Re-land Move ScopedFileDescriptor to dbus/file_descriptor.h

dbus/file_descriptor.h

 // 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.
 
 #ifndef DBUS_FILE_DESCRIPTOR_H_
 #define DBUS_FILE_DESCRIPTOR_H_
 
 #include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
 #include "dbus/dbus_export.h"
 
 namespace dbus {
 
 // FileDescriptor is a type used to encapsulate D-Bus file descriptors
 // and to follow the RAII idiom appropiate for use with message operations
 // where the descriptor might be easily leaked.  To guard against this the
 // descriptor is closed when an instance is destroyed if it is owned.
 // Ownership is asserted only when PutValue is used and TakeValue can be
 // used to take ownership.
 //
 // For example, in the following
 //  FileDescriptor fd;
 //  if (!reader->PopString(&name) ||
 //      !reader->PopFileDescriptor(&fd) ||
 //      !reader->PopUint32(&flags)) {
 // the descriptor in fd will be closed if the PopUint32 fails.  But
 //   writer.AppendFileDescriptor(dbus::FileDescriptor(1));
 // will not automatically close "1" because it is not owned.
 //
 // Descriptors must be validated before marshalling in a D-Bus message
 // or using them after unmarshalling.  We disallow descriptors to a
 // directory to reduce the security risks.  Splitting out validation
 // also allows the caller to do this work on the File thread to conform
 // with i/o restrictions.
 class CHROME_DBUS_EXPORT FileDescriptor {
  public:
+  // This provides a simple way to pass around file descriptors since they must
+  // be closed on a thread that is allowed to perform I/O.
+  struct Deleter {
+    void CHROME_DBUS_EXPORT operator()(FileDescriptor* fd);
+  };
+
   // Permits initialization without a value for passing to
   // dbus::MessageReader::PopFileDescriptor to fill in and from int values.
   FileDescriptor() : value_(-1), owner_(false), valid_(false) {}
   explicit FileDescriptor(int value) : value_(value), owner_(false),
       valid_(false) {}
 
   virtual ~FileDescriptor();
 
   // Retrieves value as an int without affecting ownership.
   int value() const;
@@ skipping 17 matching lines @@
   void CheckValidity();
 
  private:
   int value_;
   bool owner_;
   bool valid_;
 
   DISALLOW_COPY_AND_ASSIGN(FileDescriptor);
 };
 
+using ScopedFileDescriptor =
+    scoped_ptr<FileDescriptor, FileDescriptor::Deleter>;
+
 }  // namespace dbus
 
 #endif  // DBUS_FILE_DESCRIPTOR_H_