Syntax to capture tcp-request content? How to access the captured data later? (2 replies)

Hello haproxy users!

I am trying to get my head around the feature to capture arbitrary
tcp-request content.
(I've already found a previous thread -
http://haproxy.formilux.narkive.com/dwcoXP7y/haproxy-with-mqtt where
someone asked a something similar to extract data from MQTT requests)

In the documentation
https://cbonte.github.io/haproxy-dconv/1.5/configuration.html#4.2-tcp-request%20content
Is says that the action "capture" will allow for samples to be captured.
In my case I want to capture a few bytes of the payload
like it's described for acl samples at
https://cbonte.github.io/haproxy-dconv/1.5/configuration.html#7.3.5-req.payload
..


After some trial an error I found that config syntax:
tcp-request content capture req.payload_lv(3,8) len 8

will at least parse correctly. But how can I access the captured bytes
later to i.e. log them to the access log or to use them for load
balancing rules?




Thanks for any hints
Regards


Christian