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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 */
#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 {
FileDescriptorShuffle() = default;
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(); }
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