fix: sending datagram (#104)

quic/transport/ngtcp2/native/connection.nim

@@ -155,23 +155,12 @@ proc send(
   let written = addr result
   var datagram = trySend(connection, streamId, messagePtr, messageLen, written, isFin)
 
-  # Special handling for empty data - avoid infinite waiting
-  if messageLen == 0:
-    if isFin:
-      # For FIN-only packets, handle them properly without waiting
-      if datagram.data.len > 0:
-        connection.onSend(datagram)
-      else:
-        # Force a general send to flush any pending packets
-        connection.send()
-      connection.updateExpiryTimer()
-      return
-    else:
-      # For empty writes without FIN, treat as no-op
-      # Return 0 bytes written since there was nothing to write
-      result = 0
-      connection.updateExpiryTimer()
-      return
+  # For empty writes without FIN, treat as no-op
+  # Return 0 bytes written since there was nothing to write
+  if messageLen == 0 and not isFin:
+    result = 0
+    connection.updateExpiryTimer()
+    return
 
   # Normal flow control for data packets
   while datagram.data.len == 0:
@@ -189,10 +178,10 @@ proc send*(
   var done = false
   while not done:
     let written = await connection.send(streamId, messagePtr, messageLen, isFin)
-    if written != -1:
+    if written >= 0:
       messagePtr = messagePtr + written
       messageLen = messageLen - written.uint
-    done = messageLen == 0
+      done = messageLen == 0
 
 proc tryReceive(connection: Ngtcp2Connection, datagram: openArray[byte], ecn: ECN) =
   let conn = connection.conn.valueOr: