Add --sudo-service-user flag

cmd/services.rb

@@ -40,6 +40,7 @@ def services_args
         Remove all unused services.
       EOS
       flag "--file=", description: "Use the service file from this location to `start` the service."
+      flag "--sudo-service-user=", description: "When run as root on macOS, run the service(s) as this user."
       switch "--all", description: "Run <subcommand> on all services."
       switch "--json", description: "Output as JSON."
     end
@@ -63,6 +64,21 @@ def services
             "`brew services` is supported only on macOS or Linux (with systemd)!"
     end
 
+    if (sudo_service_user = args.sudo_service_user)
+      unless ::Service::System.root?
+        raise UsageError,
+              "`brew services` is supported only when running as root!"
+      end
+
+      unless ::Service::System.launchctl?
+        raise UsageError,
+              "`brew services --sudo-service-user` is currently supported only on macOS " \
+              "(but we'd love a PR to add Linux support)!"
+      end
+
+      ::Service::ServicesCli.sudo_service_user = sudo_service_user
+    end
+
     # Parse arguments.
     subcommand, formula, custom_plist, = args.named
 

lib/service/formula_wrapper.rb

@@ -120,6 +120,16 @@ def service_file_present?(opts = { for: false })
     end
 
     def owner
+      if System.launchctl? && dest.exist?
+        require "rexml/document"
+
+        # read the username from the plist file
+        plist = REXML::Document.new(dest.read)
+        username_xpath = "/plist/dict/key[text()='UserName']/following-sibling::*[1]"
+        plist_username = REXML::XPath.first(plist, username_xpath)&.text
+
+        return plist_username if plist_username.present?
+      end
       return "root" if boot_path_service_file_present?
       return System.user if user_path_service_file_present?
 

lib/service/services_cli.rb

@@ -6,6 +6,14 @@ module ServicesCli
 
     module_function
 
+    def sudo_service_user
+      @sudo_service_user
+    end
+
+    def sudo_service_user=(sudo_service_user)
+      @sudo_service_user = sudo_service_user
+    end
+
     # Binary name.
     def bin
       "brew services"
@@ -183,6 +191,7 @@ def kill(targets, verbose: false)
     # protections to avoid users editing root services
     def take_root_ownership(service)
       return unless System.root?
+      return if sudo_service_user
 
       root_paths = []
 
@@ -284,7 +293,22 @@ def install_service_file(service, file)
 
       temp = Tempfile.new(service.service_name)
       temp << if file.blank?
-        service.service_file.read
+        contents = service.service_file.read
+
+        if sudo_service_user && System.launchctl?
+          require "rexml/document"
+
+          # set the username in the new plist file
+          ohai "Setting username in #{service.service_name} to #{System.user}"
+          plist = REXML::Document.new(contents)
+          dict_element = REXML::XPath.first(plist, "/plist/dict/")
+          dict_element.add_element("key").text = "UserName"
+          dict_element.add_element("string").text = sudo_service_user
+
+          plist.to_s
+        else
+          contents
+        end
       else
         file.read
       end