update-check: T3476: Allow update-check for VyOS images

Ability to autocheck available new images
Parse remote URL JSON image-version.json file and compare version
VyOS with a local current version, if find diff sent wall
message that the new image is available
Also, add op-mode command to check images "show system image"
With option "auto-check" check will be once per 12 hours

  set system update-check auto-check
  set system update-check url 'http://example.com/image-version.json'

If new version is available shows it per login (MOTD)

1 files changed, 92 insertions, 0 deletions

diff --git a/src/op_mode/system.py b/src/op_mode/system.py
new file mode 100755
index 000000000..11a3a8730
--- /dev/null
+++ b/src/op_mode/system.py
@@ -0,0 +1,92 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2022 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# 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 jmespath
+import json
+import sys
+import requests
+import typing
+
+from sys import exit
+
+from vyos.configquery import ConfigTreeQuery
+
+import vyos.opmode
+import vyos.version
+
+config = ConfigTreeQuery()
+base = ['system', 'update-check']
+
+
+def _compare_version_raw():
+    url = config.value(base + ['url'])
+    local_data = vyos.version.get_full_version_data()
+    remote_data = vyos.version.get_remote_version(url)
+    if not remote_data:
+        return {"error": True,
+                "reason": "Unable to get remote version"}
+    if local_data.get('version') and remote_data:
+        local_version = local_data.get('version')
+        remote_version = jmespath.search('[0].version', remote_data)
+        image_url = jmespath.search('[0].url', remote_data)
+        if local_data.get('version') != remote_version:
+            return {"error": False,
+                    "update_available": True,
+                    "local_version": local_version,
+                    "remote_version": remote_version,
+                    "url": image_url}
+        return {"update_available": False,
+                "local_version": local_version,
+                "remote_version": remote_version}
+
+
+def _formatted_compare_version(data):
+    local_version = data.get('local_version')
+    remote_version = data.get('remote_version')
+    url = data.get('url')
+    if {'update_available','local_version', 'remote_version', 'url'} <= set(data):
+        return f'Current version: {local_version}\n\nUpdate available: {remote_version}\nUpdate URL: {url}'
+    elif local_version == remote_version and remote_version is not None:
+        return f'No available updates for your system \n' \
+               f'current version: {local_version}\nremote version: {remote_version}'
+    else:
+        return 'Update not found'
+
+
+def _verify():
+    if not config.exists(base):
+        return False
+    return True
+
+
+def show_update(raw: bool):
+    if not _verify():
+        raise vyos.opmode.UnconfiguredSubsystem("system update-check not configured")
+    data = _compare_version_raw()
+    if raw:
+        return data
+    else:
+        return _formatted_compare_version(data)
+
+
+if __name__ == '__main__':
+    try:
+        res = vyos.opmode.run(sys.modules[__name__])
+        if res:
+            print(res)
+    except (ValueError, vyos.opmode.Error) as e:
+        print(e)
+        sys.exit(1)