EventSourceLogger does not propagate state data during ActivityStart

[wiktork]

EventSourceLogger only sends IReadOnlyList<KeyValuePair<string, object>> state objects as part of the ActivityStart payload. This means calls like:
logger.BeginScope("string scope")
logger.BeginScope(new Dictionary<string, object>{"key", "value"}

do not contain any payload when listening to ActivityStart events.

[wiktork]

Related pull requests:
aspnet/Logging/pull/424
dotnet/extensions/pull/870

[ericstj]

/cc @noahfalk @maryamariyan

[maryamariyan]

/cc: @tarekgh @shirhatti

[saurabh500]

Wrong Saurabh ? :)

[maryamariyan]

sorry @saurabh500 :) updated

[shirhatti]

@wiktork Do we need this for dotnet-monitor?

[wiktork]

@wiktork Do we need this for dotnet-monitor?

I wouldn't say need, more of a nice to have. It's a gap between inproc ILoggers and what we can collect.

[maryamariyan]

It's a gap between inproc ILoggers and what we can collect.

@wiktork could you please share a small code snippet to illustrate this limitation a bit better and showcase the difference in behavior you found?

[wiktork]

We collect ActivityStart events that are emitted through EventSourceLogger:

https://github.com/dotnet/diagnostics/blob/b8f033696de1a1261040ac15273854cc42b8eddf/src/Microsoft.Diagnostics.Monitoring/DiagnosticsEventPipeProcessor.cs#L149-L182

However, EventSourceLogger only cares about object state that is of a specific type:

runtime/src/libraries/Microsoft.Extensions.Logging.EventSource/src/EventSourceLogger.cs

Lines 196 to 199 in 6072e4d

	private IReadOnlyList<KeyValuePair<string, string>> GetProperties(object state)
	{
	if (state is IReadOnlyList<KeyValuePair<string, object>> keyValuePairs)
	{

In the Asp.net app:

    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;

        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;
        }

        public IActionResult Index()
        {
            _logger.BeginScope(new Dictionary<string, object> { { "key", "value" } });
            _logger.BeginScope("some scope");

            return View();
        }

The scope data such as key/value and "some scope" are lost, since they are not IReadOnlyList<KeyValuePair<string, object>>. While it's probably not practical to serialize every object to json, at least dictionaries and strings should be supported.

Related to this issue is how the data is serialized:

runtime/src/libraries/Microsoft.Extensions.Logging.EventSource/src/EventSourceLogger.cs

Lines 217 to 222 in 6072e4d

	writer.WriteStartObject();
	foreach (KeyValuePair<string, string> keyValue in keyValues)
	{
	writer.WriteString(keyValue.Key, keyValue.Value);
	}
	writer.WriteEndObject();

Json supports more than just strings, but all the data becomes string values after serialization.

Please let me know if you need any more info.