import sys
import os
import time
import _thread
import weakref

try:
    from _pypy_openssl import ffi
    from _pypy_openssl import lib
except ImportError as e:
    import os
    msg = "\n\nThe _ssl cffi module either doesn't exist or is incompatible with your machine's shared libraries.\n" + \
          "If you have a compiler installed, you can try to rebuild it by running:\n" + \
          "cd %s\n" % os.path.abspath(os.path.dirname(os.path.dirname(os.path.dirname(__file__)))) + \
          "%s _ssl_build.py\n" % sys.executable
    raise ModuleNotFoundError(str(e) + msg, name='_cffi_ssl')

from _cffi_ssl._stdssl.certificate import (_test_decode_cert,
    _decode_certificate, _certificate_to_der)
from _cffi_ssl._stdssl.utility import (_str_with_len, _bytes_with_len,
    _str_to_ffi_buffer, _str_from_buf, _cstr_decode_fs)
from _cffi_ssl._stdssl.error import (
    ssl_error, pyssl_error, SSLError, SSLCertVerificationError,
    SSLZeroReturnError, SSLWantReadError, SSLWantWriteError, SSLSyscallError,
    SSLEOFError)
from _cffi_ssl._stdssl.error import (SSL_ERROR_NONE,
        SSL_ERROR_SSL, SSL_ERROR_WANT_READ, SSL_ERROR_WANT_WRITE,
        SSL_ERROR_WANT_X509_LOOKUP, SSL_ERROR_SYSCALL,
        SSL_ERROR_ZERO_RETURN, SSL_ERROR_WANT_CONNECT,
        SSL_ERROR_EOF, SSL_ERROR_NO_SOCKET, SSL_ERROR_INVALID_ERROR_CODE,
        pyerr_write_unraisable)
from _cffi_ssl._stdssl import error
from _pypy_util_cffi import StackNew
from select import select
import socket
from enum import IntEnum as _IntEnum

if sys.platform == 'win32':
    from _cffi_ssl._stdssl.win32_extra import enum_certificates, enum_crls
    HAVE_POLL = False
else:
    from select import poll, POLLIN, POLLOUT
    HAVE_POLL = True

_MAX_INT = 2147483647
OPENSSL_VERSION = ffi.string(lib.OPENSSL_VERSION_TEXT).decode('utf-8')
OPENSSL_VERSION_NUMBER = lib.OPENSSL_VERSION_NUMBER
ver = OPENSSL_VERSION_NUMBER
ver, status = divmod(ver, 16)
ver, patch  = divmod(ver, 256)
ver, fix    = divmod(ver, 256)
ver, minor  = divmod(ver, 256)
ver, major  = divmod(ver, 256)
version_info = (major, minor, fix, patch, status)
OPENSSL_VERSION_INFO = version_info
_OPENSSL_API_VERSION = version_info
del ver, version_info, status, patch, fix, minor, major

HAS_ECDH = True
HAS_SNI = bool(lib.Cryptography_HAS_TLSEXT_HOSTNAME)
HAS_ALPN = bool(lib.Cryptography_HAS_ALPN)
HAS_NPN = bool(lib.OPENSSL_NPN_NEGOTIATED)
HAS_CTRL_GET_MAX_PROTO_VERSION = bool(lib.Cryptography_HAS_CTRL_GET_MAX_PROTO_VERSION)
HAS_TLS_UNIQUE = True

CLIENT = 0
SERVER = 1

VERIFY_DEFAULT = 0
VERIFY_CRL_CHECK_LEAF = lib.X509_V_FLAG_CRL_CHECK
VERIFY_CRL_CHECK_CHAIN = lib.X509_V_FLAG_CRL_CHECK | lib.X509_V_FLAG_CRL_CHECK_ALL
VERIFY_X509_STRICT = lib.X509_V_FLAG_X509_STRICT
if lib.Cryptography_HAS_X509_V_FLAG_TRUSTED_FIRST:
    VERIFY_X509_TRUSTED_FIRST = lib.X509_V_FLAG_TRUSTED_FIRST

CERT_NONE = 0
CERT_OPTIONAL = 1
CERT_REQUIRED = 2

for name in dir(lib):
    if name.startswith('SSL_OP'):
        value = getattr(lib, name)
        if value != 0:
            globals()[name[4:]] = getattr(lib, name)

OP_ALL = lib.SSL_OP_ALL & ~lib.SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
OP_NO_SSLv2 = lib.SSL_OP_NO_SSLv2
OP_NO_SSLv3 = lib.SSL_OP_NO_SSLv3
OP_NO_TLSv1_3 = lib.SSL_OP_NO_TLSv1_3
if OPENSSL_VERSION_INFO > (1, 1, 0, 0, 0):
    # OP_ENABLE_MIDDLEBOX_COMPAT = lib.SSL_OP_ENABLE_MIDDLEBOX_COMPAT
    # XXX should be conditionally compiled into lib
    OP_ENABLE_MIDDLEBOX_COMPAT = 0x00100000



SSL_CLIENT = 0
SSL_SERVER = 1

SSL_CB_MAXLEN=128

if lib.Cryptography_HAS_SSL2:
    PROTOCOL_SSLv2  = 0
SSLv3_method_ok = False
if lib.Cryptography_HAS_SSL3_METHOD:
    # Some Ubuntu systems disable SSLv3
    ctx = lib.SSL_CTX_new(lib.SSLv3_method())
    if ctx:
        PROTOCOL_SSLv3  = 1
        lib.SSL_CTX_free(ctx)
        SSLv3_method_ok = True

PROTOCOL_SSLv23 = 2
PROTOCOL_TLS    = PROTOCOL_SSLv23
PROTOCOL_TLSv1    = 3
if lib.Cryptography_HAS_TLSv1_2:
    PROTOCOL_TLSv1 = 3
    PROTOCOL_TLSv1_1 = 4
    PROTOCOL_TLSv1_2 = 5
PROTOCOL_TLS_CLIENT = 0x10
PROTOCOL_TLS_SERVER = 0x11
HAS_SSLv2 = bool(lib.Cryptography_HAS_SSL2)
HAS_SSLv3 = SSLv3_method_ok
HAS_TLSv1 = True # XXX
HAS_TLSv1_1 = bool(lib.Cryptography_HAS_TLSv1_1)
HAS_TLSv1_2 = bool(lib.Cryptography_HAS_TLSv1_2)
HAS_TLSv1_3 = bool(lib.Cryptography_HAS_TLSv1_3)

# Values brute-copied from CPython 3.7. They're documented as meaningless.
PROTO_MINIMUM_SUPPORTED = -2
PROTO_MAXIMUM_SUPPORTED = -1
PROTO_SSLv3 = 0x300
PROTO_TLSv1 = 0x301
PROTO_TLSv1_1 = 0x302
PROTO_TLSv1_2 = 0x303
PROTO_TLSv1_3 = 0x304

# OpenSSL has no dedicated API to set the minimum version to the maximum
# available version, and the other way around. We have to figure out the
# minimum and maximum available version on our own and hope for the best.
if HAS_SSLv3:
    PROTO_MINIMUM_AVAILABLE = PROTO_SSLv3
elif HAS_TLSv1:
    PROTO_MINIMUM_AVAILABLE = PROTO_TLSv1
elif HAS_TLSv1_1:
    PROTO_MINIMUM_AVAILABLE = PROTO_TLSv1_1
elif HAS_TLSv1_2:
    PROTO_MINIMUM_AVAILABLE = PROTO_TLSv1_2
elif HAS_TLSv1_3:
    PROTO_MINIMUM_AVAILABLE = PROTO_TLSv1_3
else:
    raise ValueError("PROTO_MINIMUM_AVAILABLE not found")

if HAS_TLSv1_3:
    PROTO_MAXIMUM_AVAILABLE = PROTO_TLSv1_3
elif HAS_TLSv1_2:
    PROTO_MAXIMUM_AVAILABLE = PROTO_TLSv1_2
elif HAS_TLSv1_1:
    PROTO_MAXIMUM_AVAILABLE = PROTO_TLSv1_1
elif HAS_TLSv1:
    PROTO_MAXIMUM_AVAILABLE = PROTO_TLSv1
elif HAS_SSLv3:
    PROTO_MAXIMUM_AVAILABLE = PROTO_SSLv3
else:
    raise ValueError("PROTO_MAXIMUM_AVAILABLE not found")


_PROTOCOL_NAMES = (name for name in dir(lib) if name.startswith('PROTOCOL_'))

_IntEnum._convert('_SSLMethod', __name__,
        lambda name: name.startswith('PROTOCOL_'))

if HAS_TLS_UNIQUE:
    CHANNEL_BINDING_TYPES = ['tls-unique']
else:
    CHANNEL_BINDING_TYPES = []

for name in error.SSL_AD_NAMES:
    lib_attr = 'SSL_AD_' + name
    attr = 'ALERT_DESCRIPTION_' + name
    if hasattr(lib, lib_attr):
        globals()[attr] = getattr(lib, lib_attr)

# from CPython
_DEFAULT_CIPHERS = "DEFAULT:!aNULL:!eNULL:!MD5:!3DES:!DES:!RC4:!IDEA:!SEED:!aDSS:!SRP:!PSK"

# init open ssl
lib.SSL_load_error_strings()
lib.SSL_library_init()
if (lib.Cryptography_HAS_LOCKING_CALLBACKS and
        lib.CRYPTO_get_locking_callback() == ffi.NULL):
    lib.Cryptography_setup_ssl_threads()
lib.OpenSSL_add_all_algorithms()


class ErrState():
    ws = 0
    c = 0
    ssl = 0

NO_ERROR = ErrState()


def _PySSL_errno(failed, ssl, retcode):
    if failed:
        err = ErrState()
        if sys.platform == 'win32':
            err.ws = lib.WSAGetLastError()
        err.c = ffi.errno
        err.ssl = lib.SSL_get_error(ssl, retcode)
        return err
    return NO_ERROR 

def check_signals():
    # nothing to do, we are on python level, signals are
    # checked frequently in the bytecode dispatch loop
    pass

def _socket_timeout(s):
    if s is None:
        return 0.0
    t = s.gettimeout()
    if t is None:
        return -1.0
    return t

class PasswordInfo(object):
    callable = None
    password = None
    operationerror = None
    handle = None
PWINFO_STORAGE = {}

def _Cryptography_pem_password_cb(buf, size, rwflag, userdata):
    pw_info = ffi.from_handle(userdata)

    password = pw_info.password

    if pw_info.callable:
        try:
            password = pw_info.callable()
        except Exception as e:
            pw_info.operationerror = e
            return 0

        if not isinstance(password, (str, bytes, bytearray)):
            pw_info.operationerror = TypeError("password callback must return a string")
            return 0

    password = _str_to_ffi_buffer(password)

    if (len(password) > size):
        pw_info.operationerror = ValueError("password cannot be longer than %d bytes" % size)
        return 0

    ffi.memmove(buf, password, len(password))
    return len(password)

if 0:
    ffi.def_extern(_Cryptography_pem_password_cb)
    Cryptography_pem_password_cb = lib.Cryptography_pem_password_cb
else:
    Cryptography_pem_password_cb = ffi.callback("int(char*,int,int,void*)")(_Cryptography_pem_password_cb)

if hasattr(time, 'monotonic'):
    def _monotonic_clock():
        return time.monotonic()
else:
    def _monotonic_clock():
        return time.clock_gettime(time.CLOCK_MONOTONIC)

def _ssl_select(sock, writing, timeout):
    if HAVE_POLL:
        p = poll()

    # Nothing to do unless we're in timeout mode (not non-blocking)
    if sock is None or timeout == 0:
        return SOCKET_IS_NONBLOCKING
    elif timeout < 0:
        t = _socket_timeout(sock)
        if t > 0:
            return SOCKET_HAS_TIMED_OUT
        else:
            return SOCKET_IS_BLOCKING

    # Guard against closed socket
    if sock.fileno() < 0:
        return SOCKET_HAS_BEEN_CLOSED

    # Prefer poll, if available, since you can poll() any fd
    # which can't be done with select().
    if HAVE_POLL:
        p.register(sock.fileno(), POLLOUT if writing else POLLIN)

        rc = len(p.poll(timeout * 1000.0))
    else:
        # currently disabled, see HAVE_POLL
        fd = sock.fileno()
        #if (!_PyIsSelectable_fd(s->sock_fd))
        #    return SOCKET_TOO_LARGE_FOR_SELECT;
        if writing:
            rr, wr, xr = select([],[fd],[], timeout)
        else:
            rr, wr, xr = select([fd],[],[], timeout)
        rc = len(rr) + len(wr)
    if rc != 0:
        return SOCKET_OPERATION_OK
    return SOCKET_HAS_TIMED_OUT

SOCKET_IS_NONBLOCKING = 0
SOCKET_IS_BLOCKING = 1
SOCKET_HAS_TIMED_OUT = 2
SOCKET_HAS_BEEN_CLOSED = 3
SOCKET_TOO_LARGE_FOR_SELECT = 4
SOCKET_OPERATION_OK = 5

class _SSLSocket(object):

    @staticmethod
    def _new__ssl_socket(sslctx, sock, socket_type, server_hostname, owner,
            session, inbio, outbio):
        self = _SSLSocket(sslctx)
        ctx = sslctx.ctx
        self.owner = None

        if server_hostname:
            self.server_hostname = server_hostname.decode('ascii', 'strict')
            if '\x00' in self.server_hostname:
                raise TypeError("argument must be encoded string without null "
                                "bytes, not {}".format(type(server_hostname)))
        else:
            self.server_hostname = None

        lib.ERR_clear_error()
        self.ssl = ssl = ffi.gc(lib.SSL_new(ctx), lib.SSL_free)

        # bpo43522 and OpenSSL < 1.1.1l: copy hostflags manually
        if OPENSSL_VERSION_INFO < (1, 1, 1, 12):  # 12 == 'l'
            params = lib.SSL_CTX_get0_param(ctx)
            lib.X509_VERIFY_PARAM_set_hostflags(params, sslctx.hostflags);

        self._app_data_handle = ffi.new_handle(self)
        lib.SSL_set_app_data(ssl, ffi.cast("char*", self._app_data_handle))
        if sock:
            lib.SSL_set_fd(ssl, sock.fileno())
        else:
            # BIOs are reference counted and SSL_set_bio borrows our reference.
            # To prevent a double free in memory_bio_dealloc() we need to take an
            # extra reference here.
            lib.BIO_up_ref(inbio.bio);
            lib.BIO_up_ref(outbio.bio);
            lib.SSL_set_bio(self.ssl, inbio.bio, outbio.bio)

        mode = lib.SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER
        mode |= lib.SSL_MODE_AUTO_RETRY
        lib.SSL_set_mode(ssl, mode)

        if HAS_TLSv1_3:
            if sslctx._post_handshake_auth == 1:
                if socket_type == SSL_SERVER:
                    # bpo-37428: OpenSSL does not ignore SSL_VERIFY_POST_HANDSHAKE.
                    # Set SSL_VERIFY_POST_HANDSHAKE flag only for server sockets and
                    # only in combination with SSL_VERIFY_PEER flag.
                    mode = lib.SSL_CTX_get_verify_mode(lib.SSL_get_SSL_CTX(self.ssl))
                    if (mode & lib.SSL_VERIFY_PEER):
                        verify_cb = lib.SSL_get_verify_callback(self.ssl)
                        mode |= lib.SSL_VERIFY_POST_HANDSHAKE
                        lib.SSL_set_verify(ssl, mode, verify_cb)
                else:
                    lib.SSL_set_post_handshake_auth(ssl, 1)

        if server_hostname is not None:
            self._ssl_configure_hostname(server_hostname)


        # If the socket is in non-blocking mode or timeout mode, set the BIO
        # to non-blocking mode (blocking is the default)
        #
        timeout = _socket_timeout(sock)
        if sock and timeout >= 0:
            lib.BIO_set_nbio(lib.SSL_get_rbio(ssl), 1)
            lib.BIO_set_nbio(lib.SSL_get_wbio(ssl), 1)

        if socket_type == SSL_CLIENT:
            lib.SSL_set_connect_state(ssl)
        else:
            lib.SSL_set_accept_state(ssl)
        self.socket_type = socket_type

        if sock:
            self.socket = weakref.ref(sock)

        if owner is not None:
            self.owner = owner
        if session is not None:
            self.session = session

        return self

    def __init__(self, sslctx):
        self.ctx = sslctx
        self.peer_cert = ffi.NULL
        self.ssl = ffi.NULL
        self.shutdown_seen_zero = 0
        self.handshake_done = 0
        self._owner = None
        self.server_hostname = None
        self.socket = None

    def _ssl_configure_hostname(self, server_hostname):
        # Disable OpenSSL's special mode with leading dot in hostname:
        # When name starts with a dot (e.g ".example.com"), it will be
        # matched by a certificate valid for any sub-domain of name.
        length = len(server_hostname)
        if length == 0 or server_hostname[0] == '.':
            raise ValueError("server_hostname cannot be an empty string or "
                             "start with a leading dot.")

        # inet_pton is not available on all platforms
        ip = lib.a2i_IPADDRESS(server_hostname)
        if not ip:
            lib.ERR_clear_error()
            if not lib.SSL_set_tlsext_host_name(self.ssl, server_hostname):
                raise ssl_error(None)
        if self.ctx.check_hostname:
            param = lib.SSL_get0_param(self.ssl)
            if not ip:
                if not lib.X509_VERIFY_PARAM_set1_host(
                        param, server_hostname, len(server_hostname)):
                    raise ssl_error(None)
            else:
                if not lib.X509_VERIFY_PARAM_set1_ip(
                        param, lib.ASN1_STRING_data(ip), lib.ASN1_STRING_length(ip)):
                    raise ssl_error(None)

    @property
    def owner(self):
        if self._owner is None:
            return None
        return self._owner()

    @owner.setter
    def owner(self, value):
        if value is None:
            self._owner = None
        else:
            self._owner = weakref.ref(value)

    @property
    def context(self):
        return self.ctx

    @context.setter
    def context(self, value):
        """ _setter_context(ctx)

        This changes the context associated with the SSLSocket. This is typically
        used from within a callback function set by the sni_callback
        on the SSLContext to change the certificate information associated with the
        SSLSocket before the cryptographic exchange handshake messages
        """
        if isinstance(value, _SSLContext):
            if not HAS_SNI:
                raise NotImplementedError("setting a socket's "
                        "context is not supported by your OpenSSL library")
            self.ctx = value
            lib.SSL_set_SSL_CTX(self.ssl, self.ctx.ctx);
        else:
            raise TypeError("The value must be a SSLContext")

    @property
    def server_side(self):
        return self.socket_type == SSL_SERVER

    def do_handshake(self):
        sock = self.get_socket_or_connection_gone()
        ssl = self.ssl
        timeout = _socket_timeout(sock)
        if sock:
            nonblocking = timeout >= 0
            lib.BIO_set_nbio(lib.SSL_get_rbio(ssl), nonblocking)
            lib.BIO_set_nbio(lib.SSL_get_wbio(ssl), nonblocking)

        has_timeout = timeout > 0
        deadline = -1
        if has_timeout:
            deadline = _monotonic_clock() + timeout;
        # Actually negotiate SSL connection
        # XXX If SSL_do_handshake() returns 0, it's also a failure.
        while True:
            # allow threads
            ret = lib.SSL_do_handshake(ssl)
            err = _PySSL_errno(ret<1, self.ssl, ret)
            # end allow threads
            self.err = err

            check_signals()

            if has_timeout:
                # REIVIEW monotonic clock?
                timeout = deadline - _monotonic_clock()

            if err.ssl == SSL_ERROR_WANT_READ:
                sockstate = _ssl_select(sock, 0, timeout)
            elif err.ssl == SSL_ERROR_WANT_WRITE:
                sockstate = _ssl_select(sock, 1, timeout)
            else:
                sockstate = SOCKET_OPERATION_OK

            if sockstate == SOCKET_HAS_TIMED_OUT:
                raise socket.timeout("The handshake operation timed out")
            elif sockstate == SOCKET_HAS_BEEN_CLOSED:
                raise SSLError("Underlying socket has been closed.")
            elif sockstate == SOCKET_TOO_LARGE_FOR_SELECT:
                raise SSLError("Underlying socket too large for select().")
            elif sockstate == SOCKET_IS_NONBLOCKING:
                break
            if not (err.ssl == SSL_ERROR_WANT_READ or err.ssl == SSL_ERROR_WANT_WRITE):
                break
        if ret < 1:
            raise pyssl_error(self, ret)

        self.handshake_done = 1
        return None

    def getpeercert(self, binary_mode):
        if not self.handshake_done:
            raise ValueError("handshake not done yet")
        peer_cert = lib.SSL_get_peer_certificate(self.ssl);
        if peer_cert == ffi.NULL:
            return None

        if binary_mode:
            # return cert in DER-encoded format
            return _certificate_to_der(peer_cert)
        else:
            verification = lib.SSL_CTX_get_verify_mode(lib.SSL_get_SSL_CTX(self.ssl))
            if (verification & lib.SSL_VERIFY_PEER) == 0:
                return {}
            else:
                return _decode_certificate(peer_cert)

    def write(self, bytestring):
        return self._write_with_length(_str_to_ffi_buffer(bytestring), len(bytestring))

    def _write_with_length(self, b, lgt):
        sock = self.get_socket_or_connection_gone()
        ssl = self.ssl

        if lgt > _MAX_INT:
            raise OverflowError("string longer than %d bytes" % _MAX_INT)

        timeout = _socket_timeout(sock)
        if sock:
            nonblocking = timeout >= 0
            lib.BIO_set_nbio(lib.SSL_get_rbio(ssl), nonblocking)
            lib.BIO_set_nbio(lib.SSL_get_wbio(ssl), nonblocking)


        has_timeout = timeout > 0
        if has_timeout:
            deadline = _monotonic_clock() + timeout

        sockstate = _ssl_select(sock, 1, timeout)
        if sockstate == SOCKET_HAS_TIMED_OUT:
            raise socket.timeout("The write operation timed out")
        elif sockstate == SOCKET_HAS_BEEN_CLOSED:
            raise ssl_error("Underlying socket has been closed.")
        elif sockstate == SOCKET_TOO_LARGE_FOR_SELECT:
            raise ssl_error("Underlying socket too large for select().")

        while True:
            length = lib.SSL_write(self.ssl, b, lgt)
            err = _PySSL_errno(length<=0, self.ssl, length)
            self.err = err

            check_signals()

            if has_timeout:
                timeout = deadline - _monotonic_clock()

            if err.ssl == SSL_ERROR_WANT_READ:
                sockstate = _ssl_select(sock, 0, timeout)
            elif err.ssl == SSL_ERROR_WANT_WRITE:
                sockstate = _ssl_select(sock, 1, timeout)
            else:
                sockstate = SOCKET_OPERATION_OK

            if sockstate == SOCKET_HAS_TIMED_OUT:
                raise socket.timeout("The write operation timed out")
            elif sockstate == SOCKET_HAS_BEEN_CLOSED:
                raise ssl_error("Underlying socket has been closed.")
            elif sockstate == SOCKET_IS_NONBLOCKING:
                break
            if not (err.ssl == SSL_ERROR_WANT_READ or err.ssl == SSL_ERROR_WANT_WRITE):
                break

        if length > 0:
            return length
        else:
            raise pyssl_error(self, length)

    def read(self, length, buffer_into=None):
        if length < 0 and buffer_into is None:
            raise ValueError("size should not be negative")

        if buffer_into is None:
            return self._read_no_buf(length)
        return self._read_buf(length, buffer_into)

    def _read_no_buf(self, length):
        ssl = self.ssl
        sock = self.get_socket_or_connection_gone()

        if length == 0:
            return b""
        with StackNew("char[]", length) as dest:
            mem = dest

            if sock:
                timeout = _socket_timeout(sock)
                nonblocking = timeout >= 0
                lib.BIO_set_nbio(lib.SSL_get_rbio(ssl), nonblocking)
                lib.BIO_set_nbio(lib.SSL_get_wbio(ssl), nonblocking)

            deadline = 0
            timeout = _socket_timeout(sock)

            has_timeout = timeout > 0
            if has_timeout:
                deadline = _monotonic_clock() + timeout

            shutdown = False
            while True:
                count = lib.SSL_read(self.ssl, mem, length)
                err = _PySSL_errno(count<=0, self.ssl, count)
                self.err = err

                check_signals()

                if has_timeout:
                    timeout = deadline - _monotonic_clock()

                if err.ssl == SSL_ERROR_WANT_READ:
                    sockstate = _ssl_select(sock, 0, timeout)
                elif err.ssl == SSL_ERROR_WANT_WRITE:
                    sockstate = _ssl_select(sock, 1, timeout)
                elif err.ssl == SSL_ERROR_ZERO_RETURN and \
                     lib.SSL_get_shutdown(self.ssl) == lib.SSL_RECEIVED_SHUTDOWN:
                    shutdown = True
                    break;
                else:
                    sockstate = SOCKET_OPERATION_OK

                if sockstate == SOCKET_HAS_TIMED_OUT:
                    raise socket.timeout("The read operation timed out")
                elif sockstate == SOCKET_IS_NONBLOCKING:
                    break
                if not (err.ssl == SSL_ERROR_WANT_READ or err.ssl == SSL_ERROR_WANT_WRITE):
                    break

            if count <= 0 and not shutdown:
                raise pyssl_error(self, count)

            return _bytes_with_len(dest, count)

    def _read_buf(self, length, buffer_into):
        ssl = self.ssl
        sock = self.get_socket_or_connection_gone()

        mem = ffi.from_buffer(buffer_into)
        if length <= 0 or length > len(buffer_into):
            length = len(buffer_into)
            if length > _MAX_INT:
                raise OverflowError("maximum length can't fit in a C 'int'")
            if len(buffer_into) == 0:
                return 0

        if sock:
            timeout = _socket_timeout(sock)
            nonblocking = timeout >= 0
            lib.BIO_set_nbio(lib.SSL_get_rbio(ssl), nonblocking)
            lib.BIO_set_nbio(lib.SSL_get_wbio(ssl), nonblocking)

        timeout = _socket_timeout(sock)
        deadline = 0
        has_timeout = timeout > 0
        if has_timeout:
            deadline = _monotonic_clock() + timeout

        shutdown = False
        while True:
            count = lib.SSL_read(self.ssl, mem, length);
            err = _PySSL_errno(count<=0, self.ssl, count)
            self.err = err

            check_signals()

            if has_timeout:
                timeout = deadline - _monotonic_clock()

            if err.ssl == SSL_ERROR_WANT_READ:
                sockstate = _ssl_select(sock, 0, timeout)
            elif err.ssl == SSL_ERROR_WANT_WRITE:
                sockstate = _ssl_select(sock, 1, timeout)
            elif err.ssl == SSL_ERROR_ZERO_RETURN and \
                 lib.SSL_get_shutdown(self.ssl) == lib.SSL_RECEIVED_SHUTDOWN:
                shutdown = True
                break;
            else:
                sockstate = SOCKET_OPERATION_OK

            if sockstate == SOCKET_HAS_TIMED_OUT:
                raise socket.timeout("The read operation timed out")
            elif sockstate == SOCKET_IS_NONBLOCKING:
                break
            if not (err.ssl == SSL_ERROR_WANT_READ or err.ssl == SSL_ERROR_WANT_WRITE):
                break

        if count <= 0 and not shutdown:
            raise pyssl_error(self, count)

        return count

    if HAS_ALPN:
        def selected_alpn_protocol(self):
            out = ffi.new("const unsigned char **")
            outlen = ffi.new("unsigned int*")

            lib.SSL_get0_alpn_selected(self.ssl, out, outlen);
            if out[0] == ffi.NULL:
                return None
            return _str_with_len(out[0], outlen[0]);

    def shared_ciphers(self):
        ciphers = lib.SSL_get_ciphers(self.ssl)
        if ciphers == ffi.NULL:
            return None
        res = []
        count = lib.sk_SSL_CIPHER_num(ciphers)
        for i in range(count):
            tup = cipher_to_tuple(lib.sk_SSL_CIPHER_value(ciphers, i))
            if not tup:
                return None
            res.append(tup)
        return res

    def cipher(self):
        if self.ssl == ffi.NULL:
            return None
        current = lib.SSL_get_current_cipher(self.ssl)
        if current == ffi.NULL:
            return None
        return cipher_to_tuple(current)

    def compression(self):
        if not lib.Cryptography_HAS_COMPRESSION or self.ssl == ffi.NULL:
            return None

        comp_method = lib.SSL_get_current_compression(self.ssl);
        if comp_method == ffi.NULL: # or lib.SSL_COMP_get_type(comp_method) == lib.NID_undef:
            return None
        short_name = lib.SSL_COMP_get_name(comp_method)
        if short_name == ffi.NULL:
            return None
        return _cstr_decode_fs(short_name)

    def version(self):
        if self.ssl == ffi.NULL:
            return None
        version = _str_from_buf(lib.SSL_get_version(self.ssl))
        if version == "unknown":
            return None
        return version

    def get_socket_or_None(self):
        if self.socket is None:
            return None
        return self.socket()

    def get_socket_or_connection_gone(self):
        """ There are three states:
            1) self.socket is None (In C that would mean: self->Socket == NULL)
            2) self.socket() is None (-> The socket is gone)
            3) self.socket() is not None
            This method returns True if there is not weakref object allocated
        """
        if self.socket is None:
            return None
        sock = self.socket()
        if not sock:
            raise ssl_error("Underlying socket connection gone", SSL_ERROR_NO_SOCKET)
        return sock

    def shutdown(self):
        sock = self.get_socket_or_None()
        nonblocking = False
        ssl = self.ssl

        if self.socket is not None:
            # Guard against closed socket
            sock = self.socket()
            if sock is None or sock.fileno() < 0:
                raise ssl_error("Underlying socket connection gone", SSL_ERROR_NO_SOCKET)

            timeout = _socket_timeout(sock)
            nonblocking = timeout >= 0
            if sock and timeout >= 0:
                lib.BIO_set_nbio(lib.SSL_get_rbio(ssl), nonblocking)
                lib.BIO_set_nbio(lib.SSL_get_wbio(ssl), nonblocking)
        else:
            timeout = 0

        has_timeout = (timeout > 0);
        if has_timeout:
            deadline = _monotonic_clock() + timeout;

        zeros = 0

        while True:
            # Disable read-ahead so that unwrap can work correctly.
            # Otherwise OpenSSL might read in too much data,
            # eating clear text data that happens to be
            # transmitted after the SSL shutdown.
            # Should be safe to call repeatedly every time this
            # function is used and the shutdown_seen_zero != 0
            # condition is met.
            #
            if self.shutdown_seen_zero:
                lib.SSL_set_read_ahead(self.ssl, 0)
            ret = lib.SSL_shutdown(self.ssl)
            self.err = err = _PySSL_errno(ret<0, self.ssl, ret)

            # If err == 1, a secure shutdown with SSL_shutdown() is complete
            if ret > 0:
                break
            if ret == 0:
                # Don't loop endlessly; instead preserve legacy
                #   behaviour of trying SSL_shutdown() only twice.
                #   This looks necessary for OpenSSL < 0.9.8m
                zeros += 1
                if zeros > 1:
                    break
                # Shutdown was sent, now try receiving
                self.shutdown_seen_zero = 1
                continue

            if has_timeout:
                timeout = deadline - _monotonic_clock()

            # Possibly retry shutdown until timeout or failure
            if err.ssl == SSL_ERROR_WANT_READ:
                sockstate = _ssl_select(sock, 0, timeout)
            elif err.ssl == SSL_ERROR_WANT_WRITE:
                sockstate = _ssl_select(sock, 1, timeout)
            else:
                break

            if sockstate == SOCKET_HAS_TIMED_OUT:
                if err.ssl == SSL_ERROR_WANT_READ:
                    raise socket.timeout("The read operation timed out")
                else:
                    raise socket.timeout("The write operation timed out")
            elif sockstate == SOCKET_TOO_LARGE_FOR_SELECT:
                raise ssl_error("Underlying socket too large for select().")
            elif sockstate != SOCKET_OPERATION_OK:
                # Retain the SSL error code
                break;

        if ret < 0:
            raise pyssl_error(self, err)
        if sock:
            return sock
        else:
            return None

    def get_channel_binding(self, cb_type):
        buf = ffi.new("char[]", SSL_CB_MAXLEN)
        if cb_type == 'tls-unique':
            if lib.SSL_session_reused(self.ssl) ^ self.socket_type:
                length = lib.SSL_get_finished(self.ssl, buf, SSL_CB_MAXLEN)
            else:
                length = lib.SSL_get_peer_finished(self.ssl, buf, SSL_CB_MAXLEN)
        else:
            raise ValueError(f"'{cb_type}' channel binding type not implemented")
        if length == 0:
            return None
        return _bytes_with_len(buf, length) 

    def verify_client_post_handshake(self):

        if not HAS_TLSv1_3:
            raise NotImplementedError("Post-handshake auth is not supported by "
                                      "your OpenSSL version.")
        err = lib.SSL_verify_client_post_handshake(self.ssl);
        if err == 0:
            raise ssl_error(None)

    def pending(self):
        count = lib.SSL_pending(self.ssl)
        if count < 0:
            raise pyssl_error(self, count)
        else:
            return count

    def tls_unique_cb(self):
        buf = ffi.new("char[]", SSL_CB_MAXLEN)

        if lib.SSL_session_reused(self.ssl) ^ (not self.server_side):
            # if session is resumed XOR we are the client
            length = lib.SSL_get_finished(self.ssl, buf, SSL_CB_MAXLEN)
        else:
            # if a new session XOR we are the server
            length = lib.SSL_get_peer_finished(self.ssl, buf, SSL_CB_MAXLEN)

        # It cannot be negative in current OpenSSL version as of July 2011
        if length == 0:
            return None

        return _bytes_with_len(buf, length)

    if HAS_NPN:
        def selected_npn_protocol(self):
            out = ffi.new("unsigned char**")
            outlen = ffi.new("unsigned int*")
            lib.SSL_get0_next_proto_negotiated(self.ssl, out, outlen)
            if (out[0] == ffi.NULL):
                return None
            return _str_with_len(out[0], outlen[0])

    @property
    def session(self):
        "Get / set SSLSession."
        return SSLSession(self)

    @session.setter
    def session(self, value):
        if not isinstance(value, SSLSession):
            raise TypeError("Value is not a SSLSession.")
        if self.ctx.ctx != value._ctx.ctx:
            raise ValueError("Session refers to a different SSLContext.")
        if self.socket_type != SSL_CLIENT:
            raise ValueError("Cannot set session for server-side SSLSocket.")
        if self.handshake_done:
            raise ValueError("Cannot set session after handshake.")
        if not lib.SSL_set_session(self.ssl, value._session):
            raise pyssl_error(self, 0)

    @property
    def session_reused(self):
        "Was the client session reused during handshake?"
        return bool(lib.SSL_session_reused(self.ssl))



def _fs_decode(name):
    return name.decode(sys.getfilesystemencoding())
def _fs_converter(name):
    """ name must not be None """
    if isinstance(name, str):
        return name.encode(sys.getfilesystemencoding())
    return bytes(name)


def cipher_to_tuple(cipher):
    ccipher_name = lib.SSL_CIPHER_get_name(cipher)
    if ccipher_name == ffi.NULL:
        cipher_name = None
    else:
        cipher_name = _str_from_buf(ccipher_name)

    ccipher_protocol = lib.SSL_CIPHER_get_version(cipher)
    if ccipher_protocol == ffi.NULL:
        cipher_protocol = None
    else:
        cipher_protocol = _str_from_buf(ccipher_protocol)

    bits = lib.SSL_CIPHER_get_bits(cipher, ffi.NULL)
    return (cipher_name, cipher_protocol, bits)

def cipher_to_dict(cipher):
    ccipher_name = lib.SSL_CIPHER_get_name(cipher)
    buf = ffi.new('char[512]')
    alg_bits = ffi.new('int[4]')
    if ccipher_name == ffi.NULL:
        cipher_name = None
    else:
        cipher_name = _str_from_buf(ccipher_name)

    ccipher_protocol = lib.SSL_CIPHER_get_version(cipher)
    if ccipher_protocol == ffi.NULL:
        cipher_protocol = None
    else:
        cipher_protocol = _str_from_buf(ccipher_protocol)

    cipher_id = lib.SSL_CIPHER_get_id(cipher);
    lib.SSL_CIPHER_description(cipher, buf, 511)
    description = _str_from_buf(buf)
    strength_bits = lib.SSL_CIPHER_get_bits(cipher, alg_bits)
    ret = {
            'id'           : cipher_id,
            'name'         : cipher_name,
            'protocol'     : cipher_protocol,
            'description'  : description,
            'strength_bits': strength_bits,
            'alg_bits'     : alg_bits[0],
           }
    if OPENSSL_VERSION_INFO > (1, 1, 0, 0, 0):
        aead = lib.SSL_CIPHER_is_aead(cipher)
        nid = lib.SSL_CIPHER_get_cipher_nid(cipher)
        skcipher = lib.OBJ_nid2ln(nid) if nid != lib.NID_undef else None
        nid = lib.SSL_CIPHER_get_digest_nid(cipher);
        digest = lib.OBJ_nid2ln(nid) if nid != lib.NID_undef else None
        nid = lib.SSL_CIPHER_get_kx_nid(cipher);
        kx = lib.OBJ_nid2ln(nid) if nid != lib.NID_undef else None
        nid = lib.SSL_CIPHER_get_auth_nid(cipher);
        auth = lib.OBJ_nid2ln(nid) if nid != lib.NID_undef else None
        ret.update({'aead' : bool(aead),
            'symmmetric'   : skcipher,
            'digest'       : digest,
            'kea'          : kx,
            'auth'         : auth,
           })
    return ret


class SSLSession(object):
    def __new__(cls, ssl):
        self = object.__new__(cls)
        session = lib.SSL_get1_session(ssl.ssl)
        if not session:
            return None
        self._session = ffi.gc(session, lib.SSL_SESSION_free)
        self._ctx = ssl.ctx
        return self

    def __eq__(self, other):
        if not isinstance(other, SSLSession):
            return NotImplemented;
        return self.id == other.id

    @property
    def id(self):
        lenp = ffi.new("unsigned int*")
        id = lib.SSL_SESSION_get_id(self._session, lenp)
        return ffi.unpack(id, lenp[0])

    @property
    def time(self):
        return lib.SSL_SESSION_get_time(self._session)

    @property
    def timeout(self):
        return lib.SSL_SESSION_get_timeout(self._session)

    @property
    def has_ticket(self):
        return bool(lib.SSL_SESSION_has_ticket(self._session))

    @property
    def ticket_lifetime_hint(self):
        return lib.SSL_SESSION_get_ticket_lifetime_hint(self._session)


SSL_CTX_STATS_NAMES = """
    number connect connect_good connect_renegotiate accept accept_good
    accept_renegotiate hits misses timeouts cache_full""".split()
SSL_CTX_STATS = []
for name in SSL_CTX_STATS_NAMES:
    attr = 'SSL_CTX_sess_'+name
    assert hasattr(lib, attr)
    SSL_CTX_STATS.append((name, getattr(lib, attr)))

class _SSLContext(object):
    __slots__ = ('ctx', '_check_hostname',
                 'alpn_protocols', '_alpn_protocols_handle', '_protocol'
                 'npn_protocols', 'set_hostname', '_post_handshake_auth',
                 '_sni_cb', '_sni_cb_handle', '_npn_protocols_handle')
    def __new__(cls, protocol):
        self = object.__new__(cls)
        self.ctx = ffi.NULL
        self._sni_cb = None
        if protocol == PROTOCOL_TLSv1:
            method = lib.TLSv1_method()
        elif lib.Cryptography_HAS_TLSv1_1 and protocol == PROTOCOL_TLSv1_1:
            method = lib.TLSv1_1_method()
        elif lib.Cryptography_HAS_TLSv1_2 and protocol == PROTOCOL_TLSv1_2 :
            method = lib.TLSv1_2_method()
        elif SSLv3_method_ok and protocol == PROTOCOL_SSLv3:
            method = lib.SSLv3_method()
        elif lib.Cryptography_HAS_SSL2 and protocol == PROTOCOL_SSLv2:
            method = lib.SSLv2_method()
        elif protocol == PROTOCOL_SSLv23:
            method = lib.TLS_method()
        elif protocol == PROTOCOL_TLS_CLIENT:
            method = lib.TLS_client_method()
        elif protocol == PROTOCOL_TLS_SERVER:
            method = lib.TLS_server_method()
        else:
            raise ValueError("invalid protocol version")

        ctx = lib.SSL_CTX_new(method)
        if ctx == ffi.NULL:
            raise ssl_error("failed to allocate SSL context")
        self.ctx = ffi.gc(lib.SSL_CTX_new(method), lib.SSL_CTX_free)
        self._post_handshake_auth = 0;
        self._protocol = protocol
        self.hostflags = lib.X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS

        # Don't check host name by default
        if protocol == PROTOCOL_TLS_CLIENT:
            self._check_hostname = True
            self._set_verify_mode(CERT_REQUIRED)
        else:
            self._check_hostname = False
            self._set_verify_mode(CERT_NONE)
        # Defaults
        options = lib.SSL_OP_ALL & ~lib.SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
        if not lib.Cryptography_HAS_SSL2 or protocol != PROTOCOL_SSLv2:
            options |= lib.SSL_OP_NO_SSLv2
        if not SSLv3_method_ok or protocol != PROTOCOL_SSLv3:
            options |= lib.SSL_OP_NO_SSLv3
        # Minimal security flags for server and client side context.
        # Client sockets ignore server-side parameters.
        options |= lib.SSL_OP_NO_COMPRESSION
        options |= lib.SSL_OP_CIPHER_SERVER_PREFERENCE
        options |= lib.SSL_OP_SINGLE_DH_USE
        options |= lib.SSL_OP_SINGLE_ECDH_USE
        if lib.Crytpography_HAS_OP_IGNORE_UNEXPECTED_EOF:
            options |= lib.SSL_OP_IGNORE_UNEXPECTED_EOF
        lib.SSL_CTX_set_options(self.ctx, options)
        lib.SSL_CTX_set_session_id_context(self.ctx, b"Python", len(b"Python"))

        # A bare minimum cipher list without completely broken cipher suites.
        # It's far from perfect but gives users a better head start.
        if lib.Cryptography_HAS_SSL2 and protocol == PROTOCOL_SSLv2:
            # SSLv2 needs MD5
            default_ciphers = b"HIGH:!aNULL:!eNULL"
        else:
            default_ciphers = b"HIGH:!aNULL:!eNULL:!MD5"
        if not lib.SSL_CTX_set_cipher_list(ctx, default_ciphers):
            lib.ERR_clear_error()
            raise SSLError("No cipher can be selected.")

        if HAS_ECDH:
            # Allow automatic ECDH curve selection (on
            # OpenSSL 1.0.2+), or use prime256v1 by default.
            # This is Apache mod_ssl's initialization
            # policy, so we should be safe.
            if lib.Cryptography_HAS_SET_ECDH_AUTO:
                lib.SSL_CTX_set_ecdh_auto(self.ctx, 1)
            else:
                key = lib.EC_KEY_new_by_curve_name(lib.NID_X9_62_prime256v1)
                lib.SSL_CTX_set_tmp_ecdh(self.ctx, key)
                lib.EC_KEY_free(key)
        params = lib.SSL_CTX_get0_param(self.ctx);
        if lib.Cryptography_HAS_X509_V_FLAG_TRUSTED_FIRST:
            # Improve trust chain building when cross-signed intermediate
            # certificates are present. See https://bugs.python.org/issue23476.
            lib.X509_VERIFY_PARAM_set_flags(params, lib.X509_V_FLAG_TRUSTED_FIRST)
        lib.X509_VERIFY_PARAM_set_hostflags(params, self.hostflags);
        if HAS_TLSv1_3:
            lib.SSL_CTX_set_post_handshake_auth(self.ctx, self.post_handshake_auth)
        return self

    @property
    def options(self):
        return lib.SSL_CTX_get_options(self.ctx)

    @options.setter
    def options(self, value):
        new_opts = int(value)
        opts = lib.SSL_CTX_get_options(self.ctx)
        clear = opts & ~new_opts
        set = ~opts & new_opts
        if clear:
            if lib.Cryptography_HAS_SSL_CTX_CLEAR_OPTIONS:
                lib.SSL_CTX_clear_options(self.ctx, clear)
            else:
                raise ValueError("can't clear options before OpenSSL 0.9.8m")
        if set:
            lib.SSL_CTX_set_options(self.ctx, set)

    def _set_verify_mode(self, n):
        if n == CERT_NONE:
            mode = lib.SSL_VERIFY_NONE
        elif n == CERT_OPTIONAL:
            mode = lib.SSL_VERIFY_PEER
        elif n == CERT_REQUIRED:
            mode = lib.SSL_VERIFY_PEER | lib.SSL_VERIFY_FAIL_IF_NO_PEER_CERT
        else:
            raise ValueError("invalid value for verify_mode")

        # bpo-37428: newPySSLSocket() sets SSL_VERIFY_POST_HANDSHAKE flag for
        # server sockets and SSL_set_post_handshake_auth() for client.

        # keep current verify cb
        verify_cb = lib.SSL_CTX_get_verify_callback(self.ctx);
        lib.SSL_CTX_set_verify(self.ctx, mode, verify_cb);

    @property
    def verify_mode(self):
        # ignore SSL_VERIFY_CLIENT_ONCE and SSL_VERIFY_POST_HANDSHAKE
        mask = (lib.SSL_VERIFY_NONE | lib.SSL_VERIFY_PEER |
                lib.SSL_VERIFY_FAIL_IF_NO_PEER_CERT)
        mode = lib.SSL_CTX_get_verify_mode(self.ctx) & mask
        if mode == lib.SSL_VERIFY_NONE:
            return CERT_NONE
        elif mode == lib.SSL_VERIFY_PEER:
            return CERT_OPTIONAL
        elif mode == lib.SSL_VERIFY_PEER | lib.SSL_VERIFY_FAIL_IF_NO_PEER_CERT:
            return CERT_REQUIRED
        raise ssl_error("invalid return value from SSL_CTX_get_verify_mode")

    @verify_mode.setter
    def verify_mode(self, value):
        n = int(value)
        if n == CERT_NONE and self.check_hostname:
            raise ValueError("Cannot set verify_mode to CERT_NONE when " \
                             "check_hostname is enabled.")
        self._set_verify_mode(n)
        
    @property
    def verify_flags(self):
        param = lib.SSL_CTX_get0_param(self.ctx)
        flags = lib.X509_VERIFY_PARAM_get_flags(param)
        return int(flags)

    @verify_flags.setter
    def verify_flags(self, value):
        new_flags = int(value)
        param = lib.SSL_CTX_get0_param(self.ctx)
        flags = lib.X509_VERIFY_PARAM_get_flags(param);
        clear = flags & ~new_flags;
        set = ~flags & new_flags;
        if clear:
            if not lib.X509_VERIFY_PARAM_clear_flags(param, clear):
                raise ssl_error(None)
        if set:
            if not lib.X509_VERIFY_PARAM_set_flags(param, set):
                raise ssl_error(None)

    if HAS_CTRL_GET_MAX_PROTO_VERSION:
        def set_min_max_proto_version(self, arg, what):
            v = int(arg)
            if self.protocol not in (PROTOCOL_TLS_CLIENT, PROTOCOL_TLS_SERVER,
                                     PROTOCOL_TLS):
                raise ValueError("The context's protocol doesn't support"
                    "modification of highest and lowest version.")
            if what == 0:
                if v == PROTO_MINIMUM_SUPPORTED:
                    v = 0
                elif v == PROTO_MAXIMUM_SUPPORTED:
                    # Emulate max for set_min_proto_version
                    v = PROTO_MAXIMUM_AVAILABLE
                result = lib.SSL_CTX_set_min_proto_version(self.ctx, v)
            else:
                if v == PROTO_MAXIMUM_SUPPORTED:
                    v = 0
                elif v == PROTO_MINIMUM_SUPPORTED:
                    # Emulate max for set_min_proto_version
                    v = PROTO_MINIMUM_AVAILABLE
                result = lib.SSL_CTX_set_max_proto_version(self.ctx, v)
            if result == 0:
                raise ValueError('Unsupported protocol version 0x%x' % v)
            return 0

        @property
        def minimum_version(self):
            v = lib.SSL_CTX_get_min_proto_version(self.ctx)
            if v == 0:
                v = PROTO_MINIMUM_SUPPORTED
            return v

        @minimum_version.setter
        def minimum_version(self, arg):
            return self.set_min_max_proto_version(arg, 0);

        @property
        def maximum_version(self):
            v = lib.SSL_CTX_get_max_proto_version(self.ctx)
            if v == 0:
                v = PROTO_MAXIMUM_SUPPORTED
            return v

        @maximum_version.setter
        def maximum_version(self, arg):
            return self.set_min_max_proto_version(arg, 1);
         

    @property
    def protocol(self):
        return self._protocol

    @property
    def check_hostname(self):
        return self._check_hostname

    @check_hostname.setter
    def check_hostname(self, value):
        check_hostname = bool(value)
        if check_hostname and lib.SSL_CTX_get_verify_mode(self.ctx) == lib.SSL_VERIFY_NONE:
            self._set_verify_mode(CERT_REQUIRED)
        self._check_hostname = check_hostname


    @property
    def _host_flags(self):
        return self.hostflags

    @_host_flags.setter
    def _host_flags(self, arg):
        new_flags = int(arg)
        param = lib.SSL_CTX_get0_param(self.ctx);
        self.hostflags = new_flags;
        lib.X509_VERIFY_PARAM_set_hostflags(param, new_flags)

    def set_ciphers(self, cipherlist):
        cipherlistbuf = _str_to_ffi_buffer(cipherlist)
        ret = lib.SSL_CTX_set_cipher_list(self.ctx, cipherlistbuf)
        if ret == 0:
            # Clearing the error queue is necessary on some OpenSSL
            # versions, otherwise the error will be reported again
            # when another SSL call is done.
            lib.ERR_clear_error()
            raise ssl_error("No cipher can be selected.")

    def get_ciphers(self):
        ssl = lib.SSL_new(self.ctx)
        try:
            ciphers = lib.SSL_get_ciphers(ssl)
            if ciphers == ffi.NULL:
                return None
            count = lib.sk_SSL_CIPHER_num(ciphers)
            res = [None] * count
            for i in range(count):
                dct = cipher_to_dict(lib.sk_SSL_CIPHER_value(ciphers, i))
                res[i] = dct
            return res
        finally:
            lib.SSL_free(ssl)

    def load_cert_chain(self, certfile, keyfile=None, password=None):
        if keyfile is None:
            keyfile = certfile
        pw_info = PasswordInfo()
        index = -1
        orig_passwd_cb = lib.SSL_CTX_get_default_passwd_cb(self.ctx)
        orig_passwd_userdata = lib.SSL_CTX_get_default_passwd_cb_userdata(self.ctx)
        if password is not None:

            if callable(password):
                pw_info.callable = password
            else:
                if isinstance(password, (str, bytes, bytearray)):
                    pw_info.password = password
                else:
                    raise TypeError("password should be a string or callable")

            pw_info.handle = ffi.new_handle(pw_info)
            index = _thread.get_ident()
            PWINFO_STORAGE[index] = pw_info
            lib.SSL_CTX_set_default_passwd_cb(self.ctx, Cryptography_pem_password_cb)
            lib.SSL_CTX_set_default_passwd_cb_userdata(self.ctx, pw_info.handle)

        prev_errno = ffi.errno
        try:
            ffi.errno = 0
            certfilebuf = _str_to_ffi_buffer(certfile)
            ret = lib.SSL_CTX_use_certificate_chain_file(self.ctx, certfilebuf)
            if ret != 1:
                if pw_info.operationerror:
                    lib.ERR_clear_error()
                    raise pw_info.operationerror
                _errno = ffi.errno
                if _errno:
                    lib.ERR_clear_error()
                    raise OSError(_errno, "Error")
                else:
                    raise ssl_error(None)

            ffi.errno = 0
            buf = _str_to_ffi_buffer(keyfile)
            ret = lib.SSL_CTX_use_PrivateKey_file(self.ctx, buf,
                                                  lib.SSL_FILETYPE_PEM)
            if ret != 1:
                if pw_info.operationerror:
                    lib.ERR_clear_error()
                    raise pw_info.operationerror
                _errno = ffi.errno
                if _errno:
                    lib.ERR_clear_error()
                    raise OSError(_errno, None)
                else:
                    raise ssl_error(None)

            ret = lib.SSL_CTX_check_private_key(self.ctx)
            if ret != 1:
                raise ssl_error(None)
        finally:
            ffi.errno = prev_errno
            if index >= 0:
                del PWINFO_STORAGE[index]
            lib.SSL_CTX_set_default_passwd_cb(self.ctx, orig_passwd_cb)
            lib.SSL_CTX_set_default_passwd_cb_userdata(self.ctx, orig_passwd_userdata)


    def _wrap_socket(self, sock, server_side, server_hostname=None, *,
            owner=None, session=None):
        if server_hostname:
            server_hostname = server_hostname.encode('ascii')
        return _SSLSocket._new__ssl_socket(self, sock, server_side,
                server_hostname, owner, session, None, None)

    def load_verify_locations(self, cafile=None, capath=None, cadata=None):
        prev_errno = ffi.errno
        try:
            ffi.errno = 0
            if cadata is None:
                ca_file_type = -1
            else:
                if not isinstance(cadata, str):
                    ca_file_type = lib.SSL_FILETYPE_ASN1
                else:
                    ca_file_type = lib.SSL_FILETYPE_PEM
                    try:
                        cadata = cadata.encode('ascii')
                    except UnicodeEncodeError:
                        raise TypeError("cadata should be a ASCII string or a bytes-like object")
            if cafile is None and capath is None and cadata is None:
                raise TypeError("cafile and capath cannot be both omitted")
            # load from cadata
            if cadata is not None:
                buf = _str_to_ffi_buffer(cadata)
                self._add_ca_certs(buf, len(buf), ca_file_type)

            # load cafile or capath
            if cafile is not None or capath is not None:
                if cafile is None:
                    cafilebuf = ffi.NULL
                else:
                    cafilebuf = _str_to_ffi_buffer(cafile)
                if capath is None:
                    capathbuf = ffi.NULL
                else:
                    capathbuf = _str_to_ffi_buffer(capath)
                ret = lib.SSL_CTX_load_verify_locations(self.ctx, cafilebuf, capathbuf)
                if ret != 1:
                    _errno = ffi.errno
                    if _errno:
                        lib.ERR_clear_error()
                        raise OSError(_errno, '')
                    else:
                        raise ssl_error(None)
        finally:
            ffi.errno = prev_errno

    def _add_ca_certs(self, data, size, ca_file_type):
        biobuf = lib.BIO_new_mem_buf(data, size)
        if biobuf == ffi.NULL:
            raise ssl_error("Can't allocate buffer")
        try:
            store = lib.SSL_CTX_get_cert_store(self.ctx)
            loaded = 0
            while True:
                if ca_file_type == lib.SSL_FILETYPE_ASN1:
                    cert = lib.d2i_X509_bio(biobuf, ffi.NULL)
                else:
                    cert = lib.PEM_read_bio_X509(biobuf, ffi.NULL,
                                                 lib.SSL_CTX_get_default_passwd_cb(self.ctx),
                                                 lib.SSL_CTX_get_default_passwd_cb_userdata(self.ctx),
                                                )
                if not cert:
                    break
                try:
                    r = lib.X509_STORE_add_cert(store, cert)
                finally:
                    lib.X509_free(cert)
                if not r:
                    err = lib.ERR_peek_last_error()
                    if (lib.ERR_GET_LIB(err) == lib.ERR_LIB_X509 and
                        lib.ERR_GET_REASON(err) ==
                        lib.X509_R_CERT_ALREADY_IN_HASH_TABLE):
                        # cert already in hash table, not an error
                        lib.ERR_clear_error()
                    else:
                        break
                loaded += 1

            err = lib.ERR_peek_last_error()
            if (ca_file_type == lib.SSL_FILETYPE_ASN1 and
                loaded > 0 and
                lib.ERR_GET_LIB(err) == lib.ERR_LIB_ASN1 and
                lib.ERR_GET_REASON(err) == lib.ASN1_R_HEADER_TOO_LONG):
                # EOF ASN1 file, not an error
                lib.ERR_clear_error()
            elif (ca_file_type == lib.SSL_FILETYPE_PEM and
                  loaded > 0 and
                  lib.ERR_GET_LIB(err) == lib.ERR_LIB_PEM and
                  lib.ERR_GET_REASON(err) == lib.PEM_R_NO_START_LINE):
                # EOF PEM file, not an error
                lib.ERR_clear_error()
            elif err != 0:
                raise ssl_error(None)
        finally:
            lib.BIO_free(biobuf)

    @property
    def sni_callback(self):
        r"""Set a callback that will be called when a server name is
        provided by the SSL/TLS client in the SNI extension.

        If the argument is None then the callback is disabled. The method
        is called with the SSLSocket, the server name as a string, and the
        SSLContext object. See RFC 6066 for details of the SNI
        extension.
        """

        return self._sni_cb

    @sni_callback.setter
    def sni_callback(self, cb):
        if self._protocol == PROTOCOL_TLS_CLIENT:
            raise ValueError('sni_callback cannot be set on TLS_CLIENT context')
        if not HAS_SNI:
            raise NotImplementedError("The TLS extension servername callback, "
                    "SSL_CTX_set_tlsext_servername_callback, "
                    "is not in the current OpenSSL library.")
        if cb is None:
            lib.SSL_CTX_set_tlsext_servername_callback(self.ctx, ffi.NULL)
            self._sni_cb = None
            lib.SSL_CTX_set_tlsext_servername_arg(self.ctx, ffi.NULL)
            self._sni_cb_handle = None
            return
        if not callable(cb):
            lib.SSL_CTX_set_tlsext_servername_callback(self.ctx, ffi.NULL)
            raise TypeError("not a callable object")
        self._sni_cb = ServernameCallback(cb, self)
        self._sni_cb_handle = sni_cb = ffi.new_handle(self._sni_cb)
        lib.SSL_CTX_set_tlsext_servername_callback(self.ctx, _servername_callback)
        lib.SSL_CTX_set_tlsext_servername_arg(self.ctx, sni_cb)

    def cert_store_stats(self):
        store = lib.SSL_CTX_get_cert_store(self.ctx)
        x509 = 0
        x509_ca = 0
        crl = 0
        objs = lib.X509_STORE_get0_objects(store)
        count = lib.sk_X509_OBJECT_num(objs)
        for i in range(count):
            obj = lib.sk_X509_OBJECT_value(objs, i)
            _type = lib.X509_OBJECT_get_type(obj)
            if _type == lib.X509_LU_X509:
                x509 += 1
                cert = lib.X509_OBJECT_get0_X509(obj)
                if lib.X509_check_ca(cert):
                    x509_ca += 1
            elif _type == lib.X509_LU_CRL:
                crl += 1
            else:
                # Ignore X509_LU_FAIL, X509_LU_RETRY, X509_LU_PKEY.
                # As far as I can tell they are internal states and never
                # stored in a cert store
                pass
        return {'x509': x509, 'x509_ca': x509_ca, 'crl': crl}


    def session_stats(self):
        stats = {}
        for name, ssl_func in SSL_CTX_STATS:
            stats[name] = ssl_func(self.ctx)
        return stats

    def set_default_verify_paths(self):
        if (not os.environ.get('SSL_CERT_FILE') and
            not os.environ.get('SSL_CERT_DIR') and
            not sys.platform == 'win32'):
                locations = get_default_verify_paths()
                self.load_verify_locations(locations[1], locations[3])
                return
        if not lib.SSL_CTX_set_default_verify_paths(self.ctx):
            raise ssl_error(None)

    def load_dh_params(self, filepath):
        prev_errno = ffi.errno
        try:
            ffi.errno = 0
            if filepath is None:
                raise TypeError("filepath must not be None")
            buf = _fs_converter(filepath)
            mode = ffi.new("char[]",b"r")
            ffi.errno = 0
            bio = lib.BIO_new_file(buf, mode)
            if bio == ffi.NULL:
                _errno = ffi.errno
                lib.ERR_clear_error()
                raise OSError(_errno, '')
            try:
                dh = lib.PEM_read_bio_DHparams(bio, ffi.NULL, ffi.NULL, ffi.NULL)
            finally:
                lib.BIO_free(bio)
            if dh == ffi.NULL:
                _errno = ffi.errno
                if _errno != 0:
                    lib.ERR_clear_error()
                    raise OSError(_errno, '')
                else:
                    raise ssl_error(None)
            try:
                if lib.SSL_CTX_set_tmp_dh(self.ctx, dh) == 0:
                    raise ssl_error(None)
            finally:
                lib.DH_free(dh)
        finally:
            ffi.errno = prev_errno

    def get_ca_certs(self, binary_form=None):
        binary_mode = bool(binary_form)
        _list = []
        store = lib.SSL_CTX_get_cert_store(self.ctx)
        objs = lib.X509_STORE_get0_objects(store)
        count = lib.sk_X509_OBJECT_num(objs)
        for i in range(count):
            obj = lib.sk_X509_OBJECT_value(objs, i)
            _type = lib.X509_OBJECT_get_type(obj)
            if _type != lib.X509_LU_X509:
                # not a x509 cert
                continue
            # CA for any purpose
            cert = lib.X509_OBJECT_get0_X509(obj)
            if not lib.X509_check_ca(cert):
                continue
            if binary_mode:
                _list.append(_certificate_to_der(cert))
            else:
                _list.append(_decode_certificate(cert))
        return _list

    def set_ecdh_curve(self, name):
        # needs to be zero terminated
        if name is None:
            raise TypeError()
        buf = _fs_converter(name)
        nid = lib.OBJ_sn2nid(buf)
        if nid == 0:
            raise ValueError("unknown elliptic curve name '%s'" % name)
        key = lib.EC_KEY_new_by_curve_name(nid)
        if not key:
            raise ssl_error(None)
        try:
            lib.SSL_CTX_set_tmp_ecdh(self.ctx, key)
        finally:
            lib.EC_KEY_free(key)

    def _set_alpn_protocols(self, protos):
        if HAS_ALPN:
            self.alpn_protocols = protocols = ffi.from_buffer(protos)
            length = len(protocols)

            if lib.SSL_CTX_set_alpn_protos(self.ctx,ffi.cast("unsigned char*", protocols), length):
                return MemoryError()
            self._alpn_protocols_handle = handle = ffi.new_handle(self)
            lib.SSL_CTX_set_alpn_select_cb(self.ctx, select_alpn_callback, handle)
        else:
            raise NotImplementedError("The ALPN extension requires OpenSSL 1.0.2 or later.")

    def _set_npn_protocols(self, protos):
        if HAS_NPN:
            self.npn_protocols = ffi.from_buffer(protos)
            handle = ffi.new_handle(self)
            self._npn_protocols_handle = handle # track a reference to the handle
            lib.SSL_CTX_set_next_protos_advertised_cb(self.ctx, advertise_npn_callback, handle)
            lib.SSL_CTX_set_next_proto_select_cb(self.ctx, select_npn_callback, handle)
        else:
            raise NotImplementedError("The NPN extension requires OpenSSL 1.0.1 or later.")

    def _wrap_bio(self, incoming, outgoing, server_side, server_hostname, *,
            owner=None, session=None):
        # server_hostname is either None (or absent), or to be encoded
        # using the ascii encoding.
        hostname = None
        if server_hostname is not None:
            hostname = server_hostname.encode("ascii")

        sock = _SSLSocket._new__ssl_socket(
            self, None, server_side, hostname, owner, session, incoming,
            outgoing)
        return sock

    @property
    def post_handshake_auth(self):
        if HAS_TLSv1_3:
            return bool(self._post_handshake_auth)
        return None

    @post_handshake_auth.setter
    def post_handshake_auth(self, arg):
        if arg is None:
            raise AttributeError("cannot delete attribute")
        pha = int(bool(arg))

        self._post_handshake_auth = pha

        return 0;



# cryptography constraint: OPENSSL_NO_TLSEXT will never be set!
if HAS_SNI:
    @ffi.callback("int(SSL*,int*,void*)")
    def _servername_callback(s, al, arg):
        scb = ffi.from_handle(arg)
        ssl_ctx = scb.ctx
        servername = lib.SSL_get_servername(s, lib.TLSEXT_NAMETYPE_host_name)
        set_hostname = scb.callback
        #ifdef WITH_THREAD
            # TODO PyGILState_STATE gstate = PyGILState_Ensure();
        #endif

        if set_hostname is None:
            #/* remove race condition in this the call back while if removing the
            # * callback is in progress */
            #ifdef WITH_THREAD
                    # TODO PyGILState_Release(gstate);
            #endif
            return lib.SSL_TLSEXT_ERR_OK

        ssl = ffi.from_handle(lib.SSL_get_app_data(s))
        assert isinstance(ssl, _SSLSocket)

        # The servername callback expects an argument that represents the current
        # SSL connection and that has a .context attribute that can be changed to
        # identify the requested hostname. Since the official API is the Python
        # level API we want to pass the callback a Python level object rather than
        # a _ssl.SSLSocket instance. If there's an "owner" (typically an
        # SSLObject) that will be passed. Otherwise if there's a socket then that
        # will be passed. If both do not exist only then the C-level object is
        # passed.
        ssl_socket = ssl.owner
        if not ssl_socket:
            ssl_socket = ssl.get_socket_or_None()

        if ssl_socket is None:
            al[0] = lib.SSL_AD_INTERNAL_ERROR
            return lib.SSL_TLSEXT_ERR_ALERT_FATAL

        if servername == ffi.NULL:
            try:
                result = set_hostname(ssl_socket, None, ssl_ctx)
            except Exception as e:
                pyerr_write_unraisable(e, set_hostname)
                al[0] = lib.SSL_AD_HANDSHAKE_FAILURE
                return lib.SSL_TLSEXT_ERR_ALERT_FATAL
        else:
            servername = ffi.string(servername)

            try:
                # server_hostname was encoded to an A-label by our caller; put it
                # back into a str object, but still as an A-label (bpo-28414)
                servername_str = servername.decode("ascii")
            except UnicodeDecodeError as e:
                pyerr_write_unraisable(e, servername)

            try:
                result = set_hostname(ssl_socket, servername_str, ssl_ctx)
            except Exception as e:
                pyerr_write_unraisable(e, set_hostname)
                al[0] = lib.SSL_AD_HANDSHAKE_FAILURE
                return lib.SSL_TLSEXT_ERR_ALERT_FATAL

        if result is not None:
            # this is just a poor man's emulation:
            # in CPython this works a bit different, it calls all the way
            # down from PyLong_AsLong to _PyLong_FromNbInt which raises
            # a TypeError if there is no nb_int slot filled.
            try:
                if isinstance(result, int):
                    al[0] = result
                else:
                    if result is not None:
                        if hasattr(result,'__int__'):
                            al[0] = result.__int__()
                            return lib.SSL_TLSEXT_ERR_ALERT_FATAL
                    # needed because sys.exec_info is used in pyerr_write_unraisable
                    raise TypeError("an integer is required (got type %s)" % result)
            except TypeError as e:
                pyerr_write_unraisable(e, result)
                al[0] = lib.SSL_AD_INTERNAL_ERROR
            return lib.SSL_TLSEXT_ERR_ALERT_FATAL
        else:
            # TODO gil state release?
            return lib.SSL_TLSEXT_ERR_OK

class ServernameCallback(object):
    def __init__(self, callback, ctx):
        self.callback = callback
        self.ctx = ctx

SERVERNAME_CALLBACKS = weakref.WeakValueDictionary()

def _asn1obj2py(obj):
    nid = lib.OBJ_obj2nid(obj)
    if nid == lib.NID_undef:
        raise ValueError("Unknown object")
    sn = _str_from_buf(lib.OBJ_nid2sn(nid))
    ln = _str_from_buf(lib.OBJ_nid2ln(nid))
    buf = ffi.new("char[]", 255)
    length = lib.OBJ_obj2txt(buf, len(buf), obj, 1)
    if length < 0:
        ssl_error(None)
    if length > 0:
        return (nid, sn, ln, _str_with_len(buf, length))
    else:
        return (nid, sn, ln, None)

def txt2obj(txt, name):
    _bytes = _str_to_ffi_buffer(txt)
    is_name = 0 if name else 1
    obj = lib.OBJ_txt2obj(_bytes, is_name)
    if obj == ffi.NULL:
        raise ValueError("unknown object '%s'" % txt)
    result = _asn1obj2py(obj)
    lib.ASN1_OBJECT_free(obj)
    return result

def nid2obj(nid):
    if nid < lib.NID_undef:
        raise ValueError("NID must be positive.")
    obj = lib.OBJ_nid2obj(nid);
    if obj == ffi.NULL:
        raise ValueError("unknown NID %i" % nid)
    result = _asn1obj2py(obj);
    lib.ASN1_OBJECT_free(obj);
    return result;


class MemoryBIO(object):
    def __init__(self):
        bio = lib.BIO_new(lib.BIO_s_mem());
        if bio == ffi.NULL:
            raise ssl_error("failed to allocate BIO")

        # Since our BIO is non-blocking an empty read() does not indicate EOF,
        # just that no data is currently available. The SSL routines should retry
        # the read, which we can achieve by calling BIO_set_retry_read().
        lib.BIO_set_retry_read(bio);
        lib.BIO_set_mem_eof_return(bio, -1);

        self.bio = ffi.gc(bio, lib.BIO_free)
        self.eof_written = False

    @property
    def eof(self):
        """Whether the memory BIO is at EOF."""
        return lib.BIO_ctrl_pending(self.bio) == 0 and self.eof_written

    def write(self, strlike):
        INT_MAX = 2**31-1
        if isinstance(strlike, memoryview):
            # FIXME pypy must support get_raw_address for
            # StringBuffer to remove this case!
            strlike = strlike.tobytes()
        buf = ffi.from_buffer(strlike)
        if len(buf) > INT_MAX:
            raise OverflowError("string longer than %d bytes", INT_MAX)

        if self.eof_written:
            raise ssl_error("cannot write() after write_eof()")
        nbytes = lib.BIO_write(self.bio, buf, len(buf));
        if nbytes < 0:
            raise ssl_error(None)
        return nbytes

    def write_eof(self):
        self.eof_written = True
        # After an EOF is written, a zero return from read() should be a real EOF
        # i.e. it should not be retried. Clear the SHOULD_RETRY flag.
        lib.BIO_clear_retry_flags(self.bio)
        lib.BIO_set_mem_eof_return(self.bio, 0)

    def read(self, size=-1):
        """Read up to size bytes from the memory BIO.

        If size is not specified, read the entire buffer.
        If the return value is an empty bytes instance, this means either
        EOF or that no data is available. Use the "eof" property to
        distinguish between the two.
        """
        count = size
        avail = lib.BIO_ctrl_pending(self.bio);
        if count < 0 or count > avail:
            count = avail;
        if count == 0:
            return b''

        buf = ffi.new("char[]", count)

        nbytes = lib.BIO_read(self.bio, buf, count);
        if nbytes < 0:
            raise ssl_error(None)
        #  There should never be any short reads but check anyway.
        if nbytes < count:
            pass
            # adaptation of BPO 34824: just return a short buffer
            # return b""
        return _bytes_with_len(buf, nbytes)

    @property
    def pending(self):
        return lib.BIO_ctrl_pending(self.bio)


def RAND_status():
    return lib.RAND_status()

def _RAND_bytes(count, pseudo):
    if count < 0:
        raise ValueError("num must be positive")
    buf = ffi.new("unsigned char[]", count)
    if pseudo:
        # note by reaperhulk, RAND_pseudo_bytes is deprecated in 3.6 already,
        # it is totally fine to just call RAND_bytes instead
        ok = lib.RAND_bytes(buf, count)
        if ok == 1 or ok == 0:
            _bytes = _bytes_with_len(buf, count)
            return (_bytes, ok == 1)
    else:
        ok = lib.RAND_bytes(buf, count)
        if ok == 1 or (pseudo and ok == 0):
            return _bytes_with_len(buf, count)
    raise ssl_error(None, errcode=lib.ERR_get_error())

def RAND_pseudo_bytes(count):
    return _RAND_bytes(count, True)

def RAND_bytes(count):
    return _RAND_bytes(count, False)

def RAND_add(view, entropy):
    buf = _str_to_ffi_buffer(view)
    lib.RAND_add(buf, len(buf), entropy)

def get_default_verify_paths():
    '''
    Find a certificate store and associated values

    Returns something like
    `('SSL_CERT_FILE', '/usr/lib/ssl/cert.pem', 'SSL_CERT_DIR', '/usr/lib/ssl/certs')`
    on Ubuntu and windows10

    `('SSL_CERT_FILE', '/usr/local/cert.pem', 'SSL_CERT_DIR', '/usr/local/certs')`
    on CentOS

    `('SSL_CERT_FILE', '/Library/Frameworks/Python.framework/Versions/2.7/etc/openssl/cert.pem',
      'SSL_CERT_DIR', '/Library/Frameworks/Python.framework/Versions/2.7/etc/openssl/certs')`
    on Darwin

    For portable builds (based on CentOS, but could be running on any glibc
    linux) we need to check other locations. The list of places to try was taken
    from golang in Dec 2018:
     https://golang.org/src/crypto/x509/root_unix.go (for the directories),
     https://golang.org/src/crypto/x509/root_linux.go (for the files)
    '''
    certFiles = [
        "/etc/ssl/certs/ca-certificates.crt",                # Debian/Ubuntu/Gentoo etc.
        "/etc/pki/tls/certs/ca-bundle.crt",                  # Fedora/RHEL 6
        "/etc/ssl/ca-bundle.pem",                            # OpenSUSE
        "/etc/pki/tls/cacert.pem",                           # OpenELEC
        "/etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem", # CentOS/RHEL 7
        "/etc/ssl/cert.pem",                                 # Alpine Linux
    ]
    certDirectories = [
        "/etc/ssl/certs",               # SLES10/SLES11
        "/system/etc/security/cacerts", # Android
        "/usr/local/share/certs",       # FreeBSD
        "/etc/pki/tls/certs",           # Fedora/RHEL
        "/etc/openssl/certs",           # NetBSD
        "/var/ssl/certs",               # AIX
    ]

    # optimization: reuse the values from a local varaible
    if getattr(get_default_verify_paths, 'retval', None):
        return get_default_verify_paths.retval

    # This should never fail, it should always return SSL_CERT_FILE and SSL_CERT_DIR
    ofile_env = _cstr_decode_fs(lib.X509_get_default_cert_file_env())
    odir_env = _cstr_decode_fs(lib.X509_get_default_cert_dir_env())

    # Platform depenedent
    ofile = _cstr_decode_fs(lib.X509_get_default_cert_file())
    odir = _cstr_decode_fs(lib.X509_get_default_cert_dir())

    if os.path.exists(ofile) and os.path.exists(odir):
        get_default_verify_paths.retval = (ofile_env, ofile, odir_env, odir)
        return get_default_verify_paths.retval

    # OpenSSL didn't supply the goods. Try some other options
    for f in certFiles:
        if os.path.exists(f):
            ofile = f
    for f in certDirectories:
        if os.path.exists(f):
            odir = f
    get_default_verify_paths.retval = (ofile_env, ofile, odir_env, odir)
    return get_default_verify_paths.retval


@ffi.callback("int(SSL*,unsigned char **,unsigned char *,const unsigned char *,unsigned int,void *)")
def select_alpn_callback(ssl, out, outlen, client_protocols, client_protocols_len, args):
    ctx = ffi.from_handle(args)
    return do_protocol_selection(1, out, outlen,
                                 ffi.cast("unsigned char*",ctx.alpn_protocols), len(ctx.alpn_protocols),
                                 client_protocols, client_protocols_len)

if lib.OPENSSL_NPN_NEGOTIATED:
    @ffi.callback("int(SSL*,unsigned char **,unsigned char *,const unsigned char *,unsigned int,void *)")
    def select_npn_callback(ssl, out, outlen, server_protocols, server_protocols_len, args):
        ctx = ffi.from_handle(args)
        return do_protocol_selection(0, out, outlen, server_protocols, server_protocols_len,
                                     ffi.cast("unsigned char*",ctx.npn_protocols), len(ctx.npn_protocols))


    @ffi.callback("int(SSL*,const unsigned char**, unsigned int*, void*)")
    def advertise_npn_callback(ssl, data, length, args):
        ctx = ffi.from_handle(args)

        if not ctx.npn_protocols:
            data[0] = ffi.new("unsigned char*", b"")
            length[0] = 0
        else:
            data[0] = ffi.cast("unsigned char*",ctx.npn_protocols)
            length[0] = len(ctx.npn_protocols)

        return lib.SSL_TLSEXT_ERR_OK


    def do_protocol_selection(alpn, out, outlen, server_protocols, server_protocols_len,
                                                 client_protocols, client_protocols_len):
        if client_protocols == ffi.NULL:
            client_protocols = b""
            client_protocols_len = 0
        if server_protocols == ffi.NULL:
            server_protocols = ""
            server_protocols_len = 0

        ret = lib.SSL_select_next_proto(out, outlen,
                                        server_protocols, server_protocols_len,
                                        client_protocols, client_protocols_len);
        if alpn and ret != lib.OPENSSL_NPN_NEGOTIATED:
            return lib.SSL_TLSEXT_ERR_NOACK

        return lib.SSL_TLSEXT_ERR_OK

if lib.Cryptography_HAS_EGD:
    def RAND_egd(path):
        bytecount = lib.RAND_egd_bytes(ffi.from_buffer(path), len(path))
        if bytecount == -1:
            raise SSLError("EGD connection failed or EGD did not return "
                           "enough data to seed the PRNG");
        return bytecount

socket.RAND_add = RAND_add
socket.RAND_status = RAND_status
