Consume original-resource

Author: javiercn

src/StaticAssets/src/Development/StaticAssetDevelopmentRuntimeHandler.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.Globalization;
 using System.IO.Compression;
 using System.IO.Pipelines;
@@ -22,51 +23,34 @@
 namespace Microsoft.AspNetCore.Builder;
 
 // Handles changes during development to support common scenarios where for example, a developer changes a file in the wwwroot folder.
-internal sealed partial class StaticAssetDevelopmentRuntimeHandler(List<StaticAssetDescriptor> descriptors)
+internal sealed partial class StaticAssetDevelopmentRuntimeHandler
 {
-    private readonly Dictionary<(string Route, string ETag), StaticAssetDescriptor> _descriptorsMap;
+    internal const string ReloadStaticAssetsAtRuntimeKey = "ReloadStaticAssetsAtRuntime";
 
-    public StaticAssetDevelopmentRuntimeHandler(List<StaticAssetDescriptor> descriptors)
-    {
-        _descriptorsMap = new();
-        for (var i = 0; i < descriptors.Count; i++)
-        {
-            var descriptor = descriptors[i];
-            var etag = GetDescriptorETagResponseHeader(descriptor);
-            if (!_descriptorsMap.TryGetValue((descriptor.Route, etag), out var existing))
-            {
-                _descriptorsMap[(descriptor.Route, etag)] = descriptor;
-            }
-        }
-    }
+    private readonly Dictionary<(string Route, string ETag), StaticAssetDescriptor> _descriptorsMap = [];
 
-    private static string? GetDescriptorETagResponseHeader(StaticAssetDescriptor descriptor)
+    public StaticAssetDevelopmentRuntimeHandler(List<StaticAssetDescriptor> descriptors)
     {
-        for (var i = 0; i < descriptor.ResponseHeaders.Count; i++)
-        {
-            var header = descriptor.ResponseHeaders[i];
-            if (string.Equals(header.Name, HeaderNames.ETag, StringComparison.OrdinalIgnoreCase))
-            {
-                return header.Value;
-            }
-        }
-
-        return null;
+        CreateDescriptorMap(descriptors);
     }
 
-    internal const string ReloadStaticAssetsAtRuntimeKey = "ReloadStaticAssetsAtRuntime";
-
     public void AttachRuntimePatching(EndpointBuilder builder)
     {
         var original = builder.RequestDelegate!;
         var asset = builder.Metadata.OfType<StaticAssetDescriptor>().Single();
         if (asset.HasContentEncoding())
         {
             var originalETag = GetDescriptorOriginalResourceProperty(asset);
-            if (originalETag is not null && _descriptorsMap.TryGetValue((descriptors.Route, originalETag), out var originalAsset))
+            StaticAssetDescriptor? originalAsset = null;
+            if (originalETag is not null && _descriptorsMap.TryGetValue((asset.Route, originalETag), out originalAsset))
             {
                 asset = originalAsset;
             }
+            else
+            {
+                Debug.Assert(originalETag != null, $"The static asset descriptor {asset.Route} - {asset.AssetPath} does not have an original-resource property.");
+                Debug.Assert(originalAsset != null, $"The static asset descriptor {asset.Route} - {asset.AssetPath} has an original-resource property that does not match any known static asset descriptor.");
+            }
         }
 
         builder.RequestDelegate = async context =>
@@ -102,6 +86,43 @@ public void AttachRuntimePatching(EndpointBuilder builder)
         return null;
     }
 
+    private static string? GetDescriptorETagResponseHeader(StaticAssetDescriptor descriptor)
+    {
+        for (var i = 0; i < descriptor.ResponseHeaders.Count; i++)
+        {
+            var header = descriptor.ResponseHeaders[i];
+            if (string.Equals(header.Name, HeaderNames.ETag, StringComparison.OrdinalIgnoreCase))
+            {
+                return header.Value;
+            }
+        }
+
+        return null;
+    }
+
+    private void CreateDescriptorMap(List<StaticAssetDescriptor> descriptors)
+    {
+        for (var i = 0; i < descriptors.Count; i++)
+        {
+            var descriptor = descriptors[i];
+            if (descriptor.HasContentEncoding())
+            {
+                continue;
+            }
+            var etag = GetDescriptorETagResponseHeader(descriptor);
+            if (etag != null && !_descriptorsMap.ContainsKey((descriptor.Route, etag)))
+            {
+                _descriptorsMap[(descriptor.Route, etag)] = descriptor;
+            }
+            else
+            {
+                Debug.Assert(etag != null, $"The static asset descriptor {descriptor.Route} - {descriptor.AssetPath} does not have an ETag response header.");
+                Debug.Assert(_descriptorsMap.ContainsKey((descriptor.Route, etag)),
+                    $"The static asset descriptor {descriptor.Route} - {descriptor.AssetPath} has an ETag response header that is already registered in the map. This should not happen, as the ETag should be unique for each static asset.");
+            }
+        }
+    }
+
     internal static string GetETag(IFileInfo fileInfo)
     {
         using var stream = fileInfo.CreateReadStream();