Source code for fixie.request_handler

"""A request handler for fixie that expects JSON data and validates it."""
import cerberus
import tornado.web
from tornado.escape import utf8

import fixie.jsonutils as json


class RequestHandler(tornado.web.RequestHandler):
    """A Tornado request handler that prepare the data by loading a
    JSON request and then validating the resultant object against
    the cerberus schema defined on the class as the 'schema' attribute.
    This class is meant to be subclassed.
    """

    @property
    def validator(self):
        v = getattr(self.__class__, '_validator', None)
        if v is None:
            v = cerberus.Validator(self.schema)
            self.__class__._validator = v
        return v

    def prepare(self):
        self.response = {}
        body = self.request.body
        if not body:
            return
        try:
            data = json.decode(body)
        except ValueError:
            self.send_error(400, message='Unable to parse JSON.')
            return
        if not self.validator.validate(data):
            msg = 'Input to ' + self.__class__.__name__ + ' is not valid: '
            msg += str(self.validator.errors)
            self.send_error(400, message=msg)
            return
        self.request.arguments.clear()
        self.request.arguments.update(data)

    def set_default_headers(self):
        self.set_header('Content-Type', 'application/json')

    def write(self, chunk):
        """Writes the given chunk to the output buffer. This overrides (and almost
        completely reimplements) ``tornado.web.RequestHandler.write() so that we
        can use the default fixie JSON tools.
        """
        if self._finished:
            raise RuntimeError("Cannot write() after finish()")
        if not isinstance(chunk, (bytes, str, dict)):
            message = "write() only accepts bytes, unicode, and dict objects"
            if isinstance(chunk, list):
                message += ". Lists not accepted for security reasons; see http://www.tornadoweb.org/en/stable/web.html#tornado.web.RequestHandler.write"
            raise TypeError(message)
        if isinstance(chunk, dict):
            chunk = json.encode(chunk) + '\n'
            self.set_header("Content-Type", "application/json; charset=UTF-8")
        chunk = utf8(chunk)
        self._write_buffer.append(chunk)

    def write_error(self, status_code, **kwargs):
        if 'message' not in kwargs:
            if status_code == 405:
                kwargs['message'] = 'Invalid HTTP method.'
            else:
                kwargs['message'] = 'Unknown error.'
        self.response = kwargs
        self.write(kwargs)