使用Logstash从JSON响应中剥离XSSI前缀

Question

I have a fairly simple problem but it's confusing to me. I'm trying to use Logstash to get Gerrit data via rest api. I'm using http_poller and I get a right response with my configuration, so I'm almost there.

Now I need to strip the XSSI prefix )]}' from the start of Gerrits JSON response. The question is, how? How to strip or split or mutate it, or how should I proceed?

My input configuration:

input {
  http_poller {
    urls => {
      gerrit_projects => {
        method => get
        url => "http://url.to/gerrit/a/projects/"
        headers => { Accept => "application/json" }
        auth => { user => "userid" password => "supresecret" }
      }
    }
    target => "http_poller_data"
    metadata_target => "http_poller_metadata"
    request_timeout => 60
    interval => 60
  }
}
filter {
  if [http_poller_metadata] {
    mutate { 
      add_field => {
        "http_poller_host" => "%{http_poller_metadata[host]}"
        "http_poller" => "%{http_poller_metadata[name]}"
      }
    }
  }
  if [http_poller_metadata][runtime_seconds] and [http_poller_metadata][runtime_seconds] > 0.5 {
    mutate { add_tag => "slow_request" }
  }
  if [http_request_failure] or [http_poller_metadata][code] != 200 {
    mutate { add_tag => "bad_request" }
  }
}

output {
  stdout { codec => rubydebug }
}

And parts of the response:

Pipeline main started
JSON parse failure. Falling back to plain-text {:error=>#<LogStash::Json::ParserError: Unexpected character (')' (code 41)): expected a valid value (number, String, array, object, 'true', 'false' or 'null') 
at ... (bunch of lines)...
    {
            "http_poller_data" => {
               "message" => ")]}'\n{\"All-Users\":{\"id\":\"All-Users\",....(more valid JSON)...",
     "tags" => [
                [0] "_jsonparsefailure"
            ],
              "@version" => "1",
            "@timestamp" => "2016-12-13T09:48:25.397Z"
        },
                    "@version" => "1",
                  "@timestamp" => "2016-12-13T09:48:25.397Z",
        "http_poller_metadata" => { ... }

This is my first question to StackOverflow. Thank you for being kind with your answers!

Answer 1

I use "sed 1d" to remove the ")]}'" prefix and "jq" to process the JSON output. For example, to get the state of a Gerrit project I execute:

curl -s --header 'Content-Type:application/json' --request GET --netrc https://<GERRIT-SERVER>/a/projects/?r=<GERRIT-PROJECT> | sed 1d | jq --raw-output ".[] | .state"

ACTIVE

Answer 2

You can use the mutate filter with the gsub option ( link ) to remove the )]}

mutate {
  gsub => [
    "message", "\)]}'", ""   
  ]
}

But the gsub replace all occurences of a regex, so you have to be sure that the pattern only appears once.