Using sprintf strings for `action` breaks `update` params

[shnhrrsn]

I ran into an issue where _retry_on_conflict wasn’t being included in my requests, I initially posted about it on the forums, however additional debugging has lead me to believe this is a bug:

output {
	stdout { codec => json_lines }
	elasticsearch {
		hosts => "search:9200"
		index => "posts"
		template => "/indexer/templates/posts.json"
		action => "%{[@metadata][index_action]}"
		document_id => "%{id}"
		retry_on_conflict => 5
	}
}

I added some debug code to common.rb around line 189:

      @logger.warn "About to set update params", action: @action

      if @action == 'update'
        params[:_upsert] = LogStash::Json.load(event.sprintf(@upsert)) if @upsert != ""
        params[:_script] = event.sprintf(@script) if @script != ""
        params[:_retry_on_conflict] = @retry_on_conflict
        @logger.warn "Set update params"
      end

The output is as follows:

[2018-02-08T16:17:06,751][WARN ][logstash.outputs.elasticsearch] About to set update params {:action=>"%{[@metadata][index_action]}"}

Since action isn’t evaluated at this point, the if conditional fails and the check is ignored.

[guyboertje]

PR pending.