Flask-restx request parser returns 400 Bad Request

Question

I'm using flask-restx in my flask application but each time I use the swagger ui to make a request it returns this 400:

http://127.0.0.1:5000/api/user/register/?password=test&email=test&username=test

{
  "message": "Did not attempt to load JSON data because the request Content-Type was not 'application/json'."
}

My file structure:

flask-project/
├─ run.py
├─ app/
│  ├─ main/
│  │  ├─ __init__.py
│  │  ├─ api/
│  │  │  ├─ __init__.py
│  │  │  ├─ user.py
│  ├─ __init__.py

app/_init_.py

import os
from dotenv import load_dotenv

from flask import Flask

# Extensions
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
from flask_socketio import SocketIO

db = SQLAlchemy()
ma = Marshmallow()
socketio = SocketIO()

load_dotenv()


def create_app(debug=False):
    from app.main.api import api_blueprint

    app = Flask(__name__)
    app.debug = debug
    app.config['SECRET_KEY'] = os.getenv('SECRET_KEY')
    app.config['SQLALCHEMY_DATABASE_URI'] = "sqlite:///database.sqlite3"
    app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
    os.environ["OAUTHLIB_INSECURE_TRANSPORT"] = "true"  # !! Only in development environment.

    db.init_app(app)  # Flask-SQLAlchemy must be initialized before Flask-Marshmallow.
    ma.init_app(app)
    socketio.init_app(app)

    app.register_blueprint(api_blueprint, url_prefix='/api')

    with app.app_context():
        db.create_all()

    @app.before_first_request
    def create_tables():
        """ Pre-populate specific tables """
        pass

    return app

user.py

from flask_restx import Namespace, Resource, reqparse

api = Namespace('user')

@api.route('/register')
@api.param('username', 'Username')
@api.param('email', 'Email')
@api.param('password', 'Password')
class CreateUser(Resource):
    def put(self):
        parser = reqparse.RequestParser()
        parser.add_argument('username', location='json', type=str)
        parser.add_argument('email', location='json', type=str)
        parser.add_argument('password', location='json', type=str)
        args = parser.parse_args()
        
        return args

When I placed print statements in the put method, I found that the method is called and anything before I define args will print. After the line where I define args nothing prints. What am I doing wrong?

Answer 1

I figured out that by downgrading from Werkzeug 2.1.2 to 2.0.2 it fixed the issue.

Answer 2

I just went through this on a project this weekend.

api.param is for parameters that are in the path, like /users/<user_id>. The parameters you are using are query parameters, not path parameters. So remove the 3 @api.param decorators.

As I understand it, location='json' is for extracting data from the body of a request sent in JSON. Your parameters are query parameters. Change your parser.add_argument calls to use location='args'.Then after calling parse_args() as you have in your posted code, you should be able to do args['username'] to get the value of the username query arg, which will give None if username arg was not given.