Filter parameter causes HTTP Status 400 – Bad Request

[Bob Tee]

I have a JEE application with the Prometheus servlet added to my web.xml file. The metrics work as expected except for when I pass the filter parameter to the /metrics endpoint. The [] characters cause a HTTP Status 400 error.

For example:

/metrics?name[]=jvm_threads_current

HTTP Status 400 – Bad Request
Type Exception Report

Message Invalid character found in the request target [/metrics?name[]=jvm_threads_current ]. The valid characters are defined in RFC 7230 and RFC 3986

Description The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

Apache Tomcat/10.1.15

I am following the documentation on this page:
https://prometheus.github.io/client_java/exporters/filter/

I can make it work if I URL Encode the [] characters. For example:

/metrics?name%5B%5D=jvm_threads_current

Perhaps there is no actual issue but the documentation could be updated to show the encoded version.

[Doug Hoard]

@bob-tee great catch! This is a documentation issue.