Provide a DMG Blockmap file for releases

[machawk1]

Some other open source tools (e.g., qri, https://github.com/qri-io/frontend/releases/) include a DMG blockmap file with releases. These provide checksums, among other things, so would be useful to include.

• [ ] Figure out the extent to what can be expressed in a DMG blockmap
• [ ] Figure out how to generate one
• [ ] Research the potential for usage for version diffs.

[machawk1]

Ping @b5 with the hope that he can provide some insight on how DMG blockmaps are useful for releasing macOS software using DMGs. :)

[b5]

Hey @machawk1! The .blockmap file is created as part of our publish process by electron builder. the auto-update from that same suite of software uses the blockmap to resume downloads as needed.

I took a spin through the documentation & a quick look at the source, and couldn't find much in the way of documentation of the blockmap file (it's referred to as a "build artifact" in the docs), let alone how to generate one :/

[machawk1]

Thanks for the pointer and 2¢, @b5. Like most things on this project, it will probably need to be generated through some Python and bash-y duct taping. I suppose I'll document it if I find a programmatic way to do it beyond Electron.