refactor transportMonitor t.error case

clientconn.go

@@ -949,28 +949,22 @@ func (ac *addrConn) transportMonitor() {
 			ac.adjustParams(t.GetGoAwayReason())
 			// If GoAway happens without any network I/O error, the underlying transport
 			// will be gracefully closed, and a new transport will be created.
-			// (the transport will be closed when all the pending RPCs finished or failed.).
+			// (the transport will be closed when all the pending RPCs finished or failed.)
 			// If GoAway and some network I/O error happen concurrently, the underlying transport
 			// will be closed, and a new transport will be created.
+			var drain bool
 			select {
 			case <-t.Error():
-				if err := ac.resetTransport(false); err != nil {
-					grpclog.Infof("get error from resetTransport %v, transportMonitor returning", err)
-					if err != errConnClosing {
-						// Keep this ac in cc.conns, to get the reason it's torn down.
-						ac.tearDown(err)
-					}
-					return
-				}
 			default:
-				if err := ac.resetTransport(true); err != nil {
-					grpclog.Infof("get error from resetTransport %v, transportMonitor returning", err)
-					if err != errConnClosing {
-						// Keep this ac in cc.conns, to get the reason it's torn down.
-						ac.tearDown(err)
-					}
-					return
+				drain = true
+			}
+			if err := ac.resetTransport(drain); err != nil {
+				grpclog.Infof("get error from resetTransport %v, transportMonitor returning", err)
+				if err != errConnClosing {
+					// Keep this ac in cc.conns, to get the reason it's torn down.
+					ac.tearDown(err)
 				}
+				return
 			}
 		case <-t.Error():
 			select {