bpo-35925: Skip SSL tests that fail due to weak external certs. (GH-13124)

Modern Linux distros such as Debian Buster have default OpenSSL system
configurations that reject connections to servers with weak certificates
by default.  This causes our test suite run with external networking
resources enabled to skip these tests when they encounter such a failure.

Fixing the network servers is a separate issue.

1 files changed, 29 insertions, 8 deletions

diff --git a/Lib/test/test_nntplib.py b/Lib/test/test_nntplib.py
index 8c1032b986..618b403bfb 100644
--- a/Lib/test/test_nntplib.py
+++ b/Lib/test/test_nntplib.py
@@ -6,6 +6,7 @@ import unittest
 import functools
 import contextlib
 import os.path
+import re
 import threading
 
 from test import support
@@ -21,6 +22,13 @@ except ImportError:
 TIMEOUT = 30
 certfile = os.path.join(os.path.dirname(__file__), 'keycert3.pem')
 
+if ssl is not None:
+    SSLError = ssl.SSLError
+else:
+    class SSLError(Exception):
+        """Non-existent exception class when we lack SSL support."""
+        reason = "This will never be raised."
+
 # TODO:
 # - test the `file` arg to more commands
 # - test error conditions
@@ -261,14 +269,21 @@ class NetworkedNNTPTestsMixin:
                 return False
             return True
 
-        with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
-            self.assertTrue(is_connected())
-            self.assertTrue(server.help())
-        self.assertFalse(is_connected())
-
-        with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
-            server.quit()
-        self.assertFalse(is_connected())
+        try:
+            with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
+                self.assertTrue(is_connected())
+                self.assertTrue(server.help())
+            self.assertFalse(is_connected())
+
+            with self.NNTP_CLASS(self.NNTP_HOST, timeout=TIMEOUT, usenetrc=False) as server:
+                server.quit()
+            self.assertFalse(is_connected())
+        except SSLError as ssl_err:
+            # matches "[SSL: DH_KEY_TOO_SMALL] dh key too small"
+            if re.search(r'(?i)KEY.TOO.SMALL', ssl_err.reason):
+                raise unittest.SkipTest(f"Got {ssl_err} connecting "
+                                        f"to {self.NNTP_HOST!r}")
+            raise
 
 
 NetworkedNNTPTestsMixin.wrap_methods()
@@ -294,6 +309,12 @@ class NetworkedNNTPTests(NetworkedNNTPTestsMixin, unittest.TestCase):
             try:
                 cls.server = cls.NNTP_CLASS(cls.NNTP_HOST, timeout=TIMEOUT,
                                             usenetrc=False)
+            except SSLError as ssl_err:
+                # matches "[SSL: DH_KEY_TOO_SMALL] dh key too small"
+                if re.search(r'(?i)KEY.TOO.SMALL', ssl_err.reason):
+                    raise unittest.SkipTest(f"{cls} got {ssl_err} connecting "
+                                            f"to {cls.NNTP_HOST!r}")
+                raise
             except EOF_ERRORS:
                 raise unittest.SkipTest(f"{cls} got EOF error on connecting "
                                         f"to {cls.NNTP_HOST!r}")