bug: Plugin "Flash Messages" not working with "Redirect" Response

[saltcable]

Litestar (2.8.0)

from litestar import Litestar, Request, get, post
from litestar.contrib.jinja import JinjaTemplateEngine
from litestar.plugins.flash import FlashConfig, FlashPlugin, flash
from litestar.response import Template, Redirect
from litestar.template.config import TemplateConfig

template_config = TemplateConfig(engine=JinjaTemplateEngine, directory="templates")
flash_plugin = FlashPlugin(config=FlashConfig(template_config=template_config))


@get('/')
async def index() -> Redirect:
    return Redirect('/login')


@get('/login')
async def login(request: Request) -> Template:
    flash(request, "Flash Test!", category="info")
    return Template(template_str='{% for f in get_flashes() %} <p>{{ f.message }}</p>{% endfor %}'
                                 '<form action="/check" method="post"><button type="submit">login</button></form>')


@post('/check')
async def check(request: Request) -> Redirect:
    flash(request, "User not Found!", category="warning")
    return Redirect('/login')


app = Litestar(plugins=[flash_plugin], route_handlers=[index,login, check], template_config=template_config)

if __name__ == '__main__':
    import uvicorn

    uvicorn.run('1:app')

INFO:     Started server process [13056]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     127.0.0.1:50961 - "GET / HTTP/1.1" 302 Found
INFO:     127.0.0.1:50961 - "GET /login HTTP/1.1" 200 OK
INFO:     127.0.0.1:50961 - "GET /login HTTP/1.1" 200 OK
INFO:     127.0.0.1:50961 - "POST /check HTTP/1.1" 302 Found
INFO:     127.0.0.1:50961 - "GET /login HTTP/1.1" 200 OK
INFO:     Shutting down
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [13056]

Process finished with exit code 0

Problem: Flash Message from "POST /check" is missing at final page (screenshot above)

---

Flask (3.0.2)

from flask import Flask, flash, render_template_string, redirect

app = Flask(__name__)
app.secret_key = b'123'


@app.get('/')
def index() -> redirect:
    return redirect('/login')


@app.get('/login')
def login():
    flash('Flash Test!')
    return render_template_string('{% for m in get_flashed_messages() %} <p>{{ m }}</p>{% endfor %}'
                                  '<form action="/check" method="post"><button type="submit">login</button></form>')


@app.post('/check')
def check():
    flash("User not Found!")
    return redirect('/login')


if __name__ == '__main__':
    app.run()

 * Serving Flask app '2'
 * Debug mode: off
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:5000
Press CTRL+C to quit
127.0.0.1 - - [06/Apr/2024 14:50:47] "GET / HTTP/1.1" 302 -
127.0.0.1 - - [06/Apr/2024 14:50:47] "GET /login HTTP/1.1" 200 -
127.0.0.1 - - [06/Apr/2024 14:50:48] "POST /check HTTP/1.1" 302 -
127.0.0.1 - - [06/Apr/2024 14:50:48] "GET /login HTTP/1.1" 200 -

---

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[provinzkraut]

@euri10? 👀

[saltcable]

If it helps, this is how we are doing it manually in Litestar

from litestar import Litestar, Request, get, post
from litestar.contrib.jinja import JinjaTemplateEngine
from litestar.middleware.session.server_side import ServerSideSessionConfig
from litestar.response import Template, Redirect
from litestar.template.config import TemplateConfig

template_config = TemplateConfig(engine=JinjaTemplateEngine, directory="templates")


def flash(request: Request, message: str, category: str = "primary") -> None:
    if "_messages" not in request.session:
        request.session["_messages"] = []
    request.session["_messages"].append({"message": message, "category": category})


def get_flashed_messages(request: Request) -> list[str]:
    return request.session.pop("_messages") if "_messages" in request.session else []


template_config.engine_instance.engine.globals["get_flashed_messages"] = get_flashed_messages


@get('/')
async def index() -> Redirect:
    return Redirect('/login')


@get('/login')
async def login(request: Request) -> Template:
    flash(request, "Flash Test!", category="info")
    return Template(template_str='{% for f in get_flashed_messages(request) %} <p>{{ f.message }}</p>{% endfor %}'
                                 '<form action="/check" method="post"><button type="submit">login</button></form>')


@post('/check')
async def check(request: Request) -> Redirect:
    flash(request, "User not Found!", category="warning")
    return Redirect('/login')


app = Litestar(route_handlers=[index, login, check], template_config=template_config,
               middleware=[ServerSideSessionConfig().middleware])

if __name__ == '__main__':
    import uvicorn

    uvicorn.run('1:app')

INFO:     Started server process [8416]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     127.0.0.1:51887 - "GET / HTTP/1.1" 302 Found
INFO:     127.0.0.1:51887 - "GET /login HTTP/1.1" 200 OK
INFO:     127.0.0.1:51887 - "POST /check HTTP/1.1" 302 Found
INFO:     127.0.0.1:51887 - "GET /login HTTP/1.1" 200 OK
INFO:     Shutting down
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [8416]

[saltcable]

We hoped 'flash Messages' would be integrated into the core functionality rather than as a plugin, which can often get abandoned. It's a feature present in Flask and Django, so it's likely quite important. Nonetheless, appreciate the work done so far. Litestar is at its best and continually improving. That's wonderful. Thank you!

[peterschutt]

Configuring Litestar via plugins is an explicit architectural decision - we also use them extensively for internal things. This plugin is in the main code base and is maintained alongside the rest of the library code so there should be no need to be concerned about commitment to its maintenance any more than any other part of the library.

[euri10]

ok I have the same issue now that I'm trying to switch from my implenetation (which is exactly the same as @saltcable ) to the official plugin:)

I'm not sure why I went passing the messages in the request state rather than in the session in the plugin though.

This said, this could be either fixed using the same method for passing flash messages around ie in a session (but that means the plugin requires to have the session middleware installed, we could check for that in the app_init and / or install a default config for it, I'd prefer just raise a misconfiguration error rather than providing a default config)
Or there is a way for the Redirect response to be aware of the scope state from the handler that issued the flash message, but I'm not sure that is possible.

[github-actions]

This issue has been closed in #3420. The change will be included in the upcoming patch release.

[github-actions]

A fix for this issue has been released in v2.9.0