out_datadog: Fix formatting issue when setting a static hostname

[ddrthall]

Providing a static hostname via the dd_hostname configuration options is currently bugged, with an off-by-one error in the message packing loop causing dropped attributes and/or malformed output json. This PR corrects the issue, incrementing the msgpack map size by one when a dd_hostname property is detected.

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Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[ddrthall]

Example configuration file:

pipeline:
  inputs:
  - name: dummy
    tag: dummy
    dummy: |
      {
        "message": "From Fluent Bit",
        "test": "default"
      }

  outputs:
  - name: datadog
    match: "*"
    apikey: ${DD_API_KEY}
    dd_hostname: foobar

In the old version of the plugin, the "test" attribute would be dropped and not sent to datadog:

After this change, datadog now sees:

[ddrthall]

Valgrind output:

==638690==
==638690== HEAP SUMMARY:
==638690==     in use at exit: 0 bytes in 0 blocks
==638690==   total heap usage: 10,305 allocs, 10,305 frees, 63,260,421 bytes allocated
==638690==
==638690== All heap blocks were freed -- no leaks are possible
==638690==
==638690== For lists of detected and suppressed errors, rerun with: -s
==638690== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

[ddrthall]

Debug output:

[2025/03/19 13:19:16] [ info]  flush time     | 1.000000 seconds
[2025/03/19 13:19:16] [ info]  grace          | 5 seconds
[2025/03/19 13:19:16] [ info]  daemon         | 0
[2025/03/19 13:19:16] [ info] ___________
[2025/03/19 13:19:16] [ info]  inputs:
[2025/03/19 13:19:16] [ info]      dummy
[2025/03/19 13:19:16] [ info] ___________
[2025/03/19 13:19:16] [ info]  filters:
[2025/03/19 13:19:16] [ info] ___________
[2025/03/19 13:19:16] [ info]  outputs:
[2025/03/19 13:19:16] [ info]      datadog.0
[2025/03/19 13:19:16] [ info] ___________
[2025/03/19 13:19:16] [ info]  collectors:
[2025/03/19 13:19:16] [ info] [fluent bit] version=4.0.0, commit=cfc9ba95ef, pid=638863
[2025/03/19 13:19:16] [debug] [engine] coroutine stack size: 196608 bytes (192.0K)
[2025/03/19 13:19:16] [ info] [storage] ver=1.5.2, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2025/03/19 13:19:16] [ info] [simd    ] disabled
[2025/03/19 13:19:16] [ info] [cmetrics] version=0.9.9
[2025/03/19 13:19:16] [ info] [ctraces ] version=0.6.1
[2025/03/19 13:19:16] [ info] [input:dummy:dummy.0] initializing
[2025/03/19 13:19:16] [ info] [input:dummy:dummy.0] storage_strategy='memory' (memory only)
[2025/03/19 13:19:16] [debug] [dummy:dummy.0] created event channels: read=25 write=26
[2025/03/19 13:19:16] [debug] [datadog:datadog.0] created event channels: read=27 write=28
[2025/03/19 13:19:16] [debug] [output:datadog:datadog.0] scheme: http://
[2025/03/19 13:19:16] [debug] [output:datadog:datadog.0] uri: /api/v2/logs
[2025/03/19 13:19:16] [debug] [output:datadog:datadog.0] host: http-intake.logs.datad0g.com
[2025/03/19 13:19:16] [debug] [output:datadog:datadog.0] port: 80
[2025/03/19 13:19:16] [debug] [output:datadog:datadog.0] json_date_key: timestamp
[2025/03/19 13:19:16] [debug] [output:datadog:datadog.0] compress_gzip: 0
[2025/03/19 13:19:16] [ info] [sp] stream processor started
[2025/03/19 13:19:17] [debug] [task] created task=0xe955fc0199b0 id=0 OK
[2025/03/19 13:19:18] [debug] [task] created task=0xe955fc027150 id=1 OK
[2025/03/19 13:19:18] [debug] [upstream] KA connection #36 to http-intake.logs.datad0g.com:80 is connected
[2025/03/19 13:19:18] [debug] [http_client] not using http_proxy for header
[2025/03/19 13:19:18] [debug] [upstream] KA connection #35 to http-intake.logs.datad0g.com:80 is connected
[2025/03/19 13:19:18] [debug] [http_client] not using http_proxy for header
[2025/03/19 13:19:18] [debug] [output:datadog:datadog.0] http://http-intake.logs.datad0g.com, port=80, HTTP status=202 payload={}
[2025/03/19 13:19:18] [debug] [upstream] KA connection #35 to http-intake.logs.datad0g.com:80 is now available
[2025/03/19 13:19:18] [debug] [out flush] cb_destroy coro_id=1
[2025/03/19 13:19:18] [debug] [task] destroy task=0xe955fc027150 (task_id=1)
[2025/03/19 13:19:18] [debug] [output:datadog:datadog.0] http://http-intake.logs.datad0g.com, port=80, HTTP status=202 payload={}
[2025/03/19 13:19:18] [debug] [upstream] KA connection #36 to http-intake.logs.datad0g.com:80 is now available
[2025/03/19 13:19:18] [debug] [out flush] cb_destroy coro_id=0
[2025/03/19 13:19:18] [debug] [task] destroy task=0xe955fc0199b0 (task_id=0)
[2025/03/19 13:19:19] [debug] [task] created task=0xe955fc01a650 id=0 OK
[2025/03/19 13:19:19] [debug] [upstream] KA connection #35 to http-intake.logs.datad0g.com:80 has been assigned (recycled)
[2025/03/19 13:19:19] [debug] [http_client] not using http_proxy for header
[2025/03/19 13:19:19] [debug] [output:datadog:datadog.0] http://http-intake.logs.datad0g.com, port=80, HTTP status=202 payload={}
[2025/03/19 13:19:19] [debug] [upstream] KA connection #35 to http-intake.logs.datad0g.com:80 is now available
[2025/03/19 13:19:19] [debug] [out flush] cb_destroy coro_id=2
[2025/03/19 13:19:19] [debug] [task] destroy task=0xe955fc01a650 (task_id=0)
[2025/03/19 13:19:20] [debug] [task] created task=0xe955fc019870 id=0 OK
[2025/03/19 13:19:20] [debug] [upstream] KA connection #36 to http-intake.logs.datad0g.com:80 has been assigned (recycled)
[2025/03/19 13:19:20] [debug] [http_client] not using http_proxy for header
[2025/03/19 13:19:20] [debug] [output:datadog:datadog.0] http://http-intake.logs.datad0g.com, port=80, HTTP status=202 payload={}
[2025/03/19 13:19:20] [debug] [upstream] KA connection #36 to http-intake.logs.datad0g.com:80 is now available
[2025/03/19 13:19:20] [debug] [out flush] cb_destroy coro_id=3
[2025/03/19 13:19:20] [debug] [task] destroy task=0xe955fc019870 (task_id=0)```