Invalid regexp in URLValidator can't handle file:// schemes

[Marcin Nowak]

Regexp does not allow to use file scheme in URLValidator.

Steps to reproduce

from django.core.validators import URLValidator
URLValidator(schemes=['file'])('file:///tmp/somefile')

Expected result

No exception should be raised.

Current result

ValidationError: [u'Enter a valid URL.']

[Tim Graham]

Can this be fixed without special casing the file scheme in the validation?

[Claude Paroz]

It's URLValidator not URIValidator, I think you might need your own custom validator for this. The current regex is already bloated, I'm not sure we should continue to complexify it...

[Tim Graham]

I had a similar skepticism. If we don't make a change, then let's clarify the documentation to prevent further tickets about this.

[Johannes Maron]

I thinks this is both a documentation and code problem. The URLValidator should raise a value error, if a unsupported schema is set. In the documentation it should be explained which schemas are supported. Currently one gets the impression that all are.

[Johannes Maron]

Interestingly enough, if you include the optional host parameter in RFC1738 it works: file://localhost/tmp/file/name

[Adam Zapletal]

I opened a PR adding a warning about this to the documentation. I'm happy to handle it in a different way if that'd be better.

For what it's worth, if someone out there wants to validate local file URIs, you could start with something like this:

@deconstructible
class CustomURLValidator(URLValidator):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        self.schemes.append('file')

    def __call__(self, value):
        if value.startswith('file:///'):
            value = value.replace('file:///', 'file://localhost/')

        return super().__call__(value)

[Mariusz Felisiak <felisiak.mariusz@…>]

In 7326513a:

Fixed #25595 -- Doc'd that URLValidator rejects ​file:// URIs without a host.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 710ca576:

[5.0.x] Fixed #25595 -- Doc'd that URLValidator rejects ​file:// URIs without a host.

Backport of 7326513a8f5d4d4e0aeec28540f9451b939b1dda from main