refactor(netxlite): allow easy QUIC dialer chain customization (#771)

Like the previous diff, but for creating QUIC dialers.

See https://github.com/ooni/probe/issues/2121.

internal/engine/netx/netx.go

@@ -131,28 +131,26 @@ func NewQUICDialer(config Config) model.QUICDialer {
 	if config.FullResolver == nil {
 		config.FullResolver = NewResolver(config)
 	}
-	var ql model.QUICListener = &netxlite.QUICListenerStdlib{}
-	ql = &netxlite.ErrorWrapperQUICListener{QUICListener: ql}
+	ql := netxlite.NewQUICListener()
 	if config.ReadWriteSaver != nil {
 		ql = &quicdialer.QUICListenerSaver{
 			QUICListener: ql,
 			Saver:        config.ReadWriteSaver,
 		}
 	}
-	var d model.QUICDialer = &netxlite.QUICDialerQUICGo{
-		QUICListener: ql,
-	}
-	d = &netxlite.ErrorWrapperQUICDialer{
-		QUICDialer: d,
+	var logger model.DebugLogger = model.DiscardLogger
+	if config.Logger != nil {
+		logger = config.Logger
 	}
+	extensions := []netxlite.QUICDialerWrapper{
+		func(dialer model.QUICDialer) model.QUICDialer {
 			if config.TLSSaver != nil {
-		d = quicdialer.HandshakeSaver{Saver: config.TLSSaver, QUICDialer: d}
+				dialer = quicdialer.HandshakeSaver{Saver: config.TLSSaver, QUICDialer: dialer}
 			}
-	d = &netxlite.QUICDialerResolver{
-		Resolver: config.FullResolver,
-		Dialer:   d,
+			return dialer
+		},
 	}
-	return d
+	return netxlite.NewQUICDialerWithResolver(ql, logger, config.FullResolver, extensions...)
 }
 
 // NewTLSDialer creates a new TLSDialer from the specified config

internal/netxlite/dialer.go

@@ -135,7 +135,7 @@ func NewDialerWithoutResolver(dl model.DebugLogger, w ...DialerWrapper) model.Di
 	return NewDialerWithResolver(dl, &NullResolver{}, w...)
 }
 
-// DialerSystem is a model.Dialer that users TProxy.NewSimplerDialer
+// DialerSystem is a model.Dialer that uses TProxy.NewSimplerDialer
 // to construct the new SimpleDialer used for dialing. This dialer has
 // a fixed timeout for each connect operation equal to 15 seconds.
 type DialerSystem struct {

internal/netxlite/quic.go

@@ -32,39 +32,32 @@ func (qls *quicListenerStdlib) Listen(addr *net.UDPAddr) (model.UDPLikeConn, err
 	return TProxy.ListenUDP("udp", addr)
 }
 
-// NewQUICDialerWithResolver returns a QUICDialer using the given
-// QUICListener to create listening connections and the given Resolver
-// to resolve domain names (if needed).
+// QUICDialerWrapper is a function that allows you to customize the kind of QUICDialer
+// returned by NewQUICDialerWithResolver and NewQUICDialerWithoutResolver.
+type QUICDialerWrapper func(dialer model.QUICDialer) model.QUICDialer
+
+// NewQUICDialerWithResolver is the WrapDialer equivalent for QUIC where
+// we return a composed QUICDialer modified by optional wrappers.
 //
-// Properties of the dialer:
-//
-// 1. logs events using the given logger;
-//
-// 2. resolves domain names using the givern resolver;
-//
-// 3. when using a resolver, _may_ attempt multiple dials
-// in parallel (happy eyeballs) and _may_ return an aggregate
-// error to the caller;
-//
-// 4. wraps errors;
-//
-// 5. has a configured connect timeout;
-//
-// 6. if a dialer wraps a resolver, the dialer will forward
-// the CloseIdleConnection call to its resolver (which is
-// instrumental to manage a DoH resolver connections properly).
-func NewQUICDialerWithResolver(listener model.QUICListener,
-	logger model.DebugLogger, resolver model.Resolver) model.QUICDialer {
-	return &quicDialerLogger{
-		Dialer: &quicDialerResolver{
-			Dialer: &quicDialerLogger{
-				Dialer: &quicDialerErrWrapper{
+// Unlike the dialer returned by WrapDialer, this dialer MAY attempt
+// happy eyeballs, perform parallel dial attempts, and return an error
+// that aggregates all the errors that occurred.
+func NewQUICDialerWithResolver(listener model.QUICListener, logger model.DebugLogger,
+	resolver model.Resolver, wrappers ...QUICDialerWrapper) (outDialer model.QUICDialer) {
+	outDialer = &quicDialerErrWrapper{
 		QUICDialer: &quicDialerHandshakeCompleter{
 			Dialer: &quicDialerQUICGo{
 				QUICListener: listener,
 			},
 		},
-				},
+	}
+	for _, wrapper := range wrappers {
+		outDialer = wrapper(outDialer) // extend with user-supplied constructors
+	}
+	return &quicDialerLogger{
+		Dialer: &quicDialerResolver{
+			Dialer: &quicDialerLogger{
+				Dialer:          outDialer,
 				Logger:          logger,
 				operationSuffix: "_address",
 			},
@@ -74,12 +67,11 @@ func NewQUICDialerWithResolver(listener model.QUICListener,
 	}
 }
 
-// NewQUICDialerWithoutResolver is like NewQUICDialerWithResolver
-// except that there is no configured resolver. So, if you pass in
-// an address containing a domain name, the dial will fail with
-// the ErrNoResolver failure.
-func NewQUICDialerWithoutResolver(listener model.QUICListener, logger model.DebugLogger) model.QUICDialer {
-	return NewQUICDialerWithResolver(listener, logger, &NullResolver{})
+// NewQUICDialerWithoutResolver is equivalent to calling NewQUICDialerWithResolver
+// with the resolver argument set to &NullResolver{}.
+func NewQUICDialerWithoutResolver(listener model.QUICListener,
+	logger model.DebugLogger, wrappers ...QUICDialerWrapper) model.QUICDialer {
+	return NewQUICDialerWithResolver(listener, logger, &NullResolver{}, wrappers...)
 }
 
 // quicDialerQUICGo dials using the lucas-clemente/quic-go library.

internal/netxlite/quic_test.go

@@ -22,9 +22,25 @@ func TestNewQUICListener(t *testing.T) {
 	_ = qew.QUICListener.(*quicListenerStdlib)
 }
 
+type extensionQUICDialerFirst struct {
+	model.QUICDialer
+}
+
+type extensionQUICDialerSecond struct {
+	model.QUICDialer
+}
+
 func TestNewQUICDialer(t *testing.T) {
 	ql := NewQUICListener()
-	dlr := NewQUICDialerWithoutResolver(ql, log.Log)
+	extensions := []QUICDialerWrapper{
+		func(dialer model.QUICDialer) model.QUICDialer {
+			return &extensionQUICDialerFirst{dialer}
+		},
+		func(dialer model.QUICDialer) model.QUICDialer {
+			return &extensionQUICDialerSecond{dialer}
+		},
+	}
+	dlr := NewQUICDialerWithoutResolver(ql, log.Log, extensions...)
 	logger := dlr.(*quicDialerLogger)
 	if logger.Logger != log.Log {
 		t.Fatal("invalid logger")
@@ -37,7 +53,9 @@ func TestNewQUICDialer(t *testing.T) {
 	if logger.Logger != log.Log {
 		t.Fatal("invalid logger")
 	}
-	errWrapper := logger.Dialer.(*quicDialerErrWrapper)
+	ext2 := logger.Dialer.(*extensionQUICDialerSecond)
+	ext1 := ext2.QUICDialer.(*extensionQUICDialerFirst)
+	errWrapper := ext1.QUICDialer.(*quicDialerErrWrapper)
 	handshakeCompleter := errWrapper.QUICDialer.(*quicDialerHandshakeCompleter)
 	base := handshakeCompleter.Dialer.(*quicDialerQUICGo)
 	if base.QUICListener != ql {