libbb: set new listening sockets to dual-stack mode

IPv6 sockets are created in IPv6-only mode on Microsoft Windows.
The IPv6 socket option IPV6_V6ONLY needs to be turned off to permit
dual-stack operation.

Without this change netcat only listens on IPv6 addresses when run
with no explicit IP address argument.

1 files changed, 4 insertions, 0 deletions

diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index 0a4d8f128..c318af419 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -353,6 +353,10 @@ int FAST_FUNC xsocket_type(len_and_sockaddr **lsap, int family, int sock_type)
 #if ENABLE_FEATURE_IPV6
                 fd = socket(AF_INET6, sock_type, 0);
                 if (fd >= 0) {
+#if ENABLE_PLATFORM_MINGW32
+                        DWORD buffer = 0;
+                        setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &buffer, sizeof(DWORD));
+#endif
                         family = AF_INET6;
                         goto done;
                 }