Extend URL handling for Alertmanager Templates

[StopMotionCuber]

We have a setup where we are using Alertmanager in combination with Prometheus and Grafana. I would like to share a "See in Grafana" Link and convert the URL that prometheus sends within a template to a link in our internal Grafana instance.

What I would like to do here is the following:

1. Extract the expr Part of the URL query
2. Convert all + to /%20 (this is just a difference between Grafana and Prometheus)
3. Embed this in a link in a template

The issue I'm facing now is that the URL I'm getting from Prometheus is URL-encoded. When parsing these with html/template, that encoding is encoded again. Now I see 3 possible solutions:

1. Decode the URL with some kind of urldecode (not possible within a template, as that function is not exposed)
2. Don't do a urldecode, but mark the string as safe (also not possible within a template, as that function is not exposed. We do have safeHtml and would need something like safeUrl)
3. Manually do the URL decoding with a lot of reReplaceAll calls (note: this is not exhaustive and doesn't do a full decode, it's just "good enough" for some of our queries. Still exploring what else needs to be replaced):

<a href="https://<grafana_url>/explore?left=%7B%22datasource%22%3A%22prometheus%22%2C%22queries%22%3A%5B%7B%22expr%22%3A%22{{ ( reReplaceAll ".*expr=([^&]+).*" "$1" .GeneratorURL ) | reReplaceAll "+" " " | reReplaceAll "%28" "(" | reReplaceAll "%29" ")" | reReplaceAll "%7B" "{" | reReplaceAll "%7D" "}" | reReplaceAll "%3D" "=" | reReplaceAll "%2F" "/" | reReplaceAll "%3A" ":" | reReplaceAll "%2C" "," | reReplaceAll "%3C" "<" | reReplaceAll "%3E" ">" | reReplaceAll "%5C" "\\" | reReplaceAll "%22" "\"" | reReplaceAll "\\\\" "\\\\\\\\" | reReplaceAll "\"" "\\\"" }}%22%2C%22refId%22%3A%22A%22%7D%5D%2C%22range%22%3A%7B%22from%22%3A%22now-6h%22%2C%22to%22%3A%22now%22%7D%7D">See in Grafana</a><br>

I settled now for Option 3, as that is the only option possible currently with alertmanager. But I would like to be able to go for either option 1 or option 2.

Is this something that is desirable for the alertmanager, and if yes, would it make more sense to go for 1, 2 or implement both? I think 2 should be really easy to implement (basically the same as safeHtml), while 1 is probably also not hard to do.

I would be happy to contribute here