Store content length as header instead of separate field

Author: JunTaoLuo

src/Microsoft.AspNetCore.ResponseCaching/Internal/CacheEntry/CachedResponse.cs

@@ -16,7 +16,5 @@ public class CachedResponse : IResponseCacheEntry
         public IHeaderDictionary Headers { get; set; }
 
         public Stream Body { get; set; }
-
-        public string BodyLengthString { get; set; }
     }
 }

src/Microsoft.AspNetCore.ResponseCaching/Internal/MemoryCachedResponse.cs

@@ -18,7 +18,5 @@ internal class MemoryCachedResponse
         public List<byte[]> BodySegments { get; set; }
 
         public long BodyLength { get; set; }
-
-        public string BodyLengthString { get; set; }
     }
 }

src/Microsoft.AspNetCore.ResponseCaching/Internal/MemoryResponseCache.cs

@@ -35,7 +35,6 @@ public Task<IResponseCacheEntry> GetAsync(string key)
                     StatusCode = memoryCachedResponse.StatusCode,
                     Headers = memoryCachedResponse.Headers,
                     Body = new SegmentReadStream(memoryCachedResponse.BodySegments, memoryCachedResponse.BodyLength),
-                    BodyLengthString = memoryCachedResponse.BodyLengthString
                 });
             }
             else
@@ -60,8 +59,7 @@ public async Task SetAsync(string key, IResponseCacheEntry entry, TimeSpan valid
                         StatusCode = cachedResponse.StatusCode,
                         Headers = cachedResponse.Headers,
                         BodySegments = segmentStream.GetSegments(),
-                        BodyLength = segmentStream.Length,
-                        BodyLengthString = HeaderUtilities.FormatInt64(segmentStream.Length)
+                        BodyLength = segmentStream.Length
                     },
                     new MemoryCacheEntryOptions
                     {

src/Microsoft.AspNetCore.ResponseCaching/ResponseCachingMiddleware.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Features;
@@ -151,12 +150,6 @@ internal async Task<bool> TryServeCachedResponseAsync(ResponseCachingContext con
                     var body = context.CachedResponse.Body;
                     if (body.Length > 0)
                     {
-                        // Add a content-length if required
-                        if (!response.ContentLength.HasValue && StringValues.IsNullOrEmpty(response.Headers[HeaderNames.TransferEncoding]))
-                        {
-                            response.Headers[HeaderNames.ContentLength] = context.CachedResponse.BodyLengthString;
-                        }
-
                         try
                         {
                             await body.CopyToAsync(response.Body, StreamUtilities.BodySegmentSize, context.HttpContext.RequestAborted);
@@ -292,6 +285,13 @@ internal async Task FinalizeCacheBodyAsync(ResponseCachingContext context)
                 var bufferStream = context.ResponseCachingStream.GetBufferStream();
                 if (!contentLength.HasValue || contentLength == bufferStream.Length)
                 {
+                    var response = context.HttpContext.Response;
+                    // Add a content-length if required
+                    if (!response.ContentLength.HasValue && StringValues.IsNullOrEmpty(response.Headers[HeaderNames.TransferEncoding]))
+                    {
+                        context.CachedResponse.Headers[HeaderNames.ContentLength] = HeaderUtilities.FormatInt64(bufferStream.Length);
+                    }
+
                     context.CachedResponse.Body = bufferStream;
                     _logger.LogResponseCached();
                     await _cache.SetAsync(context.StorageVaryKey ?? context.BaseKey, context.CachedResponse, context.CachedResponseValidFor);

test/Microsoft.AspNetCore.ResponseCaching.Tests/ResponseCachingMiddlewareTests.cs

@@ -668,7 +668,10 @@ public async Task FinalizeCacheBody_Cache_IfContentLengthAbsent()
             await context.HttpContext.Response.WriteAsync(new string('0', 10));
 
             context.ShouldCacheResponse = true;
-            context.CachedResponse = new CachedResponse();
+            context.CachedResponse = new CachedResponse()
+            {
+                Headers = new HeaderDictionary()
+            };
             context.BaseKey = "BaseKey";
             context.CachedResponseValidFor = TimeSpan.FromSeconds(10);