docs: add an example how to check connection credentials

Author: bednar

examples/connection_check.py

@@ -3,6 +3,8 @@
 """
 
 from influxdb_client import InfluxDBClient
+from influxdb_client.client.write_api import SYNCHRONOUS
+from influxdb_client.rest import ApiException
 
 """
 Define credentials
@@ -15,17 +17,39 @@
 
 def check_connection():
     """Check that the InfluxDB is running."""
-    pass
+    print("> Checking connection ...", end=" ")
+    client.api_client.call_api('/ping', 'GET')
+    print("ok")
 
 
 def check_query():
     """Check that the credentials has permission to query from the Bucket"""
-    pass
+    print("> Checking credentials for query ...", end=" ")
+    try:
+        client.query_api().query(f"from(bucket:\"{bucket}\") |> range(start: -1m) |> limit(n:1)", org)
+    except ApiException as e:
+        # missing credentials
+        if e.status == 404:
+            raise Exception(f"The specified token doesn't have sufficient credentials to read from '{bucket}' "
+                            f"or specified bucket doesn't exists.") from e
+        raise
+    print("ok")
 
 
 def check_write():
     """Check that the credentials has permission to write into the Bucket"""
-    pass
+    print("> Checking credentials for write ...", end=" ")
+    try:
+        client.write_api(write_options=SYNCHRONOUS).write(bucket, org, b"")
+    except ApiException as e:
+        # missing credentials
+        if e.status == 404:
+            raise Exception(f"The specified token doesn't have sufficient credentials to write to '{bucket}' "
+                            f"or specified bucket doesn't exists.") from e
+        # 400 (BadRequest) caused by empty LineProtocol
+        if e.status != 400:
+            raise
+    print("ok")
 
 
 with InfluxDBClient(url=url, token=token, org=org) as client: