    """RPC servlets."""

    import traceback, sys

    from HTTPServlet import HTTPServlet

    class RPCServlet(HTTPServlet):
        """RPCServlet is a base class for RPC servlets."""

        def call(self, methodName, *args, **keywords):
            """Call custom method.

            Subclasses may override this class for custom handling of methods.

            """
            if methodName in self.exposedMethods():
                return getattr(self, methodName)(*args, **keywords)
            else:
                raise NotImplementedError(methodName)

        @staticmethod
        def exposedMethods():
            """Get exposed methods.

            Subclasses should return a list of methods that will be exposed
            through XML-RPC.

            """
            return ['exposedMethods']

        def resultForException(self, e, trans):
            """Get text for exception.

            Given an unhandled exception, returns the string that should be
            sent back in the RPC response as controlled by the
            RPCExceptionReturn setting.

            """
            # report exception back to server
            setting = trans.application().setting('RPCExceptionReturn')
            assert setting in ('occurred', 'exception', 'traceback'), \
                'setting = %r' % setting
            if setting == 'occurred':
                result = 'unhandled exception'
            elif setting == 'exception':
                result = str(e)
            elif setting == 'traceback':
                result = ''.join(traceback.format_exception(*sys.exc_info()))
            return result

        @staticmethod
        def sendOK(contentType, contents, trans, contentEncoding=None):
            """Send a 200 OK response with the given contents."""
            response = trans.response()
            response.setStatus(200, 'OK')
            response.setHeader('Content-Type', contentType)
            response.setHeader('Content-Length', str(len(contents)))
            if contentEncoding:
                response.setHeader('Content-Encoding', contentEncoding)
            response.write(contents)

        @staticmethod
        def handleException(transaction):
            """Handle exception.

            If ReportRPCExceptionsInWebKit is set to True, then flush the response
            (because we don't want the standard HTML traceback to be appended to
            the response) and then handle the exception in the standard WebKit way.
            This means logging it to the console, storing it in the error log,
            sending error email, etc. depending on the settings.

            """
            setting = transaction.application().setting('ReportRPCExceptionsInWebKit')
            if setting:
                transaction.response().flush()
                transaction.application().handleExceptionInTransaction(
                    sys.exc_info(), transaction)

        def transaction(self):
            """Get the corresponding transaction.

            Most uses of RPC will not need this.

            """
            return self._transaction

        def awake(self, transaction):
            """Begin transaction."""
            HTTPServlet.awake(self, transaction)
            self._transaction = transaction

        def sleep(self, transaction):
            """End transaction."""
            self._transaction = None
            HTTPServlet.sleep(self, transaction)