How can I calculate and format difference between two DTs within custom-api template?

[MartyX98]

Hello!

I am making a custom-api widget that utilizes Unraid's now native API (available from v7.2.0+) to display some server stats and I am a bit stuck on finding a way to calculate the server's current uptime. The API provides data.info.os.uptime DT representing when the server was last booted up, and data.info.time as the current server's time. Below is the example of the JSON response from the API with example DTs.

{
  "data": {
    "info": {
      "os": {
        "uptime": "2025-11-15T18:30:04.326Z"
      },
      "time": "2025-11-17T22:36:07.465Z"
    }
  }
}

So naturally, in my custom-api widget template i parsed those strings;

{{ $uptimeDT := parseTime "RFC3339" (.JSON.String "data.info.time") }}
{{ $timeDT := parseTime "RFC3339" (.JSON.String "data.info.os.uptime") }}

which parses them seemingly fine as I can print the DTs successfully in the widget, but after that i realized i cannot use the glance's sub(a, b float) function on DTs to get the time.Duration diff because the sub accepts only float. I therefore tried converting the DTs to unix timestamp using:

{{ $timeDT_unix := $timeDT.Unix }}
{{ $uptimeDT_unix := $uptimeDT.Unix }}
{{ $diff := sub $timeDT_unix $uptimeDT_unix }}

and while timeDT_unix and uptimeDT_unix print as valid unix timestamps, the diff always prints as NaN. I also realized that even if I got the diff as unix timestamp, i might not be able to convert it to time.Duration as I currently don't see relevant functions for it in custom-api Functions docs.

My goal is to format the difference of the DTs into something human readable, like 2 days, 3 hours, 34 minutes. Am I missing some obvious way to achieve what I want or is Glance lacking the relevant DT functions? I don't mind trying to implement them and make a PR, but i wanted to ask first in case I am not seeing something obvious due to my limited knowledge of Go lang or the expressions syntax which is very well possible since I am working with/learning this all just for Glance.

[ralphocdol]

The closest you can get is something like:

{{ $diffDT := $timeDT.Sub $uptimeDT }}
{{ $negateDiffDT := concat "-" $diffDT.String }}
{{ $diff := offsetNow $negateDiffDT }}
<div>{{ $diffDT }}</div>
<div {{ $diff | toRelativeTime }}></div>

[MartyX98]

That will do it, thank you!