Nginx 499 and IntegrityError

[JulienPalard]

I'm mostly opening the issue to document the fact. This could not be considered as a django-registration bug.

I'm getting a few IntegrityError on my Django Registration setup, like :

IntegrityError at /accounts/register/

duplicate key value violates unique constraint "auth_user_username_key"
DETAIL:  Key (username)=(test) already exists.

I found this is correlated with errors 499 in nginx, meaning "client closed the connection", so I dug the issue and here's what I found:

• A user fills the registration form and double clicks on the submit button (Firefox prevents this, but not Chromium, I did not tested other browsers).
• At the 1st click, a first POST request is sent.
• The 2nd click happen, the browser "cancels" the 1st POST by closing the connection and emit a 2nd POST request.
• The 1st POST successfully passes form validation, INSERTs the user, ...
• The 2nd POST successfully passes form validation (username uniqueness).
• The 1st POST commits to the database.
• Nginx notices the first POST connection has closed and logs a 499.
• The 2nd POST tries to INSERT the user and gets an IntegrityError, gives back a 500 error.

In the nginx logs it looks like this:

www.hackinscience.org 2001:redacted:8aba - - [14/May/2024:09:41:12 +0200] "POST /accounts/register/ HTTP/2.0" 499 0.192 0 "https://www.hackinscience.org/accounts/register/" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36"
www.hackinscience.org 2001:redacted:8aba - - [14/May/2024:09:41:13 +0200] "POST /accounts/register/ HTTP/2.0" 500 1.426 145 "https://www.hackinscience.org/accounts/register/" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36"

Now, what's the correct way to fix this? Should I add JS client-side to avoid double-form submission?

It's tempting to say that IntegrityError could be catched and re-raised as ValidationError in django-registration but it does not fix the issue: the user would be presented with a false "Username already exists" error, while he just had successfully created an account...

It's also tempting to say it's a Django design issue: separating form validation and form saving looks like calling for race conditions, but same as previous: "fixing" this design issue would just lead to present a "Username already exists" instead of a 500, I prefer the error :D

[JulienPalard]

I'm not a front-end dev, but I tried hard, I came by this:

https://framagit.org/hackinscience/hkis-website/-/commit/62f479c0eb7c7db8ee0c49eb0a98560ea710bb99

window.addEventListener("DOMContentLoaded", function (event) {
    const form = document.getElementById('registration_form');
    const button = document.getElementById('registration_button');
    form.addEventListener('submit', function(event) {
        if (button.disabled)
	    return false;
        button.disabled = true;
    });
});