Почему происходит сбой установления связи при попытке запустить TLS поверх TLS с этим кодом?

Я попытался реализовать протокол, который может запускать TLS поверх TLS, используя twisted.protocols.tls , интерфейс к OpenSSL с использованием памяти BIO.

Я реализовал это как оболочку протокола, которая в основном выглядит как обычный транспорт TCP, но имеет методы startTLS и stopTLS для добавления и удаления уровня TLS соответственно. Это отлично работает для первого уровня TLS. Он также отлично работает, если я запускаю его через «родной» транспорт Twisted TLS. Однако, если я попытаюсь добавить второй уровень TLS с помощью метода startTLS , предоставляемого этой оболочкой, сразу возникает ошибка установления связи, и соединение оказывается в каком-то неизвестном непригодном для использования состоянии.

Обертка и два помощника, которые позволяют ей работать, выглядят следующим образом:

from twisted.python.components import proxyForInterface
from twisted.internet.error import ConnectionDone
from twisted.internet.interfaces import ITCPTransport, IProtocol
from twisted.protocols.tls import TLSMemoryBIOFactory, TLSMemoryBIOProtocol
from twisted.protocols.policies import ProtocolWrapper, WrappingFactory

class TransportWithoutDisconnection(proxyForInterface(ITCPTransport)):
    """
    A proxy for a normal transport that disables actually closing the connection.
    This is necessary so that when TLSMemoryBIOProtocol notices the SSL EOF it
    doesn't actually close the underlying connection.

    All methods except loseConnection are proxied directly to the real transport.
    """
    def loseConnection(self):
        pass


class ProtocolWithoutConnectionLost(proxyForInterface(IProtocol)):
    """
    A proxy for a normal protocol which captures clean connection shutdown
    notification and sends it to the TLS stacking code instead of the protocol.
    When TLS is shutdown cleanly, this notification will arrive.  Instead of telling
    the protocol that the entire connection is gone, the notification is used to
    unstack the TLS code in OnionProtocol and hidden from the wrapped protocol.  Any
    other kind of connection shutdown (SSL handshake error, network hiccups, etc) are
    treated as real problems and propagated to the wrapped protocol.
    """
    def connectionLost(self, reason):
        if reason.check(ConnectionDone):
            self.onion._stopped()
        else:
            super(ProtocolWithoutConnectionLost, self).connectionLost(reason)


class OnionProtocol(ProtocolWrapper):
    """
    OnionProtocol is both a transport and a protocol.  As a protocol, it can run over
    any other ITransport.  As a transport, it implements stackable TLS.  That is,
    whatever application traffic is generated by the protocol running on top of
    OnionProtocol can be encapsulated in a TLS conversation.  Or, that TLS conversation
    can be encapsulated in another TLS conversation.  Or **that** TLS conversation can
    be encapsulated in yet *another* TLS conversation.

    Each layer of TLS can use different connection parameters, such as keys, ciphers,
    certificate requirements, etc.  At the remote end of this connection, each has to
    be decrypted separately, starting at the outermost and working in.  OnionProtocol
    can do this itself, of course, just as it can encrypt each layer starting with the
    innermost.
    """
    def makeConnection(self, transport):
        self._tlsStack = []
        ProtocolWrapper.makeConnection(self, transport)


    def startTLS(self, contextFactory, client, bytes=None):
        """
        Add a layer of TLS, with SSL parameters defined by the given contextFactory.

        If *client* is True, this side of the connection will be an SSL client.
        Otherwise it will be an SSL server.

        If extra bytes which may be (or almost certainly are) part of the SSL handshake
        were received by the protocol running on top of OnionProtocol, they must be
        passed here as the **bytes** parameter.
        """
        # First, create a wrapper around the application-level protocol
        # (wrappedProtocol) which can catch connectionLost and tell this OnionProtocol 
        # about it.  This is necessary to pop from _tlsStack when the outermost TLS
        # layer stops.
        connLost = ProtocolWithoutConnectionLost(self.wrappedProtocol)
        connLost.onion = self
        # Construct a new TLS layer, delivering events and application data to the
        # wrapper just created.
        tlsProtocol = TLSMemoryBIOProtocol(None, connLost, False)
        tlsProtocol.factory = TLSMemoryBIOFactory(contextFactory, client, None)

        # Push the previous transport and protocol onto the stack so they can be
        # retrieved when this new TLS layer stops.
        self._tlsStack.append((self.transport, self.wrappedProtocol))

        # Create a transport for the new TLS layer to talk to.  This is a passthrough
        # to the OnionProtocol's current transport, except for capturing loseConnection
        # to avoid really closing the underlying connection.
        transport = TransportWithoutDisconnection(self.transport)

        # Make the new TLS layer the current protocol and transport.
        self.wrappedProtocol = self.transport = tlsProtocol

        # And connect the new TLS layer to the previous outermost transport.
        self.transport.makeConnection(transport)

        # If the application accidentally got some bytes from the TLS handshake, deliver
        # them to the new TLS layer.
        if bytes is not None:
            self.wrappedProtocol.dataReceived(bytes)


    def stopTLS(self):
        """
        Remove a layer of TLS.
        """
        # Just tell the current TLS layer to shut down.  When it has done so, we'll get
        # notification in *_stopped*.
        self.transport.loseConnection()


    def _stopped(self):
        # A TLS layer has completely shut down.  Throw it away and move back to the
        # TLS layer it was wrapping (or possibly back to the original non-TLS
        # transport).
        self.transport, self.wrappedProtocol = self._tlsStack.pop()

У меня есть простые клиентские и серверные программы для выполнения этого, доступные на панели запуска ( bzr branch lp: ~ exarkun / + junk / onion ). Когда я использую его для вызова описанного выше метода startTLS дважды, без промежуточного вызова stopTLS , возникает эта ошибка OpenSSL:

OpenSSL.SSL.Error: [('SSL routines', 'SSL23_GET_SERVER_HELLO', 'unknown protocol')]

Почему что-то идет не так?