fix to raise error if injected hostname_key is also specified in buffer chunk key

lib/fluent/plugin_helper/inject.rb

@@ -97,6 +97,17 @@ def configure(conf)
         if @inject_config
           @_inject_hostname_key = @inject_config.hostname_key
           if @_inject_hostname_key
+            if self.respond_to?(:buffer_config)
+              # Output plugin cannot use "hostname"(specified by @hostname_key),
+              # injected by this plugin helper, in chunk keys.
+              # This plugin helper works in `#format` (in many cases), but modified record
+              # don't have any side effect in chunking of output plugin.
+              if self.buffer_config.chunk_keys.include?(@_inject_hostname_key)
+                log.error "Use filters to inject hostname to use it in buffer chunking."
+                raise Fluent::ConfigError, "the key specified by 'hostname_key' in <inject> cannot be used in buffering chunk key."
+              end
+            end
+
             @_inject_hostname =  @inject_config.hostname
             unless @_inject_hostname
               @_inject_hostname = Socket.gethostname

test/plugin_helper/test_inject.rb

@@ -1,5 +1,6 @@
 require_relative '../helper'
 require 'fluent/plugin_helper/inject'
+require 'fluent/plugin/output'
 require 'fluent/event'
 require 'time'
 
@@ -15,6 +16,13 @@ class Dummy2 < Fluent::Plugin::TestBase
     end
   end
 
+  class Dummy3 < Fluent::Plugin::Output
+    helpers :inject
+    def write(chunk)
+      # dummy
+    end
+  end
+
   def config_inject_section(hash = {})
     config_element('ROOT', '', {}, [config_element('inject', '', hash)])
   end
@@ -27,7 +35,9 @@ def config_inject_section(hash = {})
   teardown do
     if @d
       @d.stop unless @d.stopped?
+      @d.before_shutdown unless @d.before_shutdown?
       @d.shutdown unless @d.shutdown?
+      @d.after_shutdown unless @d.after_shutdown?
       @d.close unless @d.closed?
       @d.terminate unless @d.terminated?
     end
@@ -93,6 +103,17 @@ def config_inject_section(hash = {})
     assert_not_nil @d.instance_eval{ @_inject_time_formatter }
   end
 
+  test 'raise an error when injected hostname is used in buffer chunk key too' do
+    @d = Dummy3.new
+    conf = config_element('ROOT', '', {}, [
+      config_element('inject', '', {'hostname_key' => 'h'}),
+      config_element('buffer', 'tag,h'),
+    ])
+    assert_raise Fluent::ConfigError.new("the key specified by 'hostname_key' in <inject> cannot be used in buffering chunk key.") do
+      @d.configure(conf)
+    end
+  end
+
   sub_test_case 'using inject_values_to_record' do
     test 'injects hostname automatically detected' do
       detected_hostname = `hostname`.chomp