def get_pdf(self, params: Dict[str,str], response: QgsServerResponse ) -> None:
        """ Get PDF files previously exported
        """
        ptoken = params.get('TOKEN')
        if not ptoken:
            raise CadastreError(400,"Missing parameter: token")

        path = self.cachedir / ('%s.pdf' % ptoken)

        if self.debugMode:
            QgsMessageLog.logMessage("GetPDF = path is %s" % path.as_posix(),'cadastre', Qgis.Debug)

        if not path.exists():
            raise CadastreError(404,"PDF not found")

        # Send PDF
        response.setHeader('Content-type', 'application/pdf')
        response.setStatusCode(200)
        try:
            response.write(path.read_bytes())
            path.unlink()
        except:
            QgsMessageLog.logMessage("Error occured while reading PDF file",'cadastre',QGis.Critical)
            raise

 def __init__( self ):
     QgsServerResponse.__init__(self)
     self._buffer = QBuffer()
     self._buffer.open(QIODevice.ReadWrite)

 def formatResponse(self, response: QgsServerResponse) -> None:
     """ Format error response
     """
     body = { 'status': 'fail', 'message': self.msg }
     response.clear()
     write_json_response(body, response, self.code)

def write_json_response( data: Dict[str,str], response: QgsServerResponse, code: int=200) -> None:
    """ Write data as json response
    """
    response.setStatusCode(code)
    response.setHeader("Content-Type", "application/json")
    response.write(json.dumps(data))