Do not set asyncio future if it is already done. [#740]

diff --git a/dns/_asyncio_backend.py b/dns/_asyncio_backend.py
index 4c8c0548163a08718f3fb1660969b4055c43b7d0..d737d13c7e4421d05d4510164819a654786963ab 100644 (file)
--- a/dns/_asyncio_backend.py
+++ b/dns/_asyncio_backend.py
@@ -28,7 +28,7 @@ class _DatagramProtocol:
         self.transport = transport
 
     def datagram_received(self, data, addr):
-        if self.recvfrom:
+        if self.recvfrom and not self.recvfrom.done():
             self.recvfrom.set_result((data, addr))
             self.recvfrom = None