    from Common import *
    from MiscUtils.Funcs import uniqueId, hostName
    from time import localtime, time

    # Only compute this once, for improved speed.
    _hostname = hostName()

    class SessionError(Exception):
        pass

    class Session(Object):
        """
        All methods that deal with time stamps, such as creationTime(),
        treat time as the number of seconds since January 1, 1970.

        Session identifiers are stored in cookies. Therefore, clients
        must have cookies enabled.

        Unlike Response and Request, which have HTTP subclass versions
        (e.g., HTTPRequest and HTTPResponse respectively), Session does
        not. This is because there is nothing protocol specific in
        Session. (Is that true considering cookies? @@ 2000-04-09 ce)
        2000-04-27 ce: With regards to ids/cookies, maybe the notion
        of a session id should be part of the interface of a Request.

        Note that the session id should be a string that is valid
        as part of a filename. This is currently true, and should
        be maintained if the session id generation technique is
        modified. Session ids can be used in filenames.

        FUTURE

            * invalidate()
            * Sessions don't actually time out and invalidate themselves.
            * Should this be called 'HTTPSession'?
            * Should "numTransactions" be exposed as a method? Should it
              be common to all transaction objects that do the
              awake()-respond()-sleep() thing? And should there be an
              abstract super class to codify that?
        """

        ## Init ##

        def __init__(self, trans):
            Object.__init__(self)
            self._lastAccessTime  = self._creationTime = time()
            self._isExpired       = 0
            self._numTrans        = 0
            self._values          = {}
            self._timeout = trans.application().setting('SessionTimeout')*60
            sessionPrefix = trans.application().setting('SessionPrefix', None)
            if sessionPrefix == 'hostname':
                self._prefix = _hostname + '-'
            elif sessionPrefix is None:
                self._prefix = ''
            else:
                self._prefix = sessionPrefix + '-'

            attempts = 0
            while attempts<10000:
                self._identifier = self._prefix + string.join(map(lambda x: '%02d' % x, localtime(time())[:6]), '') + '-' + uniqueId(self)
                if not trans.application().hasSession(self._identifier):
                    break
                attempts = attempts + 1
            else:
                raise SessionError, "Can't create valid session id after %d attempts." % attempts
            if trans.application().setting('Debug')['Sessions']:
                print '>> [session] Created session, timeout=%s, id=%s, self=%s' % (
                    self._timeout, self._identifier, self)

        ## Access ##

        def creationTime(self):
            """ Returns the time when this session was created. """
            return self._creationTime

        def lastAccessTime(self):
            """ Returns the last time the user accessed the session through interaction. This attribute is updated in awake(), which is invoked at the beginning of a transaction. """
            return self._lastAccessTime

        def identifier(self):
            """ Returns a string that uniquely identifies the session. This method will create the identifier if needed. """
            return self._identifier

        def isExpired(self):
            """
            Returns true if the session has been previously expired.
            See also: expiring()
            """
            return getattr(self, '_isExpired', 0)

        def isNew(self):
            return self._numTrans<2

        def timeout(self):
            """ Returns the timeout for this session in seconds. """
            return self._timeout

        def setTimeout(self, timeout):
            """ Set the timeout on this session in seconds. """
            self._timeout = timeout

        ## Invalidate ##

        def invalidate(self):
            """
            Invalidates the session.
            It will be discarded the next time it is accessed.
            """
            self._lastAccessTime = 0
            self._values = {}
            self._timeout = 0

        ## Values ##

        def value(self, name, default=NoDefault):
            if default is NoDefault:
                return self._values[name]
            else:
                return self._values.get(name, default)

        def hasValue(self, name):
            return self._values.has_key(name)

        def setValue(self, name, value):
            self._values[name] = value

        def delValue(self, name):
            del self._values[name]

        def values(self):
            return self._values

        def __getitem__(self, name):
            return self.value(name)

        def __setitem__(self, name, value):
            self.setValue(name, value)

        def __delitem__(self, name):
            self.delValue(self, name)

        ## Transactions ##

        def awake(self, trans):
            """ Invoked during the beginning of a transaction, giving a Session an opportunity to perform any required setup. The default implementation updates the 'lastAccessTime'. """
            self._lastAccessTime = time()
            self._numTrans += 1

        def respond(self, trans):
            """ The default implementation does nothing, but could do something in the future. Subclasses should invoke super. """
            pass

        def sleep(self, trans):
            """ Invoked during the ending of a transaction, giving a Session an opportunity to perform any required shutdown. The default implementation does nothing, but could do something in the future. Subclasses should invoke super. """
            pass

        def expiring(self):
            """
            Called when session is expired by the application.
            Subclasses should invoke super.
            Session store __delitem__()s should invoke if not isExpired().
            """
            self._isExpired = 1

        ## Utility ##

        def sessionEncode(self, url):
            """
            Encode the session ID as a parameter to a url.
            """
            import urlparse
            sid = '_SID_=' + self.identifier()
            url=list(urlparse.urlparse(url)) #make a list
            if url[4] == '':
                url.pop(4)
                url.insert(4, sid)
            else:
                params=url.pop(4)
                url.insert(4, params + "&" + sid)
            url = urlparse.urlunparse(url)
            return url

        ## Exception reports ##

        exceptionReportAttrNames = 'lastAccessTime isExpired numTrans timeout values'.split()

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