avoid a memcopy by writing directly to the buffer bytes (and increasing DRY)

Author: mgravell

src/Middleware/OutputCaching/src/FormatterBinaryWriter.cs

@@ -74,7 +74,9 @@ public void Write(byte value)
         DebugAssertValid();
     }
 
-    public void Write(string value)
+    public void Write(string value) => Write(value, 0);
+
+    internal void Write(string value, int lengthShift)
     {
         ArgumentNullException.ThrowIfNull(value);
 
@@ -85,17 +87,19 @@ public void Write(string value)
         }
 
         var bytes = Encoding.UTF8.GetByteCount(value);
-        Write7BitEncodedInt(bytes); // length prefix
+        Write7BitEncodedInt(bytes << lengthShift); // length prefix
         if (bytes <= length - offset)
         {
-            Encoding.UTF8.GetBytes(value, AvailableBuffer);
+            var actual = Encoding.UTF8.GetBytes(value, AvailableBuffer);
+            Debug.Assert(actual == bytes);
             offset += bytes;
         }
         else
         {
             Flush();
             // get the encoding to do the heavy lifting directly
-            Encoding.UTF8.GetBytes(value, target);
+            var actual = Encoding.UTF8.GetBytes(value, target);
+            Debug.Assert(actual == bytes);
         }
         DebugAssertValid();
     }

src/Middleware/OutputCaching/src/Microsoft.AspNetCore.OutputCaching.csproj

@@ -6,8 +6,6 @@
     <IsAspNetCoreApp>true</IsAspNetCoreApp>
     <IsPackable>false</IsPackable>
     <IsTrimmable>true</IsTrimmable>
-    <!-- for skip-locals-init -->
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
   <ItemGroup>

src/Middleware/OutputCaching/src/OutputCacheEntryFormatter.cs

@@ -189,7 +189,6 @@ private static void Serialize(IBufferWriter<byte> output, OutputCacheEntry entry
         writer.Flush();
     }
 
-    [SkipLocalsInit]
     static void WriteCommonHeader(ref FormatterBinaryWriter writer, string? value)
     {
         if (string.IsNullOrEmpty(value))
@@ -204,20 +203,9 @@ static void WriteCommonHeader(ref FormatterBinaryWriter writer, string? value)
             }
             else
             {
-                var bytes = Encoding.UTF8.GetByteCount(value);
-                writer.Write7BitEncodedInt(bytes << 1);
-
-                const int MAX_STACK_BYTES = 256;
-                byte[]? leased = null;
-
-                Span<byte> buffer = bytes <= MAX_STACK_BYTES ? stackalloc byte[MAX_STACK_BYTES] : (leased = ArrayPool<byte>.Shared.Rent(bytes));
-                int actual = Encoding.UTF8.GetBytes(value, buffer);
-                Debug.Assert(actual == bytes);
-                writer.WriteRaw(buffer.Slice(0, actual));
-                if (leased is not null)
-                {
-                    ArrayPool<byte>.Shared.Return(leased);
-                }
+                // use the length-prefixed UTF8 write in FormatterBinaryWriter,
+                // but with a left-shift applied
+                writer.Write(value, lengthShift: 1);
             }
         }
     }