examples: Add an example of how to use Netplan's CFFI bindings

examples/cffi-bindings.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2023 Canonical, Ltd.
+# Author: Lukas Märdian <slyon@ubuntu.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 3.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import io
+import tempfile
+from netplan import Parser, State, _create_yaml_patch
+from netplan import NetplanException, NetplanParserException
+FALLBACK_FILENAME = '70-netplan-set.yaml'
+
+# This script is a demo/example, making use of Netplan's CFFI Python bindings.
+# It does process your local /etc/netplan/ hierarchy, so be careful using it.
+# At first, it creates a Parser() object and a YAML patch, setting a
+# "network.ethernets.eth99.dhcp4=true" value. It loads any existing Netplan
+# YAML hierarcy from /etc/netplan/ and loads/applies the above mentioned patch
+# on top of it. Afterwards, it creates a State() object, importing parsed data
+# for validation and checks for any errors.
+# On succesful validation, it walks through all NetDefs in the validated
+# Netplan state and prints the Netplan ID and backend renderer of given NetDef.
+# Finally, it writes the validated state (including the eth99.dhcp4 setting)
+# back to disk in /etc/netplan/.
+if __name__ == '__main__':
+    yaml_path = ['network', 'ethernets', 'eth99', 'dhcp4']
+    value = 'true'
+
+    parser = Parser()
+    with tempfile.TemporaryFile() as tmp:
+        _create_yaml_patch(yaml_path, value, tmp)
+        tmp.flush()
+
+        # Parse the full, existing YAML config hierarchy
+        parser.load_yaml_hierarchy(rootdir='/')
+
+        # Load YAML patch, containing our new settings
+        tmp.seek(0, io.SEEK_SET)
+        parser.load_yaml(tmp)
+
+        # Validate the final parser state
+        state = State()
+        try:
+            # validation of current state + new settings
+            state.import_parser_results(parser)
+        except NetplanParserException as e:
+            print('Error in', e.filename, 'Row/Col', e.line, e.column, '->', e.message)
+        except NetplanException as e:
+            print('Error:', e.message)
+
+        # Walk through all NetdefIDs in the state and print their backend
+        # renderer, to demonstrate working with NetDefinitionIterator &
+        # NetDefinition
+        for netdef_id, netdef in state.netdefs.items():
+            print('Netdef', netdef_id, 'is managed by:', netdef.backend)
+
+        # Write the new data from the YAML patch to disk, updating an
+        # existing Netdef, if file already exists, or FALLBACK_FILENAME
+        state._update_yaml_hierarchy(FALLBACK_FILENAME, rootdir='/')