Move capability check

Author: Bastian Schmidt

lib/proxy/archive_extract.rb

@@ -29,5 +29,9 @@ def start
         end
       end
     end
+
+    def self.has_capability?
+      which(SHELL_COMMAND) ? 'extraction' : nil
+    end
   end
 end

modules/tftp/tftp_plugin.rb

@@ -11,7 +11,7 @@ class Plugin < ::Proxy::Plugin
     validate :verify_server_cert, boolean: true
 
     # Expose automatic iso handling capability
-    capability -> { which(Proxy::ArchiveExtract::SHELL_COMMAND) ? 'extraction' : nil }
+    capability -> { Proxy::ArchiveExtract.has_capability? }
 
     expose_setting :tftp_servername
   end