refactor: allow automatically wrap net/quic conn (#867)

See https://github.com/ooni/probe/issues/2219

internal/netxlite/dialer.go

@@ -224,7 +224,7 @@ func (d *dialerResolverWithTracing) DialContext(ctx context.Context, network, ad
 		trace.OnConnectDone(started, network, onlyhost, target, err, finished)
 		if err == nil {
 			conn = &dialerErrWrapperConn{conn}
-			return conn, nil
+			return trace.MaybeWrapNetConn(conn), nil
 		}
 		errorslist = append(errorslist, err)
 	}

internal/netxlite/quic.go

@@ -135,6 +135,7 @@ func (d *quicDialerQUICGo) DialContext(ctx context.Context, network string,
 	}
 	tlsConfig = d.maybeApplyTLSDefaults(tlsConfig, udpAddr.Port)
 	trace := ContextTraceOrDefault(ctx)
+	pconn = trace.MaybeWrapUDPLikeConn(pconn)
 	started := trace.TimeNow()
 	trace.OnQUICHandshakeStart(started, address, quicConfig)
 	qconn, err := d.dialEarlyContext(

internal/netxlite/trace.go

@@ -7,6 +7,7 @@ package netxlite
 import (
 	"context"
 	"crypto/tls"
+	"net"
 	"time"
 
 	"github.com/lucas-clemente/quic-go"
@@ -50,6 +51,16 @@ func (*traceDefault) TimeNow() time.Time {
 	return time.Now()
 }
 
+// MaybeWrapNetConn implements model.Trace.MaybeWrapNetConn
+func (*traceDefault) MaybeWrapNetConn(conn net.Conn) net.Conn {
+	return conn
+}
+
+// MaybeWrapUDPLikeConn implements model.Trace.MaybeWrapUDPLikeConn
+func (*traceDefault) MaybeWrapUDPLikeConn(conn model.UDPLikeConn) model.UDPLikeConn {
+	return conn
+}
+
 // OnDNSRoundTripForLookupHost implements model.Trace.OnDNSRoundTripForLookupHost.
 func (*traceDefault) OnDNSRoundTripForLookupHost(started time.Time, reso model.Resolver, query model.DNSQuery,
 	response model.DNSResponse, addrs []string, err error, finished time.Time) {