fix setting config with DOCKER_CONFIG_FILE (#23096)

Fixes #23095

Fixed issue preventing a caller from setting a docker
configuration file (e.g. docker.yml) by specifing the
config file path in the `DOCKER_CONFIG_FILE` environment
variable. Previously, the cli argument parser set a default value for
the `--config-file` argument which would prevent ever checking the
environment variable, regardless of whether or not the `--config-file`
argument even specified a valid file.

This commit adds a global `DEFAULT_DOCKER_CONFIG_FILE` variable, which
points to the current default `docker.yml` config in the
contrib/inventory directory. Now, when this script is called from the
command line, the config file passed with the cli `--config-file` arg
will be given the highest precedence; if it is absent, this script will
then check if the `DOCKER_CONFIG_FILE` env var is set, and load the
config file specified if possible. If neither the environment variable
or cli argument are specified, then the script will attempt to parse the
config file `docker.yml` in this script's directory (if present).

If either the `DOCKER_CONFIG_FILE` environment variable or the
`--config-file` argument are given but point to a nonexistant file, then
the script will print an error message and exit with an error code.

It is *not* an error condition if the fallback `docker.yml` does not
exist.

contrib/inventory/docker.py

@@ -391,6 +391,7 @@ except ImportError as exc:
         class Client:
             pass
 
+DEFAULT_DOCKER_CONFIG_FILE = os.path.splitext(os.path.basename(__file__))[0] + '.yml'
 DEFAULT_DOCKER_HOST = 'unix://var/run/docker.sock'
 DEFAULT_TLS = False
 DEFAULT_TLS_VERIFY = False
@@ -784,29 +785,29 @@ class DockerInventory(object):
 
     def _parse_config_file(self):
         config = dict()
-        config_path = None
+        config_file = DEFAULT_DOCKER_CONFIG_FILE
 
         if self._args.config_file:
-            config_path = self._args.config_file
+            config_file = self._args.config_file
         elif self._env_args.config_file:
-            config_path = self._env_args.config_file
+            config_file = self._env_args.config_file
 
-        if config_path:
-            try:
-                config_file = os.path.abspath(config_path)
-                # default config path is docker.yml in same directory as this script
-                # old behaviour is docker.yml in current directory. Handle both.
-                if not os.path.exists(config_file):
-                    config_file = os.path.abspath(os.path.basename(config_path))
-            except:
-                config_file = None
-
-            if config_file and os.path.exists(config_file):
-                with open(config_file) as f:
-                    try:
-                        config = yaml.safe_load(f.read())
-                    except Exception as exc:
-                        self.fail("Error: parsing %s - %s" % (config_path, str(exc)))
+        config_file = os.path.abspath(config_file)
+
+        if os.path.isfile(config_file):
+            with open(config_file) as f:
+                try:
+                    config = yaml.safe_load(f.read())
+                except Exception as exc:
+                    self.fail("Error: parsing %s - %s" % (config_file, str(exc)))
+        else:
+            msg = "Error: config file given by {} does not exist - " + config_file
+            if self._args.config_file:
+                self.fail(msg.format('command line argument'))
+            elif self._env_args.config_file:
+                self.fail(msg.format(DOCKER_ENV_ARGS.get('config_file')))
+            else:
+                self.log(msg.format('DEFAULT_DOCKER_CONFIG_FILE'))
         return config
 
     def log(self, msg, pretty_print=False):
@@ -831,9 +832,6 @@ class DockerInventory(object):
     def _parse_cli_args(self):
         # Parse command line arguments
 
-        basename = os.path.splitext(os.path.basename(__file__))[0]
-        default_config = os.path.join(os.path.dirname(__file__), basename + '.yml')
-
         parser = argparse.ArgumentParser(
             description='Return Ansible inventory for one or more Docker hosts.')
         parser.add_argument('--list', action='store_true', default=True,
@@ -844,8 +842,8 @@ class DockerInventory(object):
                             help='Only get information for a specific container.')
         parser.add_argument('--pretty', action='store_true', default=False,
                             help='Pretty print JSON output(default: False)')
-        parser.add_argument('--config-file', action='store', default=default_config,
-                            help="Name of the config file to use. Default is %s" % (default_config))
+        parser.add_argument('--config-file', action='store', default=None,
+                            help="Name of the config file to use. Default is %s" % (DEFAULT_DOCKER_CONFIG_FILE))
         parser.add_argument('--docker-host', action='store', default=None,
                             help="The base url or Unix sock path to connect to the docker daemon. Defaults to %s"
                                  % (DEFAULT_DOCKER_HOST))