base_url getting appended twice in redirects when applying filters? about datasette HOT 3 OPEN

Yeah we're seeing this too only on specific routes. The one that's breaker for us is the CSV export URL. Potentially related to #1619

I'm gonna work on this issue next week because it's a show stopper for us using Datasette in prod.

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I traced the problem down to two areas in the Datasette code and am working on a fix.

The first is in datasette/url_builder.py inside the Urls.path method:

In the last line, sometimes the path here already has the base_url prepended and the path is not an instance of PrefixedUrlString so the base_url gets added twice.

The second issue is datasette/app.py inside the absolute_url method:

The path sometimes comes in here with a base_url prepended but without a leading slash and the request.url also has the base_url at the end of the URL so this results in a double prepend of the base_url.

I'm currently adding some tests, but it's very unclear what the intended functionality was with these methods. So far I have test cases on the datasette.urls.path method like so:

@pytest.mark.parametrize(
    "base_url,path,format,expected",
    [
        ("/", "/", None, "/"),
        (None, "/", None, "/"),
        (None, "", None, ""),
        ("/prefix/", "/prefix/table/1", None, "/prefix/table/1"),
        ("/prefix/", "prefix/table/1", None, "prefix/table/1"),
        ("/prefix/", "/table/1", None, "/prefix/table/1"),
        ("/prefix/", "/table/1", "json", "/prefix/table/1.json"),
        ("/prefix/", "-/static/app.css", None, "/prefix/-/static/app.css"),
        (None, "table/1", None, "table/1"),
        (None, "table/1", "csv", "table/1.csv"),
        (None, "-/static/app.css", None, "-/static/app.css"),
    ],
)
def test_url_path_construction(ds, base_url, path, format, expected):
    ds._settings["base_url"] = base_url
    actual = ds.urls.path(path, format=format)
    assert actual == expected
    assert isinstance(actual, PrefixedUrlString)

Working on profiling the app to see how it seems to be expecting to handle URLs and will add more tests onto path as well as absolute_url.

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Tracking code here: https://github.com/brandonrobertz/datasette/tree/fix-repeated-base_url

from datasette.