Handle application paths for remote calls

src/Microsoft.AspNetCore.SystemWebAdapters.CoreServices/RemoteAppClientExtensions.cs

@@ -3,6 +3,8 @@
 
 using System;
 using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.SystemWebAdapters;
 using Microsoft.Extensions.Options;
 
@@ -29,6 +31,7 @@ public static ISystemWebAdapterBuilder AddRemoteAppClient(this ISystemWebAdapter
         builder.Services.AddOptions<RemoteAppClientOptions>()
             .ValidateDataAnnotations();
 
+        builder.Services.AddTransient<VirtualDirectoryHandler>();
         builder.Services.AddHttpClient(RemoteConstants.HttpClientName)
             .ConfigurePrimaryHttpMessageHandler(sp =>
             {
@@ -42,6 +45,7 @@ public static ISystemWebAdapterBuilder AddRemoteAppClient(this ISystemWebAdapter
                 // Disable cookies in the HTTP client because the service will manage the cookie header directly
                 return new HttpClientHandler { UseCookies = false, AllowAutoRedirect = false };
             })
+            .AddHttpMessageHandler<VirtualDirectoryHandler>()
             .ConfigureHttpClient((sp, client) =>
             {
                 var options = sp.GetRequiredService<IOptions<RemoteAppClientOptions>>().Value;
@@ -73,6 +77,37 @@ public static ISystemWebAdapterRemoteClientAppBuilder Configure(this ISystemWebA
         return builder;
     }
 
+    /// <summary>
+    /// <see cref="HttpClient.BaseAddress"/> is set automatically, but if this is supposed to have a path, then that gets
+    /// lost. This handler will append that back if necessary.
+    /// </summary>
+    private class VirtualDirectoryHandler : DelegatingHandler
+    {
+        private readonly string? _path;
+
+        public VirtualDirectoryHandler(IOptions<RemoteAppClientOptions> options)
+        {
+            _path = options.Value.RemoteAppUrl.AbsolutePath;
+
+            if (_path == "/")
+            {
+                _path = null;
+            }
+        }
+
+        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            if (_path is not null && request.RequestUri is { } uri)
+            {
+                var builder = new UriBuilder(uri);
+                builder.Path = $"{_path}{builder.Path}";
+                request.RequestUri = builder.Uri;
+            }
+
+            return base.SendAsync(request, cancellationToken);
+        }
+    }
+
     private class Builder : ISystemWebAdapterRemoteClientAppBuilder
     {
         public Builder(IServiceCollection services)

src/Microsoft.AspNetCore.SystemWebAdapters.FrameworkServices/RemoteModule.cs

@@ -50,11 +50,14 @@ void IHttpModule.Dispose()
 
     void IHttpModule.Init(HttpApplication context)
     {
+        var appRelativePath = $"~{Path}";
+
         context.PostMapRequestHandler += (s, _) =>
         {
             var context = ((HttpApplication)s).Context;
 
-            if (!string.Equals(context.Request.Path, Path, StringComparison.Ordinal))
+            // Compare against the AppRelativeCurrentExecutionFilePath to account for potential virtual directories
+            if (!string.Equals(context.Request.AppRelativeCurrentExecutionFilePath, appRelativePath, StringComparison.Ordinal))
             {
                 return;
             }