Send "Content-Type" Header When Scraping Metrics for Prometheus 3.0 Compatibility

[eramnes]

Thanks for putting this exporter out, it has been very useful to our organization. We've recently upgraded to Prometheus 3.0 and it appears that there's no Content-Type header set by this exporter when metrics are returned.

Prometheus 3.0 is more strict with the Content-Type header and checking the curl output for the WLS exporter, it appears to not be providing one (sanitized output):

$ curl -vs http://wls-server.example.com:9111/metrics --user monitor
Enter host password for user 'monitor':
*   Trying 192.168.0.20:9111...
* Connected to wls-server.example.com (192.168.0.20) port 9111 (#0)
* Server auth using Basic with user 'monitor'
> GET /metrics HTTP/1.1
> Host: wls-server.example.com:9111
> Authorization: Basic abcdefg1234567
> User-Agent: curl/7.76.1
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Date: Thu, 2 Jan 2025 08:45:44 -0600
< Connection: keep-alive
< Content-Length: 1052
< 
execute_thread_total_count{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 36
hogging_thread_count{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 0
overload_rejected_requests_count{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 0
pending_user_request_count{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 0
standby_thread_count{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 6
stuck_thread_count{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 0
throughput{domain="DEFAULT",server="PIA",app="ThreadPoolRuntime"} 1.999000499750125
jvm_heap_free_current{domain="DEFAULT",server="PIA",name="PIA"} 3867602632
jvm_heap_free_percent{domain="DEFAULT",server="PIA",name="PIA"} 90
jvm_heap_size_current{domain="DEFAULT",server="PIA",name="PIA"} 4294967296
wls_scrape_mbeans_count_total{instance="wls-server"} 10
wls_scrape_duration_seconds{instance="wls-server"} 0.03
wls_scrape_cpu_seconds{instance="wls-server"} 0.00
exporter_version{instance="wls-server",version="0073701 (1 commits since v2.2.2)"} 1
* Connection #0 to host wls-server.example.com left intact

This can be currently worked around by placing

fallback_scrape_protocol: PrometheusText0.0.4

in the scrape job, but it would be nice if the Content-Type was provided. We're using the sidecar exporter and I am not sure if this is an issue in the web application or not.

[russgold]

Yes, thanks. I am working on this at present.