fixed error with missing sync() after parse/describe error (#42)

* Added test demonstrating a potential hang after errors found in github.com/xo/usql project.

* fixed issue with missing sync() call on Parse/Describe() error
made 0-length messages show up in log as intended

Author: huebnerr

connection.go

@@ -234,16 +234,14 @@ func (v *connection) sendMessage(msg msgs.FrontEndMsg) error {
 		if result == nil {
 			if len(msgBytes) > 0 {
 				_, result = v.conn.Write(msgBytes)
-
-				if result == nil {
-					connectionLogger.Debug("-> " + msg.String())
-				}
 			}
 		}
 	}
 
 	if result != nil {
 		connectionLogger.Error("-> FAILED SENDING "+msg.String()+": %v", result.Error())
+	} else {
+		connectionLogger.Debug("-> " + msg.String())
 	}
 
 	return result
@@ -473,6 +471,10 @@ func (v *connection) authSendSHA512Password(extraAuthData []byte) error {
 	return v.sendMessage(msg)
 }
 
+func (v *connection) sync() error {
+	return v.sendMessage(&msgs.FESyncMsg{})
+}
+
 func (v *connection) lockSessionMutex() {
 	v.sessMutex.Lock()
 }

driver_test.go

@@ -677,6 +677,29 @@ func TestSTDINCopyWithStream(t *testing.T) {
 	assertNoNext(t, rows)
 }
 
+func TestHangAfterError(t *testing.T) {
+	connDB := openConnection(t)
+	defer closeConnection(t, connDB)
+
+	rows, err := connDB.QueryContext(ctx, "SELECT 1")
+	defer rows.Close()
+
+	assertNoErr(t, err)
+	assertNext(t, rows)
+	assertNoNext(t, rows)
+
+	rows, err = connDB.QueryContext(ctx, "SELECT 1+'abcd'")
+
+	assertErr(t, err, "Invalid")
+
+	rows, err = connDB.QueryContext(ctx, "SELECT 2")
+	defer rows.Close()
+
+	assertNoErr(t, err)
+	assertNext(t, rows)
+	assertNoNext(t, rows)
+}
+
 var verticaUserName = flag.String("user", "dbadmin", "the user name to connect to Vertica")
 var verticaPassword = flag.String("password", os.Getenv("VERTICA_TEST_PASSWORD"), "Vertica password for this user")
 var verticaHostPort = flag.String("locator", "localhost:5433", "Vertica's host and port")

stmt.go

@@ -88,8 +88,8 @@ func (s *stmt) Close() error {
 	if s.parseState == parseStateParsed {
 		closeMsg := &msgs.FECloseMsg{TargetType: msgs.CmdTargetTypeStatement, TargetName: s.preparedName}
 
-		s.conn.lockSessionMutex()
-		defer s.conn.unlockSessionMutex()
+		//s.conn.lockSessionMutex()
+		//defer s.conn.unlockSessionMutex()
 
 		if err := s.conn.sendMessage(closeMsg); err != nil {
 			return err
@@ -354,6 +354,7 @@ func (s *stmt) prepareAndDescribe() error {
 
 		switch msg := bMsg.(type) {
 		case *msgs.BEErrorMsg:
+			s.conn.sync()
 			return msg.ToErrorType()
 		case *msgs.BEParseCompleteMsg:
 			s.parseState = parseStateParsed