[FIXED] Flask keep repeating request on return redirect

Issue

Request keep repeating when return redirect.

I made a button to send delete request to which its going to delete session data with key 'order_list', but it keep doing redirect until it stopped by the browser

cart_order.html

<script>
  function clearQuery() {
    fetch("/cart", {
      method: "DELETE",
      headers: {
        "Content-Type": "application/json",
      },
    })
      .then((response) => {
        if (response.ok) {
          return response.json();
        }
        throw new Error("Network response was not ok.");
      })
      .then((data) => {
        console.log("All orders have been deleted");
      })
      .catch((error) => {
        console.error("Error deleting orders", error);
      });
  }
</script>
<button onclick="clearQuery()">Clear Query</button>

Flask

from flask import Flask, render_template, redirect, url_for, session, request

app = Flask(__name__)
app.secret_key = 'THIS_IS_SECRET_KEY'


@app.route('/cart', methods=["GET", "DELETE"])
def cart():

    # for demonstration
    session['order_list'] = {
        'order_1': {
            'marker': True,
            'color': 'blue'
        },
        'order_2': {
            'marker': True,
            'color': 'red'
        },
        'order_3': {
            'marker': True,
            'color': 'blue'
        }
    }

    if request.method == "GET":
        if 'order_list' in session:
            print(session['order_list'])
        else:
            print(session)

        return render_template('cart_order.html')

    elif request.method == "DELETE":

        session.pop('order_list')
        session.modified = True

        return redirect(url_for('cart'))


if __name__ == "__main__":
    app.run(debug=True)

I'd like the session data with key 'order_list' get deleted, and then redirect back to itself with GET request, and print session which now should be empty

Solution

please check from wikipedia article:

... For this reason, HTTP/1.1 (RFC 2616) added the new status codes 303 and 307 to disambiguate between the two behaviours, with 303 mandating the change of request type to GET, and 307 preserving the request type as originally sent.

So according to this, adding in your redirect code=303 will do the trick:

return redirect(url_for('cart'), code=303)

And indeed it works (tested on Firefox). While Codes 302 and 307 enter the endless loop you experienced.

Answered By - ilias-sp