in_sample: support to renew record functionality

When in_sample plugin is used with filter parser which uses
remove_key_name_field, it raises the following error repeatedly.

  #0 dump an error event: error_class=ArgumentError error="message
  does not exist"

This kind of error occurs when key_name and remove_key_name_field
removes key from record with destructive change in filter parser.
It affects generated sample data.

To fix this issue, it is simple to just dup every record, but it has a
significant performance penalty.

Considering keeping compatibility and providing way to a workaround,
added option to control whether it always re-generate a new record or
re-use existing record - renew_record.

ref. #4575

Signed-off-by: Kentaro Hayashi <[email protected]>

lib/fluent/plugin/in_sample.rb

@@ -39,6 +39,8 @@ class SampleInput < Input
     config_param :auto_increment_key, :string, default: nil
     desc "The boolean to suspend-and-resume incremental value after restart"
     config_param :suspend, :bool, default: false,deprecated: 'This parameters is ignored'
+    desc "It always force to generate a new record. It has performance penalty"
+    config_param :renew_record, :bool, default: false
     desc "The sample data to be generated. An array of JSON hashes or a single JSON hash."
     config_param :sample, alias: :dummy, default: [{"message" => "sample"}] do |val|
       begin
@@ -118,14 +120,22 @@ def emit(num)
     end
 
     def generate
-      d = @sample[@sample_index]
+      if @renew_record
+        d = @sample[@sample_index].dup
+      else
+        d = @sample[@sample_index]
+      end
       unless d
         @sample_index = 0
-        d = @sample[@sample_index]
+        if @renew_record
+          d = @sample[@sample_index].dup
+        else
+          d = @sample[@sample_index]
+        end
       end
       @sample_index += 1
       if @auto_increment_key
-        d = d.dup
+        d = d.dup unless @renew_record
         d[@auto_increment_key] = @storage.update(:auto_increment_value){|v| v + 1 }
       end
       d