Incorrect URLs when served behind a proxy with base_url set

I’m running datasette serve --config base_url:/foo/ …, proxying to it with this Apache config:

    ProxyPass /foo/ http://localhost:8001/ 
    ProxyPassReverse /foo/ http://localhost:8001/ 

and then accessing it via https://example.com/foo/.

Although many of the URLs in the pages are correct (presumably because they either use absolute paths which include base_url or relative paths), the faceting and pagination links still use fully-qualified URLs pointing at http://localhost:8001.

I looked into this a little in the source code, and it seems to be an issue anywhere request.url or request.path is used, as these contain the values for the request between the frontend (Apache) and backend (Datasette) server. Those properties are primarily used via the path_with_… family of utility functions and the Datasette.absolute_url method.

[simonw]

Let’s reopen this.

[tsibley]

I think this could be solved by one of:

1. Stop generating absolute URLs, e.g. ones that include an origin. Relative URLs with absolute paths are fine, as long as they take base_url into account (as they do now, yay!).
2. Extend base_url to include the expected frontend origin, and then use that information when generating absolute URLs.
3. Document which HTTP headers the reverse proxy should set (e.g. the X-Forwarded-* family of conventional headers) to pass the frontend origin information to Datasette, and then use that information when generating absolute URLs.

Option 1 seems like the easiest to me, if you can get away with never having to generate an absolute URL.