dbus/file_descriptor.h

   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/basictypes.h"
   9 #include "base/memory/scoped_ptr.h"
  10 #include "base/move.h"
  11 #include "dbus/dbus_export.h"
  12
  13 namespace dbus {
  14
  15 // FileDescriptor is a type used to encapsulate D-Bus file descriptors
  16 // and to follow the RAII idiom appropiate for use with message operations
  17 // where the descriptor might be easily leaked.  To guard against this the
  18 // descriptor is closed when an instance is destroyed if it is owned.
  19 // Ownership is asserted only when PutValue is used and TakeValue can be
  20 // used to take ownership.
  21 //
  22 // For example, in the following
  23 //  FileDescriptor fd;
  24 //  if (!reader->PopString(&name) ||
  25 //      !reader->PopFileDescriptor(&fd) ||
  26 //      !reader->PopUint32(&flags)) {
  27 // the descriptor in fd will be closed if the PopUint32 fails.  But
  28 //   writer.AppendFileDescriptor(dbus::FileDescriptor(1));
  29 // will not automatically close "1" because it is not owned.
  30 //
  31 // Descriptors must be validated before marshalling in a D-Bus message
  32 // or using them after unmarshalling.  We disallow descriptors to a
  33 // directory to reduce the security risks.  Splitting out validation
  34 // also allows the caller to do this work on the File thread to conform
  35 // with i/o restrictions.
  36 class CHROME_DBUS_EXPORT FileDescriptor {
  37   MOVE_ONLY_TYPE_FOR_CPP_03(FileDescriptor, RValue);
  38
  39  public:
  40   // This provides a simple way to pass around file descriptors since they must
  41   // be closed on a thread that is allowed to perform I/O.
  42   struct Deleter {
  43     void CHROME_DBUS_EXPORT operator()(FileDescriptor* fd);
  44   };
  45
  46   // Permits initialization without a value for passing to
  47   // dbus::MessageReader::PopFileDescriptor to fill in and from int values.
  48   FileDescriptor() : value_(-1), owner_(false), valid_(false) {}
  49   explicit FileDescriptor(int value) : value_(value), owner_(false),
  50       valid_(false) {}
  51
  52   // Move constructor for C++03 move emulation of this type.
  53   FileDescriptor(RValue other);
  54
  55   virtual ~FileDescriptor();
  56
  57   // Move operator= for C++03 move emulation of this type.
  58   FileDescriptor& operator=(RValue other);
  59
  60   // Retrieves value as an int without affecting ownership.
  61   int value() const;
  62
  63   // Retrieves whether or not the descriptor is ok to send/receive.
  64   int is_valid() const { return valid_; }
  65
  66   // Sets the value and assign ownership.
  67   void PutValue(int value) {
  68     value_ = value;
  69     owner_ = true;
  70     valid_ = false;
  71   }
  72
  73   // Takes the value and ownership.
  74   int TakeValue();
  75
  76   // Checks (and records) validity of the file descriptor.
  77   // We disallow directories to avoid potential sandbox escapes.
  78   // Note this call must be made on a thread where file i/o is allowed.
  79   void CheckValidity();
  80
  81  private:
  82   void Swap(FileDescriptor* other);
  83
  84   int value_;
  85   bool owner_;
  86   bool valid_;
  87 };
  88
  89 using ScopedFileDescriptor =
  90     scoped_ptr<FileDescriptor, FileDescriptor::Deleter>;
  91
  92 }  // namespace dbus
  93
  94 #endif  // DBUS_FILE_DESCRIPTOR_H_