timestamp for dotnet counters in JSON Formatted Incorrectly

[kkeirstead]

Description

When outputting using the JSON format, I get a StartTime that looks like this: 5/23/2023 10:34:49 AM.

However, each individual timestamp looks like this: 2023-05-23 10:34:59Z.

My understanding is that the "Z" at the end of the time indicates that this is supposed to be UTC; however, this is still local time (as seen in StartTime). I'm not sure if this time is supposed to be in UTC, but if so, I believe .ToUniversalTime() should be used here.

This became apparent while I was working on automated testing for dotnet counters; when deserializing a JSONCounterTrace, I believe the trailing "Z" is indicating that the timestamp should be treated as UTC, causing the timestamp to be incorrect (e.g. {5/23/2023 3:34:49 AM} local time). When I made the change listed above (using .ToUniversalTime()), this fixed the issue with the test reporting the incorrect time (note that this causes dotnet-counters to actually print in UTC though).

Configuration

Debugging locally on Windows using main:

collect --format json --output "C:\\artifacts\\collect.json" --counters "HatCo.HatStore" --name CustomMetricsTest --refresh-interval 5

Regression?

This appears to have originated in this change.

Other information

[gfoidl]

Should the timestamps be formatted according ISO 8601, so they're universal readable?
E.g. via ToString("O").

The default implementation of the JSON-serializer (in .NET) uses that format too. See e.g. sharplab example.

Relevant code lines here are

diagnostics/src/Tools/dotnet-counters/Exporters/JSONExporter.cs

Line 44 in b12f924

.Append("\"StartTime\": \"").Append(DateTime.Now.ToString()).Append("\", ")

and

diagnostics/src/Tools/dotnet-counters/Exporters/JSONExporter.cs

Line 74 in b12f924

.Append("{ \"timestamp\": \"").Append(DateTime.Now.ToString("u")).Append("\", ")

[tommcdon]

@kkeirstead please feel free to submit a PR addressing this issue