CONTRIBUTING: explain how to add appcasts

[vitorgalvao]

Expands on #16464. That one was about updating, this is about creating.

There are some doubts as to how to create appcasts. That is merely an example of someone that expressed it, though, as I also see new contributions that could easily have an appcast added (github releases), but don’t. We should really add a how to add them.

• Explain how to find them:
  • If the cask uses the app stanza, look inside its Info.plist for the SUFeedURL.
    • Make /developer/bin script for it.
  • If the app is distributed via gitub releases, appcast will be of the form https://github.com/{{user}}/{{project}}/releases.atom.
  • An appcast can be any URL hosted by the app’s developer that changes every time a new release is out (e.g. a changelog).
• Explain how to find its :checkpoint (curl --compressed '{{appcast_url}} | sed 's|<pubDate>[^<]*</pubDate>||g' | shasum --algorithm 256 | awk '{print $1}').
• Add documentation from CONTRIBUTING: explain how to add appcasts #16689 (comment) to live docs.

[adidalal]

I can tackle this as part of an upcoming (further) rewrite of CONTRIBUTING

[vitorgalvao]

@adityadalal924 Will leave the documentation to you, then.

As for the script, adding it in #16701.

[adidalal]

Appcasts

Appcasts provide a mechanism for updates to applications. There are a few different ways these can be determined:

• If the app is distributed via GitHub releases, the appcast will be of the form https://github.com/{{user}}/{{project}}/releases.atom. (Example Cask - electron.rb)
• A popular update framework, Sparkle generally uses the SUFeedURL property inside Contents/Info.plist. You can use the script developer/bin/find_sparkle_appcast to add this automatically. (Example Cask - glyphs.rb)
• An appcast can be any URL hosted by the app’s developer that changes every time a new release is out (e.g. a changelog RSS feed). (Example Cask - fluid.rb)

Appcasts have a required :checkpoint property. (This is used by the Homebrew-Cask team to determine updates). You can use curl --compressed "{{appcast_url}}" | sed 's|<pubDate>[^<]*</pubDate>||g' | shasum --algorithm 256 to get the :checkpoint value for the appcast.

If the application has a Check for Updates... option in its menu, you should also add auto_updates true to the Cask.

[adidalal]

@vitorgalvao Documentation above should now be ready, according to recent updates.

[vitorgalvao]

@adityadalal924 I saw. I was editing your post (after editing the top one) and github warned me “the content you’re trying to edit has changed”.

[vitorgalvao]

@adityadalal924 Oh, you called it :checkpoint already, even. That I hadn’t noticed.

[adidalal]

Still undecided about {{appcast_url}} vs $appcast_url styling for user-replaced variables. If you like that then CONTRIBUTING.MD should also use that style - whatever we decide, it should be consistent (We can always add a footnote about this format and what it means as extra clarification)

[vitorgalvao]

Still undecided about {{appcast_url}} vs $appcast_url styling for user-replaced variables.

Whatever you prefer. You’ve been working more on CONTRIBUTING, so I trust the decision to you.

I somewhat prefer ${appcast_url} to $appcast_url, though (same with other variables) as it’s clearer where it begins and ends.

[vitorgalvao]

Made another change (addition) to the command. curl now uses --compressed. It doesn’t change anything in the ones that were already set, but it lets us use the ones that are gzipped on transfer.

[adidalal]

Will update as script is updated in cask-repair (I'm using that as "ground truth" for the documentation for now)

[vitorgalvao]

curl --silent 'https://raw.githubusercontent.com/vitorgalvao/tiny-scripts/master/cask-repair' | grep 'pubDate' should be a quick way to see how it currently works in cask-repair. It’s unlikely there’ll be more changes, though.