WIP

src/ReverseProxy/Service/Proxy/HttpProxy.cs

@@ -101,7 +101,7 @@ public async Task ProxyAsync(
                 // Mitigate https://github.com/microsoft/reverse-proxy/issues/255, IIS considers all requests upgradeable.
                 && string.Equals("WebSocket", context.Request.Headers[HeaderNames.Upgrade], StringComparison.OrdinalIgnoreCase);
 
-            var destinationRequest = CreateRequestMessage(context, destinationPrefix, isUpgradeRequest, proxyOptions.Transforms.RequestTransforms);
+            var destinationRequest = CreateRequestMessage(context, destinationPrefix, isUpgradeRequest, proxyOptions);
 
             var isClientHttp2 = ProtocolHelper.IsHttp2(context.Request.Protocol);
 
@@ -231,7 +231,7 @@ public async Task ProxyAsync(
             }
         }
 
-        private HttpRequestMessage CreateRequestMessage(HttpContext context, string destinationAddress, bool isUpgradeRequest, IReadOnlyList<RequestParametersTransform> transforms)
+        private HttpRequestMessage CreateRequestMessage(HttpContext context, string destinationAddress, bool isUpgradeRequest, RequestProxyOptions proxyOptions)
         {
             // "http://a".Length = 8
             if (destinationAddress == null || destinationAddress.Length < 8)
@@ -240,21 +240,40 @@ private HttpRequestMessage CreateRequestMessage(HttpContext context, string dest
             }
 
             // Default to HTTP/1.1 for proxying upgradeable requests. This is already the default as of .NET Core 3.1
-            // Otherwise request HTTP/2 and let HttpClient fallback to HTTP/1.1 if it cannot establish HTTP/2 with the target.
+            // Otherwise request what's set in proxyOptions (e.g. default HTTP/2) and let HttpClient negotiate the protocol
+            // based on VersionPolicy (for .NET 5 and higher). For example, downgrading to HTTP/1.1 if it cannot establish HTTP/2 with the target.
             // This is done without extra round-trips thanks to ALPN. We can detect a downgrade after calling HttpClient.SendAsync
             // (see Step 3 below). TBD how this will change when HTTP/3 is supported.
-            var httpVersion = isUpgradeRequest ? ProtocolHelper.Http11Version : ProtocolHelper.Http2Version;
+            var httpVersion = isUpgradeRequest ? ProtocolHelper.Http11Version : proxyOptions.HttpVersion;
+#if NET5_0
+            var httpVersionPolicy = isUpgradeRequest ? HttpVersionPolicy.RequestVersionOrLower : proxyOptions.VersionPolicy;
+#elif NETCOREAPP3_1
+            // HttpVersionPolicy didn't exist in .NET Core 3.1 and there's no equivalent.
+#else
+#error A target framework was added to the project and needs to be added to this condition.
+#endif
 
             // TODO Perf: We could probably avoid splitting this and just append the final path and query
             UriHelper.FromAbsolute(destinationAddress, out var destinationScheme, out var destinationHost, out var destinationPathBase, out _, out _); // Query and Fragment are not supported here.
 
             var request = context.Request;
+            var transforms = proxyOptions.Transforms.RequestTransforms;
             if (transforms.Count == 0)
             {
                 var url = UriHelper.BuildAbsolute(destinationScheme, destinationHost, destinationPathBase, request.Path, request.QueryString);
                 Log.Proxying(_logger, url);
                 var uri = new Uri(url, UriKind.Absolute);
-                return new HttpRequestMessage(HttpUtilities.GetHttpMethod(context.Request.Method), uri) { Version = httpVersion };
+                return new HttpRequestMessage(HttpUtilities.GetHttpMethod(context.Request.Method), uri)
+                {
+                    Version = httpVersion,
+#if NET5_0
+                    VersionPolicy = httpVersionPolicy,
+#elif NETCOREAPP3_1
+                    // HttpVersionPolicy didn't exist in .NET Core 3.1 and there's no equivalent.
+#else
+#error A target framework was added to the project and needs to be added to this condition.
+#endif
+                };
             }
 
             var transformContext = new RequestParametersTransformContext()
@@ -264,6 +283,14 @@ private HttpRequestMessage CreateRequestMessage(HttpContext context, string dest
                 Method = request.Method,
                 Path = request.Path,
                 Query = new QueryTransformContext(request),
+#if NET5_0
+                VersionPolicy = httpVersionPolicy,
+#elif NETCOREAPP3_1
+                // HttpVersionPolicy didn't exist in .NET Core 3.1 and there's no equivalent.
+#else
+#error A target framework was added to the project and needs to be added to this condition.
+#endif
+
             };
             foreach (var transform in transforms)
             {
@@ -273,7 +300,17 @@ private HttpRequestMessage CreateRequestMessage(HttpContext context, string dest
             var targetUrl = UriHelper.BuildAbsolute(destinationScheme, destinationHost, destinationPathBase, transformContext.Path, transformContext.Query.QueryString);
             Log.Proxying(_logger, targetUrl);
             var targetUri = new Uri(targetUrl, UriKind.Absolute);
-            return new HttpRequestMessage(HttpUtilities.GetHttpMethod(transformContext.Method), targetUri) { Version = transformContext.Version };
+            return new HttpRequestMessage(HttpUtilities.GetHttpMethod(transformContext.Method), targetUri)
+            {
+                Version = transformContext.Version,
+#if NET5_0
+                VersionPolicy = transformContext.VersionPolicy,
+#elif NETCOREAPP3_1
+                // HttpVersionPolicy didn't exist in .NET Core 3.1 and there's no equivalent.
+#else
+#error A target framework was added to the project and needs to be added to this condition.
+#endif
+            };
         }
 
         private StreamCopyHttpContent SetupRequestBodyCopy(HttpRequest request, HttpRequestMessage destinationRequest,

src/ReverseProxy/Service/Proxy/RequestProxyOptions.cs

@@ -2,6 +2,8 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Net;
+using System.Net.Http;
 using Microsoft.ReverseProxy.Service.RuntimeModel.Transforms;
 
 namespace Microsoft.ReverseProxy.Service.Proxy
@@ -22,9 +24,23 @@ public class RequestProxyOptions
         /// </summary>
         public TimeSpan RequestTimeout { get; set; } = TimeSpan.FromSeconds(100);
 
-        // Future:
-        // ResponseBodyTimeout - The time allowed to receive the full response body. Default to infinite. Not applied to Upgraded requests or gRPC streams.
-        // HttpVersion - Default to HTTP/2?
-        // HttpVersionPolicy - Default to OrLower?
+        /// <summary>
+        /// Preferred version of the outgoing request.
+        /// The default is HTTP/2.0.
+        /// </summary>
+        public Version HttpVersion { get; set; } = System.Net.HttpVersion.Version20;
+
+#if NET5_0
+        /// <summary>
+        /// The policy applied to version selection, e.g. whether to prefer downgrades, upgrades or request an exact version.
+        /// The default is `RequestVersionOrLower`.
+        /// </summary>
+        public HttpVersionPolicy VersionPolicy { get; set; } = HttpVersionPolicy.RequestVersionOrLower;
+#elif NETCOREAPP3_1
+        // HttpVersionPolicy didn't exist in .NET Core 3.1 and there's no equivalent.
+#else
+#error A target framework was added to the project and needs to be added to this condition.
+#endif
     }
 }
+

src/ReverseProxy/Service/RuntimeModel/Transforms/RequestParametersTransformContext.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Net.Http;
 using Microsoft.AspNetCore.Http;
 
 namespace Microsoft.ReverseProxy.Service.RuntimeModel.Transforms
@@ -21,6 +22,17 @@ public class RequestParametersTransformContext
         /// </summary>
         public Version Version { get; set; }
 
+#if NET5_0
+        /// <summary>
+        /// The HTTP version policy to use for the proxy request.
+        /// </summary>
+        public HttpVersionPolicy VersionPolicy { get; set; }
+#elif NETCOREAPP3_1
+        // HttpVersionPolicy didn't exist in .NET Core 3.1 and there's no equivalent.
+#else
+#error A target framework was added to the project and needs to be added to this condition.
+#endif
+
         /// <summary>
         /// The HTTP method to use for the proxy request.
         /// </summary>