extend web ui not working since 2.22.0

[obriat]

Prerequisites

• I am using the latest version of Locust
• I am reporting a bug, not asking a question

Description

Since 2.22.0 the extend web ui is not working with the new UI.

How to reproduce

git clone git@github.com:locustio/locust.git
git fetch 
git checkout tags/2.24.0 -b 2.24.0-branch
python3 -m venv .venv
source .venv/bin/activate
pip install locust flask
locust  -L DEBUG  -f examples/extend_web_ui/extend.py

Debug info

http://localhost:8089 => New UI ok
http://localhost:8089/extend =>KO: blank page with "Object of type Undefined is not JSON serializable" message

curl -v http://localhost:8089/extend
*   Trying 127.0.0.1:8089...
* Connected to localhost (127.0.0.1) port 8089 (#0)
> GET /extend HTTP/1.1
> Host: localhost:8089
> User-Agent: curl/7.81.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 500 INTERNAL SERVER ERROR
< Content-Type: text/html; charset=utf-8
< Content-Length: 49
< Access-Control-Allow-Origin: *
< Date: Wed, 13 Mar 2024 09:37:49 GMT
<
* Connection #0 to host localhost left intact
Object of type Undefined is not JSON serializable

logs :

CRITICAL/locust.web: Object of type Undefined is not JSON serializable

No stack trace or additional info. Same with "404 Not Found", it should return the missing path for debugging purpose

Command line

locust -f examples/extend_web_ui/extend.py

Locustfile contents

https://github.com/locustio/locust/tree/2.24.0/examples/extend_web_ui

Python version

Python 3.10.12

Locust version

locust 2.24.0

Operating system

WSL 2.1.5.0 (core 5.15.146.1-2), Windows : 10.0.19045.4046

[andrewbaldwin44]

Hi @obriat, as of Locust version 2.22.0, the modern UI is the new default for the web UI. If you want to view the legacy extend example you can view it with the --legacy-ui flag:

locust -f examples/extend_web_ui/extend.py --legacy-ui

The modern UI can equally be extended, see the extend_modern_web_ui.py example:

locust -f examples/extend_modern_web_ui.py

Please let us know if this fixes your issue

[obriat]

Sorry to have open this issue, but I posted a message on slack and I got no anwser :(

I missed the 2.22.0 changelog, but I think a note should be added into the doc, no?

[andrewbaldwin44]

Sorry about that, I missed your message on slack. Good idea to rename / add a comment so that it is clear one is for extending the legacy UI 👍

[obriat]

oh, also mark the "/examples/extend_web_ui" as deprecated