Buffer writes from sources of synchronous writes

Fixes #6397

Author: pranavkm

src/Http/Http/src/Internal/BufferingHelper.cs

@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.IO;
+using Microsoft.AspNetCore.Internal;
 using Microsoft.AspNetCore.WebUtilities;
 
 namespace Microsoft.AspNetCore.Http.Internal
@@ -11,33 +11,6 @@ public static class BufferingHelper
     {
         internal const int DefaultBufferThreshold = 1024 * 30;
 
-        private readonly static Func<string> _getTempDirectory = () => TempDirectory;
-
-        private static string _tempDirectory;
-
-        public static string TempDirectory
-        {
-            get
-            {
-                if (_tempDirectory == null)
-                {
-                    // Look for folders in the following order.
-                    var temp = Environment.GetEnvironmentVariable("ASPNETCORE_TEMP") ??     // ASPNETCORE_TEMP - User set temporary location.
-                               Path.GetTempPath();                                      // Fall back.
-
-                    if (!Directory.Exists(temp))
-                    {
-                        // TODO: ???
-                        throw new DirectoryNotFoundException(temp);
-                    }
-
-                    _tempDirectory = temp;
-                }
-
-                return _tempDirectory;
-            }
-        }
-
         public static HttpRequest EnableRewind(this HttpRequest request, int bufferThreshold = DefaultBufferThreshold, long? bufferLimit = null)
         {
             if (request == null)
@@ -48,7 +21,7 @@ public static HttpRequest EnableRewind(this HttpRequest request, int bufferThres
             var body = request.Body;
             if (!body.CanSeek)
             {
-                var fileStream = new FileBufferingReadStream(body, bufferThreshold, bufferLimit, _getTempDirectory);
+                var fileStream = new FileBufferingReadStream(body, bufferThreshold, bufferLimit, AspNetCoreTempDirectory.TempDirectoryFactory);
                 request.Body = fileStream;
                 request.HttpContext.Response.RegisterForDispose(fileStream);
             }
@@ -70,11 +43,11 @@ public static MultipartSection EnableRewind(this MultipartSection section, Actio
             var body = section.Body;
             if (!body.CanSeek)
             {
-                var fileStream = new FileBufferingReadStream(body, bufferThreshold, bufferLimit, _getTempDirectory);
+                var fileStream = new FileBufferingReadStream(body, bufferThreshold, bufferLimit, AspNetCoreTempDirectory.TempDirectoryFactory);
                 section.Body = fileStream;
                 registerForDispose(fileStream);
             }
             return section;
         }
     }
-}
+}

src/Http/Http/src/Microsoft.AspNetCore.Http.csproj

@@ -13,6 +13,7 @@
   <ItemGroup>
     <Compile Include="$(SharedSourceRoot)CopyOnWriteDictionary\*.cs" />
     <Compile Include="$(SharedSourceRoot)ValueTaskExtensions\**\*.cs" />
+    <Compile Include="..\..\WebUtilities\src\AspNetCoreTempDirectory.cs" LinkBase="Internal" />
   </ItemGroup>
 
   <ItemGroup>

src/Http/WebUtilities/src/AspNetCoreTempDirectory.cs

@@ -0,0 +1,37 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.IO;
+
+namespace Microsoft.AspNetCore.Internal
+{
+    internal static class AspNetCoreTempDirectory
+    {
+        private static string _tempDirectory;
+
+        public static string TempDirectory
+        {
+            get
+            {
+                if (_tempDirectory == null)
+                {
+                    // Look for folders in the following order.
+                    var temp = Environment.GetEnvironmentVariable("ASPNETCORE_TEMP") ?? // ASPNETCORE_TEMP - User set temporary location.
+                               Path.GetTempPath();                                      // Fall back.
+
+                    if (!Directory.Exists(temp))
+                    {
+                        throw new DirectoryNotFoundException(temp);
+                    }
+
+                    _tempDirectory = temp;
+                }
+
+                return _tempDirectory;
+            }
+        }
+
+        public static Func<string> TempDirectoryFactory => () => TempDirectory;
+    }
+}