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// -----------------------------------------------------------------------------
20class 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_
115