Add more debug logs

association.go

@@ -329,6 +329,8 @@ func createAssociation(config Config) *Association {
 		retryFirstWriteError:    runtime.GOOS == "linux",
 	}
 
+	a.log.Debugf("[%s] retryFirstWriteError=%v", a.name, a.retryFirstWriteError)
+
 	a.name = fmt.Sprintf("%p", a)
 
 	// RFC 4690 Sec 7.2.1
@@ -612,8 +614,11 @@ func (a *Association) write(packet []byte) (int, error) {
 		a.retryFirstWriteError = false
 		if err != nil {
 			var opErr *net.OpError
-			if errors.As(err, &opErr) && opErr.Op == "write" && opErr.Err.Error() == "operation not permitted" {
-				n, err = a.netConn.Write(packet)
+			if errors.As(err, &opErr) {
+				a.log.Debugf("write failed: op='%s' err='%s'", opErr.Op, opErr.Err.Error())
+				if opErr.Op == "write" && opErr.Err.Error() == "operation not permitted" {
+					n, err = a.netConn.Write(packet)
+				}
 			}
 		}
 	}