congestvpn/VpnPacket.cpp

#include "VpnPacket.hpp"
#include "VpnPeer.hpp"

#include <chrono>
#include <cstring>

const size_t VpnPacket::VPN_HEADER_BYTES = 8;
const size_t VpnPacket::TLV_HEADER_BYTES = 3;

static const size_t OUTER_HEADERS_BYTES =
    40 /* IPv6 header */ + 8 /* UDP header */;
    // We use a TUN device, hence we don't have a layer 2 header.

static const int
    DATA_SEQNO_POS = 0,
    DATA_TIMESTAMP_POS = 4;

VpnPacket::VpnPacket(size_t mtu)
    : _peer(nullptr), _data_space(mtu-OUTER_HEADERS_BYTES),
      _data_size(VPN_HEADER_BYTES), _reception_timestamp(0)
{
    _data = new char[mtu - OUTER_HEADERS_BYTES];
}

VpnPacket::~VpnPacket() {
    delete[] _data;
}

VpnPacketTLV VpnPacket::first_tlv() {
    return VpnPacketTLV(*this, 0);
}

size_t VpnPacket::get_tunnelled_mtu(size_t udp_mtu) {
    return udp_mtu - OUTER_HEADERS_BYTES - VPN_HEADER_BYTES - TLV_HEADER_BYTES;
}

uint32_t VpnPacket::get_seqno() const {
    return *(uint32_t*)(_data + DATA_SEQNO_POS);
}

uint32_t VpnPacket::get_sending_timestamp() const {
    return *(uint32_t*)(_data + DATA_TIMESTAMP_POS);
}

void VpnPacket::prepare_for_sending() {
    *(uint32_t*)(_data + DATA_SEQNO_POS) = next_seqno();
    *(uint32_t*)(_data + DATA_TIMESTAMP_POS) =
        std::chrono::time_point_cast<std::chrono::microseconds>(
                std::chrono::steady_clock::now()).time_since_epoch().count();
}

void VpnPacket::upon_reception() {
    _reception_timestamp =
        std::chrono::time_point_cast<std::chrono::microseconds>(
                std::chrono::steady_clock::now()).time_since_epoch().count();
}

uint32_t VpnPacket::next_seqno() {
    if(!_peer)
        throw PeerNotSet();
    return _peer->next_seqno();
}


VpnPacketTLV::VpnPacketTLV(VpnPacket& packet, size_t payload_offset)
    : _packet(packet), _tlv_pos(payload_offset)
{}

VpnPacketTLV::VpnPacketTLV(const VpnPacketTLV& other) :
    _packet(other._packet), _tlv_pos(other._tlv_pos)
{}

VpnPacketTLV VpnPacketTLV::create(
        VpnPacket& packet, VpnPacket::PayloadType type)
{
    VpnPacketTLV tlv = VpnPacketTLV(packet, packet.get_payload_size());
    packet.increase_payload_size(VpnPacket::TLV_HEADER_BYTES);

    char* data = tlv.get_data();
    data[0] = type;
    *(uint16_t*)(data+1) = 0; // Set len to 0

    return tlv;
}

VpnPacketTLV VpnPacketTLV::next_tlv() {
    size_t next_offset = _tlv_pos + get_payload_size();
    return VpnPacketTLV(_packet, next_offset);
}

void VpnPacketTLV::seek_next_tlv() {
    _tlv_pos = _tlv_pos + VpnPacket::TLV_HEADER_BYTES + get_payload_size();
}

uint16_t VpnPacketTLV::get_payload_size() const {
    return *(uint16_t*)(get_data() + 1);
}
void VpnPacketTLV::set_payload_size(uint16_t size) {
    uint16_t* data_size_ptr = (uint16_t*)(get_data() + 1);
    uint16_t old_size = *data_size_ptr;
    *data_size_ptr = size;
    _packet.increase_payload_size(size - old_size);
}

uint16_t VpnPacketTLV::get_payload_space() const {
    return _packet.get_payload_space()
        - _packet.get_payload_size()
        + get_payload_size();
}

VpnPacket::PayloadType VpnPacketTLV::get_type() const {
    return (VpnPacket::PayloadType)(*(uint8_t*)(get_data()));
}
void VpnPacketTLV::set_type(VpnPacket::PayloadType type) {
    *(uint8_t*)(get_data()) = (uint8_t) type;
}

TunnelledPacket::TunnelledPacket(VpnPacket& packet, size_t payload_offset)
    : VpnPacketTLV(packet, payload_offset)
{}

TunnelledPacket::TunnelledPacket(const VpnPacketTLV& copy)
    : VpnPacketTLV(copy._packet, copy._tlv_pos)
{}

TunnelledPacket TunnelledPacket::create(VpnPacket& packet) {
    return VpnPacketTLV::create(packet, VpnPacket::PAYLOAD_TYPE_TUNNELLED);
}

bool TunnelledPacket::parse_as_ipv6() {
    return parse_ipv6_header(get_payload(), get_payload_size(), _ipv6_header);
}