MP metrics endpoint provides JSON output by default, Prometheus format should be the default

[rsvoboda]

MP metrics endpoint provides JSON output by default, Prometheus format should be the default

Using Helidon MP Example from https://helidon.io/docs/latest/#/getting-started/02_base-example

curl http://localhost:8080/metrics returns JSON, I had to call curl -H "Accept: text/plain" http://localhost:8080/metrics to get Prometheus format

MP Metrics 1.1 spec says Prometheus text format - default response format when the HTTP Accept header does not match any more specific media type like application/json.
Se section 2.3. Exposing metrics via REST API of the spec

• Helidon Version: 0.10.4
• Helidon MP
• JDK version: 1.8.0_171
• OS: macOS Mojave

$ curl -v http://localhost:8080/metrics
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> GET /metrics HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Content-Type: application/json
< Date: Wed, 24 Oct 2018 10:11:38 +0200
< transfer-encoding: chunked
< connection: keep-alive
<
* Connection #0 to host localhost left intact
{"base":{"classloader.totalLoadedClass.count":6248,"cpu.systemLoadAverage":2.7119140625,"thread.count":19,"classloader.currentLoadedClass.count":6246,"jvm.uptime":75082,"gc.PS MarkSweep.count":1,"memory.committedHeap":211812352,"thread.max.count":26,"gc.PS Scavenge.count":4,"cpu.availableProcessors":8,"thread.daemon.count":14,"classloader.totalUnloadedClass.count":2,"memory.maxHeap":3817865216,"memory.usedHeap":66577096,"gc.PS MarkSweep.time":25,"gc.PS Scavenge.time":52},"vendor":{"requests.count":3,"requests.meter":{"count":3,"meanRate":0.0405695117705537,"oneMinRate":0.020664007757838578,"fiveMinRate":0.006037556417397182,"fifteenMinRate":0.0021495791878664424}}}

[romain-grecourt]

Thanks for reporting this issue, we need to fix this.
See also eclipse/microprofile-metrics#291

[barchetta]

Fixed by pr #158