Opentelemetry - Attributes array not supported for metric gauges

[nortenorte]

Bug Report

Describe the bug
Fluent-bit does not process opentelemetry array attribute.

Opentelemetry specification for attributs.
https://opentelemetry.io/docs/specs/otel/common/#attribute

To Reproduce
Run python script which sends a metric with attributes containing arrays to fluentbit and let fluentbit send them to otel collector.

Start otel-collector (https://github.com/open-telemetry/opentelemetry-collector) listening to OTLP on port 4319.

Run Fluent-bit 4.1.1 with this configuration:

service:
  log_level: trace 

pipeline:
  inputs:
    - name: opentelemetry
      tag: input_open
      listen: 127.0.0.1
      http2: Off
      port: 4318
      successful_response_code: 200
  outputs:
    - name: opentelemetry
      host: 127.0.0.1
      http2: Off
      port: 4319
      match: '*'

Install python SDK and API according to: https://github.com/open-telemetry/opentelemetry-python.

from opentelemetry import metrics
from opentelemetry.metrics import Observation, CallbackOptions
from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.metrics.export import PeriodicExportingMetricReader
from opentelemetry.exporter.otlp.proto.http.metric_exporter import OTLPMetricExporter

exporter = OTLPMetricExporter(
    endpoint="http://localhost:4318/v1/metrics",
)

reader = PeriodicExportingMetricReader(exporter, export_interval_millis=1)
provider = MeterProvider(metric_readers=[reader])
metrics.set_meter_provider(provider)
meter = metrics.get_meter("meter")

def callback(options: CallbackOptions):
    yield Observation(
        value=10,
        attributes={
            "int_array": (1, 2, 3, 4, 5),
            "double_array": (1.1, 2.2, 3.3, 4.4, 5.5),
            "bool_array": (True, False, True, False, True),
            "string_array": ("One", "Two", "Three", "Four", "Five"),
        }
    )

meter.create_observable_gauge(
    name="metric_gauge",
    callbacks=[callback],
    unit="unit",
    description="Meter description",
)

No output to otel collector.

Error message in fluent-bit log.

[2025/10/20 08:27:49.342324039] [trace] [input:opentelemetry:opentelemetry.0 at /fluent-bit/plugins/in_opentelemetry/opentelemetry.c:53] new TCP connection arrived FD=35
[2025/10/20 08:27:49.342375546] [trace] [input:opentelemetry:opentelemetry.0 at /fluent-bit/plugins/in_opentelemetry/http_conn.c:114] read()=663 pre_len=0 now_len=663
[2025/10/20 08:27:49.342833977] [trace] [input:opentelemetry:opentelemetry.0 at /fluent-bit/plugins/in_opentelemetry/http_conn.c:109] fd=35 closed connection
[2025/10/20 08:27:50.47041537] [debug] [task] created task=0x75c7e8030750 id=0 OK
[2025/10/20 08:27:50.47210503] [debug] [output:opentelemetry:opentelemetry.0] cmetrics msgpack size: 599
[2025/10/20 08:27:50.47385325] [error] [output:opentelemetry:opentelemetry.0] Error decoding msgpack encoded context
[2025/10/20 08:27:50.47439251] [debug] [out flush] cb_destroy coro_id=0
[2025/10/20 08:27:50.47455544] [debug] [task] destroy task=0x75c7e8030750 (task_id=0)

Expected behavior
Expected the otel-collector to receive the otel message with array attribute.

Below is the output from otel-collector when running above python script without fluentbit in between, expecting to get the same when using fluentbit.

2025-10-20T08:27:06.640+0200    info    Metrics {"kind": "exporter", "data_type": "metrics", "name": "debug", "resource metrics": 1, "metrics": 1, "data points": 1}
2025-10-20T08:27:06.640+0200    info    ResourceMetrics #0
Resource SchemaURL: 
Resource attributes:
     -> telemetry.sdk.language: Str(python)
     -> telemetry.sdk.name: Str(opentelemetry)
     -> telemetry.sdk.version: Str(1.38.0)
     -> service.name: Str(unknown_service)
ScopeMetrics #0
ScopeMetrics SchemaURL: 
InstrumentationScope meter 
Metric #0
Descriptor:
     -> Name: metric_gauge
     -> Description: Meter description
     -> Unit: unit
     -> DataType: Gauge
NumberDataPoints #0
Data point attributes:
     -> int_array: Slice([1,2,3,4,5])
     -> double_array: Slice([1.1,2.2,3.3,4.4,5.5])
     -> bool_array: Slice([true,false,true,false,true])
     -> string_array: Slice(["One","Two","Three","Four","Five"])
StartTimestamp: 1970-01-01 00:00:00 +0000 UTC
Timestamp: 2025-10-20 06:27:06.602265704 +0000 UTC
Value: 10
        {"kind": "exporter", "data_type": "metrics", "name": "debug"}

Screenshots

Your Environment
Ubuntu x86_64
Fluentbit 4.1.1 (default build configuration)

Additional context
We want to send attributes arrays with metric gauges.