Faster CopyFrom

Author: benaadams

src/Microsoft.AspNet.Server.Kestrel/Http/SocketOutput.cs

@@ -87,7 +87,7 @@ public Task WriteAsync(
             if (buffer.Count > 0)
             {
                 var tail = ProducingStart();
-                tail.CopyFrom(buffer);
+                tail.CopyFrom(buffer.Array, buffer.Offset, buffer.Count);
                 // We do our own accounting below
                 ProducingCompleteNoPreComplete(tail);
             }

src/Microsoft.AspNet.Server.Kestrel/Infrastructure/MemoryPoolIterator2.cs

@@ -589,47 +589,52 @@ public void CopyFrom(ArraySegment<byte> buffer)
             CopyFrom(buffer.Array, buffer.Offset, buffer.Count);
         }
 
-        public void CopyFrom(byte[] data, int offset, int count)
+        public unsafe void CopyFrom(byte[] data, int offset, int count)
         {
-            Debug.Assert(_block != null);
-            Debug.Assert(_block.Pool != null);
-            Debug.Assert(_block.Next == null);
-            Debug.Assert(_block.End == _index);
-
-            var pool = _block.Pool;
             var block = _block;
             var blockIndex = _index;
-
-            var bufferIndex = offset;
-            var remaining = count;
             var bytesLeftInBlock = block.Data.Offset + block.Data.Count - blockIndex;
 
-            while (remaining > 0)
+            if (bytesLeftInBlock >= count)
+            {
+                _index = blockIndex + count;
+                Buffer.BlockCopy(data, offset, block.Array, blockIndex, count);
+                block.End = _index;
+                return;
+            }
+
+            var pool = block.Pool;
+
+            while (count > 0)
             {
                 if (bytesLeftInBlock == 0)
                 {
-                    var nextBlock = pool.Lease();
                     block.End = blockIndex;
+
+                    var nextBlock = pool.Lease();
+                    blockIndex = nextBlock.Data.Offset;
+                    bytesLeftInBlock = nextBlock.Data.Count;
                     block.Next = nextBlock;
                     block = nextBlock;
-
-                    blockIndex = block.Data.Offset;
-                    bytesLeftInBlock = block.Data.Count;
                 }
 
-                var bytesToCopy = remaining < bytesLeftInBlock ? remaining : bytesLeftInBlock;
-
-                Buffer.BlockCopy(data, bufferIndex, block.Array, blockIndex, bytesToCopy);
-
-                blockIndex += bytesToCopy;
-                bufferIndex += bytesToCopy;
-                remaining -= bytesToCopy;
-                bytesLeftInBlock -= bytesToCopy;
+                if (count > bytesLeftInBlock)
+                {
+                    count -= bytesLeftInBlock;
+                    Buffer.BlockCopy(data, offset, block.Array, blockIndex, bytesLeftInBlock);
+                    blockIndex += bytesLeftInBlock;
+                    offset += bytesLeftInBlock;
+                    bytesLeftInBlock = 0;
+                }
+                else
+                {
+                    _index = blockIndex + count;
+                    Buffer.BlockCopy(data, offset, block.Array, blockIndex, count);
+                    block.End = _index;
+                    _block = block;
+                    return;
+                }
             }
-
-            block.End = blockIndex;
-            _block = block;
-            _index = blockIndex;
         }
 
         public unsafe void CopyFromAscii(string data)

test/Microsoft.AspNet.Server.KestrelTests/MemoryPoolBlock2Tests.cs

@@ -245,7 +245,7 @@ public void CopyFromCorrectlyTraversesBlocks()
 
                 Assert.Null(block1.Next);
 
-                end.CopyFrom(new ArraySegment<byte>(buffer));
+                end.CopyFrom(buffer, 0, buffer.Length);
 
                 Assert.NotNull(block1.Next);