OpenSSL/SSL.py

from sys import platform
from functools import wraps, partial
from itertools import count
from weakref import WeakValueDictionary
from errno import errorcode

from six import text_type as _text_type
from six import integer_types as integer_types

from OpenSSL._util import (
    ffi as _ffi,
    lib as _lib,
    exception_from_error_queue as _exception_from_error_queue,
    native as _native)

from OpenSSL.crypto import (
    FILETYPE_PEM, _PassphraseHelper, PKey, X509Name, X509, X509Store)

_unspecified = object()

try:
    _memoryview = memoryview
except NameError:
    class _memoryview(object):
        pass

OPENSSL_VERSION_NUMBER = _lib.OPENSSL_VERSION_NUMBER
SSLEAY_VERSION = _lib.SSLEAY_VERSION
SSLEAY_CFLAGS = _lib.SSLEAY_CFLAGS
SSLEAY_PLATFORM = _lib.SSLEAY_PLATFORM
SSLEAY_DIR = _lib.SSLEAY_DIR
SSLEAY_BUILT_ON = _lib.SSLEAY_BUILT_ON

SENT_SHUTDOWN = _lib.SSL_SENT_SHUTDOWN
RECEIVED_SHUTDOWN = _lib.SSL_RECEIVED_SHUTDOWN

SSLv2_METHOD = 1
SSLv3_METHOD = 2
SSLv23_METHOD = 3
TLSv1_METHOD = 4
TLSv1_1_METHOD = 5
TLSv1_2_METHOD = 6

OP_NO_SSLv2 = _lib.SSL_OP_NO_SSLv2
OP_NO_SSLv3 = _lib.SSL_OP_NO_SSLv3
OP_NO_TLSv1 = _lib.SSL_OP_NO_TLSv1

OP_NO_TLSv1_1 = getattr(_lib, "SSL_OP_NO_TLSv1_1", 0)
OP_NO_TLSv1_2 = getattr(_lib, "SSL_OP_NO_TLSv1_2", 0)

try:
    MODE_RELEASE_BUFFERS = _lib.SSL_MODE_RELEASE_BUFFERS
except AttributeError:
    pass

OP_SINGLE_DH_USE = _lib.SSL_OP_SINGLE_DH_USE
OP_EPHEMERAL_RSA = _lib.SSL_OP_EPHEMERAL_RSA
OP_MICROSOFT_SESS_ID_BUG = _lib.SSL_OP_MICROSOFT_SESS_ID_BUG
OP_NETSCAPE_CHALLENGE_BUG = _lib.SSL_OP_NETSCAPE_CHALLENGE_BUG
OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG = _lib.SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
OP_SSLREF2_REUSE_CERT_TYPE_BUG = _lib.SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
OP_MICROSOFT_BIG_SSLV3_BUFFER = _lib.SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
try:
    OP_MSIE_SSLV2_RSA_PADDING = _lib.SSL_OP_MSIE_SSLV2_RSA_PADDING
except AttributeError:
    pass
OP_SSLEAY_080_CLIENT_DH_BUG = _lib.SSL_OP_SSLEAY_080_CLIENT_DH_BUG
OP_TLS_D5_BUG = _lib.SSL_OP_TLS_D5_BUG
OP_TLS_BLOCK_PADDING_BUG = _lib.SSL_OP_TLS_BLOCK_PADDING_BUG
OP_DONT_INSERT_EMPTY_FRAGMENTS = _lib.SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
OP_CIPHER_SERVER_PREFERENCE = _lib.SSL_OP_CIPHER_SERVER_PREFERENCE
OP_TLS_ROLLBACK_BUG = _lib.SSL_OP_TLS_ROLLBACK_BUG
OP_PKCS1_CHECK_1 = _lib.SSL_OP_PKCS1_CHECK_1
OP_PKCS1_CHECK_2 = _lib.SSL_OP_PKCS1_CHECK_2
OP_NETSCAPE_CA_DN_BUG = _lib.SSL_OP_NETSCAPE_CA_DN_BUG
OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG= _lib.SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
try:
    OP_NO_COMPRESSION = _lib.SSL_OP_NO_COMPRESSION
except AttributeError:
    pass

OP_NO_QUERY_MTU = _lib.SSL_OP_NO_QUERY_MTU
OP_COOKIE_EXCHANGE = _lib.SSL_OP_COOKIE_EXCHANGE
OP_NO_TICKET = _lib.SSL_OP_NO_TICKET

OP_ALL   = _lib.SSL_OP_ALL

VERIFY_PEER = _lib.SSL_VERIFY_PEER
VERIFY_FAIL_IF_NO_PEER_CERT = _lib.SSL_VERIFY_FAIL_IF_NO_PEER_CERT
VERIFY_CLIENT_ONCE = _lib.SSL_VERIFY_CLIENT_ONCE
VERIFY_NONE = _lib.SSL_VERIFY_NONE

SESS_CACHE_OFF = _lib.SSL_SESS_CACHE_OFF
SESS_CACHE_CLIENT = _lib.SSL_SESS_CACHE_CLIENT
SESS_CACHE_SERVER = _lib.SSL_SESS_CACHE_SERVER
SESS_CACHE_BOTH = _lib.SSL_SESS_CACHE_BOTH
SESS_CACHE_NO_AUTO_CLEAR = _lib.SSL_SESS_CACHE_NO_AUTO_CLEAR
SESS_CACHE_NO_INTERNAL_LOOKUP = _lib.SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
SESS_CACHE_NO_INTERNAL_STORE = _lib.SSL_SESS_CACHE_NO_INTERNAL_STORE
SESS_CACHE_NO_INTERNAL = _lib.SSL_SESS_CACHE_NO_INTERNAL

SSL_ST_CONNECT = _lib.SSL_ST_CONNECT
SSL_ST_ACCEPT = _lib.SSL_ST_ACCEPT
SSL_ST_MASK = _lib.SSL_ST_MASK
SSL_ST_INIT = _lib.SSL_ST_INIT
SSL_ST_BEFORE = _lib.SSL_ST_BEFORE
SSL_ST_OK = _lib.SSL_ST_OK
SSL_ST_RENEGOTIATE = _lib.SSL_ST_RENEGOTIATE

SSL_CB_LOOP = _lib.SSL_CB_LOOP
SSL_CB_EXIT = _lib.SSL_CB_EXIT
SSL_CB_READ = _lib.SSL_CB_READ
SSL_CB_WRITE = _lib.SSL_CB_WRITE
SSL_CB_ALERT = _lib.SSL_CB_ALERT
SSL_CB_READ_ALERT = _lib.SSL_CB_READ_ALERT
SSL_CB_WRITE_ALERT = _lib.SSL_CB_WRITE_ALERT
SSL_CB_ACCEPT_LOOP = _lib.SSL_CB_ACCEPT_LOOP
SSL_CB_ACCEPT_EXIT = _lib.SSL_CB_ACCEPT_EXIT
SSL_CB_CONNECT_LOOP = _lib.SSL_CB_CONNECT_LOOP
SSL_CB_CONNECT_EXIT = _lib.SSL_CB_CONNECT_EXIT
SSL_CB_HANDSHAKE_START = _lib.SSL_CB_HANDSHAKE_START
SSL_CB_HANDSHAKE_DONE = _lib.SSL_CB_HANDSHAKE_DONE


class Error(Exception):
    """
    An error occurred in an `OpenSSL.SSL` API.
    """



_raise_current_error = partial(_exception_from_error_queue, Error)


class WantReadError(Error):
    pass



class WantWriteError(Error):
    pass



class WantX509LookupError(Error):
    pass



class ZeroReturnError(Error):
    pass



class SysCallError(Error):
    pass



class _VerifyHelper(object):
    def __init__(self, connection, callback):
        self._problems = []

        @wraps(callback)
        def wrapper(ok, store_ctx):
            cert = X509.__new__(X509)
            cert._x509 = _lib.X509_STORE_CTX_get_current_cert(store_ctx)
            error_number = _lib.X509_STORE_CTX_get_error(store_ctx)
            error_depth = _lib.X509_STORE_CTX_get_error_depth(store_ctx)

            try:
                result = callback(connection, cert, error_number, error_depth, ok)
            except Exception as e:
                self._problems.append(e)
                return 0
            else:
                if result:
                    _lib.X509_STORE_CTX_set_error(store_ctx, _lib.X509_V_OK)
                    return 1
                else:
                    return 0

        self.callback = _ffi.callback(
            "int (*)(int, X509_STORE_CTX *)", wrapper)


    def raise_if_problem(self):
        if self._problems:
            try:
                _raise_current_error()
            except Error:
                pass
            raise self._problems.pop(0)



def _asFileDescriptor(obj):
    fd = None
    if not isinstance(obj, integer_types):
        meth = getattr(obj, "fileno", None)
        if meth is not None:
            obj = meth()

    if isinstance(obj, integer_types):
        fd = obj

    if not isinstance(fd, integer_types):
        raise TypeError("argument must be an int, or have a fileno() method.")
    elif fd < 0:
        raise ValueError(
            "file descriptor cannot be a negative integer (%i)" % (fd,))

    return fd



def SSLeay_version(type):
    """
    Return a string describing the version of OpenSSL in use.

    :param type: One of the SSLEAY_ constants defined in this module.
    """
    return _ffi.string(_lib.SSLeay_version(type))



class Session(object):
    pass



class Context(object):
    """
    :py:obj:`OpenSSL.SSL.Context` instances define the parameters for setting up
    new SSL connections.
    """
    _methods = {
        SSLv3_METHOD: "SSLv3_method",
        SSLv23_METHOD: "SSLv23_method",
        TLSv1_METHOD: "TLSv1_method",
        TLSv1_1_METHOD: "TLSv1_1_method",
        TLSv1_2_METHOD: "TLSv1_2_method",
        }
    _methods = dict(
        (identifier, getattr(_lib, name))
        for (identifier, name) in _methods.items()
        if getattr(_lib, name, None) is not None)


    def __init__(self, method):
        """
        :param method: One of SSLv2_METHOD, SSLv3_METHOD, SSLv23_METHOD, or
            TLSv1_METHOD.
        """
        if not isinstance(method, int):
            raise TypeError("method must be an integer")

        try:
            method_func = self._methods[method]
        except KeyError:
            raise ValueError("No such protocol")

        method_obj = method_func()
        if method_obj == _ffi.NULL:
            # TODO: This is untested.
            _raise_current_error()

        context = _lib.SSL_CTX_new(method_obj)
        if context == _ffi.NULL:
            # TODO: This is untested.
            _raise_current_error()
        context = _ffi.gc(context, _lib.SSL_CTX_free)

        self._context = context
        self._passphrase_helper = None
        self._passphrase_callback = None
        self._passphrase_userdata = None
        self._verify_helper = None
        self._verify_callback = None
        self._info_callback = None
        self._tlsext_servername_callback = None
        self._app_data = None

        # SSL_CTX_set_app_data(self->ctx, self);
        # SSL_CTX_set_mode(self->ctx, SSL_MODE_ENABLE_PARTIAL_WRITE |
        #                             SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER |
        #                             SSL_MODE_AUTO_RETRY);
        self.set_mode(_lib.SSL_MODE_ENABLE_PARTIAL_WRITE)


    def load_verify_locations(self, cafile, capath=None):
        """
        Let SSL know where we can find trusted certificates for the certificate
        chain

        :param cafile: In which file we can find the certificates
        :param capath: In which directory we can find the certificates
        :return: None
        """
        if cafile is None:
            cafile = _ffi.NULL
        elif not isinstance(cafile, bytes):
            raise TypeError("cafile must be None or a byte string")

        if capath is None:
            capath = _ffi.NULL
        elif not isinstance(capath, bytes):
            raise TypeError("capath must be None or a byte string")

        load_result = _lib.SSL_CTX_load_verify_locations(self._context, cafile, capath)
        if not load_result:
            _raise_current_error()


    def _wrap_callback(self, callback):
        @wraps(callback)
        def wrapper(size, verify, userdata):
            return callback(size, verify, self._passphrase_userdata)
        return _PassphraseHelper(
            FILETYPE_PEM, wrapper, more_args=True, truncate=True)


    def set_passwd_cb(self, callback, userdata=None):
        """
        Set the passphrase callback

        :param callback: The Python callback to use
        :param userdata: (optional) A Python object which will be given as
                         argument to the callback
        :return: None
        """
        if not callable(callback):
            raise TypeError("callback must be callable")

        self._passphrase_helper = self._wrap_callback(callback)
        self._passphrase_callback = self._passphrase_helper.callback
        _lib.SSL_CTX_set_default_passwd_cb(
            self._context, self._passphrase_callback)
        self._passphrase_userdata = userdata


    def set_default_verify_paths(self):
        """
        Use the platform-specific CA certificate locations

        :return: None
        """
        set_result = _lib.SSL_CTX_set_default_verify_paths(self._context)
        if not set_result:
            # TODO: This is untested.
            _raise_current_error()


    def use_certificate_chain_file(self, certfile):
        """
        Load a certificate chain from a file

        :param certfile: The name of the certificate chain file
        :return: None
        """
        if isinstance(certfile, _text_type):
            # Perhaps sys.getfilesystemencoding() could be better?
            certfile = certfile.encode("utf-8")

        if not isinstance(certfile, bytes):
            raise TypeError("certfile must be bytes or unicode")

        result = _lib.SSL_CTX_use_certificate_chain_file(self._context, certfile)
        if not result:
            _raise_current_error()


    def use_certificate_file(self, certfile, filetype=FILETYPE_PEM):
        """
        Load a certificate from a file

        :param certfile: The name of the certificate file
        :param filetype: (optional) The encoding of the file, default is PEM
        :return: None
        """
        if isinstance(certfile, _text_type):
            # Perhaps sys.getfilesystemencoding() could be better?
            certfile = certfile.encode("utf-8")
        if not isinstance(certfile, bytes):
            raise TypeError("certfile must be bytes or unicode")
        if not isinstance(filetype, int):
            raise TypeError("filetype must be an integer")

        use_result = _lib.SSL_CTX_use_certificate_file(self._context, certfile, filetype)
        if not use_result:
            _raise_current_error()


    def use_certificate(self, cert):
        """
        Load a certificate from a X509 object

        :param cert: The X509 object
        :return: None
        """
        if not isinstance(cert, X509):
            raise TypeError("cert must be an X509 instance")

        use_result = _lib.SSL_CTX_use_certificate(self._context, cert._x509)
        if not use_result:
            _raise_current_error()


    def add_extra_chain_cert(self, certobj):
        """
        Add certificate to chain

        :param certobj: The X509 certificate object to add to the chain
        :return: None
        """
        if not isinstance(certobj, X509):
            raise TypeError("certobj must be an X509 instance")

        copy = _lib.X509_dup(certobj._x509)
        add_result = _lib.SSL_CTX_add_extra_chain_cert(self._context, copy)
        if not add_result:
            # TODO: This is untested.
            _lib.X509_free(copy)
            _raise_current_error()


    def _raise_passphrase_exception(self):
        if self._passphrase_helper is None:
            _raise_current_error()
        exception = self._passphrase_helper.raise_if_problem(Error)
        if exception is not None:
            raise exception


    def use_privatekey_file(self, keyfile, filetype=_unspecified):
        """
        Load a private key from a file

        :param keyfile: The name of the key file
        :param filetype: (optional) The encoding of the file, default is PEM
        :return: None
        """
        if isinstance(keyfile, _text_type):
            # Perhaps sys.getfilesystemencoding() could be better?
            keyfile = keyfile.encode("utf-8")

        if not isinstance(keyfile, bytes):
            raise TypeError("keyfile must be a byte string")

        if filetype is _unspecified:
            filetype = FILETYPE_PEM
        elif not isinstance(filetype, int):
            raise TypeError("filetype must be an integer")

        use_result = _lib.SSL_CTX_use_PrivateKey_file(
            self._context, keyfile, filetype)
        if not use_result:
            self._raise_passphrase_exception()


    def use_privatekey(self, pkey):
        """
        Load a private key from a PKey object

        :param pkey: The PKey object
        :return: None
        """
        if not isinstance(pkey, PKey):
            raise TypeError("pkey must be a PKey instance")

        use_result = _lib.SSL_CTX_use_PrivateKey(self._context, pkey._pkey)
        if not use_result:
            self._raise_passphrase_exception()


    def check_privatekey(self):
        """
        Check that the private key and certificate match up

        :return: None (raises an exception if something's wrong)
        """

    def load_client_ca(self, cafile):
        """
        Load the trusted certificates that will be sent to the client (basically
        telling the client "These are the guys I trust").  Does not actually
        imply any of the certificates are trusted; that must be configured
        separately.

        :param cafile: The name of the certificates file
        :return: None
        """

    def set_session_id(self, buf):
        """
        Set the session identifier.  This is needed if you want to do session
        resumption.

        :param buf: A Python object that can be safely converted to a string
        :returns: None
        """

    def set_session_cache_mode(self, mode):
        """
        Enable/disable session caching and specify the mode used.

        :param mode: One or more of the SESS_CACHE_* flags (combine using
            bitwise or)
        :returns: The previously set caching mode.
        """
        if not isinstance(mode, int):
            raise TypeError("mode must be an integer")

        return _lib.SSL_CTX_set_session_cache_mode(self._context, mode)


    def get_session_cache_mode(self):
        """
        :returns: The currently used cache mode.
        """
        return _lib.SSL_CTX_get_session_cache_mode(self._context)


    def set_verify(self, mode, callback):
        """
        Set the verify mode and verify callback

        :param mode: The verify mode, this is either VERIFY_NONE or
                     VERIFY_PEER combined with possible other flags
        :param callback: The Python callback to use
        :return: None

        See SSL_CTX_set_verify(3SSL) for further details.
        """
        if not isinstance(mode, int):
            raise TypeError("mode must be an integer")

        if not callable(callback):
            raise TypeError("callback must be callable")

        self._verify_helper = _VerifyHelper(self, callback)
        self._verify_callback = self._verify_helper.callback
        _lib.SSL_CTX_set_verify(self._context, mode, self._verify_callback)


    def set_verify_depth(self, depth):
        """
        Set the verify depth

        :param depth: An integer specifying the verify depth
        :return: None
        """
        if not isinstance(depth, int):
            raise TypeError("depth must be an integer")

        _lib.SSL_CTX_set_verify_depth(self._context, depth)


    def get_verify_mode(self):
        """
        Get the verify mode

        :return: The verify mode
        """
        return _lib.SSL_CTX_get_verify_mode(self._context)


    def get_verify_depth(self):
        """
        Get the verify depth

        :return: The verify depth
        """
        return _lib.SSL_CTX_get_verify_depth(self._context)


    def load_tmp_dh(self, dhfile):
        """
        Load parameters for Ephemeral Diffie-Hellman

        :param dhfile: The file to load EDH parameters from
        :return: None
        """
        if not isinstance(dhfile, bytes):
            raise TypeError("dhfile must be a byte string")

        bio = _lib.BIO_new_file(dhfile, b"r")
        if bio == _ffi.NULL:
            _raise_current_error()
        bio = _ffi.gc(bio, _lib.BIO_free)

        dh = _lib.PEM_read_bio_DHparams(bio, _ffi.NULL, _ffi.NULL, _ffi.NULL)
        dh = _ffi.gc(dh, _lib.DH_free)
        _lib.SSL_CTX_set_tmp_dh(self._context, dh)


    def set_cipher_list(self, cipher_list):
        """
        Change the cipher list

        :param cipher_list: A cipher list, see ciphers(1)
        :return: None
        """
        if isinstance(cipher_list, _text_type):
            cipher_list = cipher_list.encode("ascii")

        if not isinstance(cipher_list, bytes):
            raise TypeError("cipher_list must be bytes or unicode")

        result = _lib.SSL_CTX_set_cipher_list(self._context, cipher_list)
        if not result:
            _raise_current_error()


    def set_client_ca_list(self, certificate_authorities):
        """
        Set the list of preferred client certificate signers for this server context.

        This list of certificate authorities will be sent to the client when the
        server requests a client certificate.

        :param certificate_authorities: a sequence of X509Names.
        :return: None
        """
        name_stack = _lib.sk_X509_NAME_new_null()
        if name_stack == _ffi.NULL:
            # TODO: This is untested.
            _raise_current_error()

        try:
            for ca_name in certificate_authorities:
                if not isinstance(ca_name, X509Name):
                    raise TypeError(
                        "client CAs must be X509Name objects, not %s objects" % (
                            type(ca_name).__name__,))
                copy = _lib.X509_NAME_dup(ca_name._name)
                if copy == _ffi.NULL:
                    # TODO: This is untested.
                    _raise_current_error()
                push_result = _lib.sk_X509_NAME_push(name_stack, copy)
                if not push_result:
                    _lib.X509_NAME_free(copy)
                    _raise_current_error()
        except:
            _lib.sk_X509_NAME_free(name_stack)
            raise

        _lib.SSL_CTX_set_client_CA_list(self._context, name_stack)


    def add_client_ca(self, certificate_authority):
        """
        Add the CA certificate to the list of preferred signers for this context.

        The list of certificate authorities will be sent to the client when the
        server requests a client certificate.

        :param certificate_authority: certificate authority's X509 certificate.
        :return: None
        """
        if not isinstance(certificate_authority, X509):
            raise TypeError("certificate_authority must be an X509 instance")

        add_result = _lib.SSL_CTX_add_client_CA(
            self._context, certificate_authority._x509)
        if not add_result:
            # TODO: This is untested.
            _raise_current_error()


    def set_timeout(self, timeout):
        """
        Set session timeout

        :param timeout: The timeout in seconds
        :return: The previous session timeout
        """
        if not isinstance(timeout, int):
            raise TypeError("timeout must be an integer")

        return _lib.SSL_CTX_set_timeout(self._context, timeout)


    def get_timeout(self):
        """
        Get the session timeout

        :return: The session timeout
        """
        return _lib.SSL_CTX_get_timeout(self._context)


    def set_info_callback(self, callback):
        """
        Set the info callback

        :param callback: The Python callback to use
        :return: None
        """
        @wraps(callback)
        def wrapper(ssl, where, return_code):
            callback(Connection._reverse_mapping[ssl], where, return_code)
        self._info_callback = _ffi.callback(
            "void (*)(const SSL *, int, int)", wrapper)
        _lib.SSL_CTX_set_info_callback(self._context, self._info_callback)


    def get_app_data(self):
        """
        Get the application data (supplied via set_app_data())

        :return: The application data
        """
        return self._app_data


    def set_app_data(self, data):
        """
        Set the application data (will be returned from get_app_data())

        :param data: Any Python object
        :return: None
        """
        self._app_data = data


    def get_cert_store(self):
        """
        Get the certificate store for the context.

        :return: A X509Store object or None if it does not have one.
        """
        store = _lib.SSL_CTX_get_cert_store(self._context)
        if store == _ffi.NULL:
            # TODO: This is untested.
            return None

        pystore = X509Store.__new__(X509Store)
        pystore._store = store
        return pystore


    def set_options(self, options):
        """
        Add options. Options set before are not cleared!

        :param options: The options to add.
        :return: The new option bitmask.
        """
        if not isinstance(options, int):
            raise TypeError("options must be an integer")

        return _lib.SSL_CTX_set_options(self._context, options)


    def set_mode(self, mode):
        """
        Add modes via bitmask. Modes set before are not cleared!

        :param mode: The mode to add.
        :return: The new mode bitmask.
        """
        if not isinstance(mode, int):
            raise TypeError("mode must be an integer")

        return _lib.SSL_CTX_set_mode(self._context, mode)


    def set_tlsext_servername_callback(self, callback):
        """
        Specify a callback function to be called when clients specify a server name.

        :param callback: The callback function.  It will be invoked with one
            argument, the Connection instance.
        """
        @wraps(callback)
        def wrapper(ssl, alert, arg):
            callback(Connection._reverse_mapping[ssl])
            return 0

        self._tlsext_servername_callback = _ffi.callback(
            "int (*)(const SSL *, int *, void *)", wrapper)
        _lib.SSL_CTX_set_tlsext_servername_callback(
            self._context, self._tlsext_servername_callback)

ContextType = Context



class Connection(object):
    """
    """
    _reverse_mapping = WeakValueDictionary()

    def __init__(self, context, socket=None):
        """
        Create a new Connection object, using the given OpenSSL.SSL.Context
        instance and socket.

        :param context: An SSL Context to use for this connection
        :param socket: The socket to use for transport layer
        """
        if not isinstance(context, Context):
            raise TypeError("context must be a Context instance")

        ssl = _lib.SSL_new(context._context)
        self._ssl = _ffi.gc(ssl, _lib.SSL_free)
        self._context = context

        self._reverse_mapping[self._ssl] = self

        if socket is None:
            self._socket = None
            # Don't set up any gc for these, SSL_free will take care of them.
            self._into_ssl = _lib.BIO_new(_lib.BIO_s_mem())
            self._from_ssl = _lib.BIO_new(_lib.BIO_s_mem())

            if self._into_ssl == _ffi.NULL or self._from_ssl == _ffi.NULL:
                # TODO: This is untested.
                _raise_current_error()

            _lib.SSL_set_bio(self._ssl, self._into_ssl, self._from_ssl)
        else:
            self._into_ssl = None
            self._from_ssl = None
            self._socket = socket
            set_result = _lib.SSL_set_fd(self._ssl, _asFileDescriptor(self._socket))
            if not set_result:
                # TODO: This is untested.
                _raise_current_error()


    def __getattr__(self, name):
        """
        Look up attributes on the wrapped socket object if they are not found on
        the Connection object.
        """
        return getattr(self._socket, name)


    def _raise_ssl_error(self, ssl, result):
        if self._context._verify_helper is not None:
            self._context._verify_helper.raise_if_problem()

        error = _lib.SSL_get_error(ssl, result)
        if error == _lib.SSL_ERROR_WANT_READ:
            raise WantReadError()
        elif error == _lib.SSL_ERROR_WANT_WRITE:
            raise WantWriteError()
        elif error == _lib.SSL_ERROR_ZERO_RETURN:
            raise ZeroReturnError()
        elif error == _lib.SSL_ERROR_WANT_X509_LOOKUP:
            # TODO: This is untested.
            raise WantX509LookupError()
        elif error == _lib.SSL_ERROR_SYSCALL:
            if _lib.ERR_peek_error() == 0:
                if result < 0:
                    if platform == "win32":
                        errno = _ffi.getwinerror()[0]
                    else:
                        errno = _ffi.errno
                    raise SysCallError(errno, errorcode[errno])
                else:
                    raise SysCallError(-1, "Unexpected EOF")
            else:
                # TODO: This is untested.
                _raise_current_error()
        elif error == _lib.SSL_ERROR_NONE:
            pass
        else:
            _raise_current_error()


    def get_context(self):
        """
        Get session context
        """
        return self._context


    def set_context(self, context):
        """
        Switch this connection to a new session context

        :param context: A :py:class:`Context` instance giving the new session
            context to use.
        """
        if not isinstance(context, Context):
            raise TypeError("context must be a Context instance")

        _lib.SSL_set_SSL_CTX(self._ssl, context._context)
        self._context = context


    def get_servername(self):
        """
        Retrieve the servername extension value if provided in the client hello
        message, or None if there wasn't one.

        :return: A byte string giving the server name or :py:data:`None`.
        """
        name = _lib.SSL_get_servername(self._ssl, _lib.TLSEXT_NAMETYPE_host_name)
        if name == _ffi.NULL:
            return None

        return _ffi.string(name)


    def set_tlsext_host_name(self, name):
        """
        Set the value of the servername extension to send in the client hello.

        :param name: A byte string giving the name.
        """
        if not isinstance(name, bytes):
            raise TypeError("name must be a byte string")
        elif b"\0" in name:
            raise TypeError("name must not contain NUL byte")

        # XXX I guess this can fail sometimes?
        _lib.SSL_set_tlsext_host_name(self._ssl, name)


    def pending(self):
        """
        Get the number of bytes that can be safely read from the connection

        :return: The number of bytes available in the receive buffer.
        """
        return _lib.SSL_pending(self._ssl)


    def send(self, buf, flags=0):
        """
        Send data on the connection. NOTE: If you get one of the WantRead,
        WantWrite or WantX509Lookup exceptions on this, you have to call the
        method again with the SAME buffer.

        :param buf: The string to send
        :param flags: (optional) Included for compatibility with the socket
                      API, the value is ignored
        :return: The number of bytes written
        """
        if isinstance(buf, _memoryview):
            buf = buf.tobytes()
        if not isinstance(buf, bytes):
            raise TypeError("data must be a byte string")
        if not isinstance(flags, int):
            raise TypeError("flags must be an integer")

        result = _lib.SSL_write(self._ssl, buf, len(buf))
        self._raise_ssl_error(self._ssl, result)
        return result
    write = send


    def sendall(self, buf, flags=0):
        """
        Send "all" data on the connection. This calls send() repeatedly until
        all data is sent. If an error occurs, it's impossible to tell how much
        data has been sent.

        :param buf: The string to send
        :param flags: (optional) Included for compatibility with the socket
                      API, the value is ignored
        :return: The number of bytes written
        """
        if isinstance(buf, _memoryview):
            buf = buf.tobytes()
        if not isinstance(buf, bytes):
            raise TypeError("buf must be a byte string")
        if not isinstance(flags, int):
            raise TypeError("flags must be an integer")

        left_to_send = len(buf)
        total_sent = 0
        data = _ffi.new("char[]", buf)

        while left_to_send:
            result = _lib.SSL_write(self._ssl, data + total_sent, left_to_send)
            self._raise_ssl_error(self._ssl, result)
            total_sent += result
            left_to_send -= result


    def recv(self, bufsiz, flags=None):
        """
        Receive data on the connection. NOTE: If you get one of the WantRead,
        WantWrite or WantX509Lookup exceptions on this, you have to call the
        method again with the SAME buffer.

        :param bufsiz: The maximum number of bytes to read
        :param flags: (optional) Included for compatibility with the socket
                      API, the value is ignored
        :return: The string read from the Connection
        """
        buf = _ffi.new("char[]", bufsiz)
        result = _lib.SSL_read(self._ssl, buf, bufsiz)
        self._raise_ssl_error(self._ssl, result)
        return _ffi.buffer(buf, result)[:]
    read = recv


    def _handle_bio_errors(self, bio, result):
        if _lib.BIO_should_retry(bio):
            if _lib.BIO_should_read(bio):
                raise WantReadError()
            elif _lib.BIO_should_write(bio):
                # TODO: This is untested.
                raise WantWriteError()
            elif _lib.BIO_should_io_special(bio):
                # TODO: This is untested.  I think io_special means the socket
                # BIO has a not-yet connected socket.
                raise ValueError("BIO_should_io_special")
            else:
                # TODO: This is untested.
                raise ValueError("unknown bio failure")
        else:
            # TODO: This is untested.
            _raise_current_error()


    def bio_read(self, bufsiz):
        """
        When using non-socket connections this function reads the "dirty" data
        that would have traveled away on the network.

        :param bufsiz: The maximum number of bytes to read
        :return: The string read.
        """
        if self._from_ssl is None:
            raise TypeError("Connection sock was not None")

        if not isinstance(bufsiz, int):
            raise TypeError("bufsiz must be an integer")

        buf = _ffi.new("char[]", bufsiz)
        result = _lib.BIO_read(self._from_ssl, buf, bufsiz)
        if result <= 0:
            self._handle_bio_errors(self._from_ssl, result)

        return _ffi.buffer(buf, result)[:]


    def bio_write(self, buf):
        """
        When using non-socket connections this function sends "dirty" data that
        would have traveled in on the network.

        :param buf: The string to put into the memory BIO.
        :return: The number of bytes written
        """
        if self._into_ssl is None:
            raise TypeError("Connection sock was not None")

        if not isinstance(buf, bytes):
            raise TypeError("buf must be a byte string")

        result = _lib.BIO_write(self._into_ssl, buf, len(buf))
        if result <= 0:
            self._handle_bio_errors(self._into_ssl, result)
        return result


    def renegotiate(self):
        """
        Renegotiate the session

        :return: True if the renegotiation can be started, false otherwise
        """

    def do_handshake(self):
        """
        Perform an SSL handshake (usually called after renegotiate() or one of
        set_*_state()). This can raise the same exceptions as send and recv.

        :return: None.
        """
        result = _lib.SSL_do_handshake(self._ssl)
        self._raise_ssl_error(self._ssl, result)


    def renegotiate_pending(self):
        """
        Check if there's a renegotiation in progress, it will return false once
        a renegotiation is finished.

        :return: Whether there's a renegotiation in progress
        """

    def total_renegotiations(self):
        """
        Find out the total number of renegotiations.

        :return: The number of renegotiations.
        """
        return _lib.SSL_total_renegotiations(self._ssl)


    def connect(self, addr):
        """
        Connect to remote host and set up client-side SSL

        :param addr: A remote address
        :return: What the socket's connect method returns
        """
        _lib.SSL_set_connect_state(self._ssl)
        return self._socket.connect(addr)


    def connect_ex(self, addr):
        """
        Connect to remote host and set up client-side SSL. Note that if the socket's
        connect_ex method doesn't return 0, SSL won't be initialized.

        :param addr: A remove address
        :return: What the socket's connect_ex method returns
        """
        connect_ex = self._socket.connect_ex
        self.set_connect_state()
        return connect_ex(addr)


    def accept(self):
        """
        Accept incoming connection and set up SSL on it

        :return: A (conn,addr) pair where conn is a Connection and addr is an
                 address
        """
        client, addr = self._socket.accept()
        conn = Connection(self._context, client)
        conn.set_accept_state()
        return (conn, addr)


    def bio_shutdown(self):
        """
        When using non-socket connections this function signals end of
        data on the input for this connection.

        :return: None
        """
        if self._from_ssl is None:
            raise TypeError("Connection sock was not None")

        _lib.BIO_set_mem_eof_return(self._into_ssl, 0)


    def shutdown(self):
        """
        Send closure alert

        :return: True if the shutdown completed successfully (i.e. both sides
                 have sent closure alerts), false otherwise (i.e. you have to
                 wait for a ZeroReturnError on a recv() method call
        """
        result = _lib.SSL_shutdown(self._ssl)
        if result < 0:
            # TODO: This is untested.
            _raise_current_error()
        elif result > 0:
            return True
        else:
            return False


    def get_cipher_list(self):
        """
        Get the session cipher list

        :return: A list of cipher strings
        """
        ciphers = []
        for i in count():
            result = _lib.SSL_get_cipher_list(self._ssl, i)
            if result == _ffi.NULL:
                break
            ciphers.append(_native(_ffi.string(result)))
        return ciphers


    def get_client_ca_list(self):
        """
        Get CAs whose certificates are suggested for client authentication.

        :return: If this is a server connection, a list of X509Names representing
            the acceptable CAs as set by :py:meth:`OpenSSL.SSL.Context.set_client_ca_list` or
            :py:meth:`OpenSSL.SSL.Context.add_client_ca`.  If this is a client connection,
            the list of such X509Names sent by the server, or an empty list if that
            has not yet happened.
        """
        ca_names = _lib.SSL_get_client_CA_list(self._ssl)
        if ca_names == _ffi.NULL:
            # TODO: This is untested.
            return []

        result = []
        for i in range(_lib.sk_X509_NAME_num(ca_names)):
            name = _lib.sk_X509_NAME_value(ca_names, i)
            copy = _lib.X509_NAME_dup(name)
            if copy == _ffi.NULL:
                # TODO: This is untested.
                _raise_current_error()

            pyname = X509Name.__new__(X509Name)
            pyname._name = _ffi.gc(copy, _lib.X509_NAME_free)
            result.append(pyname)
        return result


    def makefile(self):
        """
        The makefile() method is not implemented, since there is no dup semantics
        for SSL connections

        :raise NotImplementedError
        """
        raise NotImplementedError("Cannot make file object of OpenSSL.SSL.Connection")


    def get_app_data(self):
        """
        Get application data

        :return: The application data
        """
        return self._app_data


    def set_app_data(self, data):
        """
        Set application data

        :param data - The application data
        :return: None
        """
        self._app_data = data


    def get_shutdown(self):
        """
        Get shutdown state

        :return: The shutdown state, a bitvector of SENT_SHUTDOWN, RECEIVED_SHUTDOWN.
        """
        return _lib.SSL_get_shutdown(self._ssl)


    def set_shutdown(self, state):
        """
        Set shutdown state

        :param state - bitvector of SENT_SHUTDOWN, RECEIVED_SHUTDOWN.
        :return: None
        """
        if not isinstance(state, int):
            raise TypeError("state must be an integer")

        _lib.SSL_set_shutdown(self._ssl, state)


    def state_string(self):
        """
        Get a verbose state description

        :return: A string representing the state
        """

    def server_random(self):
        """
        Get a copy of the server hello nonce.

        :return: A string representing the state
        """
        if self._ssl.session == _ffi.NULL:
            return None
        return _ffi.buffer(
            self._ssl.s3.server_random,
            _lib.SSL3_RANDOM_SIZE)[:]


    def client_random(self):
        """
        Get a copy of the client hello nonce.

        :return: A string representing the state
        """
        if self._ssl.session == _ffi.NULL:
            return None
        return _ffi.buffer(
            self._ssl.s3.client_random,
            _lib.SSL3_RANDOM_SIZE)[:]


    def master_key(self):
        """
        Get a copy of the master key.

        :return: A string representing the state
        """
        if self._ssl.session == _ffi.NULL:
            return None
        return _ffi.buffer(
            self._ssl.session.master_key,
            self._ssl.session.master_key_length)[:]


    def sock_shutdown(self, *args, **kwargs):
        """
        See shutdown(2)

        :return: What the socket's shutdown() method returns
        """
        return self._socket.shutdown(*args, **kwargs)


    def get_peer_certificate(self):
        """
        Retrieve the other side's certificate (if any)

        :return: The peer's certificate
        """
        cert = _lib.SSL_get_peer_certificate(self._ssl)
        if cert != _ffi.NULL:
            pycert = X509.__new__(X509)
            pycert._x509 = _ffi.gc(cert, _lib.X509_free)
            return pycert
        return None


    def get_peer_cert_chain(self):
        """
        Retrieve the other side's certificate (if any)

        :return: A list of X509 instances giving the peer's certificate chain,
                 or None if it does not have one.
        """
        cert_stack = _lib.SSL_get_peer_cert_chain(self._ssl)
        if cert_stack == _ffi.NULL:
            return None

        result = []
        for i in range(_lib.sk_X509_num(cert_stack)):
            # TODO could incref instead of dup here
            cert = _lib.X509_dup(_lib.sk_X509_value(cert_stack, i))
            pycert = X509.__new__(X509)
            pycert._x509 = _ffi.gc(cert, _lib.X509_free)
            result.append(pycert)
        return result


    def want_read(self):
        """
        Checks if more data has to be read from the transport layer to complete an
        operation.

        :return: True iff more data has to be read
        """
        return _lib.SSL_want_read(self._ssl)


    def want_write(self):
        """
        Checks if there is data to write to the transport layer to complete an
        operation.

        :return: True iff there is data to write
        """
        return _lib.SSL_want_write(self._ssl)


    def set_accept_state(self):
        """
        Set the connection to work in server mode. The handshake will be handled
        automatically by read/write.

        :return: None
        """
        _lib.SSL_set_accept_state(self._ssl)


    def set_connect_state(self):
        """
        Set the connection to work in client mode. The handshake will be handled
        automatically by read/write.

        :return: None
        """
        _lib.SSL_set_connect_state(self._ssl)


    def get_session(self):
        """
        Returns the Session currently used.

        @return: An instance of :py:class:`OpenSSL.SSL.Session` or :py:obj:`None` if
            no session exists.
        """
        session = _lib.SSL_get1_session(self._ssl)
        if session == _ffi.NULL:
            return None

        pysession = Session.__new__(Session)
        pysession._session = _ffi.gc(session, _lib.SSL_SESSION_free)
        return pysession


    def set_session(self, session):
        """
        Set the session to be used when the TLS/SSL connection is established.

        :param session: A Session instance representing the session to use.
        :returns: None
        """
        if not isinstance(session, Session):
            raise TypeError("session must be a Session instance")

        result = _lib.SSL_set_session(self._ssl, session._session)
        if not result:
            _raise_current_error()

ConnectionType = Connection

# This is similar to the initialization calls at the end of OpenSSL/crypto.py
# but is exercised mostly by the Context initializer.
_lib.SSL_library_init()