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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
//
// Handle ACK tracking for reliability layer
#pragma once
#include <deque>
#include <algorithm>
#include <limits>
#include <openvpn/common/socktypes.hpp>
#include <openvpn/buffer/buffer.hpp>
#include <openvpn/crypto/packet_id_control.hpp>
#include <openvpn/reliable/relcommon.hpp>
namespace openvpn {
class ReliableAck
{
public:
static constexpr size_t maximum_acks_ack_v1 = 8;
static constexpr size_t maximum_acks_control_v1 = 4;
typedef reliable::id_t id_t;
explicit ReliableAck() = default;
size_t size() const;
bool empty() const;
bool acks_ready() const;
void push_back(id_t value)
{
data.push_back(value);
}
id_t front() const
{
return data.front();
}
void pop_front()
{
data.pop_front();
}
// Called to read incoming ACK IDs from buf and mark them as ACKed in rel_send.
// If live is false, read the ACK IDs, but don't modify rel_send.
// Return the number of ACK IDs read.
template <typename REL_SEND>
static size_t ack(REL_SEND &rel_send, Buffer &buf, const bool live)
{
const size_t len = buf.pop_front();
for (size_t i = 0; i < len; ++i)
{
const id_t id = read_id(buf);
if (live)
rel_send.ack(id);
}
return len;
}
static size_t ack_skip(Buffer &buf)
{
const size_t len = buf.pop_front();
for (size_t i = 0; i < len; ++i)
read_id(buf);
return len;
}
// copy ACKs from buffer to self
void read(Buffer &buf)
{
const size_t len = buf.pop_front();
for (size_t i = 0; i < len; ++i)
{
const id_t id = read_id(buf);
data.push_back(id);
}
}
/**
* handles the reACK logic and reACK/ACK list manipulation. pulls as many repeated ACKs as we can fit
* into the packet from the reACK queue, and pushes the fresh never-been-ACKed ids into the other end
* of the reACK queue. Enforces a limit on the size of the reACK queue and may discard reACKs sometimes.
*
*/
void prepend(Buffer &buf, bool ackv1)
{
size_t max_acks = ackv1 ? maximum_acks_ack_v1 : maximum_acks_control_v1;
size_t acks_added = 0;
while (acks_added < max_acks && data.size() > 0)
{
auto ack = data.front();
data.pop_front();
prepend_id(buf, ack);
acks_added++;
add_ack_to_reack(ack);
}
/* the already pushed acks are in front of the re_acks list, so we
* skip over them */
while (acks_added < re_acks.size() && acks_added < max_acks)
{
prepend_id(buf, re_acks[acks_added]);
acks_added++;
}
buf.push_front((unsigned char)acks_added);
}
static void prepend_id(Buffer &buf, const id_t id)
{
const id_t net_id = htonl(id);
buf.prepend((unsigned char *)&net_id, sizeof(net_id));
}
static id_t read_id(Buffer &buf)
{
id_t net_id;
buf.read((unsigned char *)&net_id, sizeof(net_id));
return ntohl(net_id);
}
size_t resend_size();
private:
void add_ack_to_reack(id_t ack);
std::deque<id_t> data;
std::deque<id_t> re_acks;
};
/**
* Returns the number of outstanding ACKs that have been sent.
*/
inline size_t ReliableAck::size() const
{
return data.size();
}
/**
* Returns true if all outstanding ACKs are empty, otherwise false. Acks
* that can be resend are ignored.
*
* @return Returns true if all ACKs are empty, otherwise false;
*
*/
inline bool ReliableAck::empty() const
{
return data.empty();
}
/**
* Returns true if either outstanding acks are present or ACKs for resending
* are present.
*
*/
inline bool ReliableAck::acks_ready() const
{
return !data.empty() || !re_acks.empty();
}
inline void ReliableAck::add_ack_to_reack(id_t ack)
{
/* Check if the element is already in the array to avoid duplicates */
for (auto it = re_acks.begin(); it != re_acks.end(); it++)
{
if (*it == ack)
{
re_acks.erase(it);
break;
}
}
re_acks.push_front(ack);
if (re_acks.size() > maximum_acks_ack_v1)
{
re_acks.pop_back();
}
}
inline size_t ReliableAck::resend_size()
{
return re_acks.size();
}
} // namespace openvpn
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