System.Diagnostics.Activity out of proc monitoring can't access Activity Events or Links

[CodeBlanch]

We have DiagnosticSourceEventSource which enables listening to Activity \ traces out of process.

DiagnosticSourceEventSource supports an argument FilterAndPayloadSpecs which can be used to configure the events and payload which will be written to the source. Example:

[AS]MyActivitySource/Stop:-TraceId;SpanId;ParentSpanId;ActivityTraceFlags;Kind;DisplayName;StartTimeTicks=StartTimeUtc.Ticks;DurationTicks=Duration.Ticks;Status;StatusDescription;Tags=TagObjects.*Enumerate;ActivitySourceVersion=Source.Version

Tags=TagObjects.*Enumerate; works for retrieving tags.

But this...

Events=Events.*Enumerate;Links=Links.*Enumerate;

...won't work for retrieving Events and/or Links.

The reason it doesn't work is ActivityEvent and ActivityLink structs don't provide a suitable ToString implementation which is how the data gets serialized:

• runtime/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticSourceEventSource.cs

  Line 1526 in 26a1e72

  return string.Join(",", (IEnumerable<ElementType>)obj);

• runtime/src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticSourceEventSource.cs

  Line 1494 in 26a1e72

  result.Append(currentValue.ToString());

The solution could be to implement more useful ToString operations or provide some other way to include that data via the FilterAndPayloadSpecs. ToString could be tricky for ActivityEvent because it contains its own tag collection.

/cc @noahfalk @tarekgh @samsp-msft

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