Unable to access metadata in log data received via opentelemetry input plugin

[trondhindenes]

Hi, I have an input that looks like this:

  - name: opentelemetry
    listen: 0.0.0.0
    port: 4321
    tag: logs

if I output to stdout, it looks like this (from a properly instrumented app):

[0] logs: [[1713517641.125841653, {"otelSpanID"=>"223c13433c580fcc", "otelTraceID"=>"ee0399b2524507ed56f459662d30cc2f", "otelTraceSampled"=>true, "otelServiceName"=>"stuff", "code.filepath"=>"/code/src/app/main.py", "code.function"=>"get_the_thing", "code.lineno"=>36}], {"message"=>"getting the thing: http://localhost:8000/thing2"}]

However, if I use the "json" format in the stdout, it looks like this:

{"date":1713517571.122547,"message":"getting the thing: http://localhost:8000/thing3"}

So, I'm guessing all the metadata for the log event gets truncated somehow, or not shown if outputting as json.

My problem is, I need that data to be sent to the actual logging system I want to use (loki). I've also tried accessing the metadata like so, using a filter:

filters:
- name: record_modifier
  match: logs
  record:
  - yam $otelServiceName

However, otelServiceName is not resolved even tho it exists in the metadata.

I'm struggling to get this work, and I cannot find any documentation around accessing event metadata.

Should what I'm trying to do work?