Send vl_api_sockclnt_delete_t message on disconnect (#248)

This change practically reverts previous commit [1548c7e](1548c7e), because it seems VPP is not correctly cleaning up opened sockets when they are closed from client side, which increases CPU usage of VPP.
This correctly sets client_index field for the message unlike previous implementation.

Signed-off-by: Ondrej Fabry <ondrej@fabry.dev>

Author: ondrej-fabry

adapter/socketclient/socketclient.go

@@ -295,8 +295,10 @@ func (c *Client) Disconnect() error {
 	// wait for readerLoop to return
 	c.wg.Wait()
 
-	// Don't bother sending a vl_api_sockclnt_delete_t message,
-	// just close the socket.
+	if err := c.close(); err != nil {
+		log.Debugf("closing failed: %v", err)
+	}
+
 	if err := c.disconnect(); err != nil {
 		return err
 	}
@@ -408,6 +410,49 @@ func (c *Client) open(clientName string) error {
 	return nil
 }
 
+func (c *Client) close() error {
+	var msgCodec = codec.DefaultCodec
+
+	req := &memclnt.SockclntDelete{
+		Index: c.clientIndex,
+	}
+	msg, err := msgCodec.EncodeMsg(req, c.sockDelMsgId)
+	if err != nil {
+		log.Debugln("Encode error:", err)
+		return err
+	}
+	setMsgRequestHeader(msg, c.clientIndex, uint32(deleteMsgContext))
+
+	log.Infof("sending socklntDel (%d bytes): % 0X", len(msg), msg)
+
+	if err := c.writeMsg(msg); err != nil {
+		log.Debugln("Write error: ", err)
+		return err
+	}
+
+	msgReply, err := c.readMsgTimeout(nil, c.disconnectTimeout)
+	if err != nil {
+		var nerr net.Error
+		if errors.As(err, &nerr) && nerr.Timeout() {
+			log.Info("sockclnt_delete_reply: timeout")
+			// we accept timeout for reply
+			return nil
+		}
+		log.Debugln("Read sockclnt_delete_reply error:", err)
+		return err
+	}
+
+	reply := new(memclnt.SockclntDeleteReply)
+	if err := msgCodec.DecodeMsg(msgReply, reply); err != nil {
+		log.Debugln("Decoding sockclnt_delete_reply failed:", err)
+		return err
+	} else if reply.Response != 0 {
+		return fmt.Errorf("sockclnt_delete_reply: response error (%d)", reply.Response)
+	}
+
+	return nil
+}
+
 func (c *Client) setMsgTable(msgTable map[string]uint16, sockDelMsgId uint16) {
 	c.msgTableMu.Lock()
 	defer c.msgTableMu.Unlock()