From: Guus Sliepen <guus@meshlink.io>
Date: Sat, 8 Feb 2020 13:55:21 +0000 (+0100)
Subject: Fall back to getifaddrs() to get an interface address if there is no default route.
X-Git-Url: http://git.meshlink.io/?p=meshlink;a=commitdiff_plain;h=3fe7713c4f9d16f192271bc4fa8a2ffda6bb28fd;hp=4bd83124d50260738991f59a6afe23a31cb672ab

Fall back to getifaddrs() to get an interface address if there is no default route.

When generating invitations, we try to find a suitable local interface
address by faking an outgoing connection to the Internet. However,
that doesn't work if there is no default route. In this case, fall back
to using getifaddrs() if that function is available, and filter out any
link-local and loopback addresses.
---

diff --git a/src/meshlink.c b/src/meshlink.c
index a93bdd67..5b01ad2c 100644
--- a/src/meshlink.c
+++ b/src/meshlink.c
@@ -287,6 +287,21 @@ char *meshlink_get_external_address_for_family(meshlink_handle_t *mesh, int fami
 	return hostname;
 }
 
+static bool is_localaddr(sockaddr_t *sa) {
+	switch(sa->sa.sa_family) {
+	case AF_INET:
+		return *(uint8_t *)(&sa->in.sin_addr.s_addr) == 127;
+
+	case AF_INET6: {
+		uint16_t first = sa->in6.sin6_addr.s6_addr[0] << 8 | sa->in6.sin6_addr.s6_addr[1];
+		return first == 0 || (first & 0xffc0) == 0xfe80;
+	}
+
+	default:
+		return false;
+	}
+}
+
 char *meshlink_get_local_address_for_family(meshlink_handle_t *mesh, int family) {
 	(void)mesh;
 
@@ -300,6 +315,34 @@ char *meshlink_get_local_address_for_family(meshlink_handle_t *mesh, int family)
 		success = getlocaladdrname("2606:2800:220:1:248:1893:25c8:1946", localaddr, sizeof(localaddr), mesh->netns);
 	}
 
+#ifdef HAVE_GETIFADDRS
+
+	if(!success) {
+		struct ifaddrs *ifa = NULL;
+		getifaddrs(&ifa);
+
+		for(struct ifaddrs *ifap = ifa; ifap; ifap = ifap->ifa_next) {
+			sockaddr_t *sa = (sockaddr_t *)ifap->ifa_addr;
+
+			if(sa->sa.sa_family != family) {
+				continue;
+			}
+
+			if(is_localaddr(sa)) {
+				continue;
+			}
+
+			if(!getnameinfo(&sa->sa, SALEN(sa->sa), localaddr, sizeof(localaddr), NULL, 0, NI_NUMERICHOST | NI_NUMERICSERV)) {
+				success = true;
+				break;
+			}
+		}
+
+		freeifaddrs(ifa);
+	}
+
+#endif
+
 	if(!success) {
 		meshlink_errno = MESHLINK_ENETWORK;
 		return NULL;