How to grok a multiline message?

Elastic Stack Logstash
1

(I've come across a number of similar questions, but either they don't match what I'm doing or they don't have answers.)

I've got Java log lines, to the end of which might be appended " | {<some JSON>}". Parsing the main bit of the line is fine, and splitting off the JSON at the end with "\|%{SPACE}%{GREEDYDATA:json_string}" works fine.

The problem comes when there is more than one line to the message, because it's also got a Java stacktrace. (The multiline stuff is done in Filebeat.) The GREEDYDATA eats the JSON string and the following stack trace lines, leading, not surprisingly, to a JSON parse failure when I feed json_string through the JSON filter. My reading is that it isn't supposed to do this, as GREEDYDATA is .*, and . isn't supposed to match a newline.

So, with multiline input like

<normal Java log line> | {<some JSON>}
<stack trace first line>
...
<stack trace last line>

what can I do to extract just the "{<some JSON>}" for later JSON parsing, leaving

<normal Java log line>
<stack trace first line>
...
<stack trace last line>

in one field?

2

To extrace the JSON you can match one or more not-newline followed by a newline

    grok { match => { "message" => "%{DATA} \| (?<json>[^
]+)
" } }

To remove it use a similar mutate+gsub.

3

Sorry, I suspect that's got a bit mangled by the time it gets to the browser? Or did you mean literal newlines, spreading the pattern across three lines?

4

Yes, literal newlines in the string.

5

Ah, now that I'd never have thought of. I'll give it a try - ta.

6

OK, so this works for me

    match => { "message" => [ "%{TIMESTAMP_ISO8601}%{SPACE}%{LOGLEVEL}%{SPACE}%{HOSTNAME} %{JAVACLASS} \[[^\]]*\]%{SPACE}[^|]*\|%{SPACE}(?<json_string>[^
]+)" ] }

The reason I need to parse all the preceding stuff is that there might a vertical bar character in one of the other fields (specifically inside the field delimited by [...]) so I need to make sure I don't find an earlier "|" than the one I want.

But I'm now having trouble working out how to remove what's in "json_string" from "message". mutate/gsub as you suggest can be used to remove something that matches a regex, but I want to remove a known text string ... and what's in "json_string" could be anything at this point, there's certainly no reason to suppose that there isn't stuff inside it that would look like an invalid regex, or a valid one that matches the wrong thing.

I can't use a regex to match "from a | to a newline" because there's no way I can think of to persuade it to find the right | (there might be one in the [...] field and there might be several in the JSON).

7

Use ruby

    mutate { add_field => { "someField" => "foo bar | baz" } }
    grok { match => { "someField" => "^%{WORD} %{WORD} %{GREEDYDATA:theRest}" } }
    ruby {
        code => '
            s = event.get("someField")
            s.slice!(event.get("theRest"))
            event.set("someField", s)
        '
    }

will result in

 "someField" => "foo bar ",
   "theRest" => "| baz"
8

Yeah, I'd just come to the conclusion that it'd have to be Ruby!

Thanks very much for your help.

9

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