Add process tags to client-side stats (#7791)

## Summary of changes

adding process tags at the ClientStatsPayload level.
See
[proto](https://github.com/DataDog/datadog-agent/blob/main/pkg/proto/datadog/trace/stats.proto#L52-L55)
in the agent

## Reason for change

AIDM-195

## Implementation details

## Test coverage

piggybacked on existing tests

## Other details

I realized that dotnet doesn't write the service name at the top level,
but only in the buckets. Doesn't seem to be a big issue, but there could
be a win here by writing the service in the buckets only when there is
an override.



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---------

Co-authored-by: Andrew Lock <[email protected]>

Author: vandonr

tracer/src/Datadog.Trace/Agent/ClientStatsPayload.cs

@@ -17,6 +17,8 @@ internal class ClientStatsPayload
 
         public string Version { get; set; }
 
+        public string ProcessTags { get; set; }
+
         public long GetSequenceNumber() => Interlocked.Increment(ref _sequence);
     }
 }

tracer/src/Datadog.Trace/Agent/StatsAggregator.cs

@@ -67,7 +67,8 @@ internal StatsAggregator(IApi api, TracerSettings settings, IDiscoveryService di
             {
                 Environment = settings.Environment,
                 Version = settings.ServiceVersion,
-                HostName = HostMetadata.Instance.Hostname
+                HostName = HostMetadata.Instance.Hostname,
+                ProcessTags = settings.PropagateProcessTags ? ProcessTags.SerializedTags : null
             };
 
             for (int i = 0; i < _buffers.Length; i++)

tracer/src/Datadog.Trace/Agent/StatsBuffer.cs

@@ -59,7 +59,13 @@ public void Reset()
 
         public void Serialize(Stream stream, long bucketDuration)
         {
-            MessagePackBinary.WriteMapHeader(stream, 8);
+            var count = 8;
+            if (!string.IsNullOrEmpty(_header.ProcessTags))
+            {
+                count++;
+            }
+
+            MessagePackBinary.WriteMapHeader(stream, count);
 
             MessagePackBinary.WriteString(stream, "Hostname");
             MessagePackBinary.WriteString(stream, _header.HostName ?? string.Empty);
@@ -70,6 +76,12 @@ public void Serialize(Stream stream, long bucketDuration)
             MessagePackBinary.WriteString(stream, "Version");
             MessagePackBinary.WriteString(stream, _header.Version ?? string.Empty);
 
+            if (!string.IsNullOrEmpty(_header.ProcessTags))
+            {
+                MessagePackBinary.WriteString(stream, "ProcessTags");
+                MessagePackBinary.WriteString(stream, _header.ProcessTags);
+            }
+
             MessagePackBinary.WriteString(stream, "Stats");
             MessagePackBinary.WriteArrayHeader(stream, 1);
             SerializeBuckets(stream, bucketDuration);

tracer/test/Datadog.Trace.TestHelpers/Stats/MockClientStatsPayload.cs

@@ -20,6 +20,9 @@ public class MockClientStatsPayload
         [Key("Version")]
         public string Version { get; set; }
 
+        [Key("ProcessTags")]
+        public string ProcessTags { get; set; }
+
         [Key("Lang")]
         public string Lang { get; set; }
 

tracer/test/Datadog.Trace.Tests/Agent/ApiTests.cs

@@ -165,9 +165,15 @@ public async Task SendStatsAsync_200OK_AllGood()
             factoryMock.Setup(x => x.GetEndpoint(It.Is<string>(s => s == TracesPath))).Returns(new Uri("http://localhost/traces"));
             factoryMock.Setup(x => x.GetEndpoint(It.Is<string>(s => s == StatsPath))).Returns(new Uri("http://localhost/stats"));
 
-            var api = new Api(apiRequestFactory: factoryMock.Object, statsd: null, updateSampleRates: null, partialFlushEnabled: false);
-
-            var statsBuffer = new StatsBuffer(new ClientStatsPayload());
+            var api = new Api(factoryMock.Object, statsd: null, updateSampleRates: null, partialFlushEnabled: false);
+
+            var statsBuffer = new StatsBuffer(new ClientStatsPayload
+            {
+                Environment = "myEnv",
+                HostName = "myHost",
+                ProcessTags = "tag.a:b,tag.c:d",
+                Version = "myVersion"
+            });
 
             await api.SendStatsAsync(statsBuffer, 1);
 

tracer/test/Datadog.Trace.Tests/Agent/StatsBufferTests.cs

@@ -29,7 +29,7 @@ public void Serialization()
         {
             const long expectedDuration = 42;
 
-            var payload = new ClientStatsPayload { Environment = "Env", HostName = "Hostname", Version = "v99.99" };
+            var payload = new ClientStatsPayload { Environment = "Env", HostName = "Hostname", Version = "v99.99", ProcessTags = "a.b:c_d,x.y:z" };
 
             var buffer = new StatsBuffer(payload);
 
@@ -52,6 +52,7 @@ public void Serialization()
             result.Hostname.Should().Be(payload.HostName);
             result.Env.Should().Be(payload.Environment);
             result.Version.Should().Be(payload.Version);
+            result.ProcessTags.Should().Be(payload.ProcessTags);
             result.Lang.Should().Be(TracerConstants.Language);
             result.TracerVersion.Should().Be(TracerConstants.AssemblyVersion);
             result.RuntimeId.Should().Be(Tracer.RuntimeId);