# Author: Trevor Perrin
# See the LICENSE file for legal information regarding use of this file.
"""
A state machine for using TLS Lite with asynchronous I/O.
"""
[docs]
class AsyncStateMachine:
"""
This is an abstract class that's used to integrate TLS Lite with
asyncore and Twisted.
This class signals wantsReadsEvent() and wantsWriteEvent(). When
the underlying socket has become readable or writeable, the event
should be passed to this class by calling inReadEvent() or
inWriteEvent(). This class will then try to read or write through
the socket, and will update its state appropriately.
This class will forward higher-level events to its subclass. For
example, when a complete TLS record has been received,
outReadEvent() will be called with the decrypted data.
"""
[docs]
def __init__(self):
self.result = None
self.handshaker = None
self.closer = None
self.reader = None
self.writer = None
self._clear()
def _clear(self):
#These store the various asynchronous operations (i.e.
#generators). Only one of them, at most, is ever active at a
#time.
self.handshaker = None
self.closer = None
self.reader = None
self.writer = None
#This stores the result from the last call to the
#currently active operation. If 0 it indicates that the
#operation wants to read, if 1 it indicates that the
#operation wants to write. If None, there is no active
#operation.
self.result = None
def _checkAssert(self, maxActive=1):
#This checks that only one operation, at most, is
#active, and that self.result is set appropriately.
activeOps = 0
if self.handshaker:
activeOps += 1
if self.closer:
activeOps += 1
if self.reader:
activeOps += 1
if self.writer:
activeOps += 1
if self.result == None:
if activeOps != 0:
raise AssertionError()
elif self.result in (0,1):
if activeOps != 1:
raise AssertionError()
else:
raise AssertionError()
if activeOps > maxActive:
raise AssertionError()
[docs]
def wantsReadEvent(self):
"""If the state machine wants to read.
If an operation is active, this returns whether or not the
operation wants to read from the socket. If an operation is
not active, this returns None.
:rtype: bool or None
:returns: If the state machine wants to read.
"""
if self.result != None:
return self.result == 0
return None
[docs]
def wantsWriteEvent(self):
"""If the state machine wants to write.
If an operation is active, this returns whether or not the
operation wants to write to the socket. If an operation is
not active, this returns None.
:rtype: bool or None
:returns: If the state machine wants to write.
"""
if self.result != None:
return self.result == 1
return None
[docs]
def outConnectEvent(self):
"""Called when a handshake operation completes.
May be overridden in subclass.
"""
pass
[docs]
def outCloseEvent(self):
"""Called when a close operation completes.
May be overridden in subclass.
"""
pass
[docs]
def outReadEvent(self, readBuffer):
"""Called when a read operation completes.
May be overridden in subclass."""
pass
[docs]
def outWriteEvent(self):
"""Called when a write operation completes.
May be overridden in subclass."""
pass
[docs]
def inReadEvent(self):
"""Tell the state machine it can read from the socket."""
try:
self._checkAssert()
if self.handshaker:
self._doHandshakeOp()
elif self.closer:
self._doCloseOp()
elif self.reader:
self._doReadOp()
elif self.writer:
self._doWriteOp()
else:
self.reader = self.tlsConnection.readAsync(16384)
self._doReadOp()
except:
self._clear()
raise
[docs]
def inWriteEvent(self):
"""Tell the state machine it can write to the socket."""
try:
self._checkAssert()
if self.handshaker:
self._doHandshakeOp()
elif self.closer:
self._doCloseOp()
elif self.reader:
self._doReadOp()
elif self.writer:
self._doWriteOp()
else:
self.outWriteEvent()
except:
self._clear()
raise
def _doHandshakeOp(self):
try:
self.result = next(self.handshaker)
except StopIteration:
self.handshaker = None
self.result = None
self.outConnectEvent()
def _doCloseOp(self):
try:
self.result = next(self.closer)
except StopIteration:
self.closer = None
self.result = None
self.outCloseEvent()
def _doReadOp(self):
self.result = next(self.reader)
if not self.result in (0,1):
readBuffer = self.result
self.reader = None
self.result = None
self.outReadEvent(readBuffer)
def _doWriteOp(self):
try:
self.result = next(self.writer)
except StopIteration:
self.writer = None
self.result = None
[docs]
def setHandshakeOp(self, handshaker):
"""Start a handshake operation.
:param generator handshaker: A generator created by using one of the
asynchronous handshake functions (i.e.
:py:meth:`~.TLSConnection.handshakeServerAsync` , or
handshakeClientxxx(..., async_=True).
"""
try:
self._checkAssert(0)
self.handshaker = handshaker
self._doHandshakeOp()
except:
self._clear()
raise
[docs]
def setServerHandshakeOp(self, **args):
"""Start a handshake operation.
The arguments passed to this function will be forwarded to
:py:obj:`~tlslite.tlsconnection.TLSConnection.handshakeServerAsync`.
"""
handshaker = self.tlsConnection.handshakeServerAsync(**args)
self.setHandshakeOp(handshaker)
[docs]
def setCloseOp(self):
"""Start a close operation.
"""
try:
self._checkAssert(0)
self.closer = self.tlsConnection.closeAsync()
self._doCloseOp()
except:
self._clear()
raise
[docs]
def setWriteOp(self, writeBuffer):
"""Start a write operation.
:param str writeBuffer: The string to transmit.
"""
try:
self._checkAssert(0)
self.writer = self.tlsConnection.writeAsync(writeBuffer)
self._doWriteOp()
except:
self._clear()
raise