CODEWITHSUNDEEP
pythonpython-3.xtornado
dikesh
dikesh

Reputation: 3125

How to check whether request is finished in Python Tornado?

I have two classes in my Tornado application.

First class is BaseRequestHandler, which extends tornado.web.RequestHandler and overrides prepare() method of it for API Key validation of all incoming requests.

Second one is route specific class ChildRequestHandler, which extends BaseRequestHandler.

ChildRequestHandler also has prepare() method which does some parameter validation but before that it calls prepare() method of BaseRequestHandler.

Now, prepare() method of both classes calls finish() methods of tornado.web.RequestHandler if validation fails.

Following are the examples of both the classes.

Base Class

class BaseRequestHandler(RequestHandler):
    # Override Write Error method
    def write_error(self, status_code, chunk):
        self.set_status(status_code)
        self.finish({'message': chunk})

    # Prepare method to validate API Key
    def prepare(self):
        # Send Unauthorized error
        if 'X-API-KEY' not in self.request.headers:
            self.write_error(401, 'API Key {X-API-KEY} Required')
            return None

        # Set API Key from header
        self.apikey = self.request.headers['X-API-KEY']

Child class

class ChildRequestHandler(BaseRequestHandler):

    # Check for required parameters
    def prepare(self):
        # Call Prepare of base class
        super(ChildRequestHandler, self).prepare()

        username = self.get_query_argument('username', None)
        if username is None:
            self.write_error(400, 'Username {username} Required')

The problem occurs when validation fails in Base class. Then it throws Runtime error finish() called twice as prepare() method of child class is also executed regardless of validation result of Base class.

This can be solved by returning boolean from prepare() method of Base class to identify whether the validation passed or not and then accordingly allow execution of prepare() method of child class.

But is there anything like self.finished() to identify whether the request is already finished? I checked the documentation and could not find any such method.

Upvotes: 0

Views: 685

Answers (1)

Ben Darnell
Ben Darnell

Reputation: 22134

There's not a public finished() method (although there's no reason why one couldn't be added). I recommend raising a subclass of tornado.web.HTTPError instead of calling write_error directly, so that prepare() won't return normally after producing the error.

Upvotes: 2

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