output: Replace ${chunk_id} before logging warning.

The updated implementation makes sure to replace instances of
${chunk_id} prior to looking for and warning on unreplaced keys in the
pattern. Prior to this, a warning line was printed for every chunk that
was flushed even though nothing was actually wrong (replacement happened
right after).

Signed-off-by: Brian Atkinson <brian@atkinson.mn>

lib/fluent/plugin/output.rb

@@ -769,17 +769,19 @@ def extract_placeholders(str, chunk)
             end
           end
 
-          if rvalue =~ CHUNK_KEY_PLACEHOLDER_PATTERN
-            log.warn "chunk key placeholder '#{$1}' not replaced. template:#{str}"
-          end
-
-          rvalue.sub(CHUNK_ID_PLACEHOLDER_PATTERN) {
+          rvalue = rvalue.sub(CHUNK_ID_PLACEHOLDER_PATTERN) {
             if chunk_passed
               dump_unique_id_hex(chunk.unique_id)
             else
               log.warn "${chunk_id} is not allowed in this plugin. Pass Chunk instead of metadata in extract_placeholders's 2nd argument"
             end
           }
+
+          if rvalue =~ CHUNK_KEY_PLACEHOLDER_PATTERN
+            log.warn "chunk key placeholder '#{$1}' not replaced. template:#{str}"
+          end
+
+          rvalue
         end
       end
 

test/plugin/test_output.rb

@@ -378,6 +378,18 @@ def waiting(seconds)
       assert { logs.any? { |log| log.include?("${chunk_id} is not allowed in this plugin") } }
     end
 
+    test '#extract_placeholders does not log for ${chunk_id} placeholder' do
+      @i.configure(config_element('ROOT', '', {}, [config_element('buffer', '')]))
+      tmpl = "/mypath/${chunk_id}/tail"
+      t = event_time('2016-04-11 20:30:00 +0900')
+      v = {key1: "value1", key2: "value2"}
+      c = create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+      @i.log.out.logs.clear
+      @i.extract_placeholders(tmpl, c)
+      logs = @i.log.out.logs
+      assert { logs.none? { |log| log.include?("${chunk_id}") } }
+    end
+
     test '#extract_placeholders logs warn message with not replaced key' do
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', '')]))
       tmpl = "/mypath/${key1}/test"