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diff --git a/ipc/file_descriptor_set_posix.h b/ipc/file_descriptor_set_posix.h
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+++ b/ipc/file_descriptor_set_posix.h
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+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IPC_FILE_DESCRIPTOR_SET_POSIX_H_
+#define IPC_FILE_DESCRIPTOR_SET_POSIX_H_
+#pragma once
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/file_descriptor_posix.h"
+#include "base/memory/ref_counted.h"
+#include "ipc/ipc_export.h"
+
+// -----------------------------------------------------------------------------
+// A FileDescriptorSet is an ordered set of POSIX file descriptors. These are
+// associated with IPC messages so that descriptors can be transmitted over a
+// UNIX domain socket.
+// -----------------------------------------------------------------------------
+class IPC_EXPORT FileDescriptorSet
+    : public base::RefCountedThreadSafe<FileDescriptorSet> {
+ public:
+  FileDescriptorSet();
+
+  // This is the maximum number of descriptors per message. We need to know this
+  // because the control message kernel interface has to be given a buffer which
+  // is large enough to store all the descriptor numbers. Otherwise the kernel
+  // tells us that it truncated the control data and the extra descriptors are
+  // lost.
+  //
+  // In debugging mode, it's a fatal error to try and add more than this number
+  // of descriptors to a FileDescriptorSet.
+  enum {
+    MAX_DESCRIPTORS_PER_MESSAGE = 5,
+  };
+
+  // ---------------------------------------------------------------------------
+  // Interfaces for building during message serialisation...
+
+  // Add a descriptor to the end of the set. Returns false iff the set is full.
+  bool Add(int fd);
+  // Add a descriptor to the end of the set and automatically close it after
+  // transmission. Returns false iff the set is full.
+  bool AddAndAutoClose(int fd);
+
+  // ---------------------------------------------------------------------------
+
+
+  // ---------------------------------------------------------------------------
+  // Interfaces for accessing during message deserialisation...
+
+  // Return the number of descriptors
+  unsigned size() const { return descriptors_.size(); }
+  // Return true if no unconsumed descriptors remain
+  bool empty() const { return descriptors_.empty(); }
+  // Fetch the nth descriptor from the beginning of the set. Code using this
+  // /must/ access the descriptors in order, except that it may wrap from the
+  // end to index 0 again.
+  //
+  // This interface is designed for the deserialising code as it doesn't
+  // support close flags.
+  //   returns: file descriptor, or -1 on error
+  int GetDescriptorAt(unsigned n) const;
+
+  // ---------------------------------------------------------------------------
+
+
+  // ---------------------------------------------------------------------------
+  // Interfaces for transmission...
+
+  // Fill an array with file descriptors without 'consuming' them. CommitAll
+  // must be called after these descriptors have been transmitted.
+  //   buffer: (output) a buffer of, at least, size() integers.
+  void GetDescriptors(int* buffer) const;
+  // This must be called after transmitting the descriptors returned by
+  // GetDescriptors. It marks all the descriptors as consumed and closes those
+  // which are auto-close.
+  void CommitAll();
+  // Returns true if any contained file descriptors appear to be handles to a
+  // directory.
+  bool ContainsDirectoryDescriptor() const;
+
+  // ---------------------------------------------------------------------------
+
+
+  // ---------------------------------------------------------------------------
+  // Interfaces for receiving...
+
+  // Set the contents of the set from the given buffer. This set must be empty
+  // before calling. The auto-close flag is set on all the descriptors so that
+  // unconsumed descriptors are closed on destruction.
+  void SetDescriptors(const int* buffer, unsigned count);
+
+  // ---------------------------------------------------------------------------
+
+ private:
+  friend class base::RefCountedThreadSafe<FileDescriptorSet>;
+
+  ~FileDescriptorSet();
+
+  // A vector of descriptors and close flags. If this message is sent, then
+  // these descriptors are sent as control data. After sending, any descriptors
+  // with a true flag are closed. If this message has been received, then these
+  // are the descriptors which were received and all close flags are true.
+  std::vector<base::FileDescriptor> descriptors_;
+
+  // This contains the index of the next descriptor which should be consumed.
+  // It's used in a couple of ways. Firstly, at destruction we can check that
+  // all the descriptors have been read (with GetNthDescriptor). Secondly, we
+  // can check that they are read in order.
+  mutable unsigned consumed_descriptor_highwater_;
+
+  DISALLOW_COPY_AND_ASSIGN(FileDescriptorSet);
+};
+
+#endif  // IPC_FILE_DESCRIPTOR_SET_POSIX_H_