dotnet-counters stops working when tag contains comma or equal sign

[MV10]

This is actually a dotnet/runtime problem (in my opinion), but it definitely breaks dotnet-counters so I figured I'd start here.

When a monitored application emits a System.Diagnostics.Metrics instrument whose tag values contain , or =, dotnet-counters displays the counter name but never renders any tag columns or values, and the display stops updating.

Although it's a bug in counters, the underlying problem in the runtime is that MetricsEventSource flattens the tag list for out-of-process consumers into a key=value,key=value string, which can't be reliably parsed if value contains commas or equal signs.

Minimal .NET 10 repro:

  using System.Diagnostics.Metrics;

  using var meter = new Meter("TagTest");
  var counter = meter.CreateCounter<long>("hits");

  Console.WriteLine($"PID: {Environment.ProcessId}");
  while (true)
  {
      counter.Add(1,
          new KeyValuePair<string, object?>("plain", "simple"),
          new KeyValuePair<string, object?>("comma", "a,b,c"),
          new KeyValuePair<string, object?>("equals", "x=1"),
          new KeyValuePair<string, object?>("url", "/api/items?filter=red,blue&sort=name"));
      Thread.Sleep(250);
  }

The payload looks like this, and the problem is already obvious:

comma=a,b,c,equals=x=1,plain=simple,url=/api/items?filter=red,blue&sort=name

When you run dotnet-counters monitor --process-id <PID> --counters TagTest, instead of columns for plain, comma, equals, and url, you get:

[TagTest]
    hits (Count)

...then it stops updating. I didn't dig into dotnet-counters to find that problem because I had already run into the general tagging problem in my own program, and I wondered if counters had some magic to fix it. (I did actually come up with some ugly code that resolves those, but a tag like key=a=1,b=2 where a=1,b=2 is the value can't be resolved; definitely an edge case but still a problem.)

I suppose some kind of escaping of commas and equal signs in the key values is called for, or emit the tag list in a structured fashion (JSON, a Dictionary, etc). ... obviously that's up to you folks. As far as I know OTel doesn't require any particular format, so there wouldn't be a violation of any standard if this changes.

Environment:

• dotnet-counters 9.0.661903
• .NET SDK 10.0.301
• Linux x64