NameValueCollection.ToQueryString performance optimisation

src/Elasticsearch.Net/Extensions/NameValueCollectionExtensions.cs

@@ -22,15 +22,17 @@ internal static string ToQueryString(this NameValueCollection nv)
 			var maxLength = 1 + nv.AllKeys.Length - 1; // account for '?', and any required '&' chars
 			foreach (var key in nv.AllKeys)
 			{
-				maxLength += 1 + (key.Length + nv[key]?.Length ?? 0) * 3; // '=' char + worst case assume all key/value chars are escaped
+				var bytes = Encoding.UTF8.GetByteCount(key) + Encoding.UTF8.GetByteCount(nv[key] ?? string.Empty);
+				var maxEncodedSize = bytes * 3; // worst case, assume all bytes are URL escaped to 3 chars
+				maxLength += 1 + maxEncodedSize; // '=' + encoded chars
 			}
 
 			// prefer stack allocated array for short lengths
 			// note: renting for larger lengths is slightly more efficient since no zeroing occurs
 			char[] rentedFromPool = null;
 			var buffer = maxLength > MaxCharsOnStack
 				? rentedFromPool = ArrayPool<char>.Shared.Rent(maxLength)
-				: stackalloc char[MaxCharsOnStack];
+				: stackalloc char[maxLength];
 
 			try
 			{

tests/Tests/Extensions/NameValueCollectionExtensionsTests.cs

@@ -31,7 +31,17 @@ public class NameValueCollectionExtensionsTests
 				new object[] { new NameValueCollection
 				{
 					{ "q", null },
-				}, "?q" }
+				}, "?q" },
+
+				new object[] { new NameValueCollection
+				{
+					{ "emoji", "😅"}
+				}, "?emoji=%F0%9F%98%85" },
+
+				new object[] { new NameValueCollection
+				{
+					{ "€", "€"}
+				}, "?%E2%82%AC=%E2%82%AC" }
 			};
 	}
 }