POSIX: Transfer network data using shared memory

chrome/common/file_descriptor_posix.h

-// Copyright (c) 2006-2009 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.
-
-#ifndef CHROME_COMMON_FILE_DESCRIPTOR_POSIX_H_
-#define CHROME_COMMON_FILE_DESCRIPTOR_POSIX_H_
-
-#include <vector>
-
-// -----------------------------------------------------------------------------
-// A FileDescriptor is a structure for use in IPC messages. It allows one to
-// send descriptors over an IPC channel.
-//
-// In the Windows world, processes can peek and poke the HANDLE table of other
-// processes. On POSIX, in order to transmit descriptors we need to include
-// them in a control-message (a side-channel on the UNIX domain socket).
-// Serialising this type adds descriptors to a vector in the IPC Message, from
-// which the IPC channel can package them up for the kernel.
-// -----------------------------------------------------------------------------
-struct FileDescriptor {
-  FileDescriptor()
-      : fd(-1),
-        auto_close(false) { }
-
-  int fd;
-  // If true, close this descriptor after it has been sent.
-  bool auto_close;
-};
-
-// -----------------------------------------------------------------------------
-// A DescriptorSet 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 DescriptorSet {
- public:
-  DescriptorSet();
-  ~DescriptorSet();
-
-  // 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 DescriptorSet.
-  enum {
-    MAX_DESCRIPTORS_PER_MESSAGE = 4,
-  };
-
-  // ---------------------------------------------------------------------------
-  // Interfaces for building during message serialisation...
-
-  // Add a descriptor to the end of the set
-  void Add(int fd);
-  // Add a descriptor to the end of the set and automatically close it after
-  // transmission.
-  void AddAndAutoClose(int fd);
-
-  // ---------------------------------------------------------------------------
-
-
-  // ---------------------------------------------------------------------------
-  // Interfaces for accessing during message deserialisation...
-
-  // Return the number of descriptors remaining
-  unsigned size() const { return descriptors_.size() - next_descriptor_; }
-  // Return true if no unconsumed descriptors remain
-  bool empty() const { return descriptors_.size() == next_descriptor_; }
-  // Fetch the next descriptor from the beginning of the set. This interface is
-  // designed for the deserialising code as it doesn't support close flags.
-  //   returns: file descriptor, or -1 on error
-  int NextDescriptor();
-
-  // ---------------------------------------------------------------------------
-
-
-  // ---------------------------------------------------------------------------
-  // 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 GetDescriptors(int* buffer) const;
-  // This must be called after transmitting the descriptors returned by
-  // GetDescriptors. It marks all the descriptors as consumed and closes those
-  // which are auto-close.
-  void CommitAll();
-
-  // ---------------------------------------------------------------------------
-
-
-  // ---------------------------------------------------------------------------
-  // 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 SetDescriptors(const int* buffer, unsigned count);
-
-  // ---------------------------------------------------------------------------
-
-  // ---------------------------------------------------------------------------
-  // Interfaces for IPC::Message...
-
-  // Take all the FileDescriptors from another set. Just like a copy
-  // constructor, except that the source is emptied.
-  void TakeFrom(DescriptorSet* other);
-
-  // ---------------------------------------------------------------------------
-
- private:
-  // 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<FileDescriptor> descriptors_;
-  // When deserialising the message, the descriptors will be extracted
-  // one-by-one. This contains the index of the next unused descriptor.
-  unsigned next_descriptor_;
-};
-
-#endif  // CHROME_COMMON_FILE_DESCRIPTOR_POSIX_H_