2 files changed, 75 insertions, 37 deletions
diff --git a/server/zclient.go b/server/zclient.go
index 4bba83ec..d432b96d 100644
--- a/server/zclient.go
+++ b/server/zclient.go
@@ -519,10 +519,23 @@ func newZebraClient(s *BgpServer, url string, protos []string, version uint8, nh
 	}
 	cli, err := zebra.NewClient(l[0], l[1], zebra.ROUTE_BGP, version)
 	if err != nil {
-		return nil, err
+		// Retry with another Zebra message version
+		var retry_version uint8 = 2
+		if version == 2 {
+			retry_version = 3
+		}
+		log.WithFields(log.Fields{
+			"Topic": "Zebra",
+		}).Warnf("cannot connect to Zebra with message version %d. retry with version %d", version, retry_version)
+		cli, err = zebra.NewClient(l[0], l[1], zebra.ROUTE_BGP, retry_version)
+		if err != nil {
+			return nil, err
+		}
 	}
-	cli.SendHello()
-	cli.SendRouterIDAdd()
+	// Note: HELLO/ROUTER_ID_ADD messages are automatically sent to negotiate
+	// the Zebra message version in zebra.NewClient().
+	// cli.SendHello()
+	// cli.SendRouterIDAdd()
 	cli.SendInterfaceAdd()
 	for _, typ := range protos {
 		t, err := zebra.RouteTypeFromString(typ)
diff --git a/zebra/zapi.go b/zebra/zapi.go
index 74d17f28..f4b8615e 100644
--- a/zebra/zapi.go
+++ b/zebra/zapi.go
@@ -332,46 +332,71 @@ func NewClient(network, address string, typ ROUTE_TYPE, version uint8) (*Client,
 		}
 	}()
 
-	go func() {
-		for {
-			headerBuf, err := readAll(conn, int(HeaderSize(version)))
-			if err != nil {
-				log.WithFields(log.Fields{
-					"Topic": "Zebra",
-				}).Errorf("failed to read header:%s", err)
-				return
-			}
+	// Send HELLO/ROUTER_ID_ADD messages to negotiate the Zebra message version.
+	c.SendHello()
+	c.SendRouterIDAdd()
+
+	receiveSingleMsg := func() (*Message, error) {
+		headerBuf, err := readAll(conn, int(HeaderSize(version)))
+		if err != nil {
+			err = fmt.Errorf("failed to read header: %s", err)
 			log.WithFields(log.Fields{
 				"Topic": "Zebra",
-			}).Debugf("read header from zebra: %v", headerBuf)
-			hd := &Header{}
-			err = hd.DecodeFromBytes(headerBuf)
-			if err != nil {
-				log.WithFields(log.Fields{
-					"Topic": "Zebra",
-				}).Errorf("failed to decode header:%s", err)
-				return
-			}
+			}).Error(err)
+			return nil, err
+		}
+		log.WithFields(log.Fields{
+			"Topic": "Zebra",
+		}).Debugf("read header from zebra: %v", headerBuf)
+		hd := &Header{}
+		err = hd.DecodeFromBytes(headerBuf)
+		if err != nil {
+			err = fmt.Errorf("failed to decode header: %s", err)
+			log.WithFields(log.Fields{
+				"Topic": "Zebra",
+			}).Error(err)
+			return nil, err
+		}
 
-			bodyBuf, err := readAll(conn, int(hd.Len-HeaderSize(version)))
-			if err != nil {
-				log.WithFields(log.Fields{
-					"Topic": "Zebra",
-				}).Errorf("failed to read body:%s", err)
-				return
-			}
+		bodyBuf, err := readAll(conn, int(hd.Len-HeaderSize(version)))
+		if err != nil {
+			err = fmt.Errorf("failed to read body: %s", err)
 			log.WithFields(log.Fields{
 				"Topic": "Zebra",
-			}).Debugf("read body from zebra: %v", bodyBuf)
-			m, err := ParseMessage(hd, bodyBuf)
-			if err != nil {
-				log.WithFields(log.Fields{
-					"Topic": "Zebra",
-				}).Warnf("failed to parse message:%s", err)
-				continue
-			}
+			}).Error(err)
+			return nil, err
+		}
+		log.WithFields(log.Fields{
+			"Topic": "Zebra",
+		}).Debugf("read body from zebra: %v", bodyBuf)
+		m, err := ParseMessage(hd, bodyBuf)
+		if err != nil {
+			log.WithFields(log.Fields{
+				"Topic": "Zebra",
+			}).Warnf("failed to parse message: %s", err)
+			return nil, nil
+		}
 
-			incoming <- m
+		return m, nil
+	}
+
+	// Try to receive the first message from Zebra.
+	if m, err := receiveSingleMsg(); err != nil {
+		c.Close()
+		// Return error explicitly in order to retry connection.
+		return nil, err
+	} else if m != nil {
+		incoming <- m
+	}
+
+	// Start receive loop only when the first message successfully received.
+	go func() {
+		for {
+			if m, err := receiveSingleMsg(); err != nil {
+				return
+			} else if m != nil {
+				incoming <- m
+			}
 		}
 	}()