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// OpenVPN -- An application to securely tunnel IP networks
// over a single port, with support for SSL/TLS-based
// session authentication and key exchange,
// packet encryption, packet authentication, and
// packet compression.
//
// Copyright (C) 2012- OpenVPN Inc.
//
// SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
#ifndef OPENVPN_COMMON_MSGWIN_H
#define OPENVPN_COMMON_MSGWIN_H
#include <deque>
#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
// Fundamental, lowest-level object of OpenVPN protocol reliability layer
namespace openvpn {
// MessageWindow --
// On receiving side: used to order packets which may be received out-of-order
// On sending side: used to buffer unacknowledged packets
// M : message class, must define default constructor, defined(), and erase() methods
// id_t : sequence number object, usually unsigned int
template <typename M, typename id_t>
class MessageWindow
{
public:
OPENVPN_SIMPLE_EXCEPTION(message_window_ref_by_id);
OPENVPN_SIMPLE_EXCEPTION(message_window_rm_head);
MessageWindow()
: head_id_(0), span_(0)
{
}
MessageWindow(const id_t starting_head_id, const id_t span)
: head_id_(starting_head_id), span_(span)
{
}
void init(const id_t starting_head_id, const id_t span)
{
head_id_ = starting_head_id;
span_ = span;
q_.clear();
}
// Return true if id is within current window
bool in_window(const id_t id) const
{
return id >= head_id_ && id < head_id_ + span_;
}
// Return true if id is before current window
bool pre_window(const id_t id) const
{
return id < head_id_;
}
// Return a reference to M object at id, throw exception
// if id is not in current window
M &ref_by_id(const id_t id)
{
if (in_window(id))
{
grow(id);
return q_[id - head_id_];
}
else
throw message_window_ref_by_id();
}
// Remove the M object at id, is a no-op if
// id not in window. Do a purge() as a last
// step to advance the head_id_ if it's now
// pointing at undefined M objects.
void rm_by_id(const id_t id)
{
if (in_window(id))
{
grow(id);
M &m = q_[id - head_id_];
m.erase();
}
purge();
}
// Return true if an object at head of queue is defined
bool head_defined() const
{
return (!q_.empty() && q_.front().defined());
}
// Return the id that the object at the head of the queue
// would have (even if it isn't defined yet).
id_t head_id() const
{
return head_id_;
}
// Return the id of one past the end of the window
id_t tail_id() const
{
return head_id_ + span_;
}
// Return the window size
id_t span() const
{
return span_;
}
// Return a reference to the object at the front of the queue
M &ref_head()
{
return q_.front();
}
// Remove the object at head of queue, throw an exception if undefined
void rm_head()
{
if (head_defined())
rm_head_nocheck();
else
throw message_window_rm_head();
}
// Remove the object at head of queue without error checking (other than
// that provided by std::deque object). Don't call this method unless
// head_defined() returns true.
void rm_head_nocheck()
{
q_.front().erase();
q_.pop_front();
++head_id_;
}
private:
// Expand the queue if necessary so that id maps
// to an object in the queue
void grow(const id_t id)
{
const size_t needed_index = id - head_id_;
while (q_.size() <= needed_index)
q_.push_back(M());
}
// Purge all undefined objects at the head of
// the queue, advancing the head_id_
void purge()
{
while (!q_.empty() && q_.front().erased())
{
q_.pop_front();
++head_id_;
}
}
id_t head_id_; // id of msgs[0]
id_t span_;
std::deque<M> q_;
};
} // namespace openvpn
#endif // OPENVPN_COMMON_MSGWIN_H
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