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/files/file.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/memory/scoped_vector.h"
  14 #include "ipc/ipc_export.h"
  15
  16 // -----------------------------------------------------------------------------
  17 // A FileDescriptorSet is an ordered set of POSIX file descriptors. These are
  18 // associated with IPC messages so that descriptors can be transmitted over a
  19 // UNIX domain socket.
  20 // -----------------------------------------------------------------------------
  21 class IPC_EXPORT FileDescriptorSet
  22     : public base::RefCountedThreadSafe<FileDescriptorSet> {
  23  public:
  24   FileDescriptorSet();
  25
  26   // This is the maximum number of descriptors per message. We need to know this
  27   // because the control message kernel interface has to be given a buffer which
  28   // is large enough to store all the descriptor numbers. Otherwise the kernel
  29   // tells us that it truncated the control data and the extra descriptors are
  30   // lost.
  31   //
  32   // In debugging mode, it's a fatal error to try and add more than this number
  33   // of descriptors to a FileDescriptorSet.
  34   static const size_t kMaxDescriptorsPerMessage = 7;
  35
  36   // ---------------------------------------------------------------------------
  37   // Interfaces for building during message serialisation...
  38
  39   // Add a descriptor to the end of the set. Returns false iff the set is full.
  40   bool AddToBorrow(base::PlatformFile fd);
  41   // Add a descriptor to the end of the set and automatically close it after
  42   // transmission. Returns false iff the set is full.
  43   bool AddToOwn(base::ScopedFD fd);
  44
  45   // ---------------------------------------------------------------------------
  46
  47
  48   // ---------------------------------------------------------------------------
  49   // Interfaces for accessing during message deserialisation...
  50
  51   // Return the number of descriptors
  52   unsigned size() const { return descriptors_.size(); }
  53   // Return true if no unconsumed descriptors remain
  54   bool empty() const { return 0 == size(); }
  55   // Take the nth descriptor from the beginning of the set,
  56   // transferring the ownership of the descriptor taken. Code using this
  57   // /must/ access the descriptors in order, and must do it at most once.
  58   //
  59   // This interface is designed for the deserialising code as it doesn't
  60   // support close flags.
  61   //   returns: file descriptor, or -1 on error
  62   base::PlatformFile TakeDescriptorAt(unsigned n);
  63
  64   // ---------------------------------------------------------------------------
  65
  66
  67   // ---------------------------------------------------------------------------
  68   // Interfaces for transmission...
  69
  70   // Fill an array with file descriptors without 'consuming' them. CommitAll
  71   // must be called after these descriptors have been transmitted.
  72   //   buffer: (output) a buffer of, at least, size() integers.
  73   void PeekDescriptors(base::PlatformFile* buffer) const;
  74   // This must be called after transmitting the descriptors returned by
  75   // PeekDescriptors. It marks all the descriptors as consumed and closes those
  76   // which are auto-close.
  77   void CommitAll();
  78   // Returns true if any contained file descriptors appear to be handles to a
  79   // directory.
  80   bool ContainsDirectoryDescriptor() const;
  81   // Fetch all filedescriptors with the "auto close" property.
  82   // Used instead of CommitAll() when closing must be handled manually.
  83   void ReleaseFDsToClose(std::vector<base::PlatformFile>* fds);
  84
  85   // ---------------------------------------------------------------------------
  86
  87
  88   // ---------------------------------------------------------------------------
  89   // Interfaces for receiving...
  90
  91   // Set the contents of the set from the given buffer. This set must be empty
  92   // before calling. The auto-close flag is set on all the descriptors so that
  93   // unconsumed descriptors are closed on destruction.
  94   void AddDescriptorsToOwn(const base::PlatformFile* buffer, unsigned count);
  95
  96   // ---------------------------------------------------------------------------
  97
  98  private:
  99   friend class base::RefCountedThreadSafe<FileDescriptorSet>;
 100
 101   ~FileDescriptorSet();
 102
 103   // A vector of descriptors and close flags. If this message is sent, then
 104   // these descriptors are sent as control data. After sending, any descriptors
 105   // with a true flag are closed. If this message has been received, then these
 106   // are the descriptors which were received and all close flags are true.
 107   std::vector<base::PlatformFile> descriptors_;
 108   ScopedVector<base::ScopedFD> owned_descriptors_;
 109
 110   // This contains the index of the next descriptor which should be consumed.
 111   // It's used in a couple of ways. Firstly, at destruction we can check that
 112   // all the descriptors have been read (with GetNthDescriptor). Secondly, we
 113   // can check that they are read in order.
 114   mutable unsigned consumed_descriptor_highwater_;
 115
 116   DISALLOW_COPY_AND_ASSIGN(FileDescriptorSet);
 117 };
 118
 119 #endif  // IPC_FILE_DESCRIPTOR_SET_POSIX_H_