Custom URL routing with independent tests

[simonw]

The more I think about #303 the more I feel that Datasette's URL routing needs go beyond Django-style regex matching.

If we go custom, tests should live in test_routing.py

[simonw]

Input:

• function that says if a name is a valid database
• Function that says if a table exists
• URL

Output:

• view class
• Arguments
• Redirect (if it should redirect)

[simonw]

I'm going to use a named tuple for the output. That way I can support either tuple destructing or explicit property access on the returned value.

[simonw]

To support a future where Datasette is an ASGI app that can be attached to a URL within a larger application the routing function should have the option to accept a path prefix which will then be automatically attached to any resulting redirects.

[simonw]

A neat trick could be that if the router returns a redirect it could then resolve that redirect to see if it will 404 (or redirect itself) before returning that response.

This would need its own counter to guard against infinite redirects.

I'm not going to do this though: any view that results in a chain of redirects like this is a bug that should be fixed at the source.

[simonw]

I started sketching this out in a branch, see pull request #307 - but I've decided I don't like it. I'm going to close this ticket and stick with regular expression URL routing for the moment. If I change my mind in the future the code in #307 lives in separate files (datasette/routes.py and tests/test_routes.py) so bringing it back into the project will be trivial.