measure packet round trip time

diff --git a/src/net/ConnectionHandler.hpp b/src/net/ConnectionHandler.hpp
index 77bcd7b4da179d8ab52f2c697e7eae2f4da6820f..be01d10add35ab3b597c4cec5c5efa5d8d17f4c5 100644 (file)
--- a/src/net/ConnectionHandler.hpp
+++ b/src/net/ConnectionHandler.hpp
@@ -13,8 +13,12 @@ class ConnectionHandler {
 public:
        ConnectionHandler();
 
+       /// packet loss as factor
        float PacketLoss() const noexcept { return packet_loss; }
+       /// smooth average round trip time in milliseconds
+       float RoundTripTime() const noexcept { return rtt; }
 
+       void PacketSent(std::uint16_t);
        void PacketLost(std::uint16_t);
        void PacketReceived(std::uint16_t);
 
@@ -24,6 +28,9 @@ public:
 
 private:
        void UpdatePacketLoss() noexcept;
+       void UpdateRTT(std::uint16_t) noexcept;
+       bool SamplePacket(std::uint16_t) const noexcept;
+       int HeadDiff(std::uint16_t) const noexcept;
 
        // called as soon as the remote end ack'd given packet
        virtual void OnPacketReceived(std::uint16_t) { }
@@ -49,6 +56,11 @@ private:
        unsigned int packets_received;
        float packet_loss;
 
+       Uint32 stamps[16];
+       std::size_t stamp_cursor;
+       std::uint16_t stamp_last;
+       float rtt;
+
 };
 
 }

diff --git a/src/net/net.cpp b/src/net/net.cpp
index 9b50479b135445ae0225a28f98653fee18c6f000..59176aac8251edcf5f18876d65060ccb80093657 100644 (file)
--- a/src/net/net.cpp
+++ b/src/net/net.cpp
@@ -84,6 +84,10 @@ uint16_t Connection::Send(UDPpacket &udp_pack, UDPsocket sock) {
                throw NetError("SDLNet_UDP_Send");
        }
 
+       if (HasHandler()) {
+               Handler().PacketSent(seq);
+       }
+
        FlagSend();
        return seq;
 }
@@ -151,20 +155,37 @@ uint16_t Connection::SendPing(UDPpacket &udp_pack, UDPsocket sock) {
 ConnectionHandler::ConnectionHandler()
 : packets_lost(0)
 , packets_received(0)
-, packet_loss(0.0f) {
+, packet_loss(0.0f)
+, stamp_cursor(15)
+, stamp_last(0)
+, rtt(64.0f) {
+       Uint32 now = SDL_GetTicks();
+       for (Uint32 &s : stamps) {
+               s = now;
+       }
+}
 
+void ConnectionHandler::PacketSent(uint16_t seq) {
+       if (!SamplePacket(seq)) {
+               return;
+       }
+       stamp_cursor = (stamp_cursor + 1) % 16;
+       stamps[stamp_cursor] = SDL_GetTicks();
+       stamp_last = seq;
 }
 
 void ConnectionHandler::PacketLost(uint16_t seq) {
        OnPacketLost(seq);
        ++packets_lost;
        UpdatePacketLoss();
+       UpdateRTT(seq);
 }
 
 void ConnectionHandler::PacketReceived(uint16_t seq) {
        OnPacketReceived(seq);
        ++packets_received;
        UpdatePacketLoss();
+       UpdateRTT(seq);
 }
 
 void ConnectionHandler::UpdatePacketLoss() noexcept {
@@ -176,6 +197,27 @@ void ConnectionHandler::UpdatePacketLoss() noexcept {
        }
 }
 
+void ConnectionHandler::UpdateRTT(std::uint16_t seq) noexcept {
+       if (!SamplePacket(seq)) return;
+       int diff = HeadDiff(seq);
+       if (diff > 0 || diff < -15) {
+               // packet outside observed time frame
+               return;
+       }
+       int cur_rtt = SDL_GetTicks() - stamps[(stamp_cursor + diff + 16) % 16];
+       rtt += (cur_rtt - rtt) * 0.1f;
+}
+
+bool ConnectionHandler::SamplePacket(std::uint16_t seq) const noexcept {
+       // only sample every eighth packet
+       return seq % 8 == 0;
+}
+
+int ConnectionHandler::HeadDiff(std::uint16_t seq) const noexcept {
+       int16_t diff = int16_t(seq) - int16_t(stamp_last);
+       return diff / 8;
+}
+
 
 ostream &operator <<(ostream &out, const IPaddress &addr) {
        const unsigned char *host = reinterpret_cast<const unsigned char *>(&addr.host);