Add 'netlab show defaults' command (closes #906)

docs/netlab/show.md

@@ -5,6 +5,7 @@
 The following settings can be displayed:
 
 * **[attributes](netlab-show-attributes)** -- Supported lab topology attributes
+* **[defaults](netlab-show-defaults)** -- User/system [defaults](../defaults.md)
 * **[devices](netlab-show-devices)** -- Supported devices
 * **[images](netlab-show-images)** -- Vagrant box names or container names for all supported devices or a single device
 * **[module](netlab-show-modules)** -- Configuration modules
@@ -137,6 +138,60 @@ weight:
   type: int
 ```
 
+(netlab-show-defaults)=
+## Display User/System Defaults
+
+The **netlab show defaults** displays _netlab_ defaults collected from [user/system default files](../defaults.md):
+
+```text
+usage: netlab show defaults [-h] [--system] [--format {table,text,yaml}]
+                            [--plugin PLUGIN [PLUGIN ...]]
+                            [match]
+
+Display (a subset) of system/user defaults
+
+positional arguments:
+  match                 Display defaults within the specified subtree
+
+options:
+  -h, --help            show this help message and exit
+  --system              Display system information (without user defaults)
+  --format {table,text,yaml}
+                        Output format (table, text, yaml)
+  --plugin PLUGIN [PLUGIN ...]
+                        Add plugin attributes to the system defaults
+
+```
+
+**Notes**
+
+* The `--plugin` argument must be the last parameter on the command line -- all tokens specified after it are added to the list of plugins
+* The displayed information does not include lab-specific defaults specified in lab topology or [alternate default file locations](defaults-locations).
+* You can also display system defaults with `netlab inspect defaults` (requires a running lab) or `netlab create -o yaml:defaults` (requires a working topology file)
+
+**Examples**
+
+Display [graph output module](../outputs/graph.md) defaults (**outputs.graph**):
+
+```text
+$ netlab show defaults outputs.graph
+
+netlab default settings within the outputs.graph subtree
+=============================================================================
+
+as_clusters: true
+colors:
+  as: '#e8e8e8'
+  ebgp: '#b21a1a'
+  ibgp: '#613913'
+  node: '#ff9f01'
+  stub: '#d1bfab'
+interface_labels: false
+margins:
+  as: 16
+node_address_label: true
+```
+
 (netlab-show-devices)=
 ## Display Supported Devices
 

netsim/cli/show.py

@@ -23,6 +23,7 @@
 from .show_commands import reports as _reports
 from .show_commands import providers as _providers
 from .show_commands import attributes as _attributes
+from .show_commands import defaults as _defaults
 
 show_dispatch: dict = {
   'images': {
@@ -56,6 +57,10 @@
   'attributes': {
     'exec':  _attributes.show,
     'parse': _attributes.parse
+  },
+  'defaults': {
+    'exec':  _defaults.show,
+    'parse': _defaults.parse
   }
 }
 

netsim/cli/show_commands/defaults.py

@@ -0,0 +1,50 @@
+#
+# netlab show attributes -- display supported attributes
+#
+
+import argparse
+import typing
+import textwrap
+from box import Box
+
+from ...utils import strings,log
+from ... import data
+from . import show_common_parser,parser_add_module,DEVICES_TO_SKIP,get_modlist
+
+def parse() -> argparse.ArgumentParser:
+  parser = show_common_parser('defaults','(a subset) of system/user defaults')
+  parser.add_argument(
+    nargs='?',
+    default='',
+    dest='match',
+    action='store',
+    help='Display defaults within the specified subtree')
+  parser.add_argument(
+    '--plugin',
+    nargs='+',
+    dest='plugin',
+    action='store',
+    help='Add plugin attributes to the system defaults')
+
+  return parser
+
+def get_attribute_subset(settings: Box, args: argparse.Namespace) -> typing.Optional[Box]:
+  if not args.match:
+    return settings
+
+  return settings.get(args.match,'None')
+
+def show(settings: Box, args: argparse.Namespace) -> None:
+  show = get_attribute_subset(settings, args)
+  if show is None:
+    log.fatal('There are no system/user defaults within the {args.match} subtree')
+
+  if args.format in ['text','table']:
+    print(f"""
+netlab default settings {"within the "+args.match+" subtree" if args.match else ""}
+=============================================================================
+""")
+  elif args.format == 'yaml':
+    print('---')
+
+  print(strings.get_yaml_string(show))