[geneva] Add support for sending metrics in OTLP format over UDS (#2261)

Co-authored-by: Cijo Thomas <cithomas@microsoft.com>

src/OpenTelemetry.Exporter.Geneva/CHANGELOG.md

@@ -5,14 +5,19 @@
 * Drop support for .NET 6 as this target is no longer supported.
   ([#2117](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2117))
 
-* Added support for exporting metrics via
-  [user_events](https://docs.kernel.org/trace/user_events.html) on Linux when
-  OTLP protobuf encoding is enabled via the
-  `PrivatePreviewEnableOtlpProtobufEncoding=true` connection string switch. With
-  this, `PrivatePreviewEnableOtlpProtobufEncoding=true` is now supported on both
-  Widows and Linux. Windows uses ETW as transport, while Linux uses user_events
-  as transport.
-  ([#2113](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2113))
+* Added support for exporting metrics on Linux when OTLP protobuf encoding is
+  enabled via the `PrivatePreviewEnableOtlpProtobufEncoding=true` connection
+  string switch. `PrivatePreviewEnableOtlpProtobufEncoding=true` is now
+  supported on both Windows and Linux.
+
+  * `user_events` transport:
+    [#2113](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2113).
+
+  * Unix domain socket transport:
+    [#2261](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2261).
+
+  For configuration details see:
+  [OtlpProtobufEncoding](./README.md#otlpprotobufencoding).
 
 ## 1.9.0
 

src/OpenTelemetry.Exporter.Geneva/Metrics/GenevaMetricExporter.cs

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using System.Reflection;
+using System.Runtime.InteropServices;
 using System.Text.RegularExpressions;
 using OpenTelemetry.Exporter.Geneva.Metrics;
 using OpenTelemetry.Internal;
@@ -52,14 +53,49 @@ public GenevaMetricExporter(GenevaMetricExporterOptions options)
 
         if (connectionStringBuilder.PrivatePreviewEnableOtlpProtobufEncoding)
         {
+            IMetricDataTransport transport;
+
+            if (connectionStringBuilder.Protocol == TransportProtocol.Unix)
+            {
+                if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+                {
+                    throw new ArgumentException("Unix domain socket should not be used on Windows.");
+                }
+
+                var unixDomainSocketPath = connectionStringBuilder.ParseUnixDomainSocketPath();
+
+                transport = new MetricUnixDomainSocketDataTransport(unixDomainSocketPath);
+            }
+            else
+            {
+#if NET6_0_OR_GREATER
+                transport = !RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+                    ? MetricUnixUserEventsDataTransport.Instance
+                    : MetricWindowsEventTracingDataTransport.Instance;
+#else
+                if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+                {
+                    throw new NotSupportedException("Exporting data in protobuf format is not supported on Linux.");
+                }
+
+                transport = MetricWindowsEventTracingDataTransport.Instance;
+#endif
+            }
+
+            connectionStringBuilder.TryGetMetricsAccountAndNamespace(
+                out var metricsAccount,
+                out var metricsNamespace);
+
             var otlpProtobufExporter = new OtlpProtobufMetricExporter(
                 () => { return this.Resource; },
-                connectionStringBuilder,
+                transport,
+                metricsAccount,
+                metricsNamespace,
                 options.PrepopulatedMetricDimensions);
 
-            this.exporter = otlpProtobufExporter;
-
             this.exportMetrics = otlpProtobufExporter.Export;
+
+            this.exporter = otlpProtobufExporter;
         }
         else
         {

src/OpenTelemetry.Exporter.Geneva/Metrics/OtlpProtobuf/OtlpProtobufMetricExporter.cs

@@ -2,7 +2,6 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using System.Diagnostics;
-using System.Runtime.InteropServices;
 using OpenTelemetry.Metrics;
 using OpenTelemetry.Resources;
 
@@ -18,30 +17,22 @@ internal sealed class OtlpProtobufMetricExporter : IDisposable
 
     public OtlpProtobufMetricExporter(
         Func<Resource> getResource,
-        ConnectionStringBuilder? connectionStringBuilder,
+        IMetricDataTransport transport,
+        string? metricsAccount,
+        string? metricsNamespace,
         IReadOnlyDictionary<string, object>? prepopulatedMetricDimensions)
     {
         Debug.Assert(getResource != null, "getResource was null");
+        Debug.Assert(transport != null, "transport was null");
 
         this.getResource = getResource!;
 
-#if NET6_0_OR_GREATER
-        IMetricDataTransport transport = !RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
-            ? MetricUnixUserEventsDataTransport.Instance
-            : MetricWindowsEventTracingDataTransport.Instance;
-#else
-        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-        {
-            throw new NotSupportedException("Exporting data in protobuf format is not supported on Linux.");
-        }
-
-        var transport = MetricWindowsEventTracingDataTransport.Instance;
-#endif
-
         this.otlpProtobufSerializer = new OtlpProtobufSerializer(
-            transport,
-            connectionStringBuilder,
-            prepopulatedMetricDimensions);
+            transport!,
+            metricsAccount,
+            metricsNamespace,
+            prepopulatedMetricDimensions,
+            prefixBufferWithUInt32LittleEndianLength: transport is MetricUnixDomainSocketDataTransport);
     }
 
     public ExportResult Export(in Batch<Metric> batch)
@@ -59,5 +50,9 @@ public ExportResult Export(in Batch<Metric> batch)
 
     public void Dispose()
     {
+        if (this.otlpProtobufSerializer.MetricDataTransport is MetricUnixDomainSocketDataTransport udsTransport)
+        {
+            udsTransport.Dispose();
+        }
     }
 }

src/OpenTelemetry.Exporter.Geneva/Metrics/OtlpProtobuf/OtlpProtobufSerializer.cs

@@ -1,6 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using System.Buffers.Binary;
 using System.Diagnostics;
 using System.Globalization;
 using OpenTelemetry.Metrics;
@@ -17,6 +18,7 @@ internal sealed class OtlpProtobufSerializer
     private readonly Dictionary<string, List<Metric>> scopeMetrics = new();
     private readonly string? metricNamespace;
     private readonly string? metricAccount;
+    private readonly bool prefixBufferWithUInt32LittleEndianLength;
     private readonly byte[]? prepopulatedNumberDataPointAttributes;
     private readonly int prepopulatedNumberDataPointAttributesLength;
     private readonly byte[]? prepopulatedHistogramDataPointAttributes;
@@ -37,12 +39,17 @@ internal sealed class OtlpProtobufSerializer
 
     public OtlpProtobufSerializer(
         IMetricDataTransport metricDataTransport,
-        ConnectionStringBuilder? connectionStringBuilder,
-        IReadOnlyDictionary<string, object>? prepopulatedMetricDimensions)
+        string? metricsAccount,
+        string? metricsNamespace,
+        IReadOnlyDictionary<string, object>? prepopulatedMetricDimensions,
+        bool prefixBufferWithUInt32LittleEndianLength = false)
     {
         Debug.Assert(metricDataTransport != null, "metricDataTransport was null");
 
         this.MetricDataTransport = metricDataTransport!;
+        this.metricAccount = metricsAccount;
+        this.metricNamespace = metricsNamespace;
+        this.prefixBufferWithUInt32LittleEndianLength = prefixBufferWithUInt32LittleEndianLength;
 
         // Taking a arbitrary number here for writing attributes.
         byte[] temp = new byte[20000];
@@ -68,14 +75,6 @@ public OtlpProtobufSerializer(
             Array.Copy(temp, this.prepopulatedExponentialHistogramDataPointAttributes, cursor);
             this.prepopulatedExponentialHistogramDataPointAttributesLength = cursor;
         }
-
-        if (connectionStringBuilder?.TryGetMetricsAccountAndNamespace(
-            out var metricsAccount,
-            out var metricsNamespace) == true)
-        {
-            this.metricAccount = metricsAccount;
-            this.metricNamespace = metricsNamespace;
-        }
     }
 
     internal static void WriteInstrumentDetails(byte[] buffer, ref int cursor, Metric metric)
@@ -222,7 +221,7 @@ internal void ClearScopeMetrics()
 
     internal void SerializeResourceMetrics(byte[] buffer, Resource resource)
     {
-        int cursor = 0;
+        int cursor = this.prefixBufferWithUInt32LittleEndianLength ? 4 : 0;
 
         this.resourceMetricTagAndLengthIndex = cursor;
 
@@ -734,11 +733,15 @@ private void WriteIndividualMessageTagsAndLength(byte[] buffer, ref int cursor,
 
         // Write resource metric tag and length
         ProtobufSerializerHelper.WriteTagAndLengthPrefix(buffer, ref resourceMetricIndex, cursor - this.resourceMetricValueIndex, FieldNumberConstants.ResourceMetrics_resource, WireType.LEN);
+
+        if (this.prefixBufferWithUInt32LittleEndianLength)
+        {
+            BinaryPrimitives.WriteUInt32LittleEndian(buffer, (uint)cursor - 4);
+        }
     }
 
     private void SendMetricPoint(byte[] buffer, ref int cursor)
     {
-        // TODO: Extend this for user_events.
         this.MetricDataTransport.SendOtlpProtobufEvent(buffer, cursor);
     }
 

src/OpenTelemetry.Exporter.Geneva/Metrics/Transport/MetricUnixDomainSocketDataTransport.cs

@@ -28,6 +28,11 @@ public void Send(MetricEventType eventType, byte[] body, int size)
         this.udsDataTransport.Send(body, size + this.fixedPayloadLength);
     }
 
+    public void SendOtlpProtobufEvent(byte[] body, int size)
+    {
+        this.udsDataTransport.Send(body, size);
+    }
+
     public void Dispose()
     {
         if (this.isDisposed)
@@ -38,9 +43,4 @@ public void Dispose()
         this.udsDataTransport.Dispose();
         this.isDisposed = true;
     }
-
-    public void SendOtlpProtobufEvent(byte[] body, int size)
-    {
-        throw new NotImplementedException();
-    }
 }

src/OpenTelemetry.Exporter.Geneva/README.md

@@ -270,23 +270,72 @@ For example:
 
 ##### OtlpProtobufEncoding
 
-On Windows set `PrivatePreviewEnableOtlpProtobufEncoding=true` on the
-`ConnectionString` to opt-in to the experimental feature for changing the
-underlying serialization format to binary protobuf following the schema defined
-in [OTLP
+An experimental feature flag is available to opt-into changing the underlying
+serialization format to binary protobuf following the schema defined in [OTLP
 specification](https://github.com/open-telemetry/opentelemetry-proto/blob/v1.1.0/opentelemetry/proto/metrics/v1/metrics.proto).
 
+When using OTLP protobuf encoding `Account` and `Namespace` are **NOT** required
+to be set on the `ConnectionString`. The recommended approach is to use
+OpenTelemetry Resource instead:
+
+```csharp
+using var meterProvider = Sdk.CreateMeterProviderBuilder()
+    // Other configuration not shown
+    .ConfigureResource(r => r.AddAttributes(
+        new Dictionary<string, object>()
+        {
+            ["_microsoft_metrics_account"] = "MetricsAccountGoesHere",
+            ["_microsoft_metrics_namespace"] = "MetricsNamespaceGoesHere",
+        }))
+    .AddGenevaMetricExporter(options =>
+    {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        {
+            options.ConnectionString = "PrivatePreviewEnableOtlpProtobufEncoding=true";
+        }
+        else
+        {
+            // Note: 1.10.0+ version required to use OTLP protobuf encoding on Linux
+
+            // Use Unix domain socket mode
+            options.ConnectionString = "Endpoint=unix:{OTLP UDS Path};PrivatePreviewEnableOtlpProtobufEncoding=true";
+
+            // Use user_events mode (preferred but considered experimental as this is a new capability in Linux kernel)
+            // options.ConnectionString = "PrivatePreviewEnableOtlpProtobufEncoding=true";
+        }
+    })
+    .Build();
+```
+
+###### Windows
+
+To send metric data over ETW using OTLP protobuf encoding set
+`PrivatePreviewEnableOtlpProtobufEncoding=true` on the `ConnectionString`.
+
+###### Linux
+
 As of `1.10.0` `PrivatePreviewEnableOtlpProtobufEncoding=true` is also supported
-on Linux. On Linux when using `PrivatePreviewEnableOtlpProtobufEncoding=true` an
-`Endpoint` is **NOT** required to be provided on `ConnectionString`. For
-example: `Endpoint=unix:Account={MetricAccount};Namespace={MetricNamespace}`.
+on Linux.
+
+###### When using unix domain socket
+
+To send metric data over UDS using OTLP protobuf encoding set the `Endpoint` to
+use the correct `OtlpSocketPath` path and set
+`PrivatePreviewEnableOtlpProtobufEncoding=true` on the `ConnectionString`:
+`Endpoint=unix:{OTLP UDS Path};PrivatePreviewEnableOtlpProtobufEncoding=true`.
 
 > [!IMPORTANT]
-> When `PrivatePreviewEnableOtlpProtobufEncoding` is enabled on Linux metrics
-> are written using
-> [user_events](https://docs.kernel.org/trace/user_events.html). `user_events`
-> are a newer feature of the Linux kernel and require a distro with the feature
-> enabled.
+> OTLP over UDS requires a different socket path than TLV over UDS.
+
+###### When using user_events
+
+> [!IMPORTANT]
+> [user_events](https://docs.kernel.org/trace/user_events.html) are a newer
+> feature of the Linux kernel and require a distro with the feature enabled.
+
+To send metric data over user_events using OTLP protobuf encoding do **NOT**
+specify an `Endpoint` and set `PrivatePreviewEnableOtlpProtobufEncoding=true` on
+the `ConnectionString`.
 
 #### `MetricExportIntervalMilliseconds` (optional)
 

test/OpenTelemetry.Exporter.Geneva.Benchmarks/Exporter/MetricExporterBenchmarks.cs

@@ -111,12 +111,12 @@ public void Setup()
         this.tlvMetricsExporter = new TlvMetricExporter(connectionStringBuilder, exporterOptions.PrepopulatedMetricDimensions);
 
         // Using test transport here with noop to benchmark just the serialization part.
-        this.otlpProtobufSerializer = new OtlpProtobufSerializer(new TestTransport(), null, null);
+        this.otlpProtobufSerializer = new OtlpProtobufSerializer(new TestTransport(), metricsAccount: null, metricsNamespace: null, prepopulatedMetricDimensions: null);
 
         var resourceBuilder = ResourceBuilder.CreateDefault().Clear()
            .AddAttributes(new[] { new KeyValuePair<string, object>("TestResourceKey", "TestResourceValue") });
         this.resource = resourceBuilder.Build();
-        this.otlpProtobufMetricExporter = new OtlpProtobufMetricExporter(() => { return this.resource; }, null, null);
+        this.otlpProtobufMetricExporter = new OtlpProtobufMetricExporter(() => { return this.resource; }, new TestTransport(), metricsAccount: null, metricsNamespace: null, prepopulatedMetricDimensions: null);
         this.buffer = new byte[GenevaMetricExporter.BufferSize];
 
         this.counterMetricPointWith3Dimensions = this.GenerateCounterMetricItemWith3Dimensions(out this.counterMetricDataWith3Dimensions);