nc: do not test the connection in non-interactive mode

The connection test writes four X to the socket, which corrupts data
that we may want to pipe into nc. So don't do that if stdin is not a
tty but still do it in scan mode, this is needed according to chris.

based on a diff by and ok mpf

diff --git a/usr.bin/nc/netcat.c b/usr.bin/nc/netcat.c
index e945ba6..dc60158 100644 (file)
--- a/usr.bin/nc/netcat.c
+++ b/usr.bin/nc/netcat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: netcat.c,v 1.222 2022/12/18 12:48:28 tb Exp $ */
+/* $OpenBSD: netcat.c,v 1.223 2022/12/18 12:51:10 tb Exp $ */
 /*
  * Copyright (c) 2001 Eric Jackson <ericj@monkey.org>
  * Copyright (c) 2015 Bob Beck.  All rights reserved.
@@ -1510,6 +1510,10 @@ udptest(int s)
 {
        int i, ret;
 
+       /* Only write to the socket in scan mode or interactive mode. */
+       if (!zflag && !isatty(STDIN_FILENO))
+               return 0;
+
        for (i = 0; i <= 3; i++) {
                if (write(s, "X", 1) == 1)
                        ret = 1;