lightningd: still bind to local ports even if address not public.

Now we only bind to addresses in our wireaddrs array, we would not
autobind to local sockets if they couldn't reach google's nameserver.

That's clearly wrong: we should only not bind if there's a protocol
issue (eg. no IPv6 support).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/netaddress.c

@@ -200,32 +200,35 @@ static bool IsRoutable(const struct wireaddr *addr)
 
 /* Trick I learned from Harald Welte: create UDP socket, connect() and
  * then query address. */
-static bool get_local_sockname(struct lightningd *ld,
-                               int af, void *saddr, socklen_t saddrlen)
+/* Returns 0 if protocol completely unsupported, ADDR_LISTEN if we
+ * can't reach addr, ADDR_LISTEN_AND_ANNOUNCE if we can (and fill saddr). */
+static enum addr_listen_announce get_local_sockname(struct lightningd *ld,
+						    int af, void *saddr,
+						    socklen_t saddrlen)
 {
     int fd = socket(af, SOCK_DGRAM, 0);
     if (fd < 0) {
         log_debug(ld->log, "Failed to create %u socket: %s",
                   af, strerror(errno));
-        return false;
+        return 0;
     }
 
     if (connect(fd, saddr, saddrlen) != 0) {
         log_debug(ld->log, "Failed to connect %u socket: %s",
                   af, strerror(errno));
         close(fd);
-        return false;
+        return ADDR_LISTEN;
     }
 
     if (getsockname(fd, saddr, &saddrlen) != 0) {
         log_debug(ld->log, "Failed to get %u socket name: %s",
                   af, strerror(errno));
         close(fd);
-        return false;
+        return ADDR_LISTEN;
     }
 
     close(fd);
-    return true;
+    return ADDR_LISTEN_AND_ANNOUNCE;
 }
 
 /* Return 0 if not available, or whether it's listenable-only or announceable.
@@ -236,6 +239,8 @@ static enum addr_listen_announce guess_one_address(struct lightningd *ld,
 						   u16 portnum,
 						   enum wire_addr_type type)
 {
+    enum addr_listen_announce ret;
+
     addr->type = type;
     addr->port = portnum;
 
@@ -247,8 +252,7 @@ static enum addr_listen_announce guess_one_address(struct lightningd *ld,
         /* 8.8.8.8 */
 	sin.sin_addr.s_addr = 0x08080808;
         sin.sin_family = AF_INET;
-        if (!get_local_sockname(ld, AF_INET, &sin, sizeof(sin)))
-            return 0;
+        ret = get_local_sockname(ld, AF_INET, &sin, sizeof(sin));
         addr->addrlen = sizeof(sin.sin_addr);
         memcpy(addr->addr, &sin.sin_addr, addr->addrlen);
         break;
@@ -262,8 +266,7 @@ static enum addr_listen_announce guess_one_address(struct lightningd *ld,
         sin6.sin6_port = htons(53);
         sin6.sin6_family = AF_INET6;
         memcpy(sin6.sin6_addr.s6_addr, pchGoogle, sizeof(pchGoogle));
-        if (!get_local_sockname(ld, AF_INET6, &sin6, sizeof(sin6)))
-            return 0;
+        ret = get_local_sockname(ld, AF_INET6, &sin6, sizeof(sin6));
         addr->addrlen = sizeof(sin6.sin6_addr);
         memcpy(addr->addr, &sin6.sin6_addr, addr->addrlen);
         break;
@@ -273,17 +276,24 @@ static enum addr_listen_announce guess_one_address(struct lightningd *ld,
         return 0;
     }
 
-    if (!IsRoutable(addr)) {
+    if (ret == 0)
+	return ret;
+
+    /* If we can reach it, but resulting address is unroutable, listen only */
+    if (ret == ADDR_LISTEN_AND_ANNOUNCE && !IsRoutable(addr)) {
         log_debug(ld->log, "Address %s is not routable",
                   type_to_string(tmpctx, struct wireaddr, addr));
+	ret = ADDR_LISTEN;
+    }
+
+    if (ret == ADDR_LISTEN) {
 	/* This corresponds to INADDR_ANY or in6addr_any */
 	memset(addr->addr, 0, addr->addrlen);
-        return ADDR_LISTEN;
+    } else {
+	log_debug(ld->log, "Public address %s",
+		  type_to_string(tmpctx, struct wireaddr, addr));
     }
-
-    log_debug(ld->log, "Public address %s",
-              type_to_string(tmpctx, struct wireaddr, addr));
-    return ADDR_LISTEN_AND_ANNOUNCE;
+    return ret;
 }
 
 void guess_addresses(struct lightningd *ld)