client_golang: API client Series() call can't handle minTime/maxTime set by prometheus

This is a bit of a convoluted error so I’ll do my best to explain.

If an API call to /series is made without a start/end time prometheus sets minTime/maxTime as the value (https://github.com/prometheus/prometheus/blob/master/web/api/v1/api.go#L462). If I then turn around and use this time with the API client (to presumably send the same request) I get an error:

{
"status": "error",
"errorType": "execution",
"error": "bad_data: cannot parse \"292277025-08-17T23:12:54.999-08:00\" to a valid timestamp"
}

This is because the times used for minTime/maxTime can’t be formatted to an RFC3339Nano timestamp. So for my use case in promxy I get a call from grafana (in this example) with no start/end time – so prometheus sets the time to these min/max times but then I cannot pass that time down to another prometheus to fetch the data, as its not a valid timestamp.

Go playground showing the behavior: https://play.golang.org/p/hM_DWyv0JMK

So I’m not sure what we want to do exactly to handle this. Locally I have copied the min/max times into the client package and are optionally not setting the start/end times if they match. I’m not a major fan of the copy/paste of vars, but unfortunately those times are also private in the prometheus api/v1 package (https://github.com/prometheus/prometheus/blob/master/web/api/v1/api.go#L441). Alternatively we could make it so the client doesn’t set the start/end if start/end are time.IsZero() which would allow the client/caller to pick when they don’t send the timestamp (instead of us transparently doing it in the client).