execd output with JSON format & use_batch_format = true is broken due to missing trailing newline

[carlosabalde]

Relevant telegraf.conf

[[inputs.cpu]]
 interval = '1s'

[[outputs.execd]]
 command = ['/usr/bin/bash', '/tmp/foo.sh']
 data_format = 'json'
 use_batch_format = true

Logs from Telegraf

-

System info

Telegraf 1.28.2 + Ubuntu 22.04

Docker

No response

Steps to reproduce

Use the suggested minimal configuration, being /tmp/foo.sh something like this:

while read line; do
  echo "$line" >> /tmp/foo.log
done < /dev/stdin

Expected behavior

Output logged to /tmp/foo.log, one JSON object per line.

Actual behavior

Nothing logged to /tmp/foo.log.

Additional info

Problem is, unlike the simple JSON serializer, the batch JSON serializer doesn't append a trailing newline. As a result, the execd output writes the serialized string to the stdin of the script, but without a newline, the script will never consume it.

In other words, metrics are pushed to stdin as JSON objects, but without newlines is imposible for scripts to know how to delimit those objects. Not sure if the right solution is to add the newline in the batch JSON serializer (looks dirty, but that's current behavior for the simple serializer), or adding it in the execd output.

[srebhan]

@carlosabalde can you please test the binary in PR #14150 available once CI finished all tests!? Let me know if this fixes the issue!

[carlosabalde]

@srebhan tested and working fine now. Thanks!