Carrierwave download of external url

[janz93]

Problem

Hello everyone 👋

I am facing errors from Webmock and VCR where specs fail with an unhandled web request error. e.g. UnhandledHTTPRequestError or NetConnectNotAllowedError.
During my investigation I noticed that those unhandled web requests are caused by the download! method. This method gets called if an external_url is present. Which is here the case.

Question

My goal is to have an offline test suite, therefore, I was a bit surprised about this behavior, since I set enable_processing to false.
I solved the offline approach by mocking all requests:

1. Prevent IP resolving -> Overwrite the SsrfFilter::DEFAULT_RESOLVER Add way to globally disable filter arkadiyt/ssrf_filter#33 (comment)
2. Mock the external_url URI request -> webmock/vcr

Currently, I am unsure if this is the best approach or if carrierwave should handle this automatically depending on the enable_processing setting. Especially since setting enable_processing to false causes an early exit anyway.

[rajyan]

I'm not sure with the best practices of testing carrierwave too, but I'm currently
disabling ssrf_filter by configuring skip_ssrf_protection? with a custom downloader only for test

carrierwave/lib/carrierwave/downloader/base.rb

Line 96 in 8815592

def skip_ssrf_protection?(uri)

and stubbing the external_url

Maybe some kind of configuration like
https://github.com/carrierwaveuploader/carrierwave/pull/2575/files seems reasonable?

Do you have any opinions? @mshibuya

These are related issues

arkadiyt/ssrf_filter#33
arkadiyt/ssrf_filter#59
#2573