SimpleCache: open with fewer seeks.

net/disk_cache/simple/simple_util.h

 // Copyright (c) 2013 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 NET_DISK_CACHE_SIMPLE_SIMPLE_UTIL_H_
 #define NET_DISK_CACHE_SIMPLE_SIMPLE_UTIL_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 35 matching lines @@
     const std::string& key,
     int file_index);
 
 // Same as |GetFilenameFromKeyAndIndex| above, but using a hex string.
 std::string GetFilenameFromEntryHashAndFileIndex(uint64_t entry_hash,
                                                  int file_index);
 
 // Given a |key| for an entry, returns the name of the sparse data file.
 std::string GetSparseFilenameFromEntryHash(uint64_t entry_hash);
 
+// Given the size of a key, the size in bytes of the header at the beginning
+// of a simple cache file.
+size_t GetHeaderSize(size_t key_length);
+
 // Given the size of a file holding a stream in the simple backend and the key
 // to an entry, returns the number of bytes in the stream.
-NET_EXPORT_PRIVATE int32_t GetDataSizeFromKeyAndFileSize(const std::string& key,
-                                                         int64_t file_size);
+NET_EXPORT_PRIVATE int32_t GetDataSizeFromFileSize(size_t key_length,
+                                                   int64_t file_size);
 
 // Given the size of a stream in the simple backend and the key to an entry,
 // returns the number of bytes in the file.
-NET_EXPORT_PRIVATE int64_t GetFileSizeFromKeyAndDataSize(const std::string& key,
-                                                         int32_t data_size);
+NET_EXPORT_PRIVATE int64_t GetFileSizeFromDataSize(size_t key_length,
+                                                   int32_t data_size);
 
 // Given the stream index, returns the number of the file the stream is stored
 // in.
 NET_EXPORT_PRIVATE int GetFileIndexFromStreamIndex(int stream_index);
 
 // Fills |out_time| with the time the file last modified time. Unlike the
 // functions in file.h, the time resolution is milliseconds.
 NET_EXPORT_PRIVATE bool GetMTime(const base::FilePath& path,
                                  base::Time* out_mtime);
 
 // Deletes a file, insuring POSIX semantics. Provided that all open handles to
 // this file were opened with File::FLAG_SHARE_DELETE, it is possible to delete
 // an open file and continue to use that file. After deleting an open file, it
 // is possible to immediately create a new file with the same name.
 NET_EXPORT_PRIVATE bool SimpleCacheDeleteFile(const base::FilePath& path);
 
 }  // namespace simple_util
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_UTIL_H_