fix(serializing): reuse larger pooled writers

Assets/FishNet/Runtime/Serializing/WriterPool.cs

@@ -89,6 +89,14 @@ public static PooledWriter Retrieve(NetworkManager networkManager, int length)
             PooledWriter result;
             // There is already one pooled.
             if (_lengthPool.TryGetValue(index, out stack) && stack.TryPop(out result))
+            {
+                if (stack.Count == 0)
+                    _lengthPool.Remove(index);
+
+                result.Clear(networkManager);
+            }
+            // There is a larger writer pooled.
+            else if (TryPopLengthWriterAbove(index, out result))
             {
                 result.Clear(networkManager);
             }
@@ -107,6 +115,46 @@ public static PooledWriter Retrieve(NetworkManager networkManager, int length)
             return result;
         }
 
+        /// <summary>
+        /// Tries to pop the closest writer from a bucket above minimum index.
+        /// </summary>
+        private static bool TryPopLengthWriterAbove(int minimumIndex, out PooledWriter writer)
+        {
+            int foundIndex = int.MaxValue;
+            Stack<PooledWriter> foundStack = null;
+
+            foreach (KeyValuePair<int, Stack<PooledWriter>> entry in _lengthPool)
+            {
+                if (entry.Key <= minimumIndex)
+                    continue;
+                if (entry.Value.Count == 0)
+                    continue;
+                if (entry.Key < foundIndex)
+                {
+                    foundIndex = entry.Key;
+                    foundStack = entry.Value;
+                }
+            }
+
+            if (foundStack == null)
+            {
+                writer = null;
+                return false;
+            }
+
+            bool popped = foundStack.TryPop(out writer);
+            if (!popped)
+            {
+                writer = null;
+                return false;
+            }
+
+            if (foundStack.Count == 0)
+                _lengthPool.Remove(foundIndex);
+
+            return true;
+        }
+
         /// <summary>
         /// Returns a writer to the appropriate length pool.
         /// Writers must be a minimum of 1000 bytes in length to be sorted by length.