Specifying a default, non-JSON-serializable value causes Swagger page to crash about flask_accepts

[SteadBytes]

@amickael @apryor6 sorry for the slow response. The flask-restx Flask app setting RESTX_JSON can be used to configure additional parameters for JSON serialisation. Take a look at his and let me know if it works for you 😄

from datetime import datetime
from json import JSONEncoder

from flask import Flask
from flask_accepts import accepts, responds
from flask_restx import Api, Resource
from marshmallow import Schema, fields


class CustomJSONEncoder(JSONEncoder):
    """Custom encoder for handling default values from a function call"""

    def default(self, o):
        if callable(o):
            return str(o())
        return super().default(o)


app = Flask(__name__)
# Realistically this would be set in a config file
app.config.update(RESTX_JSON={"cls": CustomJSONEncoder})

api = Api(app)

@api.route("/route")
class SomeRoute(Resource):
    @api.doc("some_route")
    @accepts(schema=AcceptSchema, api=api)
    @responds(schema=RespondSchema, api=api)
    def post(self):
        return SomeService.do_stuff(request.parsed_obj)

This setting seems to be completely undocumented so I apologise for that - I'll get it added to the documentation ASAP 👍

[amickael]

Just looking at a high level (not really sure what's the use case), shouldn't datetime.utcnow be a function call such as in datetime.utcnow()?

No, it’s a callable. If I were to specify utcnow() then all timestamps would default to the time the app was initialized.

[ribeirojose]

This is probably related to this part of utils.py. I would love to fire a PR this week but I don't have the time right now to get familiar with the code and extensively test this. If this is still open I'd be mostly happy to help down the road. @apryor6 do you think changing that for something like the following would work? I don't really like the fact that we're pre-defining the format, but I think that could be workable as well. With more time we could perhaps make this more generic to comprise other callables, which I think could happen as well in this case. I'm also curious to know more about why map the default attr in marshmallow to the example attr in flask_restx (that's sheer curiosity, I'm not familiar with the implementation of those).

    if hasattr(value, "default") and type(value.default) != ma.utils._Missing:
        fr_field_parameters["example"] = value.default
        if isinstance(value, ma.DateTime):
            fr_field_parameters["example"] = value.default().isoformat()

[amickael]

Thank you for your help @ribeirojose. This is not urgent at all, I can work around it for now.

[ribeirojose]

Just looking at a high level (not really sure what's the use case), shouldn't datetime.utcnow be a function call such as in datetime.utcnow()?

[apryor6]

I played around with this a bit using a custom JSON encoder, but it appears that this object is not used in serialization with the Swagger doc creation process.

E.g.

import datetime
import json
from flask.json import JSONEncoder

class CustomJSONEncoder(JSONEncoder):
    """Custom encoder for handling default values from a function call"""

    def default(self, o):
        if callable(o):
            return str(o())
        return super().default(o)

json.dumps(datetime.datetime.utcnow, cls=CustomJSONEncoder)

Works just fine, but if I pass this encoder to the Flask app I still receive the same error you indicated.

app = Flask(__name__)
api = Api(app)
app.json_encoder = CustomJSONEncoder

I think this would require upstream changes to flask-restx unless I am unaware of existing functionality for handling this.

[amickael]

Thanks @apryor6, if this requires upstream changes then maybe we close this issue for now? I'll leave it up to you, I can easily work around this in the meantime.

[apryor6]

Yeah, I’ve inquired about this with the restx maintainers in their Gitter channel

[amickael]

Thanks @SteadBytes! I'll try that out, appreciate the help.

[apryor6]

Did this resolve your issue @amickael ?

[amickael]

Sorry for the late response @apryor6, that worked perfectly! Thanks everyone.

[apryor6]

Wonderful, no worries!