ipc/file_descriptor_set_posix.h

   1 // Copyright (c) 2006-2009 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 IPC_FILE_DESCRIPTOR_SET_POSIX_H_
   6 #define IPC_FILE_DESCRIPTOR_SET_POSIX_H_
   7
   8 #include <vector>
   9
  10 #include "base/basictypes.h"
  11 #include "base/file_descriptor_posix.h"
  12 #include "base/ref_counted.h"
  13
  14 // -----------------------------------------------------------------------------
  15 // A FileDescriptorSet is an ordered set of POSIX file descriptors. These are
  16 // associated with IPC messages so that descriptors can be transmitted over a
  17 // UNIX domain socket.
  18 // -----------------------------------------------------------------------------
  19 class FileDescriptorSet : public base::RefCountedThreadSafe<FileDescriptorSet> {
  20  public:
  21   FileDescriptorSet();
  22
  23   // This is the maximum number of descriptors per message. We need to know this
  24   // because the control message kernel interface has to be given a buffer which
  25   // is large enough to store all the descriptor numbers. Otherwise the kernel
  26   // tells us that it truncated the control data and the extra descriptors are
  27   // lost.
  28   //
  29   // In debugging mode, it's a fatal error to try and add more than this number
  30   // of descriptors to a FileDescriptorSet.
  31   enum {
  32     MAX_DESCRIPTORS_PER_MESSAGE = 4,
  33   };
  34
  35   // ---------------------------------------------------------------------------
  36   // Interfaces for building during message serialisation...
  37
  38   // Add a descriptor to the end of the set. Returns false iff the set is full.
  39   bool Add(int fd);
  40   // Add a descriptor to the end of the set and automatically close it after
  41   // transmission. Returns false iff the set is full.
  42   bool AddAndAutoClose(int fd);
  43
  44   // ---------------------------------------------------------------------------
  45
  46
  47   // ---------------------------------------------------------------------------
  48   // Interfaces for accessing during message deserialisation...
  49
  50   // Return the number of descriptors
  51   unsigned size() const { return descriptors_.size(); }
  52   // Return true if no unconsumed descriptors remain
  53   bool empty() const { return descriptors_.empty(); }
  54   // Fetch the nth descriptor from the beginning of the set. Code using this
  55   // /must/ access the descriptors in order, except that it may wrap from the
  56   // end to index 0 again.
  57   //
  58   // This interface is designed for the deserialising code as it doesn't
  59   // support close flags.
  60   //   returns: file descriptor, or -1 on error
  61   int GetDescriptorAt(unsigned n) const;
  62
  63   // ---------------------------------------------------------------------------
  64
  65
  66   // ---------------------------------------------------------------------------
  67   // Interfaces for transmission...
  68
  69   // Fill an array with file descriptors without 'consuming' them. CommitAll
  70   // must be called after these descriptors have been transmitted.
  71   //   buffer: (output) a buffer of, at least, size() integers.
  72   void GetDescriptors(int* buffer) const;
  73   // This must be called after transmitting the descriptors returned by
  74   // GetDescriptors. It marks all the descriptors as consumed and closes those
  75   // which are auto-close.
  76   void CommitAll();
  77
  78   // ---------------------------------------------------------------------------
  79
  80
  81   // ---------------------------------------------------------------------------
  82   // Interfaces for receiving...
  83
  84   // Set the contents of the set from the given buffer. This set must be empty
  85   // before calling. The auto-close flag is set on all the descriptors so that
  86   // unconsumed descriptors are closed on destruction.
  87   void SetDescriptors(const int* buffer, unsigned count);
  88
  89   // ---------------------------------------------------------------------------
  90
  91  private:
  92   friend class base::RefCountedThreadSafe<FileDescriptorSet>;
  93
  94   ~FileDescriptorSet();
  95
  96   // A vector of descriptors and close flags. If this message is sent, then
  97   // these descriptors are sent as control data. After sending, any descriptors
  98   // with a true flag are closed. If this message has been received, then these
  99   // are the descriptors which were received and all close flags are true.
 100   std::vector<base::FileDescriptor> descriptors_;
 101
 102   // This contains the index of the next descriptor which should be consumed.
 103   // It's used in a couple of ways. Firstly, at destruction we can check that
 104   // all the descriptors have been read (with GetNthDescriptor). Secondly, we
 105   // can check that they are read in order.
 106   mutable unsigned consumed_descriptor_highwater_;
 107
 108   DISALLOW_COPY_AND_ASSIGN(FileDescriptorSet);
 109 };
 110
 111 #endif  // IPC_FILE_DESCRIPTOR_SET_POSIX_H_