Pin the DNS walk against real urllib3 types, state the git.py divergence

esphome/net_retry.py

@@ -38,11 +38,15 @@ def _is_permanent_dns_failure(e: BaseException) -> bool:
         if id(exc) in seen:
             continue
         if isinstance(exc, socket.gaierror):
-            # Everything except EAI_AGAIN is treated as permanent. Codes
-            # like EAI_NONAME can occur during a brief network outage too,
-            # but a 6s backoff rarely outlives one, and permanent means
-            # callers fall back to their cache immediately instead of
-            # sleeping first (the offline-build case).
+            # Everything except EAI_AGAIN is treated as permanent. This is
+            # deliberately narrower than git.py, which retries NXDOMAIN
+            # too: codes like EAI_NONAME can occur during a brief network
+            # outage, but a 6s backoff rarely outlives one, and permanent
+            # means callers with a cached copy fall back to it immediately
+            # instead of sleeping first (the offline-build case). The
+            # trade-off is that a hard resolver failure on a first
+            # download fails without retrying, same as before retries
+            # existed.
             return exc.errno != socket.EAI_AGAIN
         seen.add(id(exc))
         stack.extend(

tests/unit_tests/test_net_retry.py

@@ -43,18 +43,23 @@ class TestIsTransientDownloadError:
         offline builds must fall back to their cache without sleeping first.
         requests can surface the gaierror via the cause chain or via
         urllib3's MaxRetryError.reason attribute."""
+        from urllib3.exceptions import MaxRetryError, NameResolutionError
+
         gai = socket.gaierror(socket.EAI_NONAME, "nodename nor servname provided")
 
         chained = req.ConnectionError("resolution failed")
         chained.__cause__ = gai
         assert not is_transient_download_error(chained)
 
-        class _FakeMaxRetryError(Exception):
-            def __init__(self, reason: BaseException) -> None:
-                super().__init__("max retries exceeded")
-                self.reason = reason
-
-        wrapped = req.ConnectionError(_FakeMaxRetryError(gai))
+        # The real urllib3 shape, raised the way urllib3 raises it: the
+        # gaierror is NameResolutionError.__cause__ (set at the raise
+        # site), which MaxRetryError carries in its reason attribute.
+        try:
+            raise NameResolutionError("example.invalid", None, gai) from gai
+        except NameResolutionError as nre:
+            wrapped = req.ConnectionError(
+                MaxRetryError(None, "http://example.invalid/", reason=nre)
+            )
         assert not is_transient_download_error(wrapped)
 
         # A garden-variety connection reset stays transient.