added tag_keys_field

lib/fluent/plugin/out_influxdb.rb

@@ -44,6 +44,8 @@ class Fluent::Plugin::InfluxdbOutput < Fluent::Plugin::Output
                desc: "Enable/Disable auto-tagging behaviour which makes strings tags."
   config_param :tag_keys, :array, default: [],
                desc: "The names of the keys to use as influxDB tags."
+  config_param :tag_keys_field, :string, default: nil,
+               desc: "The name of the fields where influxdb key names are stored"
   config_param :sequence_tag, :string, default: nil,
                desc: <<-DESC
 The name of the tag whose value is incremented for the consecutive simultaneous
@@ -145,6 +147,10 @@ def write(chunk)
           end
         end
       end
+      if !@tag_keys_field.nil? && record.include?(tag_keys_field)
+        tags.update(record[tag_keys_field])
+        values.delete(tag_keys_field)
+      end
       if @sequence_tag
         if @prev_timestamp == timestamp
           @seq += 1

test/plugin/test_out_influxdb.rb

@@ -169,6 +169,35 @@ def test_write_with_measurement
     ], driver.instance.influxdb.points)
   end
 
+  def test_empty_tag_keys_field
+    config_with_tags = %Q(
+      #{CONFIG}
+      tag_keys_field b
+    )
+
+    driver = create_driver(config_with_tags)
+
+    time = event_time("2011-01-02 13:14:15 UTC")
+    driver.run(default_tag: 'input.influxdb') do
+      driver.feed(time, {'b' => {'a' => "2"}, 'c' => '2'})
+    end
+
+    assert_equal([
+      [
+        [
+          {
+            timestamp: 1293974055,
+            series: 'input.influxdb',
+            values: {'c' => "2"},
+            tags: {'a' => "2"}
+          },
+        ],
+        nil,
+        nil
+      ]
+    ], driver.instance.influxdb.points)
+  end
+
   def test_empty_tag_keys
     config_with_tags = %Q(
       #{CONFIG}