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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef DBUS_FILE_DESCRIPTOR_H_
      6 #define DBUS_FILE_DESCRIPTOR_H_
      7 
      8 #include "base/memory/scoped_ptr.h"
      9 #include "base/move.h"
     10 #include "dbus/dbus_export.h"
     11 
     12 namespace dbus {
     13 
     14 // FileDescriptor is a type used to encapsulate D-Bus file descriptors
     15 // and to follow the RAII idiom appropiate for use with message operations
     16 // where the descriptor might be easily leaked.  To guard against this the
     17 // descriptor is closed when an instance is destroyed if it is owned.
     18 // Ownership is asserted only when PutValue is used and TakeValue can be
     19 // used to take ownership.
     20 //
     21 // For example, in the following
     22 //  FileDescriptor fd;
     23 //  if (!reader->PopString(&name) ||
     24 //      !reader->PopFileDescriptor(&fd) ||
     25 //      !reader->PopUint32(&flags)) {
     26 // the descriptor in fd will be closed if the PopUint32 fails.  But
     27 //   writer.AppendFileDescriptor(dbus::FileDescriptor(1));
     28 // will not automatically close "1" because it is not owned.
     29 //
     30 // Descriptors must be validated before marshalling in a D-Bus message
     31 // or using them after unmarshalling.  We disallow descriptors to a
     32 // directory to reduce the security risks.  Splitting out validation
     33 // also allows the caller to do this work on the File thread to conform
     34 // with i/o restrictions.
     35 class CHROME_DBUS_EXPORT FileDescriptor {
     36   MOVE_ONLY_TYPE_FOR_CPP_03(FileDescriptor);
     37 
     38  public:
     39   // This provides a simple way to pass around file descriptors since they must
     40   // be closed on a thread that is allowed to perform I/O.
     41   struct Deleter {
     42     void CHROME_DBUS_EXPORT operator()(FileDescriptor* fd);
     43   };
     44 
     45   // Permits initialization without a value for passing to
     46   // dbus::MessageReader::PopFileDescriptor to fill in and from int values.
     47   FileDescriptor() : value_(-1), owner_(false), valid_(false) {}
     48   explicit FileDescriptor(int value) : value_(value), owner_(false),
     49       valid_(false) {}
     50 
     51   FileDescriptor(FileDescriptor&& other);
     52 
     53   virtual ~FileDescriptor();
     54 
     55   FileDescriptor& operator=(FileDescriptor&& other);
     56 
     57   // Retrieves value as an int without affecting ownership.
     58   int value() const;
     59 
     60   // Retrieves whether or not the descriptor is ok to send/receive.
     61   int is_valid() const { return valid_; }
     62 
     63   // Sets the value and assign ownership.
     64   void PutValue(int value) {
     65     value_ = value;
     66     owner_ = true;
     67     valid_ = false;
     68   }
     69 
     70   // Takes the value and ownership.
     71   int TakeValue();
     72 
     73   // Checks (and records) validity of the file descriptor.
     74   // We disallow directories to avoid potential sandbox escapes.
     75   // Note this call must be made on a thread where file i/o is allowed.
     76   void CheckValidity();
     77 
     78  private:
     79   void Swap(FileDescriptor* other);
     80 
     81   int value_;
     82   bool owner_;
     83   bool valid_;
     84 };
     85 
     86 using ScopedFileDescriptor =
     87     scoped_ptr<FileDescriptor, FileDescriptor::Deleter>;
     88 
     89 }  // namespace dbus
     90 
     91 #endif  // DBUS_FILE_DESCRIPTOR_H_
     92