service: Capture stdout/stderr when running as systemd unit

- Avoid duplicate log messages by not logging to console when running as systemd
unit.

- Retain normal logging when running on the terminal.

Tests:

- When running as systemd unit, output to stdin/stdout is captured in systemd
journal and visible with 'sudo freedombox-logs'.

- When running on terminal manually with 'sudo --user plinth ./run --develop'
both log messages and stdout/stderr prints() are visible.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

data/usr/lib/systemd/system/plinth.service

@@ -17,8 +17,6 @@ RestartSec=5
 ExecReload=/bin/kill -HUP $MAINPID
 User=plinth
 Group=plinth
-StandardOutput=null
-StandardError=null
 NotifyAccess=main
 # Uploaded files in /var/tmp/ are shared with FreedomBox privileged service by
 # joining namespaces.

plinth/log.py

@@ -5,6 +5,7 @@ Setup logging for the application.
 
 import logging
 import logging.config
+import sys
 import typing
 import warnings
 
@@ -158,5 +159,11 @@ def get_configuration():
             }
         }
     }
+    if not sys.stdin.isatty():
+        # If running on a console, say due to user manually starting it, then
+        # log everything to console. However, if we are running as a systemd
+        # unit then no need to log to console. This allows us to capture
+        # stdout/stderr in systemd unit without repeating the log messages.
+        configuration['root']['handlers'].remove('console')
 
     return configuration