[minor] refactor mail server connection code

- Added `connect_to_mail_server` function to handle mail server connection
- Moved code for connecting to the mail server from `StationQC` class to `connect_to_mail_server`
- Updated references to use `connect_to_mail_server` in `StationQC` class
- Created new function `get_credential` to retrieve credentials from Docker secrets or environment variables

survBot.py

@@ -23,7 +23,8 @@ from obspy.clients.filesystem.sds import Client
 
 from write_utils import get_html_text, get_html_link, get_html_row, html_footer, get_html_header, get_print_title_str, \
     init_html_table, finish_html_table, get_mail_html_header, add_html_image
-from utils import get_bg_color, get_font_color, modify_stream_for_plot, set_axis_yticks, set_axis_color, plot_axis_thresholds
+from utils import get_bg_color, get_font_color, modify_stream_for_plot, set_axis_yticks, set_axis_color, plot_axis_thresholds, \
+    connect_to_mail_server
 
 try:
     import smtplib
@@ -738,7 +739,6 @@ class StationQC(object):
         if add_addresses:
             # create copy of addresses ( [:] ) to prevent changing original, general list with addresses
             addresses = addresses[:] + list(add_addresses)
-        server = mail_params.get('mailserver')
         if not sender or not addresses:
             logging.info('Mail sender or addresses not (correctly) defined. Return')
             return
@@ -757,43 +757,10 @@ class StationQC(object):
         html_str = self.add_html_mail_body(text)
         msg.add_alternative(html_str, subtype='html')
 
-        # send message via SMTP server
-        # set up starttls connection if server is not "localhost"
-        if server == 'localhost':
-            # create connection to localhost
-            s = smtplib.SMTP(server)
-        else:
-            user = mail_params.get('user')
-            # read user from docker secret if it is set to 'DOCKER' or
-            # read user from environment variable if it is set to 'ENV'
-            if user == 'DOCKER':
-                try:
-                    with open('/run/secrets/mail_user', 'r') as f:
-                        user = f.read().strip()
-                except FileNotFoundError as e:
-                    logging.error('Could not read mail user from docker secret')
-                    logging.error(e)
-            elif user == 'ENV':
-                user = os.environ.get(mail_params.get('user_env'))
-            
-            password = mail_params.get('password')
-            # read password from docker secret if it is set to 'DOCKER' or
-            # read password from environment variable if it is set to 'ENV'
-            if password == 'DOCKER':
-                try:
-                    with open('/run/secrets/mail_password', 'r') as f:
-                        password = f.read().strip()
-                except FileNotFoundError as e:
-                    logging.error('Could not read mail password from docker secret')
-                    logging.error(e)
-            elif password == 'ENV':
-                password = os.environ.get(mail_params.get('password_env'))
-
-            # create SSL connection to server
-            s = smtplib.SMTP_SSL(server, mail_params.get('port'))
-            s.login(mail_params.get('user'), mail_params.get('password'))
-
-        # send mail and close connection
+        # connect to server, send mail and close connection
+        s = connect_to_mail_server(mail_params)
+        if not s: # if connection failed
+            return
         s.send_message(msg)
         s.quit()
 

utils.py

@@ -5,6 +5,7 @@ import logging
 
 import matplotlib
 import numpy as np
+import smtplib
 
 from obspy import Stream
 
@@ -279,3 +280,50 @@ def annotate_voltage_states(ax, parameters, pb_key, color='0.75'):
 
         ax.annotate(out_string, (ax.get_xlim()[-1], voltage), color=color, fontsize='xx-small',
                     horizontalalignment='right')
+
+def get_credential(source, param):
+    """
+    Retrieve a credential from a Docker secret or environment variable.
+    """
+    if source == 'DOCKER':
+        try:
+            with open('/run/secrets/'+param.lower(), 'r') as f:
+                return f.read().strip()
+        except FileNotFoundError as e:
+            logging.error(f'Could not read from Docker secret at /run/secrets/{param.lower()}')
+            logging.error(e)
+    elif source == 'ENV':
+        try:
+            return os.environ.get(param.upper())
+        except Exception as e:
+            logging.error(f'Could not read from environment variable {param.upper()}')
+            logging.error(e)
+    # return source if no credential was found
+    return source
+
+def connect_to_mail_server(self, mail_params):
+    """
+    Connect to mail server and return server object.
+    """
+    # get server from parameters
+    server = mail_params.get('mailserver')
+    # get auth_type from parameters
+    auth_type = mail_params.get('auth_type')
+    # set up connection to mail server
+    if auth_type == 'None':
+        s = smtplib.SMTP(server)
+    else:
+        # user and password from parameters, docker secret or environment variable
+        user = get_credential(mail_params.get('user'), 'mail_user')
+        password = get_credential(mail_params.get('password'), 'mail_password')
+        # create secure connection to server
+        if auth_type == 'SSL':
+            s = smtplib.SMTP_SSL(server, mail_params.get('port'))
+        elif auth_type == 'TLS':
+            s = smtplib.SMTP(server, mail_params.get('port'))
+            s.starttls()
+        else:
+            logging.error('Unknown authentication type. Mails can not be sent')
+            return
+        s.login(mail_params.get('user'), mail_params.get('password'))
+    return s