Improve exception handling in lemur_sftp, Add Authentication failure test

lemur/plugins/lemur_sftp/plugin.py

@@ -19,6 +19,7 @@
 from os import path
 
 import paramiko
+from paramiko.ssh_exception import AuthenticationException
 
 from flask import current_app
 from lemur.plugins import lemur_sftp
@@ -179,7 +180,7 @@ class SFTPDestinationPlugin(DestinationPlugin):
                 current_app.logger.error(
                     "No password or private key provided. Can't proceed"
                 )
-                raise paramiko.ssh_exception.AuthenticationException
+                raise AuthenticationException
 
             # open the sftp session inside the ssh connection
             sftp = ssh.open_sftp()
@@ -243,7 +244,7 @@ class SFTPDestinationPlugin(DestinationPlugin):
                 current_app.logger.error(
                     "No password or private key provided. Can't proceed"
                 )
-                raise paramiko.ssh_exception.AuthenticationException
+                raise AuthenticationException
 
             # split the path into it's segments, so we can create it recursively
             allparts = []
@@ -300,6 +301,9 @@ class SFTPDestinationPlugin(DestinationPlugin):
 
             ssh.close()
 
+        except AuthenticationException as e:
+            current_app.logger.error("ERROR in {0}: {1}".format(e.__class__, e))
+            raise AuthenticationException("Couldn't connect to {0}, due to an Authentication exception.")
         except Exception as e:
             current_app.logger.error("ERROR in {0}: {1}".format(e.__class__, e))
             try:
@@ -307,7 +311,7 @@ class SFTPDestinationPlugin(DestinationPlugin):
             except BaseException:
                 pass
             message = ''
-            if e.errors:
+            if hasattr(e, 'errors'):
                 for _, error in e.errors.items():
                     message = error.strerror
                 raise Exception('Couldn\'t upload file to {}, error message: {}'.format(host, message))

lemur/plugins/lemur_sftp/tests/test_sftp.py

@@ -3,6 +3,7 @@ from unittest.mock import patch, Mock, MagicMock, mock_open
 
 from flask import Flask
 from lemur.plugins.lemur_sftp import plugin
+from paramiko.ssh_exception import AuthenticationException
 
 
 class TestSftp(unittest.TestCase):
@@ -18,6 +19,15 @@ class TestSftp(unittest.TestCase):
     def tearDown(self):
         self.ctx.pop()
 
+    def test_failing_ssh_connection(self):
+        dst_path = '/var/non-existent'
+        files = {'first-file': 'data'}
+        options = [{'name': 'host', 'value': 'non-existent'}, {'name': 'port', 'value': '22'},
+                   {'name': 'user', 'value': 'test_acme'}]
+
+        with self.assertRaises(AuthenticationException):
+            self.sftp_destination.upload_file(dst_path, files, options)
+
     @patch("lemur.plugins.lemur_sftp.plugin.paramiko")
     def test_upload_file_single_with_password(self, mock_paramiko):
         dst_path = '/var/non-existent'