blob: 6843498899162392c7089f3e46da4145494ace03 [file] [log] [blame]
// 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.
// 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 the Right Thing will get done.
#include <vector>
#include "base/compiler_specific.h"
namespace base {
// A Delegate which performs the actions required to perform an injective
// multimapping in place.
class InjectionDelegate {
// Duplicate |fd|, an element of the domain, and write a fresh element of the
// domain into |result|. Returns true iff successful.
virtual bool Duplicate(int* result, int fd) = 0;
// Destructively move |src| to |dest|, overwriting |dest|. Returns true iff
// successful.
virtual bool Move(int src, int dest) = 0;
// Delete an element of the domain.
virtual void Close(int fd) = 0;
virtual ~InjectionDelegate() = default;
// An implementation of the InjectionDelegate interface using the file
// descriptor table of the current process as the domain.
class FileDescriptorTableInjection : public InjectionDelegate {
bool Duplicate(int* result, int fd) override;
bool Move(int src, int dest) override;
void Close(int fd) override;
// A single arc of the directed graph which describes an injective multimapping.
struct InjectionArc {
InjectionArc(int in_source, int in_dest, bool in_close)
: source(in_source), dest(in_dest), close(in_close) {}
int source;
int dest;
bool close; // if true, delete the source element after performing the
// mapping.
typedef std::vector<InjectionArc> InjectiveMultimap;
bool PerformInjectiveMultimap(const InjectiveMultimap& map,
InjectionDelegate* delegate);
bool PerformInjectiveMultimapDestructive(InjectiveMultimap* map,
InjectionDelegate* delegate);
// This function will not call malloc but will mutate |map|
static inline bool ShuffleFileDescriptors(InjectiveMultimap* map) {
FileDescriptorTableInjection delegate;
return PerformInjectiveMultimapDestructive(map, &delegate);
} // namespace base