parser_json: Add stream_buffer_size config param

Allow configuration of the size of the buffer that Yajl uses when
parsing streaming input.

The advantage of this is that when using `out_exec_filter`, and parsing
as JSON, it's now possible to configure this plugin to avoid having to
wait for 8092 bytes of data to be parsed before events are emitted.

Configuration in the `out_exec_filter` tests has been modified to use
this parameter, as it shaves 60 seconds off the test run time.

Signed-off-by: Ben Wheatley <contact@benwh.com>

lib/fluent/plugin/out_exec_filter.rb

@@ -95,6 +95,7 @@ class ExecFilterOutput < Output
     COMPAT_PARSE_PARAMS = {
       'out_format' => '@type',
       'out_keys' => 'keys',
+      'out_stream_buffer_size' => 'stream_buffer_size',
     }
     COMPAT_EXTRACT_PARAMS = {
       'out_tag_key' => 'tag_key',

lib/fluent/plugin/parser_json.rb

@@ -30,6 +30,12 @@ class JSONParser < Parser
       desc 'Set JSON parser'
       config_param :json_parser, :enum, list: [:oj, :yajl, :json], default: :oj
 
+      # The Yajl library defines a default buffer size of 8KiB when parsing
+      # from IO streams, so maintain this for backwards-compatibility.
+      # https://www.rubydoc.info/github/brianmario/yajl-ruby/Yajl%2FParser:parse
+      desc 'Set the buffer size that Yajl will use when parsing streaming input'
+      config_param :stream_buffer_size, :integer, default: 8192
+
       config_set_default :time_type, :float
 
       def configure(conf)
@@ -81,7 +87,7 @@ def parse_io(io, &block)
         y.on_parse_complete = ->(record){
           block.call(parse_time(record), record)
         }
-        y.parse(io)
+        y.parse(io, @stream_buffer_size)
       end
     end
   end

test/plugin/test_out_exec_filter.rb

@@ -328,6 +328,7 @@ def create_driver(conf)
     </format>
     <parse>
       @type json
+      stream_buffer_size 1
     </parse>
     <extract>
       tag_key tag
@@ -338,6 +339,7 @@ def create_driver(conf)
     command cat
     in_keys message
     out_format json
+    out_stream_buffer_size 1
     time_key time
     tag_key tag
   ]
@@ -372,6 +374,7 @@ def create_driver(conf)
     </format>
     <parse>
       @type json
+      stream_buffer_size 1
     </parse>
     <extract>
       tag_key tag
@@ -382,6 +385,7 @@ def create_driver(conf)
     command cat
     in_keys message
     out_format json
+    out_stream_buffer_size 1
     time_key time
     tag_key tag
   ]
@@ -414,6 +418,7 @@ def create_driver(conf)
     </format>
     <parse>
       @type json
+      stream_buffer_size 1
     </parse>
     <extract>
       tag_key tag
@@ -426,6 +431,7 @@ def create_driver(conf)
     command cat
     in_keys message
     out_format json
+    out_stream_buffer_size 1
     time_key time
     time_format %d/%b/%Y %H:%M:%S.%N %z
     tag_key tag

test/plugin/test_parser_json.rb

@@ -111,4 +111,28 @@ def test_parse_with_keep_time_key_without_time_format(data)
       assert_equal text, record['time']
     end
   end
+
+  def test_yajl_parse_io_with_buffer_smaller_than_input
+    parser = Fluent::Test::Driver::Parser.new(Fluent::Plugin::JSONParser)
+    parser.configure(
+                     'keep_time_key' => 'true',
+                     'json_parser' => 'yajl',
+                     'stream_buffer_size' => 1,
+                     )
+    text = "100"
+
+    waiting(5) do
+      rd, wr = IO.pipe
+      wr.write "{\"time\":\"#{text}\"}"
+
+      parser.instance.parse_io(rd) do |time, record|
+        assert_equal text.to_i, time.sec
+        assert_equal text, record['time']
+
+        # Once a record has been received the 'write' end of the pipe must be
+        # closed, otherwise the test will block waiting for more input.
+        wr.close
+      end
+    end
+  end
 end