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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.
#include <vector>
#include "base/basictypes.h"
#include "base/files/file.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_vector.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> {
// 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.
static const size_t kMaxDescriptorsPerMessage = 7;
// ---------------------------------------------------------------------------
// Interfaces for building during message serialisation...
// Add a descriptor to the end of the set. Returns false iff the set is full.
bool AddToBorrow(base::PlatformFile fd);
// Add a descriptor to the end of the set and automatically close it after
// transmission. Returns false iff the set is full.
bool AddToOwn(base::ScopedFD 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 0 == size(); }
// Take the nth descriptor from the beginning of the set,
// transferring the ownership of the descriptor taken. Code using this
// /must/ access the descriptors in order, and must do it at most once.
// This interface is designed for the deserialising code as it doesn't
// support close flags.
// returns: file descriptor, or -1 on error
base::PlatformFile TakeDescriptorAt(unsigned n);
// ---------------------------------------------------------------------------
// ---------------------------------------------------------------------------
// 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 PeekDescriptors(base::PlatformFile* buffer) const;
// This must be called after transmitting the descriptors returned by
// PeekDescriptors. 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;
// Fetch all filedescriptors with the "auto close" property.
// Used instead of CommitAll() when closing must be handled manually.
void ReleaseFDsToClose(std::vector<base::PlatformFile>* fds);
// ---------------------------------------------------------------------------
// ---------------------------------------------------------------------------
// 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 AddDescriptorsToOwn(const base::PlatformFile* buffer, unsigned count);
// ---------------------------------------------------------------------------
friend class base::RefCountedThreadSafe<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::PlatformFile> descriptors_;
ScopedVector<base::ScopedFD> owned_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_;