transmission: Read configuration as super user

Due to permission restrictions on the configuration file (due to stored
password), it is not possible to read it as plinth user.  Read it using
sudo instead.

CHANGELOG.md

@@ -7,6 +7,7 @@ All notable changes to this project will be documented in this file.
 
 ### Changed
 - dynamicdns: Allowed Plinth to run as non-root.
+- transmission: Read configuration as super user.
 
 ## [0.10.0] - 2016-08-12
 ### Added

actions/transmission

@@ -37,13 +37,10 @@ def parse_arguments():
     parser = argparse.ArgumentParser()
     subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')
 
-    # Enable service
     subparsers.add_parser('enable', help='Enable Transmission service')
-
-    # Disable service
     subparsers.add_parser('disable', help='Disable Transmission service')
-
+    subparsers.add_parser(
-    # Merge given JSON configration with existing
+        'get-configuration', help='Return the current configuration')
     subparsers.add_parser(
         'merge-configuration',
         help='Merge JSON configuration from stdin with existing')
@@ -63,6 +60,12 @@ def subcommand_disable(_):
     action_utils.service_disable('transmission-daemon')
 
 
+def subcommand_get_configuration(_):
+    """Return the current configuration in JSON format."""
+    configuration = open(TRANSMISSION_CONFIG, 'r').read()
+    print(configuration)
+
+
 def subcommand_merge_configuration(arguments):
     """Merge given JSON configuration with existing configuration."""
     configuration = sys.stdin.read()

plinth/modules/transmission/__init__.py

@@ -47,8 +47,6 @@ description = [
 
 service = None
 
-TRANSMISSION_CONFIG = '/etc/transmission-daemon/settings.json'
-
 
 def init():
     """Intialize the Transmission module."""

plinth/modules/transmission/views.py

@@ -42,7 +42,8 @@ class TransmissionServiceView(views.ServiceView):
 
     def get_initial(self):
         """Get the current settings from Transmission server."""
-        configuration = open(transmission.TRANSMISSION_CONFIG, 'r').read()
+        configuration = actions.superuser_run(
+            'transmission', ['get-configuration'])
         status = json.loads(configuration)
         status = {key.translate(str.maketrans({'-': '_'})): value
                   for key, value in status.items()}