Configuration parsing issue with UDS (DD_AGENT_HOST+DD_TRACE_AGENT_URL)

Describe the bug The tracing using UDS doesn’t work when DD_AGENT_HOST and DD_TRACE_AGENT_URL is configured. Then there won’t be any traces submitted and the logfile logs:

2022-02-11 12:56:48.626 +00:00 [ERR] An error occurred while sending 1 traces to the agent at unix:///v0.4/traces System.NotSupportedException: The 'unix' scheme is not supported.
   at Datadog.Trace.ClrProfiler.CallTarget.Handlers.Continuations.TaskContinuationGenerator`4.ContinuationAction(Task`1 previousTask, TTarget target, CallTargetState state)
   at Datadog.Trace.ClrProfiler.CallTarget.Handlers.Continuations.TaskContinuationGenerator`4.ContinuationAction(Task`1 previousTask, TTarget target, CallTargetState state)
   at System.Net.Http.HttpClient.<SendAsync>g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)
   at Datadog.Trace.Agent.Transports.HttpClientRequest.PostAsync(ArraySegment`1 bytes, String contentType)
   at Datadog.Trace.Agent.Api.SendTracesAsync(ArraySegment`1 traces, Int32 numberOfTraces, IApiRequest request, Boolean finalTry)
   at Datadog.Trace.Agent.Api.SendTracesAsync(ArraySegment`1 traces, Int32 numberOfTraces)
 { MachineName: ".", Process: "[1 dotnet]", AppDomain: "[1 ConsoleApp]", AssemblyLoadContext: "\"Default\" System.Runtime.Loader.DefaultAssemblyLoadContext #2", TracerVersion: "2.3.0.0" }

The root cause seems to be ExporterSettings.ConfigureTraceTransport, because it reads the agentHost from DD_AGENT_HOST, then checks if it starts with unix:// and sets TracesTransportType to Default. Later on the agentUri will be read from DD_TRACE_AGENT_URL. Which causes the TracesTransportStrategy to return a HttpClientRequestFactory, but the configuration is set to a UDS uri. https://github.com/DataDog/dd-trace-dotnet/blob/57f8232c2eb7837320a6ee8f2a7a4db86e37cbe2/tracer/src/Datadog.Trace/Configuration/ExporterSettings.cs#L231-L303

To Reproduce A repository with a dockerfile to reproduce can be found here: https://github.com/hiiru/dd-net-unix-issue

Basically it prepares a linux container with a .NET app and the tracer with these ENV vars set: DD_AGENT_HOST=localhost DD_TRACE_AGENT_URL unix:///var/run/datadog/apm.socket

When DD_AGENT_HOST is set, the NotSupportedException gets thrown. Otherwise the correct SocketExceptionFactory+ExtendedSocketException gets thrown (since there is no socket in the example docker).

Expected behavior I except that the TracesTransportType will be set from DD_TRACE_AGENT_URL and the tracer uses the UDS transfer. So that it’s possible to use UDS for trace and HTTP for Dogstatsd.

[pierotibou]

Hello @Dima-Diachenko , indeed the last release includes this fix. We’ve just released it today

[pierotibou]

Hello, I’ll update the ticket once this is released.