Add PacketLossManager

Those packets are probably packets truncated because the buffer is not
large enough.

TunDevice.cpp

@@ -72,6 +72,31 @@ TunDevice::~TunDevice() {
     close(_fd);
 }
 
+uint16_t TunDevice::get_mtu() const {
+    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);  // Any socket will do
+
+    struct ifreq ifr;
+    ifr.ifr_addr.sa_family = AF_INET6;
+    strncpy(ifr.ifr_name, _dev_name.c_str(), sizeof(ifr.ifr_name)-1);
+    if (ioctl(sockfd, SIOCGIFMTU, (caddr_t)&ifr) < 0)
+        return 0;
+    close(sockfd);
+    return ifr.ifr_mtu;
+}
+
+bool TunDevice::set_mtu(uint16_t mtu) {
+    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);  // Any socket will do
+
+    struct ifreq ifr;
+    ifr.ifr_addr.sa_family = AF_INET6;
+    strncpy(ifr.ifr_name, _dev_name.c_str(), sizeof(ifr.ifr_name)-1);
+    ifr.ifr_mtu = mtu;
+    if (ioctl(sockfd, SIOCSIFMTU, (caddr_t)&ifr) < 0)
+        return false;
+    close(sockfd);
+    return true;
+}
+
 size_t TunDevice::poll_packet(char* read_buffer, size_t buf_size, int timeout) {
     int poll_rc = poll(&_poll_fd, 1, timeout);
     if(poll_rc < 0) {

TunDevice.hpp

@@ -29,6 +29,12 @@ class TunDevice {
         const std::string& get_dev_name() const { return _dev_name; }
         int get_fd() const { return _fd; }
 
+        /** Get the interface's MTU */
+        uint16_t get_mtu() const;
+
+        /** Set the interface's MTU */
+        bool set_mtu(uint16_t mtu);
+
         /* Reads a packet from the device.
          * Timeouts after `timeout` ms, or never if `timeout < 0`.
          * Upon timeout, returns 0.

UdpVpn.cpp

@@ -16,6 +16,7 @@ static const size_t VPN_MTU = 1460; // TODO determine this -- issue #3
 UdpVpn::UdpVpn()
     : _stopped(false), _vpn_mtu(VPN_MTU), _tun_dev("cvpn%d"), _peer(nullptr)
 {
+    _tun_dev.set_mtu(VpnPacket::get_tunnelled_mtu(_vpn_mtu));
     _socket = socket(AF_INET6, SOCK_DGRAM, 0);
     if(_socket < 0)
         throw UdpVpn::InitializationError("Cannot create socket", errno, true);
@@ -75,13 +76,18 @@ size_t UdpVpn::read_from_tun(char* buffer, size_t len) {
 }
 
 size_t UdpVpn::read_from_tun(TunnelledPacket& packet) {
-    size_t nread =
-        read_from_tun(packet.get_payload(), packet.get_payload_space());
+    size_t payload_space = packet.get_payload_space();
+    size_t nread = read_from_tun(packet.get_payload(), payload_space);
     packet.set_payload_size(nread);
     if(!packet.parse_as_ipv6()) {
         debugf("Ignoring packet with invalid header\n");
         return 0;
     }
+    if(nread != packet.get_ipv6_header().packet_length()) {
+        debugf("Ignoring packet with bad size (expected %d, got %d, buffer %d)\n",
+               packet.get_ipv6_header().packet_length(), nread, payload_space);
+        return 0;
+    }
     return nread;
 }
 

VpnPacket.cpp

@@ -30,6 +30,10 @@ 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);
 }
@@ -98,6 +102,12 @@ void VpnPacketTLV::set_payload_size(uint16_t 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()));
 }

VpnPacket.hpp

@@ -56,6 +56,9 @@ class VpnPacket {
 
         VpnPacketTLV first_tlv();
 
+        /// Get the maximal payload space for a given tunnel MTU
+        static size_t get_tunnelled_mtu(size_t udp_mtu);
+
         /// Set packet peer -- used for sequence numbers
         void set_peer(VpnPeer* peer) { _peer = peer; }
 
@@ -156,10 +159,7 @@ class VpnPacketTLV {
         /// Set the current payload size
         void set_payload_size(uint16_t size);
         /// Get the total available raw data space
-        uint16_t get_payload_space() const {
-            return _packet.get_payload_space()
-                 - _packet.get_payload_size()
-                 - get_payload_size(); }
+        uint16_t get_payload_space() const;
 
         /// Get a pointer to the raw data (const version)
         const char* get_data() const {

VpnPeer.cpp

@@ -7,7 +7,7 @@
 
 VpnPeer::VpnPeer(UdpVpn* vpn, const sockaddr_in6& ext_addr,
         const in6_addr& int_addr)
-    : _vpn(vpn), _ext_addr(ext_addr), _int_addr(int_addr), _next_seqno(0)
+    : _vpn(vpn), _ext_addr(ext_addr), _int_addr(int_addr), _next_send_seqno(0)
 {}
 
 void VpnPeer::set_int_addr(const in6_addr& int_addr) {
@@ -28,3 +28,43 @@ size_t VpnPeer::write(const char* data, size_t len) {
 size_t VpnPeer::write(const VpnPacket& packet) {
     return write(packet.get_data(), packet.get_data_size());
 }
+
+PacketLossLogger::PacketLossLogger() : _cur_seqno(0) {}
+
+void PacketLossLogger::log_packet(uint32_t seqno) {
+    uint32_t m_seqno = seqno % PACKET_LOSS_HISTSIZE;
+    int64_t diff = (int64_t)seqno - _cur_seqno;
+
+    if(diff == 1) {
+        _cur_seqno++;
+        _packet_loss_hist.reset(m_seqno);
+        while(_received_ahead.test((_cur_seqno + 1) % PACKET_LOST_AFTER)) {
+            _cur_seqno++;
+            _packet_loss_hist.reset(_cur_seqno % PACKET_LOSS_HISTSIZE);
+            _received_ahead.reset(_cur_seqno % PACKET_LOST_AFTER);
+        }
+    } else if(LIKELY(diff > 1)) {
+        if(diff < PACKET_LOST_AFTER)
+            _received_ahead.set(seqno % PACKET_LOST_AFTER);
+        else if(diff < PACKET_LOSS_HISTSIZE) {
+            // Packet too much forwards -- consider _cur_seqno lost
+            for(int offs=1; offs < PACKET_LOST_AFTER; ++offs) {
+                _packet_loss_hist[(_cur_seqno + offs) % PACKET_LOSS_HISTSIZE] =
+                    !_received_ahead[(_cur_seqno + offs) % PACKET_LOST_AFTER];
+            }
+            _received_ahead.reset();
+            _cur_seqno = seqno;
+            _packet_loss_hist.reset(m_seqno);
+        } else
+            reboot(); // This is a huge gap -- reboot
+    } else {
+        if(diff < - 2*PACKET_LOSS_HISTSIZE)
+            reboot(); // this is too much backwards -- something's wrong, reboot
+        // else: ignore, we've moved forward and counted the packet as lost
+    }
+}
+
+void PacketLossLogger::reboot() {
+    _packet_loss_hist.reset();
+    _received_ahead.reset();
+}

VpnPeer.hpp

@@ -3,11 +3,40 @@
 /** A peer of a bound (server) instance of UdpVpn */
 
 #include <netinet/in.h>
+#include <bitset>
 #include "util.hpp"
 #include "VpnPacket.hpp"
 
 class UdpVpn;
 
+const int PACKET_LOSS_HISTSIZE = 128, PACKET_LOST_AFTER = 8;
+
+class PacketLossLogger {
+    public:
+        PacketLossLogger();
+        void log_packet(uint32_t seqno);
+        double get_loss_rate() const {
+            return (double)_packet_loss_hist.count() / PACKET_LOSS_HISTSIZE;
+        }
+
+        const std::bitset<PACKET_LOSS_HISTSIZE> get_loss_hist() const {
+            return _packet_loss_hist;
+        }
+
+        const std::bitset<PACKET_LOST_AFTER> get_received_ahead() const {
+            return _received_ahead;
+        }
+
+        uint32_t get_cur_seqno() const { return _cur_seqno; }
+
+    private:
+        void reboot(); ///< completely reset the internal state
+
+        std::bitset<PACKET_LOSS_HISTSIZE> _packet_loss_hist;
+        std::bitset<PACKET_LOST_AFTER> _received_ahead;
+        uint32_t _cur_seqno;
+};
+
 class VpnPeer {
     public:
         class NetError : public MsgException {
@@ -30,12 +59,12 @@ class VpnPeer {
         size_t write(const char* data, size_t len);
         size_t write(const VpnPacket& packet);
 
-        uint32_t peek_next_seqno() const { return _next_seqno; }
-        uint32_t next_seqno() { return _next_seqno++; }
+        uint32_t peek_next_seqno() const { return _next_send_seqno; }
+        uint32_t next_seqno() { return _next_send_seqno++; }
 
     private:
         UdpVpn* _vpn;
         sockaddr_in6 _ext_addr;
         in6_addr _int_addr;
-        uint32_t _next_seqno;
+        uint32_t _next_send_seqno;
 };

ip_header.cpp

@@ -15,5 +15,6 @@ bool parse_ipv6_header(const char* data, size_t len, IPv6Header& header) {
 
     memcpy(&(header.source), data + 8, 16);
     memcpy(&(header.dest), data + 24, 16);
+    header.payload_length = ntohs(*(uint16_t*)(data + 4));
     return true;
 }

ip_header.hpp

@@ -5,6 +5,9 @@
 struct IPv6Header {
     in6_addr source;
     in6_addr dest;
+    uint16_t payload_length;
+
+    uint16_t packet_length() const { return payload_length + 40; }
 };
 
 /** Parse an IPv6 header, filling `header`. Returns `true` on success. */

tests/test_packetloss.cpp

@@ -0,0 +1,48 @@
+#include <cstdio>
+#include <vector>
+#include "VpnPeer.hpp"
+
+template<int len>
+std::string bitset_to_string(
+        const std::bitset<len>& bs,
+        char c_f, char c_t, size_t mark_pos, char cm_f, char cm_t)
+{
+    std::string out;
+    for(size_t pos=0; pos < len; ++pos) {
+        if(pos == mark_pos)
+            out += bs[pos] ? cm_t : cm_f;
+        else
+            out += bs[pos] ? c_t : c_f;
+    }
+    return out;
+}
+
+void dump(PacketLossLogger& pllog, int received) {
+    printf("%03d, %.03lf ## %s ## %s\n",
+            received,
+            pllog.get_loss_rate(),
+            bitset_to_string<PACKET_LOSS_HISTSIZE>(
+                pllog.get_loss_hist(), '_', 'X',
+                pllog.get_cur_seqno() % PACKET_LOSS_HISTSIZE,
+                '|', '#').c_str(),
+            bitset_to_string<PACKET_LOST_AFTER>(
+                pllog.get_received_ahead(), '_', 'X',
+                pllog.get_cur_seqno() % PACKET_LOST_AFTER,
+                '|', '#').c_str());
+}
+
+int main(void) {
+    PacketLossLogger pllog;
+    std::vector<int> sequence({
+        1, 2, 3, 5, 6, 4, 8, 7, 8, 9,
+        12, 13, 14, 15, 16, 17, 18, 19, 20, 10, 21
+    });
+
+    dump(pllog, 0);
+    for(auto val=sequence.begin(); val != sequence.end(); ++val) {
+        pllog.log_packet(*val);
+        dump(pllog, *val);
+    }
+
+    return 0;
+}