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diff --git a/ipc/glue/FileDescriptorShuffle.h b/ipc/glue/FileDescriptorShuffle.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_ipc_FileDescriptorShuffle_h
+#define mozilla_ipc_FileDescriptorShuffle_h
+
+#include "mozilla/Span.h"
+#include "nsTArray.h"
+
+#include <functional>
+#include <utility>
+
+// This class converts a set of file descriptor mapping, which may
+// contain conflicts (like {a->b, b->c} or {a->b, b->a}) into a
+// sequence of dup2() operations that can be performed between fork
+// and exec, or with posix_spawn_file_actions_adddup2.  It may create
+// temporary duplicates of fds to use as the source of a dup2; they
+// are closed on destruction.
+//
+// The dup2 sequence is guaranteed to not contain dup2(x, x) for any
+// x; if such an element is present in the input, it will be dup2()ed
+// from a temporary fd to ensure that the close-on-exec bit is cleared.
+//
+// In general, this is *not* guaranteed to minimize the use of
+// temporary fds.
+
+namespace mozilla {
+namespace ipc {
+
+class FileDescriptorShuffle {
+ public:
+  FileDescriptorShuffle() = default;
+  ~FileDescriptorShuffle();
+
+  using MappingRef = mozilla::Span<const std::pair<int, int>>;
+
+  // Translate the given mapping, creating temporary fds as needed.
+  // Can fail (return false) on failure to duplicate fds.
+  bool Init(MappingRef aMapping);
+
+  // Accessor for the dup2() sequence.  Do not use the returned value
+  // or the fds contained in it after this object is destroyed.
+  MappingRef Dup2Sequence() const { return mMapping; }
+
+  // Tests whether the given fd is used as a destination in this mapping.
+  // Can be used to close other fds after performing the dup2()s.
+  bool MapsTo(int aFd) const;
+
+  // Forget the information, so that it's destructor will not try to
+  // delete FDs duped by itself.
+  void Forget() { mTempFds.Clear(); }
+
+ private:
+  nsTArray<std::pair<int, int>> mMapping;
+  nsTArray<int> mTempFds;
+  int mMaxDst;
+
+  FileDescriptorShuffle(const FileDescriptorShuffle&) = delete;
+  void operator=(const FileDescriptorShuffle&) = delete;
+};
+
+}  // namespace ipc
+}  // namespace mozilla
+
+#endif  // mozilla_ipc_FileDescriptorShuffle_h