url parsing fails if front slash before fragment is missing and no path specified

[holger-waschke]

we send azure alerts to alertmanager. alertmanager parse the url

https://github.com/prometheus/alertmanager/blob/d7ad5e12f8f823ec64e4e84e91d926b6a8e60f71/cli/alert_add.go#L127C25-L127C28

https://portal.azure.com#@930d042f-8145....

This is covered in the RFC and should be supported
https://www.rfc-editor.org/rfc/rfc3986#appendix-B

However we get an error while parsing the url

{"code":601,"message":"0.generatorURL in body must be of type uri: \"https://portal.azure.com#@930d042f-....""}

Can you please check why it fails and fix accordingly?

[fredbi]

That is correct: https://portal.azure.com#@930d042 (fragment following an empty path) is a valid URI.
We rely on go stdlib url.ParseRequestURI() to validate. And that one is confused by this construct.

https://portal.azure.com/#@930d042f-8145 -> with a slash following the hostname is less prone to errors.²