Base: Change ReadPlatformFile to perform a best

base/platform_file.h

 // Copyright (c) 2011 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 BASE_PLATFORM_FILE_H_
 #define BASE_PLATFORM_FILE_H_
 #pragma once
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
@@ skipping 99 matching lines @@
 // false otherwise.  |error_code| can be NULL.
 BASE_EXPORT PlatformFile CreatePlatformFile(const FilePath& name,
                                             int flags,
                                             bool* created,
                                             PlatformFileError* error_code);
 
 // Closes a file handle. Returns |true| on success and |false| otherwise.
 BASE_EXPORT bool ClosePlatformFile(PlatformFile file);
 
 // Reads the given number of bytes (or until EOF is reached) starting with the
-// given offset. Returns the number of bytes read, or -1 on error.
+// given offset. Returns the number of bytes read, or -1 on error. Note that
+// this function makes a best effort to read all data on all platforms, so it is
+// not intended for stream oriented files but instead for cases when the normal
+// expectation is that actually |size| bytes are read unless there is an error.
 BASE_EXPORT int ReadPlatformFile(PlatformFile file, int64 offset,
                                  char* data, int size);
 
+// Reads the given number of bytes (or until EOF is reached) starting with the
+// given offset, but does not make any effort to read all data on all platforms.
+// Returns the number of bytes read, or -1 on error.
+BASE_EXPORT int ReadPlatformFileNoBestEffort(PlatformFile file, int64 offset,
+                                             char* data, int size);
+
 // Writes the given buffer into the file at the given offset, overwritting any
 // data that was previously there. Returns the number of bytes written, or -1
 // on error. Note that this function makes a best effort to write all data on
 // all platforms.
 BASE_EXPORT int WritePlatformFile(PlatformFile file, int64 offset,
                                   const char* data, int size);
 
 // Truncates the given file to the given length. If |length| is greater than
 // the current size of the file, the file is extended with zeros. If the file
 // doesn't exist, |false| is returned.
@@ skipping 44 matching lines @@
     return temp;
   }
 
  private:
   PlatformFile* value_;
 };
 
 }  // namespace base
 
 #endif  // BASE_PLATFORM_FILE_H_