Fix assets blueprint path management

[T4rk1n]

Fixed

• Asset blueprint takes routes prefix into it's static path.
• Asset url path no longer strip routes from requests.

Changed

• assets_folder argument now default to 'assets'
• The assets folder is now always relative to the given root path of name argument, the default of __main__ will get the cwd.
• No longer coerce the name argument from the server if the server argument is provided.

Fixes #529

[ned2]

How important is this to be a user-configurable param? If we made the initial value dash-assets (which would still be prefixed by custom route values -- which was a good move btw) then it seems unlikely that a user would need to modify this.

Just thinking about slowing the rate of kwarg growth for the constructor where possible, as it will get a but unwieldy at some point.

[T4rk1n]

Good point let's remove that, there's already much clutter in the kwargs. 👌

[ned2]

Cool, the fix to adding the routes prefix to the assets URL setting and getting looks good!

With the fixes to add better support for multi-route blueprints, I'm wondering if we could improve this some more.

One scenario that I could readily see happening when trying to support multiple Dash apps alongside each other using the same Flask server:

server.py
app1/app1.py
app2/assets/app1.css
app2/app2.py
app2/assets/app2.css

Where server.py defines a Flask instance and app1.py and app2.py both define Dash instances that pass in the Flask instance from the directory above.

app1's Dash instance might look like this:

app = dash.Dash(
    server=server,
    requests_pathname_prefix='/my-app1/',
    routes_pathname_prefix='/my-app1/',
)

The assets for this app won't actually work however, as the default value of assets_folder is derived from the cwd of the Flask instance. So it will automatically be set to assets (ie at the same level as server.py. So instead the user will have to do:

app = dash.Dash(
    server=server,
    assets_folder="app1/assets",
    requests_pathname_prefix='/my-app1/',
    routes_pathname_prefix='/my-app1/',
)

There would be much less cognitive friction if the correct value of the assets path could be inferred as being relative to the Dash instance rather than the Flask instance. I guess this situation could be more generally described as when a Dash instance isn't found within the path that server.name resolves to. Which, now that I think about it, might actually be a lot harder to make happen, so maybe this is a discussion for another time...

[ned2]

Here's the example app I was using to check this was working and find that issue with the static_folder value of the Blueplrint: https://github.com/ned2/dash-embed-recipes/tree/master/flask_multi

It's has the same layout as in the example I mentioned above.

[T4rk1n]

@ned2 Your examples are missing the __name__ , but still it won't work because when we provide the server, the name is taken from the server instead so it won't be relative to the app but instead will be relative to where the server was instantiated.

Should we remove that or improve the logic here ?

dash/dash/dash.py

Line 105 in e72f483

name = name if server is None else server.name

[ned2]

@ned2 Your examples are missing the __name__ , but still it won't work because when we provide the server, the name is taken from the server instead so it won't be relative to the app but instead will be relative to where the server was instantiated.

Should we remove that or improve the logic here ?

dash/dash/dash.py

Line 105 in e72f483

name = name if server is None else server.name

Yeah, I didn't include the name argument precisely because I knew that it would be changed to be the value of server.name.

yep, so a potential change could be to remove that line overriding name, then flask.helpers.get_root_path(name) would resolve to the path the file with the Dash instance is found in, but server.name would still be whatever the original Flask instance was set to.

Are there any other places that would be affected by decoupling the Dash name param from the Flask name param? I can't see any scanning through dash.py

(also, if we did this, should it be in a separate PR?)

[ned2]

I just tested the effect of removing that line that overwrites the name variable with server.name on my example when both Dash instances are updated to pass the name parameter. Looks like it's all working exactly as it should now!

If you think this won't have any other unwanted repercussions, then I'm happy to make that change. I'm also happy with how everything else is looking.

💃

[T4rk1n]

Thanks @ned2, let's remove the line, I don't think it's useful.