generalconfig: streamlined config discovery

determine generalconfig file location in order:
  - command line argument
  - environment variable
  - git location (../cfg)
  - local location (cwd)
  - global location (/etc/frappy)

Change-Id: Ie34bcbd5188837075ee7bb7d5029d676ae72378e
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/34839
Reviewed-by: Bjoern Pedersen <bjoern.pedersen@frm2.tum.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>

bin/frappy-server

@@ -35,7 +35,15 @@ from frappy.server import Server
 
 
 def parseArgv(argv):
-    parser = argparse.ArgumentParser(description="Manage a SECoP server")
+    parser = argparse.ArgumentParser(
+        description="Manage a SECoP server",
+        epilog="""The server needs some configuration, by default from the
+            generalConfig.cfg file. the keys confdir, logdir and piddir have to
+            be set.
+            Alternatively, one can set the environment variables FRAPPY_CONFDIR
+            FRAPPY_LOGDIR and FRAPPY_PIDDIR to set the required values.
+        """
+    )
     loggroup = parser.add_mutually_exclusive_group()
     loggroup.add_argument("-v", "--verbose",
                           help="Output lots of diagnostic information",

frappy/lib/__init__.py

@@ -37,6 +37,10 @@ from pathlib import Path
 SECoP_DEFAULT_PORT = 10767
 
 
+_gcfg_help = """
+"""
+
+
 class GeneralConfig:
     """generalConfig holds server configuration items
 
@@ -57,11 +61,12 @@ class GeneralConfig:
 
         :param configfile: if present, keys and values from the [FRAPPY] section are read
 
-        default values for 'piddir', 'logdir' and 'confdir' are guessed from the
-        location of this source file and from sys.executable.
-
-        if configfile is not given, the general config file is determined by
-        the env. variable FRAPPY_CONFIG_FILE or <confdir>/generalConfig.cfg is used
+        The following locations are searched for the generalConfig.cfg file.
+          - command line argument
+          - environment variable FRAPPY_CONFIG_FILE
+          - git location (../cfg)
+          - local location (cwd)
+          - global location (/etc/frappy)
 
         if a configfile is given, the values from the FRAPPY section are
         overriding above defaults
@@ -69,37 +74,12 @@ class GeneralConfig:
         finally, the env. variables FRAPPY_PIDDIR, FRAPPY_LOGDIR and FRAPPY_CONFDIR
         are overriding these values when given
         """
+
+        configfile = self._get_file_location(configfile)
+
         cfg = {}
         mandatory = 'piddir', 'logdir', 'confdir'
         repodir = Path(__file__).parents[2].expanduser().resolve()
-        # create default paths
-        if (Path(sys.executable).suffix == ".exe"
-           and not Path(sys.executable).name.startswith('python')):
-            # special MS windows environment
-            confdir = Path('./')
-            self.update_defaults(piddir=Path('./'), logdir=Path('./log'))
-        elif path.exists(path.join(repodir, 'cfg')):
-            # running from git repo
-            confdir = repodir / 'cfg'
-            # take logdir and piddir from <repodir>/cfg/generalConfig.cfg
-        else:
-            # running on installed system (typically with systemd)
-            self.update_defaults(
-                piddir=Path('/var/run/frappy'),
-                logdir=Path('/var/log'),
-            )
-            confdir = Path('/etc/frappy')
-        self.set_default('confdir', confdir)
-        if configfile is None:
-            configfile = environ.get('FRAPPY_CONFIG_FILE')
-            if configfile:
-                configfile = Path(configfile).expanduser()
-                if not configfile.exists():
-                    raise FileNotFoundError(configfile)
-            else:
-                configfile = confdir / 'generalConfig.cfg'
-                if not configfile.exists():
-                    configfile = None
         if configfile:
             parser = ConfigParser()
             parser.optionxform = str
@@ -113,6 +93,7 @@ class GeneralConfig:
                     cfg[key] = ':'.join(path.expanduser(v) for v in value.split(':'))
             if cfg.get('confdir') is None:
                 cfg['confdir'] = configfile.parent
+        # environment variables will overwrite the config file
         for key in mandatory:
             env = environ.get(f'FRAPPY_{key.upper()}')
             if env is not None:
@@ -127,14 +108,46 @@ class GeneralConfig:
         if missing_keys:
             if configfile:
                 raise KeyError(f"missing value for {' and '.join(missing_keys)} in {configfile}")
-            raise KeyError('missing %s'
-                           % ' and '.join('FRAPPY_%s' % k.upper() for k in missing_keys))
+
+            if len(missing_keys) < 3:
+                # user specified at least one env variable already
+                missing = ' (missing %s)' % ', '.join('FRAPPY_%s' % k.upper() for k in missing_keys)
+            else:
+                missing = ''
+            raise FileNotFoundError(
+                'Could not determine config file location for the general frappy config. '
+                f'Provide a config file or all required environment variables{missing}. '
+                'For more information, see frappy-server --help.'
+            )
         if 'confdir' in cfg and isinstance(cfg['confdir'], Path):
             cfg['confdir'] = [cfg['confdir']]
         # this is not customizable
         cfg['basedir'] = repodir
         self._config = cfg
 
+    def _get_file_location(self, configfile):
+        """Determining the defaultConfig.cfg location as documented in init()"""
+        # given as command line arg
+        if configfile and Path(configfile).exists():
+            return configfile
+        # if not given as argument, check different sources
+        # env variable
+        fromenv = environ.get('FRAPPY_CONFIG_FILE')
+        if fromenv and Path(fromenv).exists():
+            return fromenv
+        # from ../cfg (there if running from checkout)
+        repodir = Path(__file__).parents[2].expanduser().resolve()
+        if (repodir / 'cfg' / 'generalConfig.cfg').exists():
+            return repodir / 'cfg' / 'generalConfig.cfg'
+        localfile = Path.cwd() / 'generalConfig.cfg'
+        if localfile.exists():
+            return localfile
+        # TODO: leave this hardcoded?
+        globalfile = Path('/etc/frappy/generalConfig.cfg')
+        if globalfile.exists():
+            return globalfile
+        return None
+
     def __getitem__(self, key):
         """access for keys known to exist