OPDS Performance Enhancements (#4332)

Co-authored-by: Amelia <77553571+Fesaa@users.noreply.github.com>

API/Extensions/HttpExtensions.cs

@@ -1,17 +1,17 @@
-using System.IO;
-using System.Linq;
-using System.Security.Cryptography;
-using System.Text;
-using System.Text.Json;
+using System.Text.Json;
 using API.Helpers;
 using Microsoft.AspNetCore.Http;
-using Microsoft.Net.Http.Headers;
 
 namespace API.Extensions;
 #nullable enable
 
 public static class HttpExtensions
 {
+    private static readonly JsonSerializerOptions Options = new()
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
+    };
+
     /// <summary>
     /// Adds pagination headers - Use with <see cref="PagedList{T}"/>
     /// </summary>
@@ -24,25 +24,8 @@ public static class HttpExtensions
         int itemsPerPage, int totalItems, int totalPages)
     {
         var paginationHeader = new PaginationHeader(currentPage, itemsPerPage, totalItems, totalPages);
-        var options = new JsonSerializerOptions()
-        {
-            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
-        };
 
-        response.Headers.Append("Pagination", JsonSerializer.Serialize(paginationHeader, options));
+        response.Headers.Append("Pagination", JsonSerializer.Serialize(paginationHeader, Options));
         response.Headers.Append("Access-Control-Expose-Headers", "Pagination");
     }
-
-    /// <summary>
-    /// Calculates SHA256 hash for a byte[] and sets as ETag. Ensures Cache-Control: private header is added.
-    /// </summary>
-    /// <param name="response"></param>
-    /// <param name="content">If byte[] is null or empty, will only add cache-control</param>
-    public static void AddCacheHeader(this HttpResponse response, byte[] content)
-    {
-        if (content is not {Length: > 0}) return;
-        response.Headers.Append(HeaderNames.ETag, string.Concat(SHA256.HashData(content).Select(x => x.ToString("X2"))));
-        response.Headers.CacheControl =  $"private, max-age=100";
-    }
-
 }