Merge PR #518

This patch simplifies the handshake-time TLS error processing and
introduces support for newer exceptions that OpenSSL triggers under
Python 3.8 and higher.

cheroot/connections.py

@@ -292,7 +292,20 @@ def _from_server_socket(self, server_socket):  # noqa: C901  # FIXME
             if self.server.ssl_adapter is not None:
                 try:
                     s, ssl_env = self.server.ssl_adapter.wrap(s)
-                except errors.NoSSLError:
+                except errors.FatalSSLAlert as tls_connection_drop_error:
+                    self.server.error_log(
+                        f'Client {addr !s} lost — peer dropped the TLS '
+                        'connection suddenly, during handshake: '
+                        f'{tls_connection_drop_error !s}',
+                    )
+                    return
+                except errors.NoSSLError as http_over_https_err:
+                    self.server.error_log(
+                        f'Client {addr !s} attempted to speak plain HTTP into '
+                        'a TCP connection configured for TLS-only traffic — '
+                        'trying to send back a plain HTTP error response: '
+                        f'{http_over_https_err !s}',
+                    )
                     msg = (
                         'The client sent a plain HTTP request, but '
                         'this server only speaks HTTPS on this port.'
@@ -311,8 +324,6 @@ def _from_server_socket(self, server_socket):  # noqa: C901  # FIXME
                         if ex.args[0] not in errors.socket_errors_to_ignore:
                             raise
                     return
-                if not s:
-                    return
                 mf = self.server.ssl_adapter.makefile
                 # Re-apply our timeout since we may have a new socket object
                 if hasattr(s, 'settimeout'):

cheroot/ssl/builtin.py

@@ -27,12 +27,9 @@
 
 from . import Adapter
 from .. import errors
-from .._compat import IS_ABOVE_OPENSSL10
 from ..makefile import StreamReader, StreamWriter
 from ..server import HTTPServer
 
-generic_socket_error = OSError
-
 
 def _assert_ssl_exc_contains(exc, *msgs):
     """Check whether SSL exception contains either of messages provided."""
@@ -265,62 +262,35 @@ def bind(self, sock):
 
     def wrap(self, sock):
         """Wrap and return the given socket, plus WSGI environ entries."""
-        EMPTY_RESULT = None, {}
         try:
             s = self.context.wrap_socket(
                 sock, do_handshake_on_connect=True, server_side=True,
             )
-        except ssl.SSLError as ex:
-            if ex.errno == ssl.SSL_ERROR_EOF:
-                # This is almost certainly due to the cherrypy engine
-                # 'pinging' the socket to assert it's connectable;
-                # the 'ping' isn't SSL.
-                return EMPTY_RESULT
-            elif ex.errno == ssl.SSL_ERROR_SSL:
-                if _assert_ssl_exc_contains(ex, 'http request'):
-                    # The client is speaking HTTP to an HTTPS server.
-                    raise errors.NoSSLError
-
-                # Check if it's one of the known errors
-                # Errors that are caught by PyOpenSSL, but thrown by
-                # built-in ssl
-                _block_errors = (
-                    'unknown protocol', 'unknown ca', 'unknown_ca',
-                    'unknown error',
-                    'https proxy request', 'inappropriate fallback',
-                    'wrong version number',
-                    'no shared cipher', 'certificate unknown',
-                    'ccs received early',
-                    'certificate verify failed',  # client cert w/o trusted CA
-                    'version too low',  # caused by SSL3 connections
-                    'unsupported protocol',  # caused by TLS1 connections
-                )
-                if _assert_ssl_exc_contains(ex, *_block_errors):
-                    # Accepted error, let's pass
-                    return EMPTY_RESULT
-            elif _assert_ssl_exc_contains(ex, 'handshake operation timed out'):
-                # This error is thrown by builtin SSL after a timeout
-                # when client is speaking HTTP to an HTTPS server.
-                # The connection can safely be dropped.
-                return EMPTY_RESULT
-            raise
-        except generic_socket_error as exc:
-            """It is unclear why exactly this happens.
-
-            It's reproducible only with openssl>1.0 and stdlib
-            :py:mod:`ssl` wrapper.
-            In CherryPy it's triggered by Checker plugin, which connects
-            to the app listening to the socket port in TLS mode via plain
-            HTTP during startup (from the same process).
-
-
-            Ref: https://github.com/cherrypy/cherrypy/issues/1618
-            """
-            is_error0 = exc.args == (0, 'Error')
-
-            if is_error0 and IS_ABOVE_OPENSSL10:
-                return EMPTY_RESULT
-            raise
+        except (
+            ssl.SSLEOFError,
+            ssl.SSLZeroReturnError,
+        ) as tls_connection_drop_error:
+            raise errors.FatalSSLAlert(
+                *tls_connection_drop_error.args,
+            ) from tls_connection_drop_error
+        except ssl.SSLError as generic_tls_error:
+            peer_speaks_plain_http_over_https = (
+                generic_tls_error.errno == ssl.SSL_ERROR_SSL and
+                _assert_ssl_exc_contains(generic_tls_error, 'http request')
+            )
+            if peer_speaks_plain_http_over_https:
+                reraised_connection_drop_exc_cls = errors.NoSSLError
+            else:
+                reraised_connection_drop_exc_cls = errors.FatalSSLAlert
+
+            raise reraised_connection_drop_exc_cls(
+                *generic_tls_error.args,
+            ) from generic_tls_error
+        except OSError as tcp_connection_drop_error:
+            raise errors.FatalSSLAlert(
+                *tcp_connection_drop_error.args,
+            ) from tcp_connection_drop_error
+
         return s, self.get_environ(s)
 
     def get_environ(self, sock):

stubtest_allowlist.txt

@@ -37,7 +37,6 @@ cheroot.ssl.pyopenssl.SSLConnection.write
 
 # false positives (https://github.com/python/mypy/issues/11843)
 cheroot.connections.IS_WINDOWS
-cheroot.ssl.builtin.IS_ABOVE_OPENSSL10
 
 # suppress is both a function and class
 cheroot._compat.suppress