[Static Web Assets] Remove weak ETag generation for compressed assets (#50291)

* We still emit the weak ETag since it is used during development to map compressed endpoints to uncompressed representations.
* We don't emit the weak ETag by default in the Release configuration, but we do so in Debug during build.
* AttachWeakETagToCompressedAssetsDuringDevelopment can be used to unconditionally configure this behavior.

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: javiercn <[email protected]>
Co-authored-by: Javier Calvarro Nelson <[email protected]>

Author: Copilot

src/StaticWebAssetsSdk/Targets/Microsoft.NET.Sdk.StaticWebAssets.Compression.targets

@@ -168,6 +168,9 @@ Copyright (c) .NET Foundation. All rights reserved.
     <CompressDiscoveredAssetsDuringBuild Condition="$(CompressDiscoveredAssetsDuringBuild) == ''">true</CompressDiscoveredAssetsDuringBuild>
     <!-- Support passing in a custom compression level to brotli and respect the old internal flag for blazor -->
     <BrotliCompressionLevel Condition="'$(_BlazorBrotliCompressionLevel)' != ''">$(_BlazorBrotliCompressionLevel)</BrotliCompressionLevel>
+
+    <!-- Attach weak ETag to compressed assets -->
+    <AttachWeakETagToCompressedAssetsDuringDevelopment Condition="'$(AttachWeakETagToCompressedAssetsDuringDevelopment)' == '' and '$(Configuration)' == 'Debug'">true</AttachWeakETagToCompressedAssetsDuringDevelopment>
   </PropertyGroup>
 
   <PropertyGroup>
@@ -250,6 +253,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     <ApplyCompressionNegotiation
       CandidateEndpoints="@(StaticWebAssetEndpoint)"
       CandidateAssets="@(_CompressionCurrentProjectBuildAssets)"
+      AttachWeakETagToCompressedAssets="$(AttachWeakETagToCompressedAssetsDuringDevelopment)"
     >
       <Output TaskParameter="UpdatedEndpoints" ItemName="_UpdatedCompressionBuildEndpoints" />
     </ApplyCompressionNegotiation>
@@ -373,8 +377,7 @@ Copyright (c) .NET Foundation. All rights reserved.
 
     <ApplyCompressionNegotiation
       CandidateEndpoints="@(StaticWebAssetEndpoint)"
-      CandidateAssets="@(_CompressionCurrentProjectPublishAssets)"
-    >
+      CandidateAssets="@(_CompressionCurrentProjectPublishAssets)">
       <Output TaskParameter="UpdatedEndpoints" ItemName="_UpdatedCompressionPublishEndpoints" />
     </ApplyCompressionNegotiation>
 

src/StaticWebAssetsSdk/Tasks/ApplyCompressionNegotiation.cs

@@ -16,6 +16,8 @@ public class ApplyCompressionNegotiation : Task
     [Required]
     public ITaskItem[] CandidateAssets { get; set; }
 
+    public bool AttachWeakETagToCompressedAssets { get; set; }
+
     [Output]
     public ITaskItem[] UpdatedEndpoints { get; set; }
 
@@ -371,7 +373,7 @@ private void ApplyRelatedEndpointCandidateHeaders(List<StaticWebAssetEndpointRes
                 Log.LogMessage(MessageImportance.Low, "  Adding header '{0}' to related endpoint '{1}'", header.Name, relatedEndpointCandidate.Route);
                 headers.Add(header);
             }
-            else if (string.Equals(header.Name, "ETag", StringComparison.Ordinal))
+            else if (AttachWeakETagToCompressedAssets && string.Equals(header.Name, "ETag", StringComparison.Ordinal))
             {
                 // A resource can have multiple ETags. Since the uncompressed resource has an ETag,
                 // and we are serving the compressed resource from the same URL, we need to update
@@ -386,8 +388,7 @@ private void ApplyRelatedEndpointCandidateHeaders(List<StaticWebAssetEndpointRes
                     Name = "ETag",
                     Value = $"W/{header.Value}"
                 });
-            }
-            else if (string.Equals(header.Name, "Content-Type", StringComparison.Ordinal))
+            }else if (string.Equals(header.Name, "Content-Type", StringComparison.Ordinal))
             {
                 Log.LogMessage(MessageImportance.Low, "Adding Content-Type '{1}' header to related endpoint '{0}'", relatedEndpointCandidate.Route, header.Value);
                 // Add the Content-Type to make sure it matches the original asset.