Make it possible to resume an automatic upgrade download

Originally created by @Anonymous on #15875 (Redmine)

reported by users, but we do it only if it’s cheap to implement because it might be superseded if we look into replacing our upgrader.

Downloading target files should be more robust on flaky Internet connections.

E.g. when a target file download times out, it should be retried a few times. Ideally, the download should be resumed using the already downloaded partial content.

Tails::IUK::TargetFile::Download currently uses Tails::IUK::LWP::UserAgent::WithProgress, which is a child class of LWP::UserAgent.

Possible implentation ideas:

• https://metacpan.org/pod/LWP::UserAgent::ExponentialBackoff - not in Debian, does not resume interrupted downloads
• https://metacpan.org/pod/LWP::UserAgent::Determined - in Debian, does not resume interrupted downloads
• https://metacpan.org/pod/LWP::UserAgent::Patch::Retry - not in Debian, does not resume interrupted downloads
• code samples that use the Range header when needed
• more code samples
• https://metacpan.org/pod/HTTP::RangeSaver

If we instead used Curl:

• we could switch to the curl CLI tool that has a --retry option
• https://curl.haxx.se/libcurl/c/CURLOPT_RESUME_FROM.html
• https://curl.haxx.se/libcurl/c/CURLOPT_RANGE.html

Alternatively, there could be a button for manually retrying or resuming an interrupted download.

Feature Branch: feature/15875-upgrader-resume-iuk-download

Testing SOCKS proxying

Thanks to anonym for figuring this out!

SOCKS proxy

ssh -N -D 127.0.0.1:6666 localhost

Target server (e.g. web server)

netcat -l 8080

Client

# /etc/tor/torsocks.conf needs "AllowOutboundLocalhost 1"
echo test1234 | torsocks --user foo --pass bar --port 6666 netcat localhost 8080