chromium/base/posix/file_descriptor_shuffle.h

// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_
#define BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_

// This code exists to shuffle file descriptors, which is commonly needed when
// forking subprocesses. The naive approach (just call dup2 to set up the
// desired descriptors) is very simple, but wrong: it won't handle edge cases
// (like mapping 0 -> 1, 1 -> 0) correctly.
//
// In order to unittest this code, it's broken into the abstract action (an
// injective multimap) and the concrete code for dealing with file descriptors.
// Users should use the code like this:
//   base::InjectiveMultimap file_descriptor_map;
//   file_descriptor_map.push_back(base::InjectionArc(devnull, 0, true));
//   file_descriptor_map.push_back(base::InjectionArc(devnull, 2, true));
//   file_descriptor_map.push_back(base::InjectionArc(pipe[1], 1, true));
//   base::ShuffleFileDescriptors(file_descriptor_map);
//
// and trust the Right Thing will get done.

#include <vector>

#include "base/base_export.h"
#include "base/compiler_specific.h"

namespace base {

// A Delegate which performs the actions required to perform an injective
// multimapping in place.
class InjectionDelegate { … };

// An implementation of the InjectionDelegate interface using the file
// descriptor table of the current process as the domain.
class BASE_EXPORT FileDescriptorTableInjection : public InjectionDelegate { … };

// A single arc of the directed graph which describes an injective multimapping.
struct InjectionArc { … };

InjectiveMultimap;

BASE_EXPORT bool PerformInjectiveMultimap(const InjectiveMultimap& map,
                                          InjectionDelegate* delegate);

BASE_EXPORT bool PerformInjectiveMultimapDestructive(
    InjectiveMultimap* map,
    InjectionDelegate* delegate);

// This function will not call malloc but will mutate |map|
inline bool ShuffleFileDescriptors(InjectiveMultimap* map) { … }

}  // namespace base

#endif  // BASE_POSIX_FILE_DESCRIPTOR_SHUFFLE_H_