How to read JSON input sent to Http input plugin in filter section

[elasticuser1]

Hi, I have sample http input plugin and posting json data to this plugin. I want to copy the json body into another field in order to standardize the output format. Invalid jsons are going into message field. I followed this link - https://www.elastic.co/blog/introducing-logstash-input-http-plugin. This link says body will be deserialized and expanded to root.. Please suggest how to do.. Thanks.

input {
  http {
    host => "xxx" # default: 0.0.0.0
    port => 8080 # default: 8080
  }
}
filter {
    grok {
        match => { "[headers][request_uri]" => "/app/%{WORD:App}/env/%{WORD:Environment}/dc/%{WORD:DataCenter}" }
    }
}
output {
kafka {
    codec => json
    bootstrap_servers => "xxx"
    topic_id => "xx-topic"
  }
}

[magnusbaeck (Magnus Bäck)]

Use a stdout { codec => rubydebug } to make debugging easier. What does an example event produced by Logstash look like?

[elasticuser1]

Thanks @magnusbaeck JSON body is being added to root.. How can I add the body to another field like message instead of root? Is there any configuration in input?

[magnusbaeck (Magnus Bäck)]

The json codec that's going to be used by default in this case (as the received data probably as application/json as the declared MIME type) always stores the parsed payload in the root of the event, but you should be able to override the codec with the additional_codecs option to force a plain codec. Then you can use the json filter to parse the JSON payload, and then you can elect to store the result under another field.