    from Common import *
    from WebUtils.Funcs import htmlEncode
    import traceback

    class Transaction(Object):
        """
        A transaction serves as:

            * A container for all objects involved in the transaction. The
              objects include application, request, response, session and
              servlet.

            * A message dissemination point. The messages include awake(),
              respond() and sleep().

        When first created, a transaction has no session. However, it will
        create or retrieve one upon being asked for session().

        The life cycle of a transaction begins and ends with Application's
        dispatchRequest().
        """

        ## Init ##

        def __init__(self, application, request=None):
            Object.__init__(self)
            self._application   = application
            self._request       = request
            self._response      = None
            self._session       = None
            self._servlet       = None
            self._errorOccurred = 0

        attrNames = 'application request response session servlet errorOccurred'.split()

        def __repr__(self):
            s = []
            for name in self.attrNames:
                s.append('%s=%r' % (name, getattr(self, '_'+name, '(no attr)')))
            s = ' '.join(s)
            return '<%s %s>' % (self.__class__.__name__, s)

        ## Access ##

        def application(self):
            return self._application

        def request(self):
            return self._request

        def response(self):
            return self._response

        def setResponse(self, response):
            self._response = response

        def hasSession(self):
            """ Returns true if the transaction has a session. """
            return self._session is not None

        def session(self):
            """ Returns the session for the transaction, creating one if necessary. Therefore, this method never returns None. Use hasSession() if you want to find out if there one already exists. """
            if not self._session:
                self._session = self._application.createSessionForTransaction(self)
            return self._session

        def setSession(self, session):
            self._session = session

        def servlet(self):
            """ Return the current servlet that is processing. Remember that servlets can be nested. """
            return self._servlet

        def setServlet(self, servlet):
            self._servlet = servlet

        def duration(self):
            """ Returns the duration, in seconds, of the transaction (basically response end time minus request start time). """
            return self._response.endTime() - self._request.time()

        def errorOccurred(self):
            return self._errorOccurred

        def setErrorOccurred(self, flag):
            """ Invoked by the application if an exception is raised to the application level. """
            self._errorOccurred = flag
            #self._servlet = None
            # @@ 2002-02-05 ce: disabled above statement so that custom exception handlers can examine the servlet

        ## Transaction stages ##

        def awake(self):
            """ Sends awake() the to session (if there is one) and the servlet. Currently, the request and response do not partake in the awake()-respond()-sleep() cycle. This could definitely be added in the future if any use was demonstrated for it. """
            if self._session:
                self._session.awake(self)
            self._servlet.awake(self)

        def respond(self):
            if self._session:
                self._session.respond(self)
            self._servlet.respond(self)

        def sleep(self):
            """ Note that sleep() is sent in reverse order as awake() (which is typical for shutdown/cleanup methods). """
            self._servlet.sleep(self)
            if self._session:
                self._session.sleep(self)

        ## Debugging ##

        def dump(self, file=None):
            """ Dumps debugging info to stdout. """
            if file is None:
                file = sys.stdout
            wr = file.write
            wr('>> Transaction: %s\n' % self)
            for attr in dir(self):
                wr('%s: %s\n' % (attr, getattr(self, attr)))
            wr('\n')

        ## Die ##

        def die(self):
            """ This method should be invoked when the entire transaction is finished with. Currently, this is invoked by AppServer. This method removes references to the different objects in the transaction, breaking cyclic reference chains and allowing either older versions of Python to collect garbage, or newer versions to collect it faster. """
            from types import InstanceType
            for attrName in self.__dict__.keys():
                # @@ 2000-05-21 ce: there's got to be a better way!
                attr = getattr(self, attrName)
                if type(attr) is InstanceType and hasattr(attr, 'resetKeyBindings'):
                    #print '>> resetting'
                    attr.resetKeyBindings()
                delattr(self, attrName)

        ## Exception handling ##

        exceptionReportAttrNames = 'application request response session servlet'.split()

        def writeExceptionReport(self, handler):
            handler.writeTitle(self.__class__.__name__)
            handler.writeAttrs(self, self.exceptionReportAttrNames)

            for name in self.exceptionReportAttrNames:
                obj = getattr(self, '_'+name, None)
                if obj:
                    try:
                        obj.writeExceptionReport(handler)
                    except Exception, e:
                        handler.writeln('<p> Uncaught exception while asking <b>%s</b> to write report:\n<pre>' % name)
                        traceback.print_exc(file=handler)
                        handler.writeln('</pre>')