Hanes you looked at using patterndb? That should let you assign the specific parts of the message to variables you choose and then use them as you like.
It should be possible to do it with json parser but I have not used it personally. 
Jim



Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------
From: "Fekete, Róbert" <robert.fekete@balabit.com>
Date: 7/3/16 1:26 PM (GMT-05:00)
To: Syslog-ng users' and developers' mailing list <syslog-ng@lists.balabit.hu>
Subject: Re: [syslog-ng] extracting jSON from $MESSAGE

Hi Jorge,

This seems to be a bit tricky message. If I see it correctly, after the syslog header, you have:

 * some additional info that ends with [captcha] (is that literally [captcha], or it changes with every message?)
 * then you have some JSON
 * "while logging request," string
 * and finally some key:value pairs.

As a first try, I would use the csv-parser() to separate the message to the four blocks I listed above. Use syslog-ng OSE 3.7, because then you can use strings as delimiters (see https://www.balabit.com/sites/default/files/documents/syslog-ng-ose-latest-guides/en/syslog-ng-ose-guide-admin/html/reference-parsers-csv.html#csv-parser-delimiter). For example, you can use the ] character and the "while logging request," string as delimiters.
Then you can run the json-parser on the macro containing the JSON-part of the message, and a kv-parser with the : delimiter to parse the last block if needed. (Note that for kv-parser part you need a recent development version of syslog-ng).

Make sure to use the prefix() option in the json-parser, because as I see the key:value block seems to have some of the same keys that the json block.

BTW, is this a publicly available application that emits such a log message? It seems ideal to showcase the wide range of available syslog-ng parsers :)

Regards,
Robert

On Sun, Jul 3, 2016 at 3:32 PM, Jorge Pereira <jpereiran@gmail.com> wrote:
Hi,

    I am not sure about the best approach and way to fix my problem, below more information.

1) I receive the below packet sent from a nginx/openresty instance.

2016/07/02 01:17:04 [emerg] 19081#0: *13163 [lua] init.lua:115: [captcha] {"fail_count":"","response_code":200,"client_ip":"192.168.1.22","hostname":"server-lab01","request_id":"2016-07-02T01:17:03Z|9175f93c0c||i0Xb3BuBWV","host":"www.mytest.com","http_request":{"verb":"GET","url":"\/","user-agent":"Mozilla\/5.0 (pc-x86_64-linux-gnu) Siege\/3.0.8","http_version":"1.1","all":"{\"host\":\"www.mytest.com\",\"x-country-code\":\"US\",\"connection\":\"close\",\"accept\":\"*\\\/*\",\"x-client-ip\":\"192.168.1.22\",\"user-agent\":\"Mozilla\\\/5.0 (pc-x86_64-linux-gnu) Siege\\\/3.0.8\",\"accept-encoding\":\"gzip\"}"},"geoip":{"location":"-90.5334,38.6500","city_name":"Chesterfield","country_name":"United States","longitude":-90.5334,"area_code":314,"latitude":38.65,"country_code2":"US","country_code3":"USA"},"got":"","action":"show","expected":"h1szmM","webapp_domain":"www.mytest.com"} while logging request, client: 192.168.1.22, server: www.mytest.com, request: "GET / HTTP/1.1", host: "www.mytest.com"

2) In my server side, I need to save the logs following a value of host: "www.mytest.com" like:

/var/log/syslog-ng/www.mytest.com.log

3) The problem is because the packet received has a part being a jSON, but I can't use the json-parser().

4) What is the best approach? I have used:

# Extracting only the jSON payload
rewrite p_nginx_wb_error_log_clean {
    subst(".*captcha] ", "", value("MESSAGE"), flags("global"));
    subst(" while logging request.*$", "", value("MESSAGE"), flags("global"));
};

parser p_nginx_wb_error_log_json {
    json-parser(
        marker("")
        prefix("j.")
    );  
};

destination d_nginx_wb_error_log {
    file("/var/log/syslog-ng/nginx/${j.webapp_domain:-unknow-payload}_error.log"                                                                                                                                                               
         create_dirs(yes)
         owner("root")
         group("root")
         perm(0644)
         dir_perm(0755)
         template("${MSG}\n")
    );  
};

--
Jorge Pereira

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