1 files changed, 16 insertions, 0 deletions
diff --git a/Library/Homebrew/cask/lib/hbc/dsl/appcast.rb b/Library/Homebrew/cask/lib/hbc/dsl/appcast.rb
index 2f1245d3d..e27870622 100644
--- a/Library/Homebrew/cask/lib/hbc/dsl/appcast.rb
+++ b/Library/Homebrew/cask/lib/hbc/dsl/appcast.rb
@@ -1,3 +1,5 @@
+require "hbc/system_command"
+
 module Hbc
   class DSL
     class Appcast
@@ -9,6 +11,20 @@ module Hbc
         @checkpoint     = @parameters[:checkpoint]
       end
 
+      def calculate_checkpoint
+        result = SystemCommand.run("/usr/bin/curl", args: ["--compressed", "--location", "--user-agent", URL::FAKE_USER_AGENT, @uri], print_stderr: false)
+
+        checkpoint = if result.success?
+          processed_appcast_text = result.stdout.gsub(%r{<pubDate>[^<]*</pubDate>}m, "")
+          Digest::SHA2.hexdigest(processed_appcast_text)
+        end
+
+        {
+          checkpoint: checkpoint,
+          command_result: result,
+        }
+      end
+
       def to_yaml
         [@uri, @parameters].to_yaml
       end