Better UX when reopening a tab after the session token has expired

[maximlt]

Problem description

Say I have this little dummy app that is served with bokeh serve ...:

from bokeh.io import curdoc
from bokeh.layouts import column
from bokeh.models import Div

# Create a simple Div element displaying "Hello World"
hello_world = Div(text="<h1>Hello World</h1>", width=200, height=100)

# Create layout
layout = column(hello_world)

# Add the layout to the current document
curdoc().add_root(layout)
curdoc().title = "Hello World App"

Visiting the app, closing the tab and reopening/restoring it in the browser after the session token has expired simply shows a blank page. The browser console logs include a couple of messages about the websocket connection being lost, e.g. [bokeh 3.6.3] Failed to load Bokeh session PyDgQvf7C2xK4IjiFtOTH6JancEvIOR4nWWcw04ZWwkc: Error: Lost websocket connection, 1005 (). The serve logs include this error traceback:

Traceback (most recent call last):
  File "/Users/mliquet/dev/panel/.pixi/envs/test-313/lib/python3.13/site-packages/tornado/websocket.py", line 938, in _accept_connection
    open_result = handler.open(*handler.open_args, **handler.open_kwargs)
  File "/Users/mliquet/dev/panel/.pixi/envs/test-313/lib/python3.13/site-packages/tornado/web.py", line 3302, in wrapper
    return method(self, *args, **kwargs)
  File "/Users/mliquet/dev/panel/.pixi/envs/test-313/lib/python3.13/site-packages/bokeh/server/views/ws.py", line 149, in open
    raise ProtocolError("Token is expired. Configure the app with a larger value for --session-token-expiration if necessary")
bokeh.protocol.exceptions.ProtocolError: Token is expired. Configure the app with a larger value for --session-token-expiration if necessary

As the app visitor, I'm not given much indication about what to do. As the app developer, I see logs that do not indicate explicitly what happened (restored tab).

Feature description

To be honest, I haven't yet given much thought to what could technically be done to improve this situation. As the app visitor, ideally, I'd like my session to be restored or automatically reloaded, at the very least some indication that I should reload the page myself would be welcome. As the app developer, I'd like if the logs could reflect more precisely what happened. The fact that this is raised at the ERROR level is also what brought me here (I'm regularly going through all the errors my app log), in this case I don't think there's much I can do about them except ignore them.

Potential alternatives

TBD

Additional information

No response

[bryevdv]

Visiting the app, closing the tab and reopening/restoring it in the browser after the session token has expired simply shows a blank page.

Does this not trigger a reload? I would expect a reload to generate a new session. E.g. If I go to https://demo.bokeh.org/sliders and hit Apple-r or repeatedly click the "reload" icon, then the a new session is generated and the page displays it as expected. Can you go into more detail about the actual HTTP requests that are being sent back to the Bokeh server?

[maximlt]

What I mean (sorry I wasn't precise enough) by closing and reopening/restoring is: close the tab, and reopen it with Ctrl+Shift+T. You can try to reproduce what I reported by running the app with bokeh app.py --show --session-token-expiration 5 --check-unused-sessions 1000 --unused-session-lifetime 1000 --log-level debug, close the tab, wait for a few seconds (enough for the token to expire and the session to be cleaned up), and reopen the closed tab.

Another scenario where this happens is when someone closes their browser window entirely and re-opens it, with their browser set up to re-open all the previous tabs on start-up.

[bryevdv]

OK I suppose I can see why this happens. When an actual load occurs, including a reload, the browser receives an HTML page with some embedded JS like this:

const render_items = [{"token":"<token>"},"root_ids":["p1145690189"],"use_for_title":true}];
root.Bokeh.embed.embed_items(docs_json, render_items);

where the session id is encoded in the token. But the crucial thing is that an actual load results in a new page with a new token.

OTOH apparently Ctrl+Shift+T simply re-renders an old page, with an old token, explaining the behavior. (Either the session, or the token, or both have expired)

So, what is the ideal desired behavior? A popup or dialog stating the session expired, and offering to reload the page? Just a div with a meaningful error message? An option to auto-reload the page without asking? Something else?

cc @bokeh/dev

[bryevdv]

@maximlt any input on the question above?

[maximlt]

A popup or dialog stating the session expired, and offering to reload the page

An option to auto-reload the page without asking

I like both these options but am unsure about which one is best. The good news is that I think anything will be better than the current state.