I'm using the newest version of Logstash 5.3.1.
While I am using a tcp input plugins, it shows that the real codec being used is not the same one with my config file.
To confirm this question, I add a log output in the source code of tcp input plugins - tcp.rb:
While my codec config is json, it actually uses json_lines:
While my codec config is plain, it actually uses line:
sorry for my poor english, hope you can understand my questions!