Send packets with timestamp and seqno

UdpVpn.cpp

@@ -90,7 +90,7 @@ size_t UdpVpn::read_from_udp(char* buffer, size_t len,
 {
     ssize_t nread;
     socklen_t peer_addr_len = sizeof(peer_addr);
-    nread = recvfrom(_socket, buffer, len, MSG_WAITALL,
+    nread = recvfrom(_socket, buffer, len, 0,
             (struct sockaddr*) &peer_addr, &peer_addr_len);
 
     if(nread < 0)
@@ -114,6 +114,7 @@ size_t UdpVpn::read_from_udp(char* buffer, size_t len,
 }
 
 size_t UdpVpn::read_from_udp(VpnPacket& packet, sockaddr_in6& peer_addr) {
+    packet.upon_reception(); // The packet is not read yet, but it has arrived
     size_t nread =
         read_from_udp(packet.get_data(), packet.get_data_space(), peer_addr);
     packet.set_data_size(nread);

UdpVpnClient.cpp

@@ -26,6 +26,7 @@ void UdpVpnClient::receive_from_tun() {
             format_address(packet.get_ipv6_header().dest.s6_addr),
             nread);
 
+    packet.prepare_for_sending();
     write_to_server(packet);
 }
 
@@ -37,7 +38,8 @@ void UdpVpnClient::receive_from_udp() {
         return;
 
     // Reinject into tun
-    kdebugf("Receiving packet of size %d from %s\n",
+    kdebugf("Receiving packet #%u of size %d from %s\n",
+            packet.get_seqno(),
             nread,
             format_address(packet.get_ipv6_header().source.s6_addr));
     _tun_dev.write(packet.get_payload(), packet.get_payload_size());

UdpVpnServer.cpp

@@ -55,11 +55,13 @@ void UdpVpnServer::receive_from_tun() {
                 format_address(peer_inner_addr.s6_addr));
         return;
     }
+    packet.set_peer(peer);
 
     kdebugf("Transmitting %s -> %s, size %d\n",
             format_address(packet.get_ipv6_header().source.s6_addr),
             format_address(packet.get_ipv6_header().dest.s6_addr),
             nread);
+    packet.prepare_for_sending();
     peer->write(packet);
 }
 
@@ -82,11 +84,11 @@ void UdpVpnServer::receive_from_udp() {
                 htons(peer_addr.sin6_port),
                 format_address(peer_inner_addr.s6_addr));
     }
-    // VpnPeer* peer = (peer_iter->second);
-    // TODO -- pass the packet to `peer` for a cleaner flow
+    packet.set_peer(peer);
 
     // Reinject into tun
-    kdebugf("Receiving packet of size %d from %s\n",
+    kdebugf("Receiving packet #%u of size %d from %s\n",
+            packet.get_seqno(),
             nread,
             format_address(packet.get_ipv6_header().source.s6_addr));
     _tun_dev.write(packet.get_payload(), packet.get_payload_size());

VpnPacket.cpp

@@ -1,15 +1,24 @@
 #include "VpnPacket.hpp"
+#include "VpnPeer.hpp"
 
-const size_t VpnPacket::VPN_HEADER_SIZE = 0;
+#include <chrono>
 
-static const size_t OUTER_HEADERS_SIZE =
+const size_t VpnPacket::VPN_HEADER_BYTES = 8;
+uint32_t VpnPacket::_next_general_seqno = 0;
+
+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)
-    : _data_space(mtu-OUTER_HEADERS_SIZE), _data_size(0)
+    : _peer(nullptr), _data_space(mtu-OUTER_HEADERS_BYTES), _data_size(0),
+      _reception_timestamp(0)
 {
-    _data = new char[mtu - OUTER_HEADERS_SIZE];
+    _data = new char[mtu - OUTER_HEADERS_BYTES];
 }
 
 VpnPacket::~VpnPacket() {
@@ -19,3 +28,30 @@ VpnPacket::~VpnPacket() {
 bool VpnPacket::parse_as_ipv6() {
     return parse_ipv6_header(get_payload(), get_payload_size(), _ipv6_header);
 }
+
+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)
+        return _peer->next_seqno();
+    return _next_general_seqno++;
+}

VpnPacket.hpp

@@ -3,29 +3,46 @@
 /** A packet to be transmitted or received over the VPN socket */
 
 #include <cstdlib>
+#include <memory>
 
 #include "ip_header.hpp"
 
+/** VPN packet layout:
+ *
+ * +-------+-------+-------+-------+-------+-------+-------+-------+
+ * |  1B   |  1B   |  1B   |  1B   |  1B   |  1B   |  1B   |  1B   |
+ * +-------+-------+-------+-------+-------+-------+-------+-------+
+ * | Sequence number [4B]          | Sending timestamp (μs) [4B]   |
+ * +---------------------------------------------------------------+
+ * | Nested packet (payload)                                       |
+ * +---------------------------------------------------------------+
+ */
+
+class VpnPeer;
+
 class VpnPacket {
     public:
-        static const size_t VPN_HEADER_SIZE;
+        static const size_t VPN_HEADER_BYTES;
 
         VpnPacket(size_t mtu);
         ~VpnPacket();
 
+        /// Set packet peer -- used for sequence numbers
+        void set_peer(std::shared_ptr<VpnPeer> peer) { _peer = peer; }
+
         /// Try to parse the packet as IPv6, return `false` upon failure.
         bool parse_as_ipv6();
         bool ipv6_parsed() const { return _ipv6_parsed; }
         const IPv6Header& get_ipv6_header() const { return _ipv6_header; }
 
-        const char* get_payload() const { return _data + VPN_HEADER_SIZE; }
-        char* get_payload() { return _data + VPN_HEADER_SIZE; }
+        const char* get_payload() const { return _data + VPN_HEADER_BYTES; }
+        char* get_payload() { return _data + VPN_HEADER_BYTES; }
         size_t get_payload_space() const {
-            return _data_space - VPN_HEADER_SIZE; }
+            return _data_space - VPN_HEADER_BYTES; }
         size_t get_payload_size() const {
-            return _data_size - VPN_HEADER_SIZE; }
+            return _data_size - VPN_HEADER_BYTES; }
         void set_payload_size(size_t payload_size) {
-            _data_size = payload_size + VPN_HEADER_SIZE; }
+            _data_size = payload_size + VPN_HEADER_BYTES; }
 
         const char* get_data() const { return _data; }
         char* get_data() { return _data; }
@@ -33,10 +50,34 @@ class VpnPacket {
         size_t get_data_size() const { return _data_size; }
         void set_data_size(size_t data_size) { _data_size = data_size; }
 
+        uint32_t get_seqno() const;
+        uint32_t get_sending_timestamp() const;
+        uint32_t get_reception_timestamp() const { return _reception_timestamp; }
+
+        /** Fill the headers of the packet. This method must be called as close
+         * to the time the packet is actually sent as possible, as it handles
+         * timestamps. */
+        void prepare_for_sending();
+
+        /** Do what must be done at reception, eg. keep the reception
+         * timestamp. This method must be called as close to the time the
+         * packet is actually received as possible, as it handles timestamps.
+         */
+        void upon_reception();
+
+    private: // methods
+        inline uint32_t next_seqno();
+
     private:
+        std::shared_ptr<VpnPeer> _peer;
+
         char* _data;
         size_t _data_space, _data_size;
 
         bool _ipv6_parsed;
         IPv6Header _ipv6_header;
+
+        uint32_t _reception_timestamp;
+
+        static uint32_t _next_general_seqno;
 };

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)
+    : _vpn(vpn), _ext_addr(ext_addr), _int_addr(int_addr), _next_seqno(0)
 {}
 
 

VpnPeer.hpp

@@ -28,8 +28,12 @@ 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++; }
+
     private:
         UdpVpn* _vpn;
         sockaddr_in6 _ext_addr;
         in6_addr _int_addr;
+        uint32_t _next_seqno;
 };