Reduce/Eliminate need for Internet during build

[Julian-O]

We have had several issues raised over a period of 7 years which have a lot of overlap because they share a common complaint. This issue is intended to consolidate them into one place.

The issues include:

• buildozer should be usable without internet #267
• - store cache about ~/.buildozer in ~/.buildozer and cache about .bui… #801
• respect the env http_proxy and https_proxy when buildozer download dependences #998
• Option to use cached packages #1030
• Feature request - better package management interfaze #1298
• Feature request: cache package downloads and builds #1363
• sdkmanager --update called even if required tools already installed #1336
• Buildozer not working offline #1560
• Ability to use proxy/DNS in Buildozer AND download every thing manually for build app #1661

The core complaint is that Buildozer spends too much time and bandwidth repeatedly checking it has up-to-date dependencies (e.g. Android SDK).

For many users, the problem is simply the time taken. However, some users have expensive bandwidth (e.g. #1030), unreliable connections (e.g. #998, #1661), or can't connect their build machine to the Internet - presumably for security reasons - (e.g. #267).

Some proposed implementations to address this include:

• Supporting Internet proxies (e.g. respect the env http_proxy and https_proxy when buildozer download dependences #998, Ability to use proxy/DNS in Buildozer AND download every thing manually for build app #1661)
  • Presumably this allows for more reliable downloads but also local caching of downloads at the proxy level.
  • Note: I believe this is now supported by Buildozer, but need confirmation from someone who uses proxies.
• Splitting the existing Buildozer caches into two, so the more volatile one could be deleted without affecting the more stable one. (e.g. - store cache about ~/.buildozer in ~/.buildozer and cache about .bui… #801)
• A switch to turn off all updates. (e.g. buildozer should be usable without internet #267)
  • Perhaps automatically detecting there is no Internet (e.g. Buildozer not working offline #1560)
• More specifically, a buildozer.spec switch to turn off Android platform updates only (implemented in Add spec option to skip automated update of installed android package #290)
• A command to upgrade only specified libraries or dependency trees (e.g. Feature request - better package management interfaze #1298)
• The ability to point to a manually-downloaded instance to use instead of going to the Internet. (e.g. Option to use cached packages #1030, Ability to use proxy/DNS in Buildozer AND download every thing manually for build app #1661)
• Arguably, the many proposals for pip caches, VM machines, and the like, try to address the same issue, but their main purpose is to resolve configuration errors, so I exclude them here.

Some challenges to these ideas have been given in comments:

• Most developers use Buildozer when on-line and have access to cheap, efficient Internet. Some of these requests are edge cases.
• Once Buildozer passes the reins over to python-for-android (in the Android case) further downloading may occur.
• Some proposals with require python-for-android support.

I am not going to propose a single implementation here, or even suggest there should only be one implementation. Instead, I am highlighting that there is a common need amongst several users, consolidating those requests into one place, and leaving it to the developers to determine which technical solutions best meet those needs.