fix(sftp): reconnect to server when connection was broken (#6416 close #6403)

* fix(sftp): reconnect to server when conn was broken (close #6403)

* fix(sftp): fix typo

---------

Co-authored-by: George Chen <gchen@isimarkets.com>

drivers/sftp/util.go

@@ -4,6 +4,7 @@ import (
 	"path"
 
 	"github.com/pkg/sftp"
+	log "github.com/sirupsen/logrus"
 	"golang.org/x/crypto/ssh"
 )
 
@@ -30,6 +31,23 @@ func (d *SFTP) initClient() error {
 		return err
 	}
 	d.client, err = sftp.NewClient(conn)
+	if err == nil {
+		d.clientConnectionError = nil
+		go func(d *SFTP) {
+			d.clientConnectionError = d.client.Wait()
+		}(d)
+	}
+	return err
+}
+
+func (d *SFTP) clientReconnectOnConnectionError() error {
+	err := d.clientConnectionError
+	if err == nil {
+		return nil
+	}
+	log.Debugf("[sftp] discarding closed sftp connection: %v", err)
+	_ = d.client.Close()
+	err = d.initClient()
 	return err
 }