Errors while parsing prometheus metrics wich : in names

[ArtoLord]

Bug Report

FluentBit's prometheus_scrape input can't handle metrics with colons (:) in their names. I'm trying to scrape metrics from a vLLM Docker container that uses names like vllm:* for its metrics. These names are totally valid according to Prometheus docs (https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels), but FluentBit's cmetrics library seems to think they're not and rejects them.

To Reproduce

• Example log message if applicable:

[2025/03/04 10:53:38] [error] [input:prometheus_scrape:prometheus_scrape.0] error decoding Prometheus Text formatsyntax error, unexpected invalid token, expecting '{' or NUMSTR or INFNAN

• Steps to reproduce the problem:
  1. Set up something that spits out Prometheus metrics with colons in names (like vLLM does with vllm:*)
  2. Try to scrape with FluentBit: fluent-bit -i prometheus_scrape --port=9100 -o stdout
  3. Watch it fail with errors

Expected behavior
FluentBit should just work with all valid Prometheus metric names, including those with colons - just like the Prometheus docs say is fine.

Your Environment

• Version used: 3.2.7
• Configuration: Simple reproduction: fluent-bit -i prometheus_scrape --port=9100 -o stdout
• Environment name and version: Kubernetes
• Filters and plugins: prometheus_scrape input plugin

Additional context
Example of metrics to reproduce issue: metrics.txt