ipc/file_descriptor_set_posix.h

   1 // Copyright (c) 2011 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/memory/ref_counted.h"
  13 #include "ipc/ipc_export.h"
  14
  15 // -----------------------------------------------------------------------------
  16 // A FileDescriptorSet is an ordered set of POSIX file descriptors. These are
  17 // associated with IPC messages so that descriptors can be transmitted over a
  18 // UNIX domain socket.
  19 // -----------------------------------------------------------------------------
  20 class IPC_EXPORT FileDescriptorSet
  21     : public base::RefCountedThreadSafe<FileDescriptorSet> {
  22  public:
  23   FileDescriptorSet();
  24
  25   // This is the maximum number of descriptors per message. We need to know this
  26   // because the control message kernel interface has to be given a buffer which
  27   // is large enough to store all the descriptor numbers. Otherwise the kernel
  28   // tells us that it truncated the control data and the extra descriptors are
  29   // lost.
  30   //
  31   // In debugging mode, it's a fatal error to try and add more than this number
  32   // of descriptors to a FileDescriptorSet.
  33   static const size_t kMaxDescriptorsPerMessage = 5;
  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   // Returns true if any contained file descriptors appear to be handles to a
  78   // directory.
  79   bool ContainsDirectoryDescriptor() const;
  80
  81   // ---------------------------------------------------------------------------
  82
  83
  84   // ---------------------------------------------------------------------------
  85   // Interfaces for receiving...
  86
  87   // Set the contents of the set from the given buffer. This set must be empty
  88   // before calling. The auto-close flag is set on all the descriptors so that
  89   // unconsumed descriptors are closed on destruction.
  90   void SetDescriptors(const int* buffer, unsigned count);
  91
  92   // ---------------------------------------------------------------------------
  93
  94  private:
  95   friend class base::RefCountedThreadSafe<FileDescriptorSet>;
  96
  97   ~FileDescriptorSet();
  98
  99   // A vector of descriptors and close flags. If this message is sent, then
 100   // these descriptors are sent as control data. After sending, any descriptors
 101   // with a true flag are closed. If this message has been received, then these
 102   // are the descriptors which were received and all close flags are true.
 103   std::vector<base::FileDescriptor> descriptors_;
 104
 105   // This contains the index of the next descriptor which should be consumed.
 106   // It's used in a couple of ways. Firstly, at destruction we can check that
 107   // all the descriptors have been read (with GetNthDescriptor). Secondly, we
 108   // can check that they are read in order.
 109   mutable unsigned consumed_descriptor_highwater_;
 110
 111   DISALLOW_COPY_AND_ASSIGN(FileDescriptorSet);
 112 };
 113
 114 #endif  // IPC_FILE_DESCRIPTOR_SET_POSIX_H_