Library import 16 (#2433)

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diff --git a/contrib/tools/python3/Lib/ssl.py b/contrib/tools/python3/Lib/ssl.py
new file mode 100644
index 0000000000..9c1fea6d36
--- /dev/null
+++ b/contrib/tools/python3/Lib/ssl.py
@@ -0,0 +1,1494 @@
+# Wrapper module for _ssl, providing some additional facilities
+# implemented in Python.  Written by Bill Janssen.
+
+"""This module provides some more Pythonic support for SSL.
+
+Object types:
+
+  SSLSocket -- subtype of socket.socket which does SSL over the socket
+
+Exceptions:
+
+  SSLError -- exception raised for I/O errors
+
+Functions:
+
+  cert_time_to_seconds -- convert time string used for certificate
+                          notBefore and notAfter functions to integer
+                          seconds past the Epoch (the time values
+                          returned from time.time())
+
+  get_server_certificate (addr, ssl_version, ca_certs, timeout) -- Retrieve the
+                          certificate from the server at the specified
+                          address and return it as a PEM-encoded string
+
+
+Integer constants:
+
+SSL_ERROR_ZERO_RETURN
+SSL_ERROR_WANT_READ
+SSL_ERROR_WANT_WRITE
+SSL_ERROR_WANT_X509_LOOKUP
+SSL_ERROR_SYSCALL
+SSL_ERROR_SSL
+SSL_ERROR_WANT_CONNECT
+
+SSL_ERROR_EOF
+SSL_ERROR_INVALID_ERROR_CODE
+
+The following group define certificate requirements that one side is
+allowing/requiring from the other side:
+
+CERT_NONE - no certificates from the other side are required (or will
+            be looked at if provided)
+CERT_OPTIONAL - certificates are not required, but if provided will be
+                validated, and if validation fails, the connection will
+                also fail
+CERT_REQUIRED - certificates are required, and will be validated, and
+                if validation fails, the connection will also fail
+
+The following constants identify various SSL protocol variants:
+
+PROTOCOL_SSLv2
+PROTOCOL_SSLv3
+PROTOCOL_SSLv23
+PROTOCOL_TLS
+PROTOCOL_TLS_CLIENT
+PROTOCOL_TLS_SERVER
+PROTOCOL_TLSv1
+PROTOCOL_TLSv1_1
+PROTOCOL_TLSv1_2
+
+The following constants identify various SSL alert message descriptions as per
+http://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-6
+
+ALERT_DESCRIPTION_CLOSE_NOTIFY
+ALERT_DESCRIPTION_UNEXPECTED_MESSAGE
+ALERT_DESCRIPTION_BAD_RECORD_MAC
+ALERT_DESCRIPTION_RECORD_OVERFLOW
+ALERT_DESCRIPTION_DECOMPRESSION_FAILURE
+ALERT_DESCRIPTION_HANDSHAKE_FAILURE
+ALERT_DESCRIPTION_BAD_CERTIFICATE
+ALERT_DESCRIPTION_UNSUPPORTED_CERTIFICATE
+ALERT_DESCRIPTION_CERTIFICATE_REVOKED
+ALERT_DESCRIPTION_CERTIFICATE_EXPIRED
+ALERT_DESCRIPTION_CERTIFICATE_UNKNOWN
+ALERT_DESCRIPTION_ILLEGAL_PARAMETER
+ALERT_DESCRIPTION_UNKNOWN_CA
+ALERT_DESCRIPTION_ACCESS_DENIED
+ALERT_DESCRIPTION_DECODE_ERROR
+ALERT_DESCRIPTION_DECRYPT_ERROR
+ALERT_DESCRIPTION_PROTOCOL_VERSION
+ALERT_DESCRIPTION_INSUFFICIENT_SECURITY
+ALERT_DESCRIPTION_INTERNAL_ERROR
+ALERT_DESCRIPTION_USER_CANCELLED
+ALERT_DESCRIPTION_NO_RENEGOTIATION
+ALERT_DESCRIPTION_UNSUPPORTED_EXTENSION
+ALERT_DESCRIPTION_CERTIFICATE_UNOBTAINABLE
+ALERT_DESCRIPTION_UNRECOGNIZED_NAME
+ALERT_DESCRIPTION_BAD_CERTIFICATE_STATUS_RESPONSE
+ALERT_DESCRIPTION_BAD_CERTIFICATE_HASH_VALUE
+ALERT_DESCRIPTION_UNKNOWN_PSK_IDENTITY
+"""
+
+import sys
+import os
+from collections import namedtuple
+from enum import Enum as _Enum, IntEnum as _IntEnum, IntFlag as _IntFlag
+from enum import _simple_enum
+
+import _ssl             # if we can't import it, let the error propagate
+
+from _ssl import OPENSSL_VERSION_NUMBER, OPENSSL_VERSION_INFO, OPENSSL_VERSION
+from _ssl import _SSLContext, MemoryBIO, SSLSession
+from _ssl import (
+    SSLError, SSLZeroReturnError, SSLWantReadError, SSLWantWriteError,
+    SSLSyscallError, SSLEOFError, SSLCertVerificationError
+    )
+from _ssl import txt2obj as _txt2obj, nid2obj as _nid2obj
+from _ssl import RAND_status, RAND_add, RAND_bytes
+try:
+    from _ssl import RAND_egd
+except ImportError:
+    # LibreSSL does not provide RAND_egd
+    pass
+
+
+from _ssl import (
+    HAS_SNI, HAS_ECDH, HAS_NPN, HAS_ALPN, HAS_SSLv2, HAS_SSLv3, HAS_TLSv1,
+    HAS_TLSv1_1, HAS_TLSv1_2, HAS_TLSv1_3
+)
+from _ssl import _DEFAULT_CIPHERS, _OPENSSL_API_VERSION
+
+_IntEnum._convert_(
+    '_SSLMethod', __name__,
+    lambda name: name.startswith('PROTOCOL_') and name != 'PROTOCOL_SSLv23',
+    source=_ssl)
+
+_IntFlag._convert_(
+    'Options', __name__,
+    lambda name: name.startswith('OP_'),
+    source=_ssl)
+
+_IntEnum._convert_(
+    'AlertDescription', __name__,
+    lambda name: name.startswith('ALERT_DESCRIPTION_'),
+    source=_ssl)
+
+_IntEnum._convert_(
+    'SSLErrorNumber', __name__,
+    lambda name: name.startswith('SSL_ERROR_'),
+    source=_ssl)
+
+_IntFlag._convert_(
+    'VerifyFlags', __name__,
+    lambda name: name.startswith('VERIFY_'),
+    source=_ssl)
+
+_IntEnum._convert_(
+    'VerifyMode', __name__,
+    lambda name: name.startswith('CERT_'),
+    source=_ssl)
+
+PROTOCOL_SSLv23 = _SSLMethod.PROTOCOL_SSLv23 = _SSLMethod.PROTOCOL_TLS
+_PROTOCOL_NAMES = {value: name for name, value in _SSLMethod.__members__.items()}
+
+_SSLv2_IF_EXISTS = getattr(_SSLMethod, 'PROTOCOL_SSLv2', None)
+
+
+@_simple_enum(_IntEnum)
+class TLSVersion:
+    MINIMUM_SUPPORTED = _ssl.PROTO_MINIMUM_SUPPORTED
+    SSLv3 = _ssl.PROTO_SSLv3
+    TLSv1 = _ssl.PROTO_TLSv1
+    TLSv1_1 = _ssl.PROTO_TLSv1_1
+    TLSv1_2 = _ssl.PROTO_TLSv1_2
+    TLSv1_3 = _ssl.PROTO_TLSv1_3
+    MAXIMUM_SUPPORTED = _ssl.PROTO_MAXIMUM_SUPPORTED
+
+
+@_simple_enum(_IntEnum)
+class _TLSContentType:
+    """Content types (record layer)
+
+    See RFC 8446, section B.1
+    """
+    CHANGE_CIPHER_SPEC = 20
+    ALERT = 21
+    HANDSHAKE = 22
+    APPLICATION_DATA = 23
+    # pseudo content types
+    HEADER = 0x100
+    INNER_CONTENT_TYPE = 0x101
+
+
+@_simple_enum(_IntEnum)
+class _TLSAlertType:
+    """Alert types for TLSContentType.ALERT messages
+
+    See RFC 8466, section B.2
+    """
+    CLOSE_NOTIFY = 0
+    UNEXPECTED_MESSAGE = 10
+    BAD_RECORD_MAC = 20
+    DECRYPTION_FAILED = 21
+    RECORD_OVERFLOW = 22
+    DECOMPRESSION_FAILURE = 30
+    HANDSHAKE_FAILURE = 40
+    NO_CERTIFICATE = 41
+    BAD_CERTIFICATE = 42
+    UNSUPPORTED_CERTIFICATE = 43
+    CERTIFICATE_REVOKED = 44
+    CERTIFICATE_EXPIRED = 45
+    CERTIFICATE_UNKNOWN = 46
+    ILLEGAL_PARAMETER = 47
+    UNKNOWN_CA = 48
+    ACCESS_DENIED = 49
+    DECODE_ERROR = 50
+    DECRYPT_ERROR = 51
+    EXPORT_RESTRICTION = 60
+    PROTOCOL_VERSION = 70
+    INSUFFICIENT_SECURITY = 71
+    INTERNAL_ERROR = 80
+    INAPPROPRIATE_FALLBACK = 86
+    USER_CANCELED = 90
+    NO_RENEGOTIATION = 100
+    MISSING_EXTENSION = 109
+    UNSUPPORTED_EXTENSION = 110
+    CERTIFICATE_UNOBTAINABLE = 111
+    UNRECOGNIZED_NAME = 112
+    BAD_CERTIFICATE_STATUS_RESPONSE = 113
+    BAD_CERTIFICATE_HASH_VALUE = 114
+    UNKNOWN_PSK_IDENTITY = 115
+    CERTIFICATE_REQUIRED = 116
+    NO_APPLICATION_PROTOCOL = 120
+
+
+@_simple_enum(_IntEnum)
+class _TLSMessageType:
+    """Message types (handshake protocol)
+
+    See RFC 8446, section B.3
+    """
+    HELLO_REQUEST = 0
+    CLIENT_HELLO = 1
+    SERVER_HELLO = 2
+    HELLO_VERIFY_REQUEST = 3
+    NEWSESSION_TICKET = 4
+    END_OF_EARLY_DATA = 5
+    HELLO_RETRY_REQUEST = 6
+    ENCRYPTED_EXTENSIONS = 8
+    CERTIFICATE = 11
+    SERVER_KEY_EXCHANGE = 12
+    CERTIFICATE_REQUEST = 13
+    SERVER_DONE = 14
+    CERTIFICATE_VERIFY = 15
+    CLIENT_KEY_EXCHANGE = 16
+    FINISHED = 20
+    CERTIFICATE_URL = 21
+    CERTIFICATE_STATUS = 22
+    SUPPLEMENTAL_DATA = 23
+    KEY_UPDATE = 24
+    NEXT_PROTO = 67
+    MESSAGE_HASH = 254
+    CHANGE_CIPHER_SPEC = 0x0101
+
+
+if sys.platform == "win32":
+    from _ssl import enum_certificates, enum_crls
+
+from socket import socket, SOCK_STREAM, create_connection
+from socket import SOL_SOCKET, SO_TYPE, _GLOBAL_DEFAULT_TIMEOUT
+import socket as _socket
+import base64        # for DER-to-PEM translation
+import errno
+import warnings
+
+
+socket_error = OSError  # keep that public name in module namespace
+
+CHANNEL_BINDING_TYPES = ['tls-unique']
+
+HAS_NEVER_CHECK_COMMON_NAME = hasattr(_ssl, 'HOSTFLAG_NEVER_CHECK_SUBJECT')
+
+
+_RESTRICTED_SERVER_CIPHERS = _DEFAULT_CIPHERS
+
+CertificateError = SSLCertVerificationError
+
+
+def _dnsname_match(dn, hostname):
+    """Matching according to RFC 6125, section 6.4.3
+
+    - Hostnames are compared lower-case.
+    - For IDNA, both dn and hostname must be encoded as IDN A-label (ACE).
+    - Partial wildcards like 'www*.example.org', multiple wildcards, sole
+      wildcard or wildcards in labels other then the left-most label are not
+      supported and a CertificateError is raised.
+    - A wildcard must match at least one character.
+    """
+    if not dn:
+        return False
+
+    wildcards = dn.count('*')
+    # speed up common case w/o wildcards
+    if not wildcards:
+        return dn.lower() == hostname.lower()
+
+    if wildcards > 1:
+        raise CertificateError(
+            "too many wildcards in certificate DNS name: {!r}.".format(dn))
+
+    dn_leftmost, sep, dn_remainder = dn.partition('.')
+
+    if '*' in dn_remainder:
+        # Only match wildcard in leftmost segment.
+        raise CertificateError(
+            "wildcard can only be present in the leftmost label: "
+            "{!r}.".format(dn))
+
+    if not sep:
+        # no right side
+        raise CertificateError(
+            "sole wildcard without additional labels are not support: "
+            "{!r}.".format(dn))
+
+    if dn_leftmost != '*':
+        # no partial wildcard matching
+        raise CertificateError(
+            "partial wildcards in leftmost label are not supported: "
+            "{!r}.".format(dn))
+
+    hostname_leftmost, sep, hostname_remainder = hostname.partition('.')
+    if not hostname_leftmost or not sep:
+        # wildcard must match at least one char
+        return False
+    return dn_remainder.lower() == hostname_remainder.lower()
+
+
+def _inet_paton(ipname):
+    """Try to convert an IP address to packed binary form
+
+    Supports IPv4 addresses on all platforms and IPv6 on platforms with IPv6
+    support.
+    """
+    # inet_aton() also accepts strings like '1', '127.1', some also trailing
+    # data like '127.0.0.1 whatever'.
+    try:
+        addr = _socket.inet_aton(ipname)
+    except OSError:
+        # not an IPv4 address
+        pass
+    else:
+        if _socket.inet_ntoa(addr) == ipname:
+            # only accept injective ipnames
+            return addr
+        else:
+            # refuse for short IPv4 notation and additional trailing data
+            raise ValueError(
+                "{!r} is not a quad-dotted IPv4 address.".format(ipname)
+            )
+
+    try:
+        return _socket.inet_pton(_socket.AF_INET6, ipname)
+    except OSError:
+        raise ValueError("{!r} is neither an IPv4 nor an IP6 "
+                         "address.".format(ipname))
+    except AttributeError:
+        # AF_INET6 not available
+        pass
+
+    raise ValueError("{!r} is not an IPv4 address.".format(ipname))
+
+
+def _ipaddress_match(cert_ipaddress, host_ip):
+    """Exact matching of IP addresses.
+
+    RFC 6125 explicitly doesn't define an algorithm for this
+    (section 1.7.2 - "Out of Scope").
+    """
+    # OpenSSL may add a trailing newline to a subjectAltName's IP address,
+    # commonly with IPv6 addresses. Strip off trailing \n.
+    ip = _inet_paton(cert_ipaddress.rstrip())
+    return ip == host_ip
+
+
+DefaultVerifyPaths = namedtuple("DefaultVerifyPaths",
+    "cafile capath openssl_cafile_env openssl_cafile openssl_capath_env "
+    "openssl_capath")
+
+def get_default_verify_paths():
+    """Return paths to default cafile and capath.
+    """
+    parts = _ssl.get_default_verify_paths()
+
+    # environment vars shadow paths
+    cafile = os.environ.get(parts[0], parts[1])
+    capath = os.environ.get(parts[2], parts[3])
+
+    return DefaultVerifyPaths(cafile if os.path.isfile(cafile) else None,
+                              capath if os.path.isdir(capath) else None,
+                              *parts)
+
+
+class _ASN1Object(namedtuple("_ASN1Object", "nid shortname longname oid")):
+    """ASN.1 object identifier lookup
+    """
+    __slots__ = ()
+
+    def __new__(cls, oid):
+        return super().__new__(cls, *_txt2obj(oid, name=False))
+
+    @classmethod
+    def fromnid(cls, nid):
+        """Create _ASN1Object from OpenSSL numeric ID
+        """
+        return super().__new__(cls, *_nid2obj(nid))
+
+    @classmethod
+    def fromname(cls, name):
+        """Create _ASN1Object from short name, long name or OID
+        """
+        return super().__new__(cls, *_txt2obj(name, name=True))
+
+
+class Purpose(_ASN1Object, _Enum):
+    """SSLContext purpose flags with X509v3 Extended Key Usage objects
+    """
+    SERVER_AUTH = '1.3.6.1.5.5.7.3.1'
+    CLIENT_AUTH = '1.3.6.1.5.5.7.3.2'
+
+
+_builtin_cadata = None
+
+
+def builtin_cadata():
+    global _builtin_cadata
+    if _builtin_cadata is None:
+        import __res
+        data = __res.find(b'/builtin/cacert')
+        # load_verify_locations expects PEM cadata to be an ASCII-only unicode
+        # object, so we discard unicode in comments.
+        _builtin_cadata = data.decode('ASCII', errors='ignore')
+    return _builtin_cadata
+
+
+class SSLContext(_SSLContext):
+    """An SSLContext holds various SSL-related configuration options and
+    data, such as certificates and possibly a private key."""
+    _windows_cert_stores = ("CA", "ROOT")
+
+    sslsocket_class = None  # SSLSocket is assigned later.
+    sslobject_class = None  # SSLObject is assigned later.
+
+    def __new__(cls, protocol=None, *args, **kwargs):
+        if protocol is None:
+            warnings.warn(
+                "ssl.SSLContext() without protocol argument is deprecated.",
+                category=DeprecationWarning,
+                stacklevel=2
+            )
+            protocol = PROTOCOL_TLS
+        self = _SSLContext.__new__(cls, protocol)
+        return self
+
+    def _encode_hostname(self, hostname):
+        if hostname is None:
+            return None
+        elif isinstance(hostname, str):
+            return hostname.encode('idna').decode('ascii')
+        else:
+            return hostname.decode('ascii')
+
+    def wrap_socket(self, sock, server_side=False,
+                    do_handshake_on_connect=True,
+                    suppress_ragged_eofs=True,
+                    server_hostname=None, session=None):
+        # SSLSocket class handles server_hostname encoding before it calls
+        # ctx._wrap_socket()
+        return self.sslsocket_class._create(
+            sock=sock,
+            server_side=server_side,
+            do_handshake_on_connect=do_handshake_on_connect,
+            suppress_ragged_eofs=suppress_ragged_eofs,
+            server_hostname=server_hostname,
+            context=self,
+            session=session
+        )
+
+    def wrap_bio(self, incoming, outgoing, server_side=False,
+                 server_hostname=None, session=None):
+        # Need to encode server_hostname here because _wrap_bio() can only
+        # handle ASCII str.
+        return self.sslobject_class._create(
+            incoming, outgoing, server_side=server_side,
+            server_hostname=self._encode_hostname(server_hostname),
+            session=session, context=self,
+        )
+
+    def set_npn_protocols(self, npn_protocols):
+        warnings.warn(
+            "ssl NPN is deprecated, use ALPN instead",
+            DeprecationWarning,
+            stacklevel=2
+        )
+        protos = bytearray()
+        for protocol in npn_protocols:
+            b = bytes(protocol, 'ascii')
+            if len(b) == 0 or len(b) > 255:
+                raise SSLError('NPN protocols must be 1 to 255 in length')
+            protos.append(len(b))
+            protos.extend(b)
+
+        self._set_npn_protocols(protos)
+
+    def set_servername_callback(self, server_name_callback):
+        if server_name_callback is None:
+            self.sni_callback = None
+        else:
+            if not callable(server_name_callback):
+                raise TypeError("not a callable object")
+
+            def shim_cb(sslobj, servername, sslctx):
+                servername = self._encode_hostname(servername)
+                return server_name_callback(sslobj, servername, sslctx)
+
+            self.sni_callback = shim_cb
+
+    def set_alpn_protocols(self, alpn_protocols):
+        protos = bytearray()
+        for protocol in alpn_protocols:
+            b = bytes(protocol, 'ascii')
+            if len(b) == 0 or len(b) > 255:
+                raise SSLError('ALPN protocols must be 1 to 255 in length')
+            protos.append(len(b))
+            protos.extend(b)
+
+        self._set_alpn_protocols(protos)
+
+    def _load_windows_store_certs(self, storename, purpose):
+        certs = bytearray()
+        try:
+            for cert, encoding, trust in enum_certificates(storename):
+                # CA certs are never PKCS#7 encoded
+                if encoding == "x509_asn":
+                    if trust is True or purpose.oid in trust:
+                        certs.extend(cert)
+        except PermissionError:
+            warnings.warn("unable to enumerate Windows certificate store")
+        if certs:
+            self.load_verify_locations(cadata=certs)
+        return certs
+
+    def load_default_certs(self, purpose=Purpose.SERVER_AUTH):
+        if not isinstance(purpose, _ASN1Object):
+            raise TypeError(purpose)
+
+        self.load_verify_locations(cadata=builtin_cadata())
+
+        if sys.platform == "win32":
+            for storename in self._windows_cert_stores:
+                self._load_windows_store_certs(storename, purpose)
+        self.set_default_verify_paths()
+
+    if hasattr(_SSLContext, 'minimum_version'):
+        @property
+        def minimum_version(self):
+            return TLSVersion(super().minimum_version)
+
+        @minimum_version.setter
+        def minimum_version(self, value):
+            if value == TLSVersion.SSLv3:
+                self.options &= ~Options.OP_NO_SSLv3
+            super(SSLContext, SSLContext).minimum_version.__set__(self, value)
+
+        @property
+        def maximum_version(self):
+            return TLSVersion(super().maximum_version)
+
+        @maximum_version.setter
+        def maximum_version(self, value):
+            super(SSLContext, SSLContext).maximum_version.__set__(self, value)
+
+    @property
+    def options(self):
+        return Options(super().options)
+
+    @options.setter
+    def options(self, value):
+        super(SSLContext, SSLContext).options.__set__(self, value)
+
+    if hasattr(_ssl, 'HOSTFLAG_NEVER_CHECK_SUBJECT'):
+        @property
+        def hostname_checks_common_name(self):
+            ncs = self._host_flags & _ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
+            return ncs != _ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
+
+        @hostname_checks_common_name.setter
+        def hostname_checks_common_name(self, value):
+            if value:
+                self._host_flags &= ~_ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
+            else:
+                self._host_flags |= _ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
+    else:
+        @property
+        def hostname_checks_common_name(self):
+            return True
+
+    @property
+    def _msg_callback(self):
+        """TLS message callback
+
+        The message callback provides a debugging hook to analyze TLS
+        connections. The callback is called for any TLS protocol message
+        (header, handshake, alert, and more), but not for application data.
+        Due to technical  limitations, the callback can't be used to filter
+        traffic or to abort a connection. Any exception raised in the
+        callback is delayed until the handshake, read, or write operation
+        has been performed.
+
+        def msg_cb(conn, direction, version, content_type, msg_type, data):
+            pass
+
+        conn
+            :class:`SSLSocket` or :class:`SSLObject` instance
+        direction
+            ``read`` or ``write``
+        version
+            :class:`TLSVersion` enum member or int for unknown version. For a
+            frame header, it's the header version.
+        content_type
+            :class:`_TLSContentType` enum member or int for unsupported
+            content type.
+        msg_type
+            Either a :class:`_TLSContentType` enum number for a header
+            message, a :class:`_TLSAlertType` enum member for an alert
+            message, a :class:`_TLSMessageType` enum member for other
+            messages, or int for unsupported message types.
+        data
+            Raw, decrypted message content as bytes
+        """
+        inner = super()._msg_callback
+        if inner is not None:
+            return inner.user_function
+        else:
+            return None
+
+    @_msg_callback.setter
+    def _msg_callback(self, callback):
+        if callback is None:
+            super(SSLContext, SSLContext)._msg_callback.__set__(self, None)
+            return
+
+        if not hasattr(callback, '__call__'):
+            raise TypeError(f"{callback} is not callable.")
+
+        def inner(conn, direction, version, content_type, msg_type, data):
+            try:
+                version = TLSVersion(version)
+            except ValueError:
+                pass
+
+            try:
+                content_type = _TLSContentType(content_type)
+            except ValueError:
+                pass
+
+            if content_type == _TLSContentType.HEADER:
+                msg_enum = _TLSContentType
+            elif content_type == _TLSContentType.ALERT:
+                msg_enum = _TLSAlertType
+            else:
+                msg_enum = _TLSMessageType
+            try:
+                msg_type = msg_enum(msg_type)
+            except ValueError:
+                pass
+
+            return callback(conn, direction, version,
+                            content_type, msg_type, data)
+
+        inner.user_function = callback
+
+        super(SSLContext, SSLContext)._msg_callback.__set__(self, inner)
+
+    @property
+    def protocol(self):
+        return _SSLMethod(super().protocol)
+
+    @property
+    def verify_flags(self):
+        return VerifyFlags(super().verify_flags)
+
+    @verify_flags.setter
+    def verify_flags(self, value):
+        super(SSLContext, SSLContext).verify_flags.__set__(self, value)
+
+    @property
+    def verify_mode(self):
+        value = super().verify_mode
+        try:
+            return VerifyMode(value)
+        except ValueError:
+            return value
+
+    @verify_mode.setter
+    def verify_mode(self, value):
+        super(SSLContext, SSLContext).verify_mode.__set__(self, value)
+
+
+def create_default_context(purpose=Purpose.SERVER_AUTH, *, cafile=None,
+                           capath=None, cadata=None):
+    """Create a SSLContext object with default settings.
+
+    NOTE: The protocol and settings may change anytime without prior
+          deprecation. The values represent a fair balance between maximum
+          compatibility and security.
+    """
+    if not isinstance(purpose, _ASN1Object):
+        raise TypeError(purpose)
+
+    # SSLContext sets OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION,
+    # OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE and OP_SINGLE_ECDH_USE
+    # by default.
+    if purpose == Purpose.SERVER_AUTH:
+        # verify certs and host name in client mode
+        context = SSLContext(PROTOCOL_TLS_CLIENT)
+        context.verify_mode = CERT_REQUIRED
+        context.check_hostname = True
+    elif purpose == Purpose.CLIENT_AUTH:
+        context = SSLContext(PROTOCOL_TLS_SERVER)
+    else:
+        raise ValueError(purpose)
+
+    if cafile or capath or cadata:
+        context.load_verify_locations(cafile, capath, cadata)
+    elif context.verify_mode != CERT_NONE:
+        # no explicit cafile, capath or cadata but the verify mode is
+        # CERT_OPTIONAL or CERT_REQUIRED. Let's try to load default system
+        # root CA certificates for the given purpose. This may fail silently.
+        context.load_default_certs(purpose)
+    # OpenSSL 1.1.1 keylog file
+    if hasattr(context, 'keylog_filename'):
+        keylogfile = os.environ.get('SSLKEYLOGFILE')
+        if keylogfile and not sys.flags.ignore_environment:
+            context.keylog_filename = keylogfile
+    return context
+
+def _create_unverified_context(protocol=None, *, cert_reqs=CERT_NONE,
+                           check_hostname=False, purpose=Purpose.SERVER_AUTH,
+                           certfile=None, keyfile=None,
+                           cafile=None, capath=None, cadata=None):
+    """Create a SSLContext object for Python stdlib modules
+
+    All Python stdlib modules shall use this function to create SSLContext
+    objects in order to keep common settings in one place. The configuration
+    is less restrict than create_default_context()'s to increase backward
+    compatibility.
+    """
+    if not isinstance(purpose, _ASN1Object):
+        raise TypeError(purpose)
+
+    # SSLContext sets OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION,
+    # OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE and OP_SINGLE_ECDH_USE
+    # by default.
+    if purpose == Purpose.SERVER_AUTH:
+        # verify certs and host name in client mode
+        if protocol is None:
+            protocol = PROTOCOL_TLS_CLIENT
+    elif purpose == Purpose.CLIENT_AUTH:
+        if protocol is None:
+            protocol = PROTOCOL_TLS_SERVER
+    else:
+        raise ValueError(purpose)
+
+    context = SSLContext(protocol)
+    context.check_hostname = check_hostname
+    if cert_reqs is not None:
+        context.verify_mode = cert_reqs
+    if check_hostname:
+        context.check_hostname = True
+
+    if keyfile and not certfile:
+        raise ValueError("certfile must be specified")
+    if certfile or keyfile:
+        context.load_cert_chain(certfile, keyfile)
+
+    # load CA root certs
+    if cafile or capath or cadata:
+        context.load_verify_locations(cafile, capath, cadata)
+    elif context.verify_mode != CERT_NONE:
+        # no explicit cafile, capath or cadata but the verify mode is
+        # CERT_OPTIONAL or CERT_REQUIRED. Let's try to load default system
+        # root CA certificates for the given purpose. This may fail silently.
+        context.load_default_certs(purpose)
+    # OpenSSL 1.1.1 keylog file
+    if hasattr(context, 'keylog_filename'):
+        keylogfile = os.environ.get('SSLKEYLOGFILE')
+        if keylogfile and not sys.flags.ignore_environment:
+            context.keylog_filename = keylogfile
+    return context
+
+# Used by http.client if no context is explicitly passed.
+_create_default_https_context = create_default_context
+
+
+# Backwards compatibility alias, even though it's not a public name.
+_create_stdlib_context = _create_unverified_context
+
+
+class SSLObject:
+    """This class implements an interface on top of a low-level SSL object as
+    implemented by OpenSSL. This object captures the state of an SSL connection
+    but does not provide any network IO itself. IO needs to be performed
+    through separate "BIO" objects which are OpenSSL's IO abstraction layer.
+
+    This class does not have a public constructor. Instances are returned by
+    ``SSLContext.wrap_bio``. This class is typically used by framework authors
+    that want to implement asynchronous IO for SSL through memory buffers.
+
+    When compared to ``SSLSocket``, this object lacks the following features:
+
+     * Any form of network IO, including methods such as ``recv`` and ``send``.
+     * The ``do_handshake_on_connect`` and ``suppress_ragged_eofs`` machinery.
+    """
+    def __init__(self, *args, **kwargs):
+        raise TypeError(
+            f"{self.__class__.__name__} does not have a public "
+            f"constructor. Instances are returned by SSLContext.wrap_bio()."
+        )
+
+    @classmethod
+    def _create(cls, incoming, outgoing, server_side=False,
+                 server_hostname=None, session=None, context=None):
+        self = cls.__new__(cls)
+        sslobj = context._wrap_bio(
+            incoming, outgoing, server_side=server_side,
+            server_hostname=server_hostname,
+            owner=self, session=session
+        )
+        self._sslobj = sslobj
+        return self
+
+    @property
+    def context(self):
+        """The SSLContext that is currently in use."""
+        return self._sslobj.context
+
+    @context.setter
+    def context(self, ctx):
+        self._sslobj.context = ctx
+
+    @property
+    def session(self):
+        """The SSLSession for client socket."""
+        return self._sslobj.session
+
+    @session.setter
+    def session(self, session):
+        self._sslobj.session = session
+
+    @property
+    def session_reused(self):
+        """Was the client session reused during handshake"""
+        return self._sslobj.session_reused
+
+    @property
+    def server_side(self):
+        """Whether this is a server-side socket."""
+        return self._sslobj.server_side
+
+    @property
+    def server_hostname(self):
+        """The currently set server hostname (for SNI), or ``None`` if no
+        server hostname is set."""
+        return self._sslobj.server_hostname
+
+    def read(self, len=1024, buffer=None):
+        """Read up to 'len' bytes from the SSL object and return them.
+
+        If 'buffer' is provided, read into this buffer and return the number of
+        bytes read.
+        """
+        if buffer is not None:
+            v = self._sslobj.read(len, buffer)
+        else:
+            v = self._sslobj.read(len)
+        return v
+
+    def write(self, data):
+        """Write 'data' to the SSL object and return the number of bytes
+        written.
+
+        The 'data' argument must support the buffer interface.
+        """
+        return self._sslobj.write(data)
+
+    def getpeercert(self, binary_form=False):
+        """Returns a formatted version of the data in the certificate provided
+        by the other end of the SSL channel.
+
+        Return None if no certificate was provided, {} if a certificate was
+        provided, but not validated.
+        """
+        return self._sslobj.getpeercert(binary_form)
+
+    def selected_npn_protocol(self):
+        """Return the currently selected NPN protocol as a string, or ``None``
+        if a next protocol was not negotiated or if NPN is not supported by one
+        of the peers."""
+        warnings.warn(
+            "ssl NPN is deprecated, use ALPN instead",
+            DeprecationWarning,
+            stacklevel=2
+        )
+
+    def selected_alpn_protocol(self):
+        """Return the currently selected ALPN protocol as a string, or ``None``
+        if a next protocol was not negotiated or if ALPN is not supported by one
+        of the peers."""
+        return self._sslobj.selected_alpn_protocol()
+
+    def cipher(self):
+        """Return the currently selected cipher as a 3-tuple ``(name,
+        ssl_version, secret_bits)``."""
+        return self._sslobj.cipher()
+
+    def shared_ciphers(self):
+        """Return a list of ciphers shared by the client during the handshake or
+        None if this is not a valid server connection.
+        """
+        return self._sslobj.shared_ciphers()
+
+    def compression(self):
+        """Return the current compression algorithm in use, or ``None`` if
+        compression was not negotiated or not supported by one of the peers."""
+        return self._sslobj.compression()
+
+    def pending(self):
+        """Return the number of bytes that can be read immediately."""
+        return self._sslobj.pending()
+
+    def do_handshake(self):
+        """Start the SSL/TLS handshake."""
+        self._sslobj.do_handshake()
+
+    def unwrap(self):
+        """Start the SSL shutdown handshake."""
+        return self._sslobj.shutdown()
+
+    def get_channel_binding(self, cb_type="tls-unique"):
+        """Get channel binding data for current connection.  Raise ValueError
+        if the requested `cb_type` is not supported.  Return bytes of the data
+        or None if the data is not available (e.g. before the handshake)."""
+        return self._sslobj.get_channel_binding(cb_type)
+
+    def version(self):
+        """Return a string identifying the protocol version used by the
+        current SSL channel. """
+        return self._sslobj.version()
+
+    def verify_client_post_handshake(self):
+        return self._sslobj.verify_client_post_handshake()
+
+
+def _sslcopydoc(func):
+    """Copy docstring from SSLObject to SSLSocket"""
+    func.__doc__ = getattr(SSLObject, func.__name__).__doc__
+    return func
+
+
+class SSLSocket(socket):
+    """This class implements a subtype of socket.socket that wraps
+    the underlying OS socket in an SSL context when necessary, and
+    provides read and write methods over that channel. """
+
+    def __init__(self, *args, **kwargs):
+        raise TypeError(
+            f"{self.__class__.__name__} does not have a public "
+            f"constructor. Instances are returned by "
+            f"SSLContext.wrap_socket()."
+        )
+
+    @classmethod
+    def _create(cls, sock, server_side=False, do_handshake_on_connect=True,
+                suppress_ragged_eofs=True, server_hostname=None,
+                context=None, session=None):
+        if sock.getsockopt(SOL_SOCKET, SO_TYPE) != SOCK_STREAM:
+            raise NotImplementedError("only stream sockets are supported")
+        if server_side:
+            if server_hostname:
+                raise ValueError("server_hostname can only be specified "
+                                 "in client mode")
+            if session is not None:
+                raise ValueError("session can only be specified in "
+                                 "client mode")
+        if context.check_hostname and not server_hostname:
+            raise ValueError("check_hostname requires server_hostname")
+
+        sock_timeout = sock.gettimeout()
+        kwargs = dict(
+            family=sock.family, type=sock.type, proto=sock.proto,
+            fileno=sock.fileno()
+        )
+        self = cls.__new__(cls, **kwargs)
+        super(SSLSocket, self).__init__(**kwargs)
+        sock.detach()
+        # Now SSLSocket is responsible for closing the file descriptor.
+        try:
+            self._context = context
+            self._session = session
+            self._closed = False
+            self._sslobj = None
+            self.server_side = server_side
+            self.server_hostname = context._encode_hostname(server_hostname)
+            self.do_handshake_on_connect = do_handshake_on_connect
+            self.suppress_ragged_eofs = suppress_ragged_eofs
+
+            # See if we are connected
+            try:
+                self.getpeername()
+            except OSError as e:
+                if e.errno != errno.ENOTCONN:
+                    raise
+                connected = False
+                blocking = self.getblocking()
+                self.setblocking(False)
+                try:
+                    # We are not connected so this is not supposed to block, but
+                    # testing revealed otherwise on macOS and Windows so we do
+                    # the non-blocking dance regardless. Our raise when any data
+                    # is found means consuming the data is harmless.
+                    notconn_pre_handshake_data = self.recv(1)
+                except OSError as e:
+                    # EINVAL occurs for recv(1) on non-connected on unix sockets.
+                    if e.errno not in (errno.ENOTCONN, errno.EINVAL):
+                        raise
+                    notconn_pre_handshake_data = b''
+                self.setblocking(blocking)
+                if notconn_pre_handshake_data:
+                    # This prevents pending data sent to the socket before it was
+                    # closed from escaping to the caller who could otherwise
+                    # presume it came through a successful TLS connection.
+                    reason = "Closed before TLS handshake with data in recv buffer."
+                    notconn_pre_handshake_data_error = SSLError(e.errno, reason)
+                    # Add the SSLError attributes that _ssl.c always adds.
+                    notconn_pre_handshake_data_error.reason = reason
+                    notconn_pre_handshake_data_error.library = None
+                    try:
+                        raise notconn_pre_handshake_data_error
+                    finally:
+                        # Explicitly break the reference cycle.
+                        notconn_pre_handshake_data_error = None
+            else:
+                connected = True
+
+            self.settimeout(sock_timeout)  # Must come after setblocking() calls.
+            self._connected = connected
+            if connected:
+                # create the SSL object
+                self._sslobj = self._context._wrap_socket(
+                    self, server_side, self.server_hostname,
+                    owner=self, session=self._session,
+                )
+                if do_handshake_on_connect:
+                    timeout = self.gettimeout()
+                    if timeout == 0.0:
+                        # non-blocking
+                        raise ValueError("do_handshake_on_connect should not be specified for non-blocking sockets")
+                    self.do_handshake()
+        except:
+            try:
+                self.close()
+            except OSError:
+                pass
+            raise
+        return self
+
+    @property
+    @_sslcopydoc
+    def context(self):
+        return self._context
+
+    @context.setter
+    def context(self, ctx):
+        self._context = ctx
+        self._sslobj.context = ctx
+
+    @property
+    @_sslcopydoc
+    def session(self):
+        if self._sslobj is not None:
+            return self._sslobj.session
+
+    @session.setter
+    def session(self, session):
+        self._session = session
+        if self._sslobj is not None:
+            self._sslobj.session = session
+
+    @property
+    @_sslcopydoc
+    def session_reused(self):
+        if self._sslobj is not None:
+            return self._sslobj.session_reused
+
+    def dup(self):
+        raise NotImplementedError("Can't dup() %s instances" %
+                                  self.__class__.__name__)
+
+    def _checkClosed(self, msg=None):
+        # raise an exception here if you wish to check for spurious closes
+        pass
+
+    def _check_connected(self):
+        if not self._connected:
+            # getpeername() will raise ENOTCONN if the socket is really
+            # not connected; note that we can be connected even without
+            # _connected being set, e.g. if connect() first returned
+            # EAGAIN.
+            self.getpeername()
+
+    def read(self, len=1024, buffer=None):
+        """Read up to LEN bytes and return them.
+        Return zero-length string on EOF."""
+
+        self._checkClosed()
+        if self._sslobj is None:
+            raise ValueError("Read on closed or unwrapped SSL socket.")
+        try:
+            if buffer is not None:
+                return self._sslobj.read(len, buffer)
+            else:
+                return self._sslobj.read(len)
+        except SSLError as x:
+            if x.args[0] == SSL_ERROR_EOF and self.suppress_ragged_eofs:
+                if buffer is not None:
+                    return 0
+                else:
+                    return b''
+            else:
+                raise
+
+    def write(self, data):
+        """Write DATA to the underlying SSL channel.  Returns
+        number of bytes of DATA actually transmitted."""
+
+        self._checkClosed()
+        if self._sslobj is None:
+            raise ValueError("Write on closed or unwrapped SSL socket.")
+        return self._sslobj.write(data)
+
+    @_sslcopydoc
+    def getpeercert(self, binary_form=False):
+        self._checkClosed()
+        self._check_connected()
+        return self._sslobj.getpeercert(binary_form)
+
+    @_sslcopydoc
+    def selected_npn_protocol(self):
+        self._checkClosed()
+        warnings.warn(
+            "ssl NPN is deprecated, use ALPN instead",
+            DeprecationWarning,
+            stacklevel=2
+        )
+        return None
+
+    @_sslcopydoc
+    def selected_alpn_protocol(self):
+        self._checkClosed()
+        if self._sslobj is None or not _ssl.HAS_ALPN:
+            return None
+        else:
+            return self._sslobj.selected_alpn_protocol()
+
+    @_sslcopydoc
+    def cipher(self):
+        self._checkClosed()
+        if self._sslobj is None:
+            return None
+        else:
+            return self._sslobj.cipher()
+
+    @_sslcopydoc
+    def shared_ciphers(self):
+        self._checkClosed()
+        if self._sslobj is None:
+            return None
+        else:
+            return self._sslobj.shared_ciphers()
+
+    @_sslcopydoc
+    def compression(self):
+        self._checkClosed()
+        if self._sslobj is None:
+            return None
+        else:
+            return self._sslobj.compression()
+
+    def send(self, data, flags=0):
+        self._checkClosed()
+        if self._sslobj is not None:
+            if flags != 0:
+                raise ValueError(
+                    "non-zero flags not allowed in calls to send() on %s" %
+                    self.__class__)
+            return self._sslobj.write(data)
+        else:
+            return super().send(data, flags)
+
+    def sendto(self, data, flags_or_addr, addr=None):
+        self._checkClosed()
+        if self._sslobj is not None:
+            raise ValueError("sendto not allowed on instances of %s" %
+                             self.__class__)
+        elif addr is None:
+            return super().sendto(data, flags_or_addr)
+        else:
+            return super().sendto(data, flags_or_addr, addr)
+
+    def sendmsg(self, *args, **kwargs):
+        # Ensure programs don't send data unencrypted if they try to
+        # use this method.
+        raise NotImplementedError("sendmsg not allowed on instances of %s" %
+                                  self.__class__)
+
+    def sendall(self, data, flags=0):
+        self._checkClosed()
+        if self._sslobj is not None:
+            if flags != 0:
+                raise ValueError(
+                    "non-zero flags not allowed in calls to sendall() on %s" %
+                    self.__class__)
+            count = 0
+            with memoryview(data) as view, view.cast("B") as byte_view:
+                amount = len(byte_view)
+                while count < amount:
+                    v = self.send(byte_view[count:])
+                    count += v
+        else:
+            return super().sendall(data, flags)
+
+    def sendfile(self, file, offset=0, count=None):
+        """Send a file, possibly by using os.sendfile() if this is a
+        clear-text socket.  Return the total number of bytes sent.
+        """
+        if self._sslobj is not None:
+            return self._sendfile_use_send(file, offset, count)
+        else:
+            # os.sendfile() works with plain sockets only
+            return super().sendfile(file, offset, count)
+
+    def recv(self, buflen=1024, flags=0):
+        self._checkClosed()
+        if self._sslobj is not None:
+            if flags != 0:
+                raise ValueError(
+                    "non-zero flags not allowed in calls to recv() on %s" %
+                    self.__class__)
+            return self.read(buflen)
+        else:
+            return super().recv(buflen, flags)
+
+    def recv_into(self, buffer, nbytes=None, flags=0):
+        self._checkClosed()
+        if nbytes is None:
+            if buffer is not None:
+                with memoryview(buffer) as view:
+                    nbytes = view.nbytes
+                if not nbytes:
+                    nbytes = 1024
+            else:
+                nbytes = 1024
+        if self._sslobj is not None:
+            if flags != 0:
+                raise ValueError(
+                  "non-zero flags not allowed in calls to recv_into() on %s" %
+                  self.__class__)
+            return self.read(nbytes, buffer)
+        else:
+            return super().recv_into(buffer, nbytes, flags)
+
+    def recvfrom(self, buflen=1024, flags=0):
+        self._checkClosed()
+        if self._sslobj is not None:
+            raise ValueError("recvfrom not allowed on instances of %s" %
+                             self.__class__)
+        else:
+            return super().recvfrom(buflen, flags)
+
+    def recvfrom_into(self, buffer, nbytes=None, flags=0):
+        self._checkClosed()
+        if self._sslobj is not None:
+            raise ValueError("recvfrom_into not allowed on instances of %s" %
+                             self.__class__)
+        else:
+            return super().recvfrom_into(buffer, nbytes, flags)
+
+    def recvmsg(self, *args, **kwargs):
+        raise NotImplementedError("recvmsg not allowed on instances of %s" %
+                                  self.__class__)
+
+    def recvmsg_into(self, *args, **kwargs):
+        raise NotImplementedError("recvmsg_into not allowed on instances of "
+                                  "%s" % self.__class__)
+
+    @_sslcopydoc
+    def pending(self):
+        self._checkClosed()
+        if self._sslobj is not None:
+            return self._sslobj.pending()
+        else:
+            return 0
+
+    def shutdown(self, how):
+        self._checkClosed()
+        self._sslobj = None
+        super().shutdown(how)
+
+    @_sslcopydoc
+    def unwrap(self):
+        if self._sslobj:
+            s = self._sslobj.shutdown()
+            self._sslobj = None
+            return s
+        else:
+            raise ValueError("No SSL wrapper around " + str(self))
+
+    @_sslcopydoc
+    def verify_client_post_handshake(self):
+        if self._sslobj:
+            return self._sslobj.verify_client_post_handshake()
+        else:
+            raise ValueError("No SSL wrapper around " + str(self))
+
+    def _real_close(self):
+        self._sslobj = None
+        super()._real_close()
+
+    @_sslcopydoc
+    def do_handshake(self, block=False):
+        self._check_connected()
+        timeout = self.gettimeout()
+        try:
+            if timeout == 0.0 and block:
+                self.settimeout(None)
+            self._sslobj.do_handshake()
+        finally:
+            self.settimeout(timeout)
+
+    def _real_connect(self, addr, connect_ex):
+        if self.server_side:
+            raise ValueError("can't connect in server-side mode")
+        # Here we assume that the socket is client-side, and not
+        # connected at the time of the call.  We connect it, then wrap it.
+        if self._connected or self._sslobj is not None:
+            raise ValueError("attempt to connect already-connected SSLSocket!")
+        self._sslobj = self.context._wrap_socket(
+            self, False, self.server_hostname,
+            owner=self, session=self._session
+        )
+        try:
+            if connect_ex:
+                rc = super().connect_ex(addr)
+            else:
+                rc = None
+                super().connect(addr)
+            if not rc:
+                self._connected = True
+                if self.do_handshake_on_connect:
+                    self.do_handshake()
+            return rc
+        except (OSError, ValueError):
+            self._sslobj = None
+            raise
+
+    def connect(self, addr):
+        """Connects to remote ADDR, and then wraps the connection in
+        an SSL channel."""
+        self._real_connect(addr, False)
+
+    def connect_ex(self, addr):
+        """Connects to remote ADDR, and then wraps the connection in
+        an SSL channel."""
+        return self._real_connect(addr, True)
+
+    def accept(self):
+        """Accepts a new connection from a remote client, and returns
+        a tuple containing that new connection wrapped with a server-side
+        SSL channel, and the address of the remote client."""
+
+        newsock, addr = super().accept()
+        newsock = self.context.wrap_socket(newsock,
+                    do_handshake_on_connect=self.do_handshake_on_connect,
+                    suppress_ragged_eofs=self.suppress_ragged_eofs,
+                    server_side=True)
+        return newsock, addr
+
+    @_sslcopydoc
+    def get_channel_binding(self, cb_type="tls-unique"):
+        if self._sslobj is not None:
+            return self._sslobj.get_channel_binding(cb_type)
+        else:
+            if cb_type not in CHANNEL_BINDING_TYPES:
+                raise ValueError(
+                    "{0} channel binding type not implemented".format(cb_type)
+                )
+            return None
+
+    @_sslcopydoc
+    def version(self):
+        if self._sslobj is not None:
+            return self._sslobj.version()
+        else:
+            return None
+
+
+# Python does not support forward declaration of types.
+SSLContext.sslsocket_class = SSLSocket
+SSLContext.sslobject_class = SSLObject
+
+
+# some utility functions
+
+def cert_time_to_seconds(cert_time):
+    """Return the time in seconds since the Epoch, given the timestring
+    representing the "notBefore" or "notAfter" date from a certificate
+    in ``"%b %d %H:%M:%S %Y %Z"`` strptime format (C locale).
+
+    "notBefore" or "notAfter" dates must use UTC (RFC 5280).
+
+    Month is one of: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
+    UTC should be specified as GMT (see ASN1_TIME_print())
+    """
+    from time import strptime
+    from calendar import timegm
+
+    months = (
+        "Jan","Feb","Mar","Apr","May","Jun",
+        "Jul","Aug","Sep","Oct","Nov","Dec"
+    )
+    time_format = ' %d %H:%M:%S %Y GMT' # NOTE: no month, fixed GMT
+    try:
+        month_number = months.index(cert_time[:3].title()) + 1
+    except ValueError:
+        raise ValueError('time data %r does not match '
+                         'format "%%b%s"' % (cert_time, time_format))
+    else:
+        # found valid month
+        tt = strptime(cert_time[3:], time_format)
+        # return an integer, the previous mktime()-based implementation
+        # returned a float (fractional seconds are always zero here).
+        return timegm((tt[0], month_number) + tt[2:6])
+
+PEM_HEADER = "-----BEGIN CERTIFICATE-----"
+PEM_FOOTER = "-----END CERTIFICATE-----"
+
+def DER_cert_to_PEM_cert(der_cert_bytes):
+    """Takes a certificate in binary DER format and returns the
+    PEM version of it as a string."""
+
+    f = str(base64.standard_b64encode(der_cert_bytes), 'ASCII', 'strict')
+    ss = [PEM_HEADER]
+    ss += [f[i:i+64] for i in range(0, len(f), 64)]
+    ss.append(PEM_FOOTER + '\n')
+    return '\n'.join(ss)
+
+def PEM_cert_to_DER_cert(pem_cert_string):
+    """Takes a certificate in ASCII PEM format and returns the
+    DER-encoded version of it as a byte sequence"""
+
+    if not pem_cert_string.startswith(PEM_HEADER):
+        raise ValueError("Invalid PEM encoding; must start with %s"
+                         % PEM_HEADER)
+    if not pem_cert_string.strip().endswith(PEM_FOOTER):
+        raise ValueError("Invalid PEM encoding; must end with %s"
+                         % PEM_FOOTER)
+    d = pem_cert_string.strip()[len(PEM_HEADER):-len(PEM_FOOTER)]
+    return base64.decodebytes(d.encode('ASCII', 'strict'))
+
+def get_server_certificate(addr, ssl_version=PROTOCOL_TLS_CLIENT,
+                           ca_certs=None, timeout=_GLOBAL_DEFAULT_TIMEOUT):
+    """Retrieve the certificate from the server at the specified address,
+    and return it as a PEM-encoded string.
+    If 'ca_certs' is specified, validate the server cert against it.
+    If 'ssl_version' is specified, use it in the connection attempt.
+    If 'timeout' is specified, use it in the connection attempt.
+    """
+
+    host, port = addr
+    if ca_certs is not None:
+        cert_reqs = CERT_REQUIRED
+    else:
+        cert_reqs = CERT_NONE
+    context = _create_stdlib_context(ssl_version,
+                                     cert_reqs=cert_reqs,
+                                     cafile=ca_certs)
+    with create_connection(addr, timeout=timeout) as sock:
+        with context.wrap_socket(sock, server_hostname=host) as sslsock:
+            dercert = sslsock.getpeercert(True)
+    return DER_cert_to_PEM_cert(dercert)
+
+def get_protocol_name(protocol_code):
+    return _PROTOCOL_NAMES.get(protocol_code, '<unknown>')