Option to throw error on extra arguments

When a request has more arguments than are specified in the parser it silently ignores them. I see a related discussion in #28.

Personally I don’t think silently ignoring is the correct thing to do, but changing the default behavior would be backwards incompatible. How about parse takes a strict option that throws an error in cases like this?

[tuukkamustonen]

@sloria I sketched something from your pointers. It’s possibly close to what @ParthGandhi has been doing:

class NoExtrasSchema(StrictSchema):

    class Meta:
        strict = True

    @pre_load
    def validate_extra(self, in_data):
        if not isinstance(in_data, dict):
            return

        extra_args = []
        for key in in_data.keys():
            if key not in self.fields:
                extra_args.append(key)

        if extra_args:
            raise ValidationError('Extra arguments passed: {}'.format(extra_args))

class StrictFlaskParser(FlaskParser):

    def _parse_request(self, schema, req, locations):
        parsed = super(StrictFlaskParser, self)._parse_request(schema, req, locations)

        # Add remaining fields
        for location in locations:
            if location == 'json':
                force = is_json_request(req)
                json_ = req.get_json(force=force, silent=True)
                if not isinstance(json_, dict):
                    continue
                source = json_
            elif location == 'querystring' or location == 'query':
                source = req.args
            elif location == 'headers':
                source = req.headers
            elif location == 'cookies':
                source = req.cookies
            elif location == 'form':
                source = req.form
            elif location == 'files':
                source = req.files

            for k, v in six.iteritems(source):
                parsed[k] = parsed.get(k, v)

        return parsed

The implementation is bound to Flask now, and I do see the problem of making it cross-framework compatible. I only tested JSON location yet, so not sure if the others really work.

Also, this “no extras” feature is probably only wanted for JSON payloads, forms, files and maybe query parameters. It doesn’t really make sense for cookies and headers, imo.

In any case, I would expect support for this to exist in the library out of the box. Do you see any reasonable possibilities to maybe generalize the implementation (like adding more parse_ methods for returning the collections or missing keys)?

[tuukkamustonen]

@ParthGandhi I would be curious to see your solution as well. It seems the flexibility in supporting multiple/varying locations per argument / set of arguments makes this one problematic…