cfg: Read configuration from .d files and multiple locations

- Read configuration files from three different locations.
/usr/share/freedombox/freedombox.config, /etc/plinth/plinth.config and
/etc/freedombox/freedombox.conf. Later listed has higher priority.

- Provide backward compatibility for /etc/plinth/plinth.config files. With lower
priority than /etc/freedombox but higher priority than /usr/share/.

- Read sorted files from config.d directories with the same suffix as original
configuration file. Parse them by priority. This allows administrator/programs
to drop in configuration bits without worry about editing files.

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

plinth/cfg.py

@@ -50,6 +50,19 @@ develop = False
 config_files = []
 
 
+def expand_to_dot_d_paths(file_paths):
+    """Expand a list of file paths to include file.d/* also."""
+    final_list = []
+    for file_path in file_paths:
+        final_list.append(str(file_path))
+        path = pathlib.Path(file_path)
+        path_d = path.with_suffix(path.suffix + '.d')
+        for dot_d_file in sorted(path_d.glob('*' + path.suffix)):
+            final_list.append(str(dot_d_file))
+
+    return final_list
+
+
 def get_develop_config_path():
     """Return config path of current source folder for development mode."""
     root_directory = os.path.dirname(os.path.realpath(__file__))
@@ -58,15 +71,20 @@ def get_develop_config_path():
     return config_path
 
 
-def get_config_path():
+def get_config_paths():
     """Get default config paths."""
-    return '/etc/freedombox/freedombox.config'
+    return [
+        '/usr/share/freedombox/freedombox.config',
+        '/etc/plinth/plinth.config',
+        '/etc/freedombox/freedombox.config',
+    ]
 
 
 def read():
     """Read all configuration files."""
-    config_path = get_config_path()
-    read_file(config_path)
+    config_paths = get_config_paths()
+    for config_path in expand_to_dot_d_paths(config_paths):
+        read_file(config_path)
 
 
 def read_file(config_path):

plinth/tests/data/configs/freedombox.config.d/01_first.config

@@ -0,0 +1,2 @@
+[Misc]
+box_name = FreedomBox01

plinth/tests/data/configs/freedombox.config.d/02_second.config

@@ -0,0 +1,2 @@
+[Misc]
+box_name = FreedomBox02

plinth/tests/data/configs/freedombox.config.d/03_third.foo

@@ -0,0 +1,2 @@
+[Misc]
+box_name = FreedomBox03

plinth/tests/test_cfg.py

@@ -45,15 +45,30 @@ def test_read_default_config_file():
     compare_configurations(parser)
 
 
-@patch('plinth.cfg.get_config_path')
-def test_read_primary_config_file(get_config_path):
+@patch('plinth.cfg.get_config_paths')
+def test_read_primary_config_file(get_config_paths):
     """Verify that the primary config file is used by default."""
     config_path = CONFIG_FILE_WITH_MISSING_OPTIONS
-    get_config_path.return_value = config_path
+    get_config_paths.return_value = [config_path]
     cfg.read()
     assert cfg.config_files[-1] == config_path
 
 
+@patch('plinth.cfg.get_config_paths')
+def test_read_dot_d_config_files(get_config_paths):
+    """Verify that the configuration is read from .d directories."""
+    root_dir = pathlib.Path(__file__).resolve().parent
+    config_path = root_dir / 'data' / 'configs' / 'freedombox.config'
+    config_path_d = config_path.with_suffix(config_path.suffix + '.d')
+
+    get_config_paths.return_value = [str(config_path)]
+    cfg.read()
+    assert cfg.config_files[-3] == str(config_path)
+    assert cfg.config_files[-2] == str(config_path_d / '01_first.config')
+    assert cfg.config_files[-1] == str(config_path_d / '02_second.config')
+    assert cfg.box_name == 'FreedomBox02'
+
+
 def test_read_develop_config_file():
     """Verify that the correct develop config file is used."""
     test_dir = os.path.dirname(os.path.realpath(__file__))