nc: make connecting to IPv4 from IPv6-enabled hosts easier

(was requiring -s <local addr>)

3 files changed, 38 insertions, 24 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 013633716..dd0f5c1cc 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -304,9 +304,12 @@ enum {
                 }
         )
 };
-/* Create stream socket, and allocated suitable lsa
- * (lsa of correct size and lsa->sa.sa_family (AF_INET/AF_INET6)) */
-int xsocket_type(len_and_sockaddr **lsap, int sock_type);
+/* Create stream socket, and allocate suitable lsa.
+ * (lsa of correct size and lsa->sa.sa_family (AF_INET/AF_INET6))
+ * af == AF_UNSPEC will result in trying to create IPv6, and
+ * if kernel doesn't support it, IPv4.
+ */
+int xsocket_type(len_and_sockaddr **lsap, USE_FEATURE_IPV6(int af,) int sock_type);
 int xsocket_stream(len_and_sockaddr **lsap);
 /* Create server socket bound to bindaddr:port. bindaddr can be NULL,
  * numeric IP ("N.N.N.N") or numeric IPv6 address,
diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index e7d510678..b90aa9add 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -208,23 +208,31 @@ len_and_sockaddr* xdotted2sockaddr(const char *host, int port)
         return str2sockaddr(host, port, AF_UNSPEC, AI_NUMERICHOST | DIE_ON_ERROR);
 }
 
-int xsocket_type(len_and_sockaddr **lsap, int sock_type)
+int xsocket_type(len_and_sockaddr **lsap, USE_FEATURE_IPV6(int family,) int sock_type)
 {
+        SKIP_FEATURE_IPV6(enum { family = AF_INET };)
         len_and_sockaddr *lsa;
         int fd;
-        int len = sizeof(struct sockaddr_in);
-        int family = AF_INET;
+        int len;
 
 #if ENABLE_FEATURE_IPV6
-        fd = socket(AF_INET6, sock_type, 0);
-        if (fd >= 0) {
-                len = sizeof(struct sockaddr_in6);
-                family = AF_INET6;
-        } else
+        if (family == AF_UNSPEC) {
+                fd = socket(AF_INET6, sock_type, 0);
+                if (fd >= 0) {
+                        family = AF_INET6;
+                        goto done;
+                }
+                family = AF_INET;
+        }
 #endif
-        {
-                fd = xsocket(AF_INET, sock_type, 0);
+        fd = xsocket(family, sock_type, 0);
+        len = sizeof(struct sockaddr_in);
+#if ENABLE_FEATURE_IPV6
+        if (family == AF_INET6) {
+ done:
+                len = sizeof(struct sockaddr_in6);
         }
+#endif
         lsa = xzalloc(offsetof(len_and_sockaddr, sa) + len);
         lsa->len = len;
         lsa->sa.sa_family = family;
@@ -234,7 +242,7 @@ int xsocket_type(len_and_sockaddr **lsap, int sock_type)
 
 int xsocket_stream(len_and_sockaddr **lsap)
 {
-        return xsocket_type(lsap, SOCK_STREAM);
+        return xsocket_type(lsap, USE_FEATURE_IPV6(AF_UNSPEC,) SOCK_STREAM);
 }
 
 static int create_and_bind_or_die(const char *bindaddr, int port, int sock_type)
@@ -247,7 +255,7 @@ static int create_and_bind_or_die(const char *bindaddr, int port, int sock_type)
                 /* user specified bind addr dictates family */
                 fd = xsocket(lsa->sa.sa_family, sock_type, 0);
         } else {
-                fd = xsocket_type(&lsa, sock_type);
+                fd = xsocket_type(&lsa, USE_FEATURE_IPV6(AF_UNSPEC,) sock_type);
                 set_nport(lsa, htons(port));
         }
         setsockopt_reuseaddr(fd);
diff --git a/networking/nc_bloaty.c b/networking/nc_bloaty.c
index 5096e3227..a318c8126 100644
--- a/networking/nc_bloaty.c
+++ b/networking/nc_bloaty.c
@@ -751,6 +751,13 @@ int nc_main(int argc, char **argv)
         /* We manage our fd's so that they are never 0,1,2 */
         /*bb_sanitize_stdio(); - not needed */
 
+        if (argv[0]) {
+                themaddr = xhost2sockaddr(argv[0],
+                        argv[1]
+                        ? bb_lookup_port(argv[1], o_udpmode ? "udp" : "tcp", 0)
+                        : 0);
+        }
+
         /* create & bind network socket */
         x = (o_udpmode ? SOCK_DGRAM : SOCK_STREAM);
         if (option_mask32 & OPT_s) { /* local address */
@@ -758,7 +765,11 @@ int nc_main(int argc, char **argv)
                 ouraddr = xhost2sockaddr(str_s, o_lport);
                 x = xsocket(ouraddr->sa.sa_family, x, 0);
         } else {
-                x = xsocket_type(&ouraddr, x);
+                /* We try IPv6, then IPv4, unless addr family is
+                 * implicitly set by way of remote addr/port spec */
+                x = xsocket_type(&ouraddr,
+                                USE_FEATURE_IPV6((themaddr ? themaddr->sa.sa_family : AF_UNSPEC),)
+                                x);
                 if (o_lport)
                         set_nport(ouraddr, htons(o_lport));
         }
@@ -789,14 +800,6 @@ int nc_main(int argc, char **argv)
                 xmove_fd(xopen(str_o, O_WRONLY|O_CREAT|O_TRUNC), ofd);
 #endif
 
-        if (argv[0]) {
-                themaddr = xhost2sockaddr(argv[0],
-                        argv[1]
-                        ? bb_lookup_port(argv[1], o_udpmode ? "udp" : "tcp", 0)
-                        : 0);
-///what if sa_family won't match??
-        }
-
         if (o_listen) {
                 dolisten();
                 /* dolisten does its own connect reporting */