enh: do not retry API requests when the server name cannot be resolved

CHANGELOG

@@ -42,6 +42,8 @@
  - enh: use the API action `dcor_group_list_for_user` (ckanext-dcor_schemas
    1.2.0) for listing the collections of a user, with a fallback for
    older servers (#108)
+ - enh: do not retry API requests when the server name cannot be
+   resolved (DCOR-Aid froze for minutes on Windows with a wrong server)
  - ref: convert `dcoraid.cli` module into a package; the upload task CLI
    now lives in `dcoraid.cli.task_upload_task`
  - ref: use `super()`, PEP 604 optional type hints, and builtin/

dcoraid/api/ckan_api.py

@@ -8,6 +8,7 @@
 import random
 import traceback
 import urllib.parse
+from urllib3.exceptions import MaxRetryError, NameResolutionError
 from urllib3.util.retry import Retry
 
 from dclab.external.packaging import parse as parse_version
@@ -34,8 +35,27 @@
 #: List of supported resource suffixes
 SERVER_RSUFFIX: dict[str, list[str]] = {}
 
+
+class RetryExceptNameResolution(Retry):
+    """Retry strategy that gives up immediately if a host cannot be resolved
+
+    A failed name lookup is rarely transient (e.g. a typo in the server
+    name), and on Windows every failed lookup may take half a minute.
+    """
+    def increment(self, method=None, url=None, response=None, error=None,
+                  _pool=None, _stacktrace=None):
+        if isinstance(error, NameResolutionError):
+            raise MaxRetryError(_pool, url, error) from error
+        return super().increment(method=method,
+                                 url=url,
+                                 response=response,
+                                 error=error,
+                                 _pool=_pool,
+                                 _stacktrace=_stacktrace)
+
+
 # Configure retry strategy
-retry_strategy = Retry(
+retry_strategy = RetryExceptNameResolution(
     total=3,  # Total retries
     backoff_factor=1.5,  # {backoff factor} * (2 ** ({number prev. retries}))
     connect=3,  # Handle connection errors (e.g. because the server is busy)

tests/test_api_base.py

@@ -1,7 +1,10 @@
+import socket
 import time
+from unittest import mock
 import uuid
 
 import pytest
+import requests
 
 from dcoraid.api import ckan_api
 
@@ -77,3 +80,22 @@ def test_api_hostname(server, api_hostname):
     api = ckan_api.CKANAPI(server=server,
                            check_ckan_version=False)
     assert api.hostname == api_hostname
+
+
+def test_api_no_retry_on_name_resolution_error():
+    """Do not retry requests when the host name cannot be resolved"""
+    host = f"{uuid.uuid4()}.does.not.exist.example.com"
+    lookups = []
+
+    def getaddrinfo(name, *args, **kwargs):
+        lookups.append(name)
+        raise socket.gaierror(socket.EAI_NONAME, "Name or service not known")
+
+    api = ckan_api.CKANAPI(server=host,
+                           check_ckan_version=False,
+                           caching=False)
+    with (mock.patch("socket.getaddrinfo", side_effect=getaddrinfo),
+          pytest.raises(requests.exceptions.ConnectionError,
+                        match="Failed to resolve")):
+        api.get("status_show")
+    assert len(lookups) == 1