refactor: cleaner way of passing a UDPConn around (#421)

* refactor: cleaner way of passing a UDPConn around

Also part of https://github.com/ooni/probe/issues/1505

* Update internal/engine/netx/quicdialer/connectionstate.go

internal/engine/netx/quicdialer/connectionstate.go

@@ -6,7 +6,7 @@ import (
 	"github.com/lucas-clemente/quic-go"
 )
 
-// ConnectionState returns the ConnectionState of a QUIC Session.
-func ConnectionState(sess quic.EarlySession) tls.ConnectionState {
+// connectionState returns the ConnectionState of a QUIC Session.
+func connectionState(sess quic.EarlySession) tls.ConnectionState {
 	return sess.ConnectionState().TLS.ConnectionState
 }

internal/engine/netx/quicdialer/quicdialer.go

@@ -14,12 +14,6 @@ type ContextDialer interface {
 		tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlySession, error)
 }
 
-// Dialer dials QUIC connections.
-type Dialer interface {
-	// Note: assumes that tlsCfg and cfg are not nil.
-	Dial(network, addr string, tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlySession, error)
-}
-
 // Resolver is the interface we expect from a resolver.
 type Resolver interface {
 	LookupHost(ctx context.Context, hostname string) (addrs []string, err error)

internal/engine/netx/quicdialer/saver.go

@@ -45,7 +45,7 @@ func (h HandshakeSaver) DialContext(ctx context.Context, network string,
 		})
 		return nil, err
 	}
-	state := ConnectionState(sess)
+	state := connectionState(sess)
 	h.Saver.Write(trace.Event{
 		Duration:           stop.Sub(start),
 		Name:               "quic_handshake_done",

internal/engine/netx/quicdialer/system.go

@@ -1,18 +1,18 @@
 package quicdialer
 
 import (
-	"errors"
 	"net"
 	"time"
 
 	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
 	"github.com/ooni/probe-cli/v3/internal/errorsx"
+	"github.com/ooni/probe-cli/v3/internal/quicx"
 )
 
 // QUICListener listens for QUIC connections.
 type QUICListener interface {
-	// Listen creates a new listening PacketConn.
-	Listen(addr *net.UDPAddr) (net.PacketConn, error)
+	// Listen creates a new listening UDPConn.
+	Listen(addr *net.UDPAddr) (quicx.UDPConn, error)
 }
 
 // QUICListenerSaver is a QUICListener that also implements saving events.
@@ -25,21 +25,16 @@ type QUICListenerSaver struct {
 }
 
 // Listen implements QUICListener.Listen.
-func (qls *QUICListenerSaver) Listen(addr *net.UDPAddr) (net.PacketConn, error) {
+func (qls *QUICListenerSaver) Listen(addr *net.UDPAddr) (quicx.UDPConn, error) {
 	pconn, err := qls.QUICListener.Listen(addr)
 	if err != nil {
 		return nil, err
 	}
-	// TODO(bassosimone): refactor to remove this restriction.
-	udpConn, ok := pconn.(*net.UDPConn)
-	if !ok {
-		return nil, errors.New("quicdialer: cannot convert to udpConn")
-	}
-	return saverUDPConn{UDPConn: udpConn, saver: qls.Saver}, nil
+	return saverUDPConn{UDPConn: pconn, saver: qls.Saver}, nil
 }
 
 type saverUDPConn struct {
-	*net.UDPConn
+	quicx.UDPConn
 	saver *trace.Saver
 }