Implement Read/WriteAtCurrentPos correctly

base/files/file_posix.cc

 // Copyright (c) 2012 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 "base/files/file.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ skipping 248 matching lines @@
 
 int File::ReadAtCurrentPos(char* data, int size) {
   base::ThreadRestrictions::AssertIOAllowed();
   DCHECK(IsValid());
   if (size < 0)
     return -1;
 
   int bytes_read = 0;
   int rv;
   do {
-    rv = HANDLE_EINTR(read(file_.get(), data, size));
+    rv = HANDLE_EINTR(read(file_.get(), data + bytes_read, size - bytes_read));
     if (rv <= 0)
       break;
 
     bytes_read += rv;
   } while (bytes_read < size);
 
   return bytes_read ? bytes_read : rv;
 }
 
 int File::ReadNoBestEffort(int64 offset, char* data, int size) {
@@ skipping 38 matching lines @@
 
 int File::WriteAtCurrentPos(const char* data, int size) {
   base::ThreadRestrictions::AssertIOAllowed();
   DCHECK(IsValid());
   if (size < 0)
     return -1;
 
   int bytes_written = 0;
   int rv;
   do {
-    rv = HANDLE_EINTR(write(file_.get(), data, size));
+    rv = HANDLE_EINTR(write(file_.get(), data + bytes_written,
+                            size - bytes_written));
     if (rv <= 0)
       break;
 
     bytes_written += rv;
   } while (bytes_written < size);
 
   return bytes_written ? bytes_written : rv;
 }
 
 int File::WriteAtCurrentPosNoBestEffort(const char* data, int size) {
@@ skipping 135 matching lines @@
       return FILE_ERROR_FAILED;
   }
 }
 
 void File::SetPlatformFile(PlatformFile file) {
   DCHECK(!file_.is_valid());
   file_.reset(file);
 }
 
 }  // namespace base