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

storage/browser/blob/blob_reader.h

Index: storage/browser/blob/blob_reader.h
diff --git a/storage/browser/blob/blob_reader.h b/storage/browser/blob/blob_reader.h
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+// Copyright 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_READER_H_
+#define STORAGE_BROWSER_BLOB_BLOB_READER_H_
+
+#include <stdint.h>
+#include <map>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "net/base/completion_callback.h"
+#include "storage/browser/storage_browser_export.h"
+
+class GURL;
+
+namespace base {
+class FilePath;
+class SequencedTaskRunner;
+class TaskRunner;
+class Time;
+}
+
+namespace net {
+class DrainableIOBuffer;
+class IOBuffer;
+}
+
+namespace storage {
+class BlobDataItem;
+class BlobDataHandle;
+class BlobDataSnapshot;
+class FileStreamReader;
+class FileSystemContext;
+
+// The blob reader is used to read a blob.  This can only be used in the browser
+// process, and we need to be on the IO thread.
+//  * There can only be one read happening at a time per reader.
+//  * If a status of Status::NET_ERROR is returned, that means there was an
+//    error and the net_error() variable contains the error code.
+// Use a BlobDataHandle to create an instance.
+class STORAGE_EXPORT BlobReader {
+ public:
+  class STORAGE_EXPORT FileStreamReaderProvider {
+   public:
+    virtual ~FileStreamReaderProvider();
+
+    virtual scoped_ptr<FileStreamReader> CreateForLocalFile(
+        base::TaskRunner* task_runner,
+        const base::FilePath& file_path,
+        int64_t initial_offset,
+        const base::Time& expected_modification_time) = 0;
+
+    virtual scoped_ptr<FileStreamReader> CreateFileStreamReader(
+        const GURL& filesystem_url,
+        int64_t offset,
+        int64_t max_bytes_to_read,
+        const base::Time& expected_modification_time) = 0;
+  };
+  enum class Status { NET_ERROR, IO_PENDING, DONE };
+  virtual ~BlobReader();
+
+  // This calculates the total size of the blob, and initializes the reading
+  // cursor.
+  //  * This should only be called once per reader.
+  //  * Status::Done means that the total_size() value is populated and you can
+  //    continue to SetReadRange or Read.
+  //  * The 'done' callback is only called if Status::IO_PENDING is returned.
+  //    The callback value contains the error code or net::OK. Please use the
+  //    total_size() value to query the blob size, as it's uint64_t.
+  Status CalculateSize(const net::CompletionCallback& done);
+
+  // Used to set the read position.
+  // * This should be called after CalculateSize and before Read.
+  // * Range can only be set once.
+  Status SetReadRange(uint64_t position, uint64_t length);
+
+  // Reads a portion of the data.
+  // * CalculateSize (and optionally SetReadRange) must be called beforehand.
+  // * bytes_read is populated only if Status::DONE is returned. Otherwise the
+  //   bytes read (or error code) is populated in the 'done' callback.
+  // * The done callback is only called if Status::IO_PENDING is returned.
+  // * This method can be called multiple times. A bytes_read value (either from
+  //   the callback for Status::IO_PENDING or the bytes_read value for
+  //   Status::DONE) of 0 means we're finished reading.
+  Status Read(net::IOBuffer* buffer,
+              size_t dest_size,
+              int* bytes_read,
+              net::CompletionCallback done);
+
+  // Kills reading and invalidates all callbacks. The reader cannot be used
+  // after this call.
+  void Kill();
+
+  // Returns if all of the blob's items are in memory.
+  bool IsInMemory() const;
+
+  // Returns the remaining bytes to be read in the blob. This is populated
+  // after CalculateSize, and is modified by SetReadRange.
+  uint64_t remaining_bytes() const { return remaining_bytes_; }
+
+  // Returns the net error code if there was an error. Defaults to net::OK.
+  int net_error() const { return net_error_; }
+
+  // Returns the total size of the blob. This is populated after CalculateSize
+  // is called.
+  uint64_t total_size() const { return total_size_; }
+
+ protected:
+  friend class BlobDataHandle;
+  friend class BlobReaderTest;
+
+  BlobReader(const BlobDataHandle* blob_handle,
+             scoped_ptr<FileStreamReaderProvider> file_stream_provider,
+             base::SequencedTaskRunner* file_task_runner);
+
+  bool total_size_calculated() const { return total_size_calculated_; }
+
+ private:
+  Status ReportError(int net_error);
+  void InvalidateCallbacksAndDone(int net_error, net::CompletionCallback done);
+
+  bool AddItemLength(size_t index, uint64_t length);
+  bool ResolveFileItemLength(const BlobDataItem& item,
+                             int64_t total_length,
+                             uint64_t* output_length);
+  void DidGetFileItemLength(size_t index, int64_t result);
+  void DidCountSize();
+
+  // For reading the blob.
+  // Returns if we're done, PENDING_IO if we're waiting on async.
+  Status ReadLoop(int* bytes_read);
+  // Called from asynchronously called methods to continue the read loop.
+  void ContinueAsyncReadLoop();
+  // PENDING_IO means we're waiting on async.
+  Status ReadItem();
+  void AdvanceItem();
+  void AdvanceBytesRead(int result);
+  void ReadBytesItem(const BlobDataItem& item, int bytes_to_read);
+  BlobReader::Status ReadFileItem(FileStreamReader* reader, int bytes_to_read);
+  void DidReadFile(int result);
+  void DeleteCurrentFileReader();
+  Status ReadDiskCacheEntryItem(const BlobDataItem& item, int bytes_to_read);
+  void DidReadDiskCacheEntry(int result);
+  void DidReadItem(int result);
+  int ComputeBytesToRead() const;
+  int BytesReadCompleted();
+
+  // Returns a FileStreamReader for a blob item at |index|.
+  // If the item at |index| is not of file this returns NULL.
+  FileStreamReader* GetOrCreateFileReaderAtIndex(size_t index);
+  // If the reader is null, then this basically performs a delete operation.
+  void SetFileReaderAtIndex(size_t index, scoped_ptr<FileStreamReader> reader);
+  // Creates a FileStreamReader for the item with additional_offset.
+  scoped_ptr<FileStreamReader> CreateFileStreamReader(
+      const BlobDataItem& item,
+      uint64_t additional_offset);
+
+  scoped_ptr<BlobDataSnapshot> blob_data_;
+  scoped_ptr<FileStreamReaderProvider> file_stream_provider_;
+  scoped_refptr<base::SequencedTaskRunner> file_task_runner_;
+
+  int net_error_;
+  bool item_list_populated_ = false;
+  std::vector<uint64_t> item_length_list_;
+
+  scoped_refptr<net::DrainableIOBuffer> read_buf_;
+
+  bool total_size_calculated_ = false;
+  uint64_t total_size_ = 0;
+  uint64_t remaining_bytes_ = 0;
+  size_t pending_get_file_info_count_ = 0;
+  std::map<size_t, FileStreamReader*> index_to_reader_;
+  size_t current_item_index_ = 0;
+  uint64_t current_item_offset_ = 0;
+
+  bool io_pending_ = false;
+
+  net::CompletionCallback size_callback_;
+  net::CompletionCallback read_callback_;
+
+  base::WeakPtrFactory<BlobReader> weak_factory_;
+  DISALLOW_COPY_AND_ASSIGN(BlobReader);
+};
+
+}  // namespace storage
+#endif  // STORAGE_BROWSER_BLOB_BLOB_READER_H_