Requests without an Accept header are not accepted

[pedroigor]

Making a request without an Accept header ends up with the following response:

curl -v -H "Accept:" -H "accept-encoding: identity" http://localhost:8080/metrics
* About to connect() to localhost port 8080 (#0)
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 8080 (#0)
> GET /metrics HTTP/1.1
> User-Agent: curl/7.29.0
> Host: localhost:8080
> accept-encoding: identity
>
< HTTP/1.1 406 Not Acceptable
< content-length: 69
<
* Connection #0 to host localhost left intact
* 

In this case (the absence of an Accept header), the server should assume that the client accepts all types, i.e. /. This is defined in the HTTP spec here: https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

If no Accept header field is present, then it is assumed that the client accepts all media types.

Looks like the issue is on how the empty Accept header is handled here https://github.com/smallrye/smallrye-metrics/blob/main/implementation/src/main/java/io/smallrye/metrics/MetricsRequestHandler.java#L229.

If empty, the server should respond with the preferred content type instead of not accepting the request. Perhaps use application/json as the default?

FYI, this behavior was found in Quarkus applications using the quarkus-smallrye-metrics.

If the issue makes sense, I can send a PR.

[jmartisk]

Hi; seems you're right, except the detail that the default for a missing Accept header should be OpenMetrics (text/plain), as per https://download.eclipse.org/microprofile/microprofile-metrics-3.0/microprofile-metrics-spec-3.0.html#rest-api, not JSON

PRs welcome :)

[jmartisk]

It's a bit complicated with branches in this repo right now, but to get it fixed in Quarkus, the most important branch for a PR would be main, and also jakarta to make sure the problem doesn't reappear after we migrate to Jakarta EE 10.
micrometer branch might be applicable too, that's currently mostly under the direction of @Channyboy

[pedroigor]

@jmartisk Sent a PR to main. Should I sent to jarkarta branch now or wait first for your review/merge?

[jmartisk]

Main PR merged, if you're eager please send the same for jakarta, otherwise I will do it myself, no problem
Let's leave micrometer to @Channyboy so he can add it too if appropriate
Thanks!

[pedroigor]

Tk u. I'll send it now to jakarta.

[jmartisk]

Thanks. I will see to it that the fix is propagated into Quarkus 2.10.0 and 2.9.3

[pedroigor]

Ok