Add Prometheus support

Directory.Build.targets

@@ -22,16 +22,17 @@
   <!-- Package versions for package references across all projects -->
   <ItemGroup>
     <PackageReference Update="coverlet.msbuild" Version="2.8.1" />
-    <PackageReference Update="Microsoft.Extensions.DependencyInjection" Version="5.0.0-preview.2.20160.3" />
-    <PackageReference Update="Microsoft.Extensions.Hosting" Version="5.0.0-preview.2.20160.3" />
-    <PackageReference Update="Microsoft.Extensions.Http" Version="5.0.0-preview.2.20160.3" />
-    <PackageReference Update="Microsoft.Extensions.Logging.Abstractions" Version="5.0.0-preview.2.20160.3" />
-    <PackageReference Update="Microsoft.Extensions.Options.ConfigurationExtensions" Version="5.0.0-preview.2.20160.3" />
-    <PackageReference Update="Microsoft.Net.Compilers.Toolset" Version="3.7.0-1.final" />
-    <PackageReference Update="Microsoft.NET.Test.Sdk" Version="16.5.0" />
-    <PackageReference Update="Microsoft.SourceLink.GitHub" Version="1.0.0" />
-    <PackageReference Update="NUnit" Version="3.12.0" />
-    <PackageReference Update="NUnit3TestAdapter" Version="3.16.1" />
+    <PackageReference Update="Microsoft.Extensions.Configuration" Version="5.0.0" />
+    <PackageReference Update="Microsoft.Extensions.DependencyInjection" Version="5.0.1" />
+    <PackageReference Update="Microsoft.Extensions.Hosting" Version="5.0.0" />
+    <PackageReference Update="Microsoft.Extensions.Http" Version="5.0.0" />
+    <PackageReference Update="Microsoft.Extensions.Logging.Abstractions" Version="5.0.0" />
+    <PackageReference Update="Microsoft.Extensions.Options.ConfigurationExtensions" Version="5.0.0" />
+    <PackageReference Update="Microsoft.Net.Compilers.Toolset" Version="3.9.0-3.final" />
+    <PackageReference Update="Microsoft.NET.Test.Sdk" Version="16.9.0-preview-20210106-01" />
+    <PackageReference Update="Microsoft.SourceLink.GitHub" Version="1.1.0-beta-20204-02" />
+    <PackageReference Update="NUnit" Version="3.13.0" />
+    <PackageReference Update="NUnit3TestAdapter" Version="3.17.0" />
   </ItemGroup>
 
 </Project>

Finite.Metrics.sln

@@ -25,6 +25,14 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Providers", "Providers", "{
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Finite.Metrics.OpenTsdb.UnitTests", "tests\Providers\OpenTsdb\Finite.Metrics.OpenTsdb.UnitTests.csproj", "{8C2BA2A6-9D4A-432D-B8B1-B07E0E01FB2C}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Prometheus", "Prometheus", "{EB50151D-8AD4-4D58-BE3A-CD5EFE1E0621}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Finite.Metrics.Prometheus.Core", "src\Providers\Prometheus\Core\Finite.Metrics.Prometheus.Core.csproj", "{A4F1FDE6-C192-4F7D-B848-39E462783AAA}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Finite.Metrics.Prometheus.AspNetCore", "src\Providers\Prometheus\AspNetCore\Finite.Metrics.Prometheus.AspNetCore.csproj", "{EADC0DC7-668B-4F94-9304-572B64D3FE67}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Finite.Metrics.Prometheus.HostedService", "src\Providers\Prometheus\HostedService\Finite.Metrics.Prometheus.HostedService.csproj", "{693B8847-B557-4B0D-BDF5-238C1DDF14AE}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -122,6 +130,42 @@ Global
 		{8C2BA2A6-9D4A-432D-B8B1-B07E0E01FB2C}.Release|x64.Build.0 = Release|Any CPU
 		{8C2BA2A6-9D4A-432D-B8B1-B07E0E01FB2C}.Release|x86.ActiveCfg = Release|Any CPU
 		{8C2BA2A6-9D4A-432D-B8B1-B07E0E01FB2C}.Release|x86.Build.0 = Release|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Debug|x64.Build.0 = Debug|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Debug|x86.Build.0 = Debug|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Release|x64.ActiveCfg = Release|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Release|x64.Build.0 = Release|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Release|x86.ActiveCfg = Release|Any CPU
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA}.Release|x86.Build.0 = Release|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Debug|x64.Build.0 = Debug|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Debug|x86.Build.0 = Debug|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Release|Any CPU.Build.0 = Release|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Release|x64.ActiveCfg = Release|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Release|x64.Build.0 = Release|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Release|x86.ActiveCfg = Release|Any CPU
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67}.Release|x86.Build.0 = Release|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Debug|x64.Build.0 = Debug|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Debug|x86.Build.0 = Debug|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Release|Any CPU.Build.0 = Release|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Release|x64.ActiveCfg = Release|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Release|x64.Build.0 = Release|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Release|x86.ActiveCfg = Release|Any CPU
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{9E815B92-5565-46FA-A666-18BC0D5333DA} = {7C493A69-008A-4F4B-9AC1-23A64682C4AB}
@@ -133,5 +177,9 @@ Global
 		{4AD95898-6A60-4B74-976A-80DD4BFCAFC5} = {62C62A44-4FCE-4B47-96CE-C9282E374813}
 		{310165FD-B3CA-49FD-929D-9E8BABAF116B} = {62C62A44-4FCE-4B47-96CE-C9282E374813}
 		{8C2BA2A6-9D4A-432D-B8B1-B07E0E01FB2C} = {310165FD-B3CA-49FD-929D-9E8BABAF116B}
+		{EB50151D-8AD4-4D58-BE3A-CD5EFE1E0621} = {13420B5B-28D6-40FF-B378-82E6FB742AB4}
+		{A4F1FDE6-C192-4F7D-B848-39E462783AAA} = {EB50151D-8AD4-4D58-BE3A-CD5EFE1E0621}
+		{EADC0DC7-668B-4F94-9304-572B64D3FE67} = {EB50151D-8AD4-4D58-BE3A-CD5EFE1E0621}
+		{693B8847-B557-4B0D-BDF5-238C1DDF14AE} = {EB50151D-8AD4-4D58-BE3A-CD5EFE1E0621}
 	EndGlobalSection
 EndGlobal

src/Configuration/Finite.Metrics.Configuration.csproj

@@ -11,6 +11,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Configuration" />
     <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" />
   </ItemGroup>
 

src/Core/MetricFactory.cs

@@ -38,10 +38,13 @@ public MetricFactory(IEnumerable<IMetricProvider> providers)
         public static IMetricFactory Create(Action<IMetricsBuilder> configure)
         {
             var collection = new ServiceCollection();
-            _ = collection.AddMetrics(configure);
+            var builder = collection.AddMetrics();
+
+            configure(builder);
+
             var provider = collection.BuildServiceProvider();
 
-            var factory = provider.GetService<IMetricFactory>();
+            var factory = provider.GetRequiredService<IMetricFactory>();
 
             return new DisposingMetricsFactory(factory, provider);
         }

src/Core/MetricsServiceCollectionExtensions.cs

@@ -21,28 +21,8 @@ public static class MetricsServiceCollectionExtensions
         /// The <see cref="IServiceCollection"/> so that additional calls can
         /// be chained.
         /// </returns>
-        public static IServiceCollection AddMetrics(
+        public static IMetricsBuilder AddMetrics(
             this IServiceCollection services)
-            => AddMetrics(services, builder => { });
-
-
-        /// <summary>
-        /// Adds metrics services to the specified
-        /// <see cref="IServiceCollection"/>.
-        /// </summary>
-        /// <param name="services">
-        /// The <see cref="IServiceCollection"/> to add services to.
-        /// </param>
-        /// <param name="configure">
-        /// The <see cref="IMetricsBuilder"/> configuration delegate.
-        /// </param>
-        /// <returns>
-        /// The <see cref="IServiceCollection"/> so that additional calls can
-        /// be chained.
-        /// </returns>
-        public static IServiceCollection AddMetrics(
-            this IServiceCollection services,
-            Action<IMetricsBuilder> configure)
         {
             if (services is null)
                 throw new ArgumentNullException(nameof(services));
@@ -51,8 +31,7 @@ public static IServiceCollection AddMetrics(
                 .Singleton<IMetricFactory, MetricFactory>());
             services.TryAdd(ServiceDescriptor.Singleton<IMetric, Metric>());
 
-            configure(new MetricsBuilder(services));
-            return services;
+            return new MetricsBuilder(services);
         }
     }
 }

src/Providers/Prometheus/AspNetCore/Finite.Metrics.Prometheus.AspNetCore.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0</TargetFramework>
+
+    <Description>ASP.NET Prometheus metrics provider implementation for Finite.Metrics</Description>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../Core/Finite.Metrics.Prometheus.Core.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <FrameworkReference Include="Microsoft.AspNetCore.App" />
+  </ItemGroup>
+
+</Project>

src/Providers/Prometheus/AspNetCore/MetricsBuilderAspNetCorePrometheusExtensions.cs

@@ -0,0 +1,36 @@
+using Finite.Metrics.Prometheus.AspNetCore;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Finite.Metrics
+{
+    /// <summary>
+    /// Prometheus extensions for <see cref="IMetricsBuilder"/>.
+    /// </summary>
+    public static class MetricsBuilderAspNetCorePrometheusExtensions
+    {
+        /// <summary>
+        /// Adds Prometheus services to the specified
+        /// <see cref="IMetricsBuilder"/>.
+        /// </summary>
+        /// <param name="builder">
+        /// The <see cref="IMetricsBuilder"/> to add services to.
+        /// </param>
+        /// <returns>
+        /// The <paramref name="builder"/>, to allow for chaining.
+        /// </returns>
+        /// <remarks>
+        /// Remember to call <see cref="PrometheusApplicationBuilderExtensions.UsePrometheus(IApplicationBuilder)"/>
+        /// to add the ASP.NET middleware to the request pipeline.
+        /// </remarks>
+        public static IMetricsBuilder AddPrometheus(
+            this IMetricsBuilder builder)
+        {
+            _ = builder.AddPrometheusCore();
+
+            _ = builder.Services.AddTransient<PrometheusMetricsMiddleware>();
+
+            return builder;
+        }
+    }
+}

src/Providers/Prometheus/AspNetCore/PrometheusApplicationBuilderExtensions.cs

@@ -0,0 +1,32 @@
+using System;
+using Finite.Metrics.Prometheus.AspNetCore;
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    /// <summary>
+    /// Extension methods for Finite.Metrics.Prometheus.
+    /// </summary>
+    public static class PrometheusApplicationBuilderExtensions
+    {
+        /// <summary>
+        /// Enables Prometheus metrics endpoints for the current request path.
+        /// </summary>
+        /// <param name="app">
+        /// The <see cref="IApplicationBuilder"/> to enable Prometheus metrics
+        /// endpoints for.
+        /// </param>
+        /// <returns>
+        /// The <see cref="IApplicationBuilder"/> passed in
+        /// <paramref name="app"/>, for chaining.
+        /// </returns>
+        public static IApplicationBuilder UsePrometheus(
+            this IApplicationBuilder app)
+        {
+            if (app is null)
+                throw new ArgumentNullException(nameof(app));
+
+            return app.UseMiddleware<PrometheusMetricsMiddleware>();
+        }
+    }
+}

src/Providers/Prometheus/AspNetCore/PrometheusMetricsMiddleware.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace Finite.Metrics.Prometheus.AspNetCore
+{
+    internal class PrometheusMetricsMiddleware : IMiddleware
+    {
+        private readonly ILogger<PrometheusMetricsMiddleware> _logger;
+        private readonly IPrometheusMetricStore _metricStore;
+        private readonly PrometheusOptions _options;
+
+        public PrometheusMetricsMiddleware(
+            ILogger<PrometheusMetricsMiddleware> logger,
+            IPrometheusMetricStore metricStore,
+            IOptions<PrometheusOptions> options)
+        {
+            _logger = logger
+                ?? throw new ArgumentNullException(nameof(logger));
+            _metricStore = metricStore
+                ?? throw new ArgumentNullException(nameof(metricStore));
+            _options = options?.Value
+                ?? throw new ArgumentNullException(nameof(options));
+        }
+
+        public Task InvokeAsync(HttpContext context, RequestDelegate next)
+        {
+            if (context.GetEndpoint() != null)
+            {
+                _logger.LogDebug(
+                    "Skipped Prometheus metrics as an endpoint was matched");
+            }
+            else if (!HttpMethods.IsGet(context.Request.Method)
+                && !HttpMethods.IsHead(context.Request.Method))
+            {
+                _logger.LogDebug(
+                    "Skipped Prometheus metrics as {Method} is not supported",
+                        context.Request.Method);
+            }
+            else if (!context.Request.Path.StartsWithSegments(
+                _options.RequestPath))
+            {
+                _logger.LogDebug(
+                    "Skipped Prometheus metrics as {Path} was not matched",
+                        context.Request.Path);
+            }
+            else
+            {
+                return WriteMetricsAsync(context);
+            }
+
+            return next(context);
+        }
+
+        private async Task WriteMetricsAsync(HttpContext context)
+        {
+            foreach (var metric in _metricStore.GetMetrics())
+            {
+                await context.Response.WriteAsync(metric,
+                    context.RequestAborted);
+                await context.Response.WriteAsync("\n",
+                    context.RequestAborted);
+            }
+        }
+    }
+}

src/Providers/Prometheus/AspNetCore/PrometheusOptions.cs

@@ -0,0 +1,16 @@
+using Microsoft.AspNetCore.Http;
+
+namespace Finite.Metrics.Prometheus
+{
+    /// <summary>
+    /// Options to Prometheus metrics middleware.
+    /// </summary>
+    public class PrometheusOptions
+    {
+        /// <summary>
+        /// Gets or sets the request path that maps to the Prometheus metrics
+        /// endpoint.
+        /// </summary>
+        public PathString RequestPath { get; set; }
+    }
+}

src/Providers/Prometheus/Core/Finite.Metrics.Prometheus.Core.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0</TargetFramework>
+
+    <Description>Prometheus metrics provider core for Finite.Metrics</Description>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../../../Configuration/Finite.Metrics.Configuration.csproj" />
+    <ProjectReference Include="../../../Core/Finite.Metrics.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Hosting" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
+    <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" />
+  </ItemGroup>
+
+</Project>

src/Providers/Prometheus/Core/IPrometheusMetricStore.cs

@@ -0,0 +1,36 @@
+using System.Collections.Generic;
+
+namespace Finite.Metrics.Prometheus
+{
+    /// <summary>
+    /// Represents a store of prometheus metrics.
+    /// </summary>
+    public interface IPrometheusMetricStore
+    {
+        /// <summary>
+        /// Stores a metric for later scraping.
+        /// </summary>
+        /// <param name="name">
+        /// The name of the metric.
+        /// </param>
+        /// <param name="tags">
+        /// The tags to store with this metric.
+        /// </param>
+        /// <param name="value">
+        /// The value to store for this metric.
+        /// </param>
+        /// <typeparam name="T">
+        /// The type of <paramref name="value"/>.
+        /// </typeparam>
+        void Store<T>(string name, TagValues? tags, T value);
+
+        /// <summary>
+        /// Gets all of the metrics converted to Prometheus' text-based
+        /// exposition format.
+        /// </summary>
+        /// <returns>
+        /// An enumerable containing the ordered, unique metrics.
+        /// </returns>
+        IEnumerable<string> GetMetrics();
+    }
+}