Add umask option to system config with validation and worker support

docs/configuration/system.md

@@ -0,0 +1,45 @@
+# System Configuration
+
+The `<system>` directive in Fluentd's configuration controls process-wide settings.
+
+## Configuration Parameters
+
+### `umask`
+
+The `umask` parameter sets the process umask (file permission mask). This affects the default permissions of files created by Fluentd.
+
+```
+<system>
+  umask 0022  # Allows r/w for owner, read for group/others
+</system>
+```
+
+You can specify the umask value in octal format (e.g., `0022`, `0027`, `0077`). The meaning of umask values:
+- `0022`: Allow read/write for owner, read for group/others
+- `0027`: Allow read/write for owner, read for group, no access for others
+- `0077`: Allow read/write for owner only, no access for group/others
+
+Note: If not specified, Fluentd will use the system default umask.
+
+### Examples
+
+Restrictive umask (owner only):
+```
+<system>
+  umask 0077
+</system>
+```
+
+Standard umask:
+```
+<system>
+  umask 0022
+</system>
+```
+
+Group readable:
+```
+<system>
+  umask 0027
+</system>
+```

lib/fluent/system_config.rb

@@ -30,7 +30,7 @@ class SystemConfig
       :file_permission, :dir_permission, :counter_server, :counter_client,
       :strict_config_value, :enable_msgpack_time_support, :disable_shared_socket,
       :metrics, :enable_input_metrics, :enable_size_metrics, :enable_jit, :source_only_buffer,
-      :config_include_dir
+      :config_include_dir, :umask
     ]
 
     config_param :workers,   :integer, default: 1
@@ -61,6 +61,7 @@ class SystemConfig
       v.to_i(8)
     end
     config_param :config_include_dir, default: Fluent::DEFAULT_CONFIG_INCLUDE_DIR
+    config_param :umask, :string, default: nil # Keep as string for validation in apply()
     config_section :log, required: false, init: true, multi: false do
       config_param :path, :string, default: nil
       config_param :format, :enum, list: [:text, :json], default: :text
@@ -151,6 +152,29 @@ def initialize(conf=nil, strict_config_value=false)
       configure(conf, strict_config_value)
     end
 
+    def apply(log)
+      return unless @umask
+
+      begin
+        # Parse as octal integer and validate
+        new_mask = Integer(@umask, 8)
+
+        if new_mask < 0 || new_mask > 0o777
+          log.warn "umask value out of range (must be between 0000 and 0777): #{@umask}"
+          return
+        end
+
+        # Only apply if valid
+        old_mask = File.umask(new_mask)
+        log.info "System umask changed from #{sprintf('0%03o', old_mask)} to #{sprintf('0%03o', new_mask)}"
+      rescue ArgumentError
+        log.warn "Invalid umask value '#{@umask}' - must be octal format (e.g., 0022)"
+      rescue => e
+        log.error "Failed to set umask", error: e
+        log.error_backtrace
+      end
+    end
+
     def configure(conf, strict_config_value=false)
       strict = strict_config_value
       if !strict && conf && conf.has_key?("strict_config_value")

test/config/test_system_config.rb

@@ -101,7 +101,81 @@ def parse_text(text)
       'enable_input_metrics' => ['enable_input_metrics', false],
       'enable_size_metrics' => ['enable_size_metrics', true],
       'enable_jit' => ['enable_jit', true],
+      'umask' => ['umask', '0022'],
     )
+    sub_test_case "umask configuration" do
+      setup do
+        @original_umask = File.umask
+      end
+
+      teardown do
+        File.umask(@original_umask) # Restore original umask
+      end
+
+      test 'valid umask is applied' do
+        conf = parse_text(<<-EOS)
+          <system>
+            umask 0022
+          </system>
+        EOS
+
+        log = Fluent::Test::TestLogger.new
+        sc = Fluent::SystemConfig.new(conf)
+        sc.apply(log)
+
+        assert_equal '0022', sc.umask
+        assert_equal 0o022, File.umask
+        assert_true log.logs.any? { |msg| msg.include?('System umask changed') }
+      end
+
+      test 'invalid umask format logs warning' do
+        conf = parse_text(<<-EOS)
+          <system>
+            umask invalid
+          </system>
+        EOS
+
+        log = Fluent::Test::TestLogger.new
+        sc = Fluent::SystemConfig.new(conf)
+        old_mask = File.umask
+        sc.apply(log)
+
+        assert_equal old_mask, File.umask # Should not change
+        assert_true log.logs.any? { |msg| msg.include?('Invalid umask value') }
+      end
+
+      test 'out of range umask logs warning' do
+        conf = parse_text(<<-EOS)
+          <system>
+            umask 0888
+          </system>
+        EOS
+
+        log = Fluent::Test::TestLogger.new
+        sc = Fluent::SystemConfig.new(conf)
+        old_mask = File.umask
+        sc.apply(log)
+
+        assert_equal old_mask, File.umask # Should not change
+        assert_true log.logs.any? { |msg| msg.include?('out of range') }
+      end
+
+      test 'nil umask is ignored' do
+        conf = parse_text(<<-EOS)
+          <system>
+          </system>
+        EOS
+
+        log = Fluent::Test::TestLogger.new
+        sc = Fluent::SystemConfig.new(conf)
+        old_mask = File.umask
+        sc.apply(log)
+
+        assert_nil sc.umask
+        assert_equal old_mask, File.umask
+      end
+    end
+
     test "accepts parameters" do |(k, v)|
       conf = parse_text(<<-EOS)
           <system>