Watch only recently modified files

lib/fluent/plugin/in_tail.rb

@@ -77,6 +77,8 @@ def initialize
     config_param :path_key, :string, default: nil
     desc 'Open and close the file on every update instead of leaving it open until it gets rotated.'
     config_param :open_on_every_update, :bool, default: false
+    desc 'Limit the watching files that the modification time is within the specified time range (when use \'*\' in path).'
+    config_param :limit_recently_modified, :time, default: nil
 
     attr_reader :paths
 
@@ -186,7 +188,11 @@ def expand_paths
         if path.include?('*')
           paths += Dir.glob(path).select { |p|
             if File.readable?(p) && !File.directory?(p)
-              true
+              if @limit_recently_modified && File.mtime(p) < (date - @limit_recently_modified)
+                false
+              else
+                true
+              end
             else
               log.warn "#{p} unreadable. It is excluded and would be examined next time."
               false

test/plugin/test_in_tail.rb

@@ -1174,4 +1174,28 @@ def test_tail_path_with_multiline_with_multiple_paths
       assert_equal(files, [events[2][2]["path"], events[3][2]["path"]].sort)
     end
   end
+
+  def test_limit_recently_modified
+    now = Time.new(2010, 1, 2, 3, 4, 5)
+    FileUtils.touch("#{TMP_DIR}/tail_unwatch.txt", mtime: (now - 3601))
+    FileUtils.touch("#{TMP_DIR}/tail_watch1.txt", mtime: (now - 3600))
+    FileUtils.touch("#{TMP_DIR}/tail_watch2.txt", mtime: now)
+
+    config = config_element('', '', {
+      'tag' => 'tail',
+      'path' => "#{TMP_DIR}/*.txt",
+      'format' => 'none',
+      'limit_recently_modified' => '3600s'
+    })
+
+    expected_files = [
+      "#{TMP_DIR}/tail_watch1.txt",
+      "#{TMP_DIR}/tail_watch2.txt"
+    ]
+
+    Timecop.freeze(now) do
+      plugin = create_driver(config, false).instance
+      assert_equal expected_files, plugin.expand_paths.sort
+    end
+  end
 end