PYTHON-3017 Properly check for closed KMS connections (#790)

Author: ShaneHarvey

pymongo/encryption.py

@@ -129,6 +129,8 @@ def kms_request(self, kms_context):
             conn.sendall(message)
             while kms_context.bytes_needed > 0:
                 data = conn.recv(kms_context.bytes_needed)
+                if not data:
+                    raise OSError('KMS connection closed')
                 kms_context.feed(data)
         finally:
             conn.close()

test/test_encryption.py

@@ -1775,9 +1775,6 @@ def test_invalid_hostname_in_kms_certificate(self):
 class TestKmsTLSOptions(EncryptionIntegrationTest):
     @unittest.skipUnless(any(AWS_CREDS.values()),
                          'AWS environment credentials are not set')
-    @unittest.skipIf(sys.version_info[:2] >= (3, 10) and
-                     sys.platform == 'win32',
-                     'These tests hang with Python 3.10 on Windows')
     def setUp(self):
         super(TestKmsTLSOptions, self).setUp()
         # 1, create client with only tlsCAFile.
@@ -1822,15 +1819,16 @@ def setUp(self):
         self.addCleanup(self.client_encryption_invalid_hostname.close)
         # Errors when client has no cert, some examples:
         # [SSL: TLSV13_ALERT_CERTIFICATE_REQUIRED] tlsv13 alert certificate required (_ssl.c:2623)
-        self.cert_error = 'certificate required|SSL handshake failed'
+        self.cert_error = ('certificate required|SSL handshake failed|'
+                           'KMS connection closed')
         # On Windows this error might be:
         # [WinError 10054] An existing connection was forcibly closed by the remote host
         if sys.platform == 'win32':
             self.cert_error += '|forcibly closed'
             # On Windows Python 3.10+ this error might be:
             # EOF occurred in violation of protocol (_ssl.c:2384)
             if sys.version_info[:2] >= (3, 10):
-                self.cert_error += '|forcibly closed'
+                self.cert_error += '|EOF'
 
     def test_01_aws(self):
         key = {