feat: add show-unit probes

probes/README.md

@@ -0,0 +1,17 @@
+# External probes
+
+These probes are meant to be run from the host where the juju client is installed,
+
+```bash
+juju export-bundle | ./probe_bundle.py
+juju status --format=yaml | ./probe_status.py
+juju show-unit --format=yaml | ./probe_show_unit.py
+```
+
+or by piping in the bundle or status yaml,
+
+```bash
+cat bundle.yaml | ./probe_bundle.py
+cat status.yaml | ./probe_status.py
+cat show_unit.yaml | ./probe_show_unit.py
+```

probes/show-unit/relation_dashboard_uid.py

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+#!/usr/bin/env python3
+
+"""Probe for juju show-unit."""
+
+import sys
+import yaml
+import json
+import base64
+import lzma
+import re
+
+
+def _uid_from_encoded_dashboard(data: bytes) -> str:
+    decoded_data = base64.b64decode(data)
+    decompressed_data = lzma.decompress(decoded_data)
+    return json.loads(decompressed_data).get("uid")
+
+
+def _is_valid_format(uid: str) -> bool:
+    if not uid:
+        return False
+    # https://grafana.com/docs/grafana/latest/developers/http_api/dashboard/#identifier-id-vs-unique-identifier-uid
+    if len(uid) > 40:
+        return False
+    # https://community.grafana.com/t/which-characters-will-never-appear-in-a-dashboard-uid/11500
+    for char in uid:
+        if not re.match(r"[a-zA-Z0-9_-]", char):
+            return False
+
+    return True
+
+
+def validate_dashboard_uid(show_unit: dict):
+    """The top-level UID for each dashboard in relation data is not empty and has a valid format.
+
+    Args:
+        show_unit: A dict containing the contents of 'juju show-unit grafana/0'
+    """
+    unit_name = next(iter(show_unit))
+    # 1. Extract the relation-info
+    relation_info = show_unit[unit_name]["relation-info"]
+    # 2. Extract the "grafana" endpoint relations
+    grafana_endpoints = [
+        relation for relation in relation_info if relation["endpoint"] == "grafana"
+    ]
+    for grafana_endpoint in grafana_endpoints:
+        # 3. Extract the application data
+        app_data = grafana_endpoint["application-data"]
+        relation_id = grafana_endpoint["relation-id"]
+        # 4. Convert dashboard data to JSON and decode
+        dashboards = json.loads(app_data["dashboards"])
+        for id in dashboards:
+            for meta in dashboards[id]:
+                decoded_uid = _uid_from_encoded_dashboard(meta["content"])
+                # 5. Check if the top-level UID exist and is not empty
+                if not _is_valid_format(decoded_uid):
+                    print(f"Invalid dashboard UID ({id}) for relation-id ({relation_id})", file=sys.stderr)
+
+    print("Probe finished!")
+
+
+if __name__ == "__main__":
+    data = yaml.safe_load(sys.stdin)
+    validate_dashboard_uid(data)