Redirect to homepage if the file is not found

[drkane]

Relies on this pull request going through. Suggested addition to index.py:

from dash import DashResponse
from flask import redirect
from tsg_insights.data.cache import get_metadata_from_cache

@app.callback(Output('for-redirect', 'data'),
              [Input('output-data-id', 'data')],
              [State('url', 'pathname')])
def update_file_id(fileid, existing_url):
    f = get_metadata_from_cache(fileid)
    if not f:
        return redirect('/?fetch={}'.format(fileid), 302) 
    return None

(relies on dcc.Store(id='for-redirect') being added to app.layout

[r-chris]

I just stumbled across your issue here. The PR plotly/dash#401 didn't make it, but plotly/dash#623 was merged in its place. You can now modify the dash.callback_response object, although I haven't figured out how to get it to perform a redirect, yet.