Error handling: Fail early when database cluster does not respond

Author: amotl

CHANGES.rst

@@ -6,6 +6,7 @@ Unreleased
 ==========
 - Modernize project definition to latest Python best practices. Thanks, @surister.
 - Exceptions: Exceptions from the BLOB API now include their full names.
+- Changed connection behaviour to fail early if the database cluster does not respond
 
 2025/01/30 2.0.0
 ================

docs/by-example/client.rst

@@ -29,12 +29,8 @@ respond, the request is automatically routed to the next server:
     >>> connection = client.connect([invalid_host, crate_host])
     >>> connection.close()
 
-If no ``servers`` are given, the default one ``http://127.0.0.1:4200`` is used:
-
-    >>> connection = client.connect()
-    >>> connection.client._active_servers
-    ['http://127.0.0.1:4200']
-    >>> connection.close()
+If no ``servers`` are supplied to the ``connect`` method, the default address
+``http://127.0.0.1:4200`` is used.
 
 If the option ``error_trace`` is set to ``True``, the client will print a whole
 traceback if a server error occurs:

src/crate/client/connection.py

@@ -20,6 +20,7 @@
 # software solely pursuant to the terms of the relevant commercial agreement.
 
 from verlib2 import Version
+from verlib2.packaging.version import InvalidVersion
 
 from .blob import BlobContainer
 from .cursor import Cursor
@@ -197,14 +198,20 @@ def get_blob_container(self, container_name):
 
     def _lowest_server_version(self):
         lowest = None
+        last_connection_error = None
         for server in self.client.active_servers:
             try:
                 _, _, version = self.client.server_infos(server)
                 version = Version(version)
-            except (ValueError, ConnectionError):
+            except ConnectionError as ex:
+                last_connection_error = ex
+                continue
+            except (ValueError, InvalidVersion):
                 continue
             if not lowest or version < lowest:
                 lowest = version
+        if lowest is None and last_connection_error is not None:
+            raise last_connection_error
         return lowest or Version("0.0.0")
 
     def __repr__(self):

tests/client/test_connection.py

@@ -4,6 +4,7 @@
 import pytest
 from urllib3 import Timeout
 
+import crate.client.exceptions
 from crate.client import connect
 from crate.client.connection import Connection
 from crate.client.exceptions import ProgrammingError
@@ -12,6 +13,13 @@
 from .settings import crate_host
 
 
+def test_invalid_server_address():
+    client = Client(servers="localhost:4202")
+    with pytest.raises(crate.client.exceptions.ConnectionError) as excinfo:
+        connect(client=client)
+    assert excinfo.match("Server not available")
+
+
 def test_lowest_server_version():
     """
     Verify the lowest server version is correctly set.