::HTTP_PARTIAL_CONTENT) {
-    set_expected_content_size(blob_reader_->remaining_bytes());
     std::string content_length_header(net::HttpRequestHeaders::kContentLength);
     content_length_header.append(": ");
-    content_length_header.append(
-        base::Int64ToString(blob_reader_->remaining_bytes()));
+    content_length_header.append(base::Int64ToString(remaining_bytes_));
     headers->AddHeader(content_length_header);
     if (status_code == net::HTTP_PARTIAL_CONTENT) {
       DCHECK(byte_range_set_);
@@ -288,22 +593,21 @@
       std::string content_range_header(net::HttpResponseHeaders::kContentRange);
       content_range_header.append(": bytes ");
       content_range_header.append(base::StringPrintf(
-          "%" PRId64 "-%" PRId64, byte_range_.first_byte_position(),
-          byte_range_.last_byte_position()));
+          "%" PRId64 "-%" PRId64,
+          byte_range_.first_byte_position(), byte_range_.last_byte_position()));
       content_range_header.append("/");
-      content_range_header.append(
-          base::StringPrintf("%" PRId64, blob_reader_->total_size()));
+      content_range_header.append(base::StringPrintf("%" PRId64, total_size_));
       headers->AddHeader(content_range_header);
     }
-    if (!blob_handle_->content_type().empty()) {
+    if (!blob_data_->content_type().empty()) {
       std::string content_type_header(net::HttpRequestHeaders::kContentType);
       content_type_header.append(": ");
-      content_type_header.append(blob_handle_->content_type());
+      content_type_header.append(blob_data_->content_type());
       headers->AddHeader(content_type_header);
     }
-    if (!blob_handle_->content_disposition().empty()) {
+    if (!blob_data_->content_disposition().empty()) {
       std::string content_disposition_header("Content-Disposition: ");
-      content_disposition_header.append(blob_handle_->content_disposition());
+      content_disposition_header.append(blob_data_->content_disposition());
       headers->AddHeader(content_disposition_header);
     }
   }
@@ -311,7 +615,69 @@
   response_info_.reset(new net::HttpResponseInfo());
   response_info_->headers = headers;
 
+  set_expected_content_size(remaining_bytes_);
+
   NotifyHeadersComplete();
 }
 
+FileStreamReader* BlobURLRequestJob::GetFileStreamReader(size_t index) {
+  const auto& items = blob_data_->items();
+  DCHECK_LT(index, items.size());
+  const BlobDataItem& item = *items.at(index);
+  if (!IsFileType(item.type()))
+    return nullptr;
+  if (index_to_reader_.find(index) == index_to_reader_.end()) {
+    if (!CreateFileStreamReader(index, 0))
+      return nullptr;
+  }
+  DCHECK(index_to_reader_[index]);
+  return index_to_reader_[index];
+}
+
+bool BlobURLRequestJob::CreateFileStreamReader(size_t index,
+                                               int64 additional_offset) {
+  const auto& items = blob_data_->items();
+  DCHECK_LT(index, items.size());
+  const BlobDataItem& item = *items.at(index);
+  DCHECK(IsFileType(item.type()));
+  DCHECK_EQ(0U, index_to_reader_.count(index));
+
+  FileStreamReader* reader = nullptr;
+  switch (item.type()) {
+    case DataElement::TYPE_FILE:
+      reader = FileStreamReader::CreateForLocalFile(
+          file_task_runner_.get(), item.path(),
+          item.offset() + additional_offset, item.expected_modification_time());
+      DCHECK(reader);
+      index_to_reader_[index] = reader;
+      return true;
+
+    case DataElement::TYPE_FILE_FILESYSTEM:
+      reader = file_system_context_
+                   ->CreateFileStreamReader(
+                         storage::FileSystemURL(file_system_context_->CrackURL(
+                             item.filesystem_url())),
+                         item.offset() + additional_offset,
+                         item.length() == std::numeric_limits<uint64>::max()
+                             ? storage::kMaximumLength
+                             : item.length() - additional_offset,
+                         item.expected_modification_time())
+                   .release();
+      if (reader) {
+        index_to_reader_[index] = reader;
+        return true;
+      }
+
+      // The file stream reader may not be obtainable if the file is on an
+      // isolated file system, which has been unmounted.
+      return false;
+
+    default:
+      break;
+  }
+
+  NOTREACHED();
+  return false;
+}
+
 }  // namespace storage