Add InMemoryExporter for Metrics (#2192)

src/OpenTelemetry.Exporter.InMemory/CHANGELOG.md

@@ -2,18 +2,23 @@
 
 ## Unreleased
 
+* Add Metrics
+  support.([#2192](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2192))
+
 ## 1.2.0-alpha1
 
 Released 2021-Jul-23
 
-* Removes support for .NET Framework 4.5.2 and 4.6. The minimum .NET Framework version
-  supported is .NET 4.6.1. ([#2138](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2138))
+* Removes support for .NET Framework 4.5.2 and 4.6. The minimum .NET Framework
+  version supported is .NET 4.6.1.
+  ([#2138](https://github.com/open-telemetry/opentelemetry-dotnet/issues/2138))
 
 ## 1.1.0
 
 Released 2021-Jul-12
 
-* Supports OpenTelemetry.Extensions.Hosting based configuration for `InMemoryExporter`
+* Supports OpenTelemetry.Extensions.Hosting based configuration for
+  `InMemoryExporter`
   ([#2129](https://github.com/open-telemetry/opentelemetry-dotnet/pull/2129))
 
 ## 1.1.0-rc1
@@ -52,8 +57,8 @@ Released 2021-Feb-04
 
 Released 2021-Jan-29
 
-* `AddInMemoryExporter` extension method for traces moved from
-  `OpenTelemetry` namespace to `OpenTelemetry.Trace` namespace.
+* `AddInMemoryExporter` extension method for traces moved from `OpenTelemetry`
+  namespace to `OpenTelemetry.Trace` namespace.
   ([#1576](https://github.com/open-telemetry/opentelemetry-dotnet/pull/1576))
 * `AddInMemoryExporter` extension method for logs moved from
   `Microsoft.Extensions.Logging` namespace to `OpenTelemetry.Logs` namespace.

src/OpenTelemetry.Exporter.InMemory/InMemoryExporterMetricHelperExtensions.cs

@@ -0,0 +1,50 @@
+// <copyright file="InMemoryExporterMetricHelperExtensions.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+using OpenTelemetry.Exporter;
+
+namespace OpenTelemetry.Metrics
+{
+    public static class InMemoryExporterMetricHelperExtensions
+    {
+        /// <summary>
+        /// Adds InMemory exporter to the TracerProvider.
+        /// </summary>
+        /// <param name="builder"><see cref="MeterProviderBuilder"/> builder to use.</param>
+        /// <param name="exportedItems">Collection which will be populated with the exported MetricItem.</param>
+        /// <param name="configure">Exporter configuration options.</param>
+        /// <returns>The instance of <see cref="MeterProviderBuilder"/> to chain the calls.</returns>
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Reliability", "CA2000:Dispose objects before losing scope", Justification = "The objects should not be disposed.")]
+        public static MeterProviderBuilder AddInMemoryExporter(this MeterProviderBuilder builder, ICollection<MetricItem> exportedItems, Action<InMemoryExporterOptions> configure = null)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            if (exportedItems == null)
+            {
+                throw new ArgumentNullException(nameof(exportedItems));
+            }
+
+            var options = new InMemoryExporterOptions();
+            configure?.Invoke(options);
+            return builder.AddMetricProcessor(new PushMetricProcessor(new InMemoryExporter<MetricItem>(exportedItems), options.MetricExportInterval, options.IsDelta));
+        }
+    }
+}

src/OpenTelemetry.Exporter.InMemory/InMemoryExporterOptions.cs

@@ -0,0 +1,32 @@
+// <copyright file="InMemoryExporterOptions.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace OpenTelemetry.Exporter
+{
+    public class InMemoryExporterOptions
+    {
+        /// <summary>
+        /// Gets or sets the metric export interval.
+        /// </summary>
+        public int MetricExportInterval { get; set; } = 1000;
+
+        /// <summary>
+        /// Gets or sets a value indicating whether to export Delta
+        /// values or not (Cumulative).
+        /// </summary>
+        public bool IsDelta { get; set; } = true;
+    }
+}