When calling /q/metrics once, http_server_bytes_written_count increases by 2

[gian1200]

Describe the bug

http_server_bytes_written_count increases by 2 per single /q/metrics invocation,

Expected behavior

http_server_bytes_written_count should increase once when /q/metrics is invoked

Actual behavior

When /q/metrics is invoked, http_server_bytes_written_count increases by 2

Also, even if there is no content-length (body) in GET requests, shouldn't http_server_bytes_read_count increase by 1 per each GET request?

How to Reproduce?

1. Basic Quarkus project with a REST API (1 POST and 1 GET), and quarkus-micrometer-registry-prometheus, quarkus-smallrye-health extensions.
2. Call /q/metrics, /q/health or any user GET API.

Output of uname -a or ver

No response

Output of java -version

openjdk version "17.0.11" 2024-04-16

Quarkus version or git rev

3.12.2

Build tool (ie. output of mvnw --version or gradlew --version)

Apache Maven 3.9.7

Additional information

No response

[quarkus-bot]

/cc @brunobat (micrometer), @ebullient (metrics,micrometer), @jmartisk (metrics)

[cescoffier]

I reproduced it.
It only happens for /metrics (and not the other framework routes or business routes)

[cescoffier]

It's not a bug.

It could happen with any response larger than the max "chunk". Let me explain.
The Prometheus response is large enough to exceed this limit. This means that there is not a single write at the TCP level but two (one at capacity and then the remaining). So, we increment the counter twice.