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235
python/gdata/tlslite/integration/AsyncStateMachine.py
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235
python/gdata/tlslite/integration/AsyncStateMachine.py
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"""
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A state machine for using TLS Lite with asynchronous I/O.
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"""
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class AsyncStateMachine:
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"""
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This is an abstract class that's used to integrate TLS Lite with
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asyncore and Twisted.
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This class signals wantsReadsEvent() and wantsWriteEvent(). When
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the underlying socket has become readable or writeable, the event
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should be passed to this class by calling inReadEvent() or
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inWriteEvent(). This class will then try to read or write through
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the socket, and will update its state appropriately.
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This class will forward higher-level events to its subclass. For
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example, when a complete TLS record has been received,
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outReadEvent() will be called with the decrypted data.
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"""
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def __init__(self):
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self._clear()
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def _clear(self):
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#These store the various asynchronous operations (i.e.
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#generators). Only one of them, at most, is ever active at a
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#time.
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self.handshaker = None
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self.closer = None
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self.reader = None
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self.writer = None
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#This stores the result from the last call to the
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#currently active operation. If 0 it indicates that the
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#operation wants to read, if 1 it indicates that the
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#operation wants to write. If None, there is no active
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#operation.
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self.result = None
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def _checkAssert(self, maxActive=1):
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#This checks that only one operation, at most, is
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#active, and that self.result is set appropriately.
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activeOps = 0
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if self.handshaker:
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activeOps += 1
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if self.closer:
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activeOps += 1
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if self.reader:
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activeOps += 1
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if self.writer:
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activeOps += 1
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if self.result == None:
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if activeOps != 0:
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raise AssertionError()
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elif self.result in (0,1):
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if activeOps != 1:
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raise AssertionError()
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else:
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raise AssertionError()
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if activeOps > maxActive:
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raise AssertionError()
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def wantsReadEvent(self):
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"""If the state machine wants to read.
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If an operation is active, this returns whether or not the
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operation wants to read from the socket. If an operation is
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not active, this returns None.
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@rtype: bool or None
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@return: If the state machine wants to read.
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"""
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if self.result != None:
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return self.result == 0
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return None
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def wantsWriteEvent(self):
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"""If the state machine wants to write.
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If an operation is active, this returns whether or not the
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operation wants to write to the socket. If an operation is
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not active, this returns None.
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@rtype: bool or None
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@return: If the state machine wants to write.
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"""
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if self.result != None:
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return self.result == 1
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return None
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def outConnectEvent(self):
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"""Called when a handshake operation completes.
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May be overridden in subclass.
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"""
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pass
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def outCloseEvent(self):
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"""Called when a close operation completes.
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May be overridden in subclass.
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"""
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pass
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def outReadEvent(self, readBuffer):
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"""Called when a read operation completes.
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May be overridden in subclass."""
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pass
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def outWriteEvent(self):
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"""Called when a write operation completes.
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May be overridden in subclass."""
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pass
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def inReadEvent(self):
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"""Tell the state machine it can read from the socket."""
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try:
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self._checkAssert()
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if self.handshaker:
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self._doHandshakeOp()
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elif self.closer:
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self._doCloseOp()
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elif self.reader:
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self._doReadOp()
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elif self.writer:
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self._doWriteOp()
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else:
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self.reader = self.tlsConnection.readAsync(16384)
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self._doReadOp()
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except:
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self._clear()
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raise
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def inWriteEvent(self):
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"""Tell the state machine it can write to the socket."""
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try:
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self._checkAssert()
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if self.handshaker:
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self._doHandshakeOp()
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elif self.closer:
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self._doCloseOp()
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elif self.reader:
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self._doReadOp()
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elif self.writer:
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self._doWriteOp()
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else:
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self.outWriteEvent()
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except:
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self._clear()
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raise
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def _doHandshakeOp(self):
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try:
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self.result = self.handshaker.next()
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except StopIteration:
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self.handshaker = None
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self.result = None
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self.outConnectEvent()
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def _doCloseOp(self):
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try:
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self.result = self.closer.next()
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except StopIteration:
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self.closer = None
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self.result = None
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self.outCloseEvent()
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def _doReadOp(self):
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self.result = self.reader.next()
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if not self.result in (0,1):
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readBuffer = self.result
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self.reader = None
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self.result = None
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self.outReadEvent(readBuffer)
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def _doWriteOp(self):
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try:
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self.result = self.writer.next()
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except StopIteration:
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self.writer = None
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self.result = None
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def setHandshakeOp(self, handshaker):
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"""Start a handshake operation.
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@type handshaker: generator
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@param handshaker: A generator created by using one of the
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asynchronous handshake functions (i.e. handshakeServerAsync, or
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handshakeClientxxx(..., async=True).
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"""
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try:
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self._checkAssert(0)
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self.handshaker = handshaker
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self._doHandshakeOp()
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except:
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self._clear()
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raise
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def setServerHandshakeOp(self, **args):
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"""Start a handshake operation.
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The arguments passed to this function will be forwarded to
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L{tlslite.TLSConnection.TLSConnection.handshakeServerAsync}.
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"""
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handshaker = self.tlsConnection.handshakeServerAsync(**args)
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self.setHandshakeOp(handshaker)
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def setCloseOp(self):
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"""Start a close operation.
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"""
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try:
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self._checkAssert(0)
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self.closer = self.tlsConnection.closeAsync()
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self._doCloseOp()
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except:
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self._clear()
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raise
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def setWriteOp(self, writeBuffer):
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"""Start a write operation.
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@type writeBuffer: str
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@param writeBuffer: The string to transmit.
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"""
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try:
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self._checkAssert(0)
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self.writer = self.tlsConnection.writeAsync(writeBuffer)
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self._doWriteOp()
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except:
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self._clear()
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raise
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