take packet rcv timestamp directly after receiving from network

server.go

@@ -6,6 +6,7 @@ import (
 	"net"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/lucas-clemente/quic-go/crypto"
 	"github.com/lucas-clemente/quic-go/handshake"
@@ -130,6 +131,8 @@ func (s *Server) handlePacket(conn *net.UDPConn, remoteAddr *net.UDPAddr, packet
 		return qerr.PacketTooLarge
 	}
 
+	rcvTime := time.Now()
+
 	r := bytes.NewReader(packet)
 
 	hdr, err := ParsePublicHeader(r)
@@ -175,6 +178,7 @@ func (s *Server) handlePacket(conn *net.UDPConn, remoteAddr *net.UDPAddr, packet
 		remoteAddr:   remoteAddr,
 		publicHeader: hdr,
 		data:         packet[len(packet)-r.Len():],
+		rcvTime:      rcvTime,
 	})
 	return nil
 }

session.go

@@ -25,6 +25,7 @@ type receivedPacket struct {
 	remoteAddr   interface{}
 	publicHeader *PublicHeader
 	data         []byte
+	rcvTime      time.Time
 }
 
 var (
@@ -179,7 +180,7 @@ func (s *Session) run() {
 			// begins with the public header and we never copy it.
 			putPacketBuffer(p.publicHeader.Raw)
 			if s.delayedAckOriginTime.IsZero() {
-				s.delayedAckOriginTime = time.Now()
+				s.delayedAckOriginTime = p.rcvTime
 			}
 		case <-s.aeadChanged:
 			s.tryDecryptingQueuedPackets()
@@ -226,7 +227,12 @@ func (s *Session) maybeResetTimer() {
 }
 
 func (s *Session) handlePacketImpl(p *receivedPacket) error {
-	s.lastNetworkActivityTime = time.Now()
+	if p.rcvTime.IsZero() {
+		// To simplify testing
+		p.rcvTime = time.Now()
+	}
+
+	s.lastNetworkActivityTime = p.rcvTime
 	hdr := p.publicHeader
 	data := p.data