Handling a JSON key with a name being an empty string ""

[geekpete (Peter Dyson)]

Given a block of JSON like:

{"":"value1","field2":"value2"}

Where the first key has a blank name "" but has a regular looking value of value1, you might want to conditionally handle such data to avoid problems once indexing into Elasticsearch where empty field names will fail to parse:

"error"=>{"type"=>"mapper_parsing_exception", "reason"=>"failed to parse", "caused_by"=>{"type"=>"illegal_argument_exception", "reason"=>"field name cannot be an empty string"}}}}}

With a test Logstash pipeline using http input:

input {
    http {
        port => 8080
    }
}

and a test curl to send the test JSON in:

curl --header "Content-Type: application/json" \
  --request POST \
  --data '{"":"value1","field2":"value2"}' \
  http://localhost:8080

if you want to just remove an a key with an empty name at the top level of the JSON, you can remove the field by name, which is "", using a Ruby filter.
This is a no-op if no key with a blank name exists so it does not need to use a conditional guard, just remove it if it exists:

ruby {
  code => '
    event.remove("")
  '
}

If you wanted to keep the blank key's value payload rather than discard it, you can copy it to a new key name like blank_key then remove the original with:

ruby {
  code => '
      testevent = event.get("")
      if testevent
        event.remove("")
        event.set("blank_key",testevent)
      end
  '
}