Preencoded header values

Author: javiercn

src/StaticWebAssetsSdk/Tasks/Data/StaticWebAssetEndpointResponseHeader.cs

@@ -142,7 +142,15 @@ internal static string ToMetadataValue(
             var header = headers[i];
             writer.WriteStartObject();
             writer.WritePropertyName(NamePropertyName);
-            writer.WriteStringValue(header.Name);
+            var preEncoded = WellKnownResponseHeaders.TryGetPreEncodedHeaderName(header.Name);
+            if (preEncoded.HasValue)
+            {
+                writer.WriteStringValue(preEncoded.Value);
+            }
+            else
+            {
+                writer.WriteStringValue(header.Name);
+            }
             writer.WritePropertyName(ValuePropertyName);
             writer.WriteStringValue(header.Value);
             writer.WriteEndObject();

src/StaticWebAssetsSdk/Tasks/Data/WellKnownResponseHeaders.cs

@@ -3,6 +3,8 @@
 
 #nullable disable
 
+using System.Text.Json;
+
 namespace Microsoft.AspNetCore.StaticWebAssets.Tasks;
 
 internal static class WellKnownResponseHeaders
@@ -17,6 +19,16 @@ internal static class WellKnownResponseHeaders
     public const string LastModified = "Last-Modified";
     public const string Vary = "Vary";
 
+    // Pre-encoded property names for high-performance JSON serialization
+    public static readonly JsonEncodedText AcceptRangesPropertyName = JsonEncodedText.Encode(AcceptRanges);
+    public static readonly JsonEncodedText CacheControlPropertyName = JsonEncodedText.Encode(CacheControl);
+    public static readonly JsonEncodedText ContentEncodingPropertyName = JsonEncodedText.Encode(ContentEncoding);
+    public static readonly JsonEncodedText ContentLengthPropertyName = JsonEncodedText.Encode(ContentLength);
+    public static readonly JsonEncodedText ContentTypePropertyName = JsonEncodedText.Encode(ContentType);
+    public static readonly JsonEncodedText ETagPropertyName = JsonEncodedText.Encode(ETag);
+    public static readonly JsonEncodedText LastModifiedPropertyName = JsonEncodedText.Encode(LastModified);
+    public static readonly JsonEncodedText VaryPropertyName = JsonEncodedText.Encode(Vary);
+
     public static string TryGetInternedHeaderName(ReadOnlySpan<byte> headerNameSpan)
     {
         return headerNameSpan.Length switch
@@ -40,4 +52,26 @@ public static string TryGetInternedHeaderName(ReadOnlySpan<byte> headerNameSpan)
             _ => null
         };
     }
+
+    public static JsonEncodedText? TryGetPreEncodedHeaderName(string name) =>
+        name?.Length switch
+        {
+            4 => name[0] switch
+            {
+                'E' when string.Equals(name, ETag, StringComparison.Ordinal) => ETagPropertyName,
+                'V' when string.Equals(name, Vary, StringComparison.Ordinal) => VaryPropertyName,
+                _ => null
+            },
+            12 when string.Equals(name, ContentType, StringComparison.Ordinal) => ContentTypePropertyName,
+            13 => name[0] switch
+            {
+                'A' when string.Equals(name, AcceptRanges, StringComparison.Ordinal) => AcceptRangesPropertyName,
+                'C' when string.Equals(name, CacheControl, StringComparison.Ordinal) => CacheControlPropertyName,
+                'L' when string.Equals(name, LastModified, StringComparison.Ordinal) => LastModifiedPropertyName,
+                _ => null
+            },
+            14 when string.Equals(name, ContentLength, StringComparison.Ordinal) => ContentLengthPropertyName,
+            16 when string.Equals(name, ContentEncoding, StringComparison.Ordinal) => ContentEncodingPropertyName,
+            _ => null
+        };
 }