fix(netxlite): gracefully handle utls panics (#462)

* fix(netxlite): gracefully handle utls panics

See https://github.com/ooni/probe/issues/1770

* fix(netxlite): remove wrong timeout from newly written test

internal/netxlite/utls.go

@@ -3,6 +3,7 @@ package netxlite
 import (
 	"context"
 	"crypto/tls"
+	"errors"
 	"net"
 
 	utls "gitlab.com/yawning/utls.git"
@@ -43,17 +44,29 @@ func newConnUTLS(clientHello *utls.ClientHelloID) func(conn net.Conn, config *tl
 	}
 }
 
-func (c *utlsConn) HandshakeContext(ctx context.Context) error {
+// ErrUTLSHandshakePanic indicates that there was panic handshaking
+// when we were using the yawning/utls library for parroting.
+//
+// See https://github.com/ooni/probe/issues/1770
+var ErrUTLSHandshakePanic = errors.New("utls: handshake panic")
+
+func (c *utlsConn) HandshakeContext(ctx context.Context) (err error) {
 	errch := make(chan error, 1)
 	go func() {
+		defer func() {
+			// See https://github.com/ooni/probe/issues/1770
+			if recover() != nil {
+				errch <- ErrUTLSHandshakePanic
+			}
+		}()
 		errch <- c.handshakefn()()
 	}()
 	select {
-	case err := <-errch:
-		return err
+	case err = <-errch:
 	case <-ctx.Done():
-		return ctx.Err()
+		err = ctx.Err()
 	}
+	return
 }
 
 func (c *utlsConn) handshakefn() func() error {

internal/netxlite/utls_test.go

@@ -49,7 +49,7 @@ func TestNewTLSHandshakerUTLSTypes(t *testing.T) {
 	}
 }
 
-func TestUTLSConnHandshakeNotInterrupted(t *testing.T) {
+func TestUTLSConnHandshakeNotInterruptedSuccess(t *testing.T) {
 	ctx := context.Background()
 	conn := &utlsConn{
 		testableHandshake: func() error {
@@ -62,6 +62,20 @@ func TestUTLSConnHandshakeNotInterrupted(t *testing.T) {
 	}
 }
 
+func TestUTLSConnHandshakeNotInterruptedFailure(t *testing.T) {
+	expected := errors.New("mocked error")
+	ctx := context.Background()
+	conn := &utlsConn{
+		testableHandshake: func() error {
+			return expected
+		},
+	}
+	err := conn.HandshakeContext(ctx)
+	if !errors.Is(err, expected) {
+		t.Fatal("not the error we expected", err)
+	}
+}
+
 func TestUTLSConnHandshakeInterrupted(t *testing.T) {
 	wg := sync.WaitGroup{}
 	wg.Add(1)
@@ -82,3 +96,20 @@ func TestUTLSConnHandshakeInterrupted(t *testing.T) {
 	close(sigch)
 	wg.Wait()
 }
+
+func TestUTLSConnHandshakePanic(t *testing.T) {
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+	ctx := context.Background()
+	conn := &utlsConn{
+		testableHandshake: func() error {
+			defer wg.Done()
+			panic("mascetti")
+		},
+	}
+	err := conn.HandshakeContext(ctx)
+	if !errors.Is(err, ErrUTLSHandshakePanic) {
+		t.Fatal("not the error we expected", err)
+	}
+	wg.Wait()
+}