fix to raise error if injected hostname_key is also specified in buff…

…er chunk key

Inject plugin helper does record.dup, so that Output plugin code cannot find any
side effect of inject plugin helper. It means output cannnot do chunking with injected values.
On the other hand, there is just few good use cases about chunking with injected hostname.
* chunking hostname (just after injected) is to route events with hostname... and hostname is unique on a host
* just one good use-case, to extract hostname into ${hostname} in configured values
  * but it can be done by ruby code eval

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 in 'hostname_key' 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 in 'hostname_key' 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