HeaderPropagation: add support for hosted services

src/Middleware/HeaderPropagation/ref/Microsoft.AspNetCore.HeaderPropagation.netcoreapp3.0.cs

@@ -14,10 +14,10 @@ namespace Microsoft.AspNetCore.HeaderPropagation
     public readonly partial struct HeaderPropagationContext
     {
         private readonly object _dummy;
-        public HeaderPropagationContext(Microsoft.AspNetCore.Http.HttpContext httpContext, string headerName, Microsoft.Extensions.Primitives.StringValues headerValue) { throw null; }
+        public HeaderPropagationContext(System.Collections.Generic.IDictionary<string, Microsoft.Extensions.Primitives.StringValues> requestHeaders, string headerName, Microsoft.Extensions.Primitives.StringValues headerValue) { throw null; }
         public string HeaderName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
         public Microsoft.Extensions.Primitives.StringValues HeaderValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-        public Microsoft.AspNetCore.Http.HttpContext HttpContext { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        public System.Collections.Generic.IDictionary<string, Microsoft.Extensions.Primitives.StringValues> RequestHeaders { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
     }
     public partial class HeaderPropagationEntry
     {
@@ -58,19 +58,28 @@ public HeaderPropagationMessageHandlerOptions() { }
     }
     public partial class HeaderPropagationMiddleware
     {
-        public HeaderPropagationMiddleware(Microsoft.AspNetCore.Http.RequestDelegate next, Microsoft.Extensions.Options.IOptions<Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationOptions> options, Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationValues values) { }
+        public HeaderPropagationMiddleware(Microsoft.AspNetCore.Http.RequestDelegate next, Microsoft.AspNetCore.HeaderPropagation.IHeaderPropagationProcessor processor) { }
         public System.Threading.Tasks.Task Invoke(Microsoft.AspNetCore.Http.HttpContext context) { throw null; }
     }
     public partial class HeaderPropagationOptions
     {
         public HeaderPropagationOptions() { }
         public Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationEntryCollection Headers { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
     }
+    public partial class HeaderPropagationProcessor : Microsoft.AspNetCore.HeaderPropagation.IHeaderPropagationProcessor
+    {
+        public HeaderPropagationProcessor(Microsoft.Extensions.Options.IOptions<Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationOptions> options, Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationValues values) { }
+        public void ProcessRequest(System.Collections.Generic.IDictionary<string, Microsoft.Extensions.Primitives.StringValues> requestHeaders) { }
+    }
     public partial class HeaderPropagationValues
     {
         public HeaderPropagationValues() { }
         public System.Collections.Generic.IDictionary<string, Microsoft.Extensions.Primitives.StringValues> Headers { get { throw null; } set { } }
     }
+    public partial interface IHeaderPropagationProcessor
+    {
+        void ProcessRequest(System.Collections.Generic.IDictionary<string, Microsoft.Extensions.Primitives.StringValues> requestHeaders);
+    }
 }
 namespace Microsoft.Extensions.DependencyInjection
 {

src/Middleware/HeaderPropagation/samples/HeaderPropagationSample/SampleHostedService.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.HeaderPropagation;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Primitives;
+
+namespace HeaderPropagationSample
+{
+    public class SampleHostedService : IHostedService
+    {
+        private readonly IHttpClientFactory _httpClientFactory;
+        private readonly HeaderPropagationProcessor _headerPropagationProcessor;
+        private readonly ILogger _logger;
+
+        public SampleHostedService(IHttpClientFactory httpClientFactory, HeaderPropagationProcessor headerPropagationProcessor, ILogger<SampleHostedService> logger)
+        {
+            _httpClientFactory = httpClientFactory ?? throw new ArgumentNullException(nameof(httpClientFactory));
+            _headerPropagationProcessor = headerPropagationProcessor ?? throw new ArgumentNullException(nameof(headerPropagationProcessor));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        }
+
+        public Task StartAsync(CancellationToken cancellationToken)
+        {
+            return DoWorkAsync();
+        }
+
+        private async Task DoWorkAsync()
+        {
+            _logger.LogInformation("Background Service is working.");
+
+            _headerPropagationProcessor.ProcessRequest(new Dictionary<string, StringValues>());
+            var client = _httpClientFactory.CreateClient("test");
+            var result = await client.GetAsync("http://localhost:62013/forwarded");
+
+            _logger.LogInformation("Background Service:\n{result}", result);
+        }
+
+        public Task StopAsync(CancellationToken cancellationToken)
+        {
+            return Task.CompletedTask;
+        }
+    }
+}

src/Middleware/HeaderPropagation/samples/HeaderPropagationSample/Startup.cs

@@ -49,6 +49,8 @@ public void ConfigureServices(IServiceCollection services)
             services
                 .AddHttpClient("another")
                 .AddHeaderPropagation(options => options.Headers.Add("X-BetaFeatures", "X-Experiments"));
+
+            services.AddHostedService<SampleHostedService>();
         }
 
         public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHttpClientFactory clientFactory)

src/Middleware/HeaderPropagation/src/DependencyInjection/HeaderPropagationServiceCollectionExtensions.cs

@@ -23,6 +23,7 @@ public static IServiceCollection AddHeaderPropagation(this IServiceCollection se
             }
 
             services.TryAddSingleton<HeaderPropagationValues>();
+            services.TryAddSingleton<IHeaderPropagationProcessor, HeaderPropagationProcessor>();
 
             return services;
         }

src/Middleware/HeaderPropagation/src/HeaderPropagationContext.cs

@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using Microsoft.AspNetCore.Http;
+using System.Collections.Generic;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.HeaderPropagation
@@ -14,32 +14,22 @@ public readonly struct HeaderPropagationContext
     {
         /// <summary>
         /// Initializes a new instance of <see cref="HeaderPropagationContext"/> with the provided
-        /// <paramref name="httpContext"/>, <paramref name="headerName"/> and <paramref name="headerValue"/>.
+        /// <paramref name="requestHeaders"/>, <paramref name="headerName"/> and <paramref name="headerValue"/>.
         /// </summary>
-        /// <param name="httpContext">The <see cref="Http.HttpContext"/> associated with the current request.</param>
+        /// <param name="requestHeaders">The headers associated with the current request.</param>
         /// <param name="headerName">The header name.</param>
         /// <param name="headerValue">The header value present in the current request.</param>
-        public HeaderPropagationContext(HttpContext httpContext, string headerName, StringValues headerValue)
+        public HeaderPropagationContext(IDictionary<string, StringValues> requestHeaders, string headerName, StringValues headerValue)
         {
-            if (httpContext == null)
-            {
-                throw new ArgumentNullException(nameof(httpContext));
-            }
-
-            if (headerName == null)
-            {
-                throw new ArgumentNullException(nameof(headerName));
-            }
-
-            HttpContext = httpContext;
-            HeaderName = headerName;
+            RequestHeaders = requestHeaders ?? throw new ArgumentNullException(nameof(requestHeaders));
+            HeaderName = headerName ?? throw new ArgumentNullException(nameof(headerName));
             HeaderValue = headerValue;
         }
 
         /// <summary>
-        /// Gets the <see cref="Http.HttpContext"/> associated with the current request.
+        /// Gets the headers associated with the current request.
         /// </summary>
-        public HttpContext HttpContext { get; }
+        public IDictionary<string, StringValues> RequestHeaders { get; }
 
         /// <summary>
         /// Gets the header name.

src/Middleware/HeaderPropagation/src/HeaderPropagationMessageHandler.cs

@@ -15,8 +15,8 @@ namespace Microsoft.AspNetCore.HeaderPropagation
     /// </summary>
     public class HeaderPropagationMessageHandler : DelegatingHandler
     {
-        private readonly HeaderPropagationValues _values;
         private readonly HeaderPropagationMessageHandlerOptions _options;
+        private readonly HeaderPropagationValues _values;
 
         /// <summary>
         /// Creates a new instance of the <see cref="HeaderPropagationMessageHandler"/>.
@@ -47,9 +47,10 @@ protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage reques
             if (captured == null)
             {
                 var message =
-                    $"The {nameof(HeaderPropagationValues)}.{nameof(HeaderPropagationValues.Headers)} property has not been " +
-                    $"initialized. Register the header propagation middleware by adding 'app.{nameof(HeaderPropagationApplicationBuilderExtensions.UseHeaderPropagation)}() " +
-                    $"in the 'Configure(...)' method.";
+                    $"The {nameof(HeaderPropagationValues)}.{nameof(HeaderPropagationValues.Headers)} property has not been initialized. " +
+                    $"If using this {nameof(HttpClient)} as part of an http request, register the header propagation middleware by adding " +
+                    $"'app.{nameof(HeaderPropagationApplicationBuilderExtensions.UseHeaderPropagation)}() in the 'Configure(...)' method. " +
+                    $"Otherwise, use {nameof(HeaderPropagationProcessor)}.{nameof(HeaderPropagationProcessor.ProcessRequest)}() before using the {nameof(HttpClient)}.";
                 throw new InvalidOperationException(message);
             }
 

src/Middleware/HeaderPropagation/src/HeaderPropagationMiddleware.cs

@@ -2,12 +2,9 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Net.Http;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
-using Microsoft.Extensions.Options;
-using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.HeaderPropagation
 {
@@ -17,61 +14,19 @@ namespace Microsoft.AspNetCore.HeaderPropagation
     public class HeaderPropagationMiddleware
     {
         private readonly RequestDelegate _next;
-        private readonly HeaderPropagationOptions _options;
-        private readonly HeaderPropagationValues _values;
+        private readonly IHeaderPropagationProcessor _processor;
 
-        public HeaderPropagationMiddleware(RequestDelegate next, IOptions<HeaderPropagationOptions> options, HeaderPropagationValues values)
+        public HeaderPropagationMiddleware(RequestDelegate next, IHeaderPropagationProcessor processor)
         {
             _next = next ?? throw new ArgumentNullException(nameof(next));
-
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
-            _options = options.Value;
-
-            _values = values ?? throw new ArgumentNullException(nameof(values));
+            _processor = processor ?? throw new ArgumentNullException(nameof(processor));
         }
 
         public Task Invoke(HttpContext context)
         {
-            // We need to intialize the headers because the message handler will use this to detect misconfiguration.
-            var headers = _values.Headers ??= new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
-
-            // Perf: avoid foreach since we don't define a struct enumerator.
-            var entries = _options.Headers;
-            for (var i = 0; i < entries.Count; i++)
-            {
-                var entry = entries[i];
-
-                // We intentionally process entries in order, and allow earlier entries to
-                // take precedence over later entries when they have the same output name.
-                if (!headers.ContainsKey(entry.CapturedHeaderName))
-                {
-                    var value = GetValue(context, entry);
-                    if (!StringValues.IsNullOrEmpty(value))
-                    {
-                        headers.Add(entry.CapturedHeaderName, value);
-                    }
-                }
-            }
+            _processor.ProcessRequest(context.Request.Headers);
 
             return _next.Invoke(context);
         }
-
-        private static StringValues GetValue(HttpContext context, HeaderPropagationEntry entry)
-        {
-            context.Request.Headers.TryGetValue(entry.InboundHeaderName, out var value);
-            if (entry.ValueFilter != null)
-            {
-                var filtered = entry.ValueFilter(new HeaderPropagationContext(context, entry.InboundHeaderName, value));
-                if (!StringValues.IsNullOrEmpty(filtered))
-                {
-                    value = filtered;
-                }
-            }
-
-            return value;
-        }
     }
 }

src/Middleware/HeaderPropagation/src/HeaderPropagationProcessor.cs

@@ -0,0 +1,79 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using Microsoft.Extensions.Options;
+using Microsoft.Extensions.Primitives;
+
+namespace Microsoft.AspNetCore.HeaderPropagation
+{
+    public class HeaderPropagationProcessor : IHeaderPropagationProcessor
+    {
+        private readonly HeaderPropagationOptions _options;
+        private readonly HeaderPropagationValues _values;
+
+        public HeaderPropagationProcessor(IOptions<HeaderPropagationOptions> options, HeaderPropagationValues values)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+            _options = options.Value;
+
+            _values = values;
+        }
+
+        public void ProcessRequest(IDictionary<string, StringValues> requestHeaders)
+        {
+            if (requestHeaders == null)
+            {
+                throw new ArgumentNullException(nameof(requestHeaders));
+            }
+
+            if (_values.Headers != null)
+            {
+                var message =
+                    $"The {nameof(HeaderPropagationValues)}.{nameof(HeaderPropagationValues.Headers)} was already initialized. "
+                    + $"Each invocation of {nameof(HeaderPropagationProcessor)}.{nameof(HeaderPropagationProcessor.ProcessRequest)}() must be in a separate async context.";
+                throw new InvalidOperationException(message);
+            }
+
+            // We need to intialize the headers because the message handler will use this to detect misconfiguration.
+            var headers = _values.Headers = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase);
+
+            // Perf: avoid foreach since we don't define a struct enumerator.
+            var entries = _options.Headers;
+            for (var i = 0; i < entries.Count; i++)
+            {
+                var entry = entries[i];
+
+                // We intentionally process entries in order, and allow earlier entries to
+                // take precedence over later entries when they have the same output name.
+                if (!headers.ContainsKey(entry.CapturedHeaderName))
+                {
+                    var value = GetValue(requestHeaders, entry);
+                    if (!StringValues.IsNullOrEmpty(value))
+                    {
+                        headers.Add(entry.CapturedHeaderName, value);
+                    }
+                }
+            }
+        }
+
+        private static StringValues GetValue(IDictionary<string, StringValues> requestHeaders, HeaderPropagationEntry entry)
+        {
+            requestHeaders.TryGetValue(entry.InboundHeaderName, out var value);
+            if (entry.ValueFilter != null)
+            {
+                var filtered = entry.ValueFilter(new HeaderPropagationContext(requestHeaders, entry.InboundHeaderName, value));
+                if (!StringValues.IsNullOrEmpty(filtered))
+                {
+                    value = filtered;
+                }
+            }
+
+            return value;
+        }
+    }
+}

src/Middleware/HeaderPropagation/src/IHeaderPropagationProcessor.cs

@@ -0,0 +1,10 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNetCore.HeaderPropagation
+{
+    public interface IHeaderPropagationProcessor
+    {
+        void ProcessRequest(System.Collections.Generic.IDictionary<string, Extensions.Primitives.StringValues> requestHeaders);
+    }
+}

src/Middleware/HeaderPropagation/test/HeaderPropagationIntegrationTest.cs

@@ -63,8 +63,9 @@ public async Task HeaderPropagation_WithoutMiddleware_Throws()
             Assert.Equal(HttpStatusCode.OK, response.StatusCode);
             Assert.IsType<InvalidOperationException>(captured);
             Assert.Equal(
-                "The HeaderPropagationValues.Headers property has not been initialized. Register the header propagation middleware " +
-                "by adding 'app.UseHeaderPropagation() in the 'Configure(...)' method.",
+                "The HeaderPropagationValues.Headers property has not been initialized. If using this HttpClient as part of an http request, " +
+                "register the header propagation middleware by adding 'app.UseHeaderPropagation() in the 'Configure(...)' method. " +
+                "Otherwise, use HeaderPropagationProcessor.ProcessRequest() before using the HttpClient.",
                 captured.Message);
         }