Determine the local node's address(es) and add them to its host config file.

Use the "UDP connect() to an external IP address" trick to determine the
local node's addresses in a platform independent way, without sending any
actual packets. Do this at meshlink_open() time, so the application has
immediate access to them when calling meshlink_export().

diff --git a/src/meshlink.c b/src/meshlink.c
index addb490092a655d0eead3d7604c932298cc2e299..cbbb64d3728abe7ca3121237ebfe50800c9bbfb9 100644 (file)
--- a/src/meshlink.c
+++ b/src/meshlink.c
@@ -712,6 +712,65 @@ static struct timeval idle(event_loop_t *loop, void *data) {
        return tmin;
 }
 
+// Find out what local address a socket would use if we connect to the given address.
+// We do this using connect() on a UDP socket, so the kernel has to resolve the address
+// of both endpoints, but this will actually not send any UDP packet.
+static bool getlocaladdrname(char *destaddr, char *host, socklen_t hostlen) {
+       struct addrinfo *rai = NULL;
+       const struct addrinfo hint = {
+               .ai_family = AF_UNSPEC,
+               .ai_socktype = SOCK_DGRAM,
+               .ai_protocol = IPPROTO_UDP,
+       };
+
+       if(getaddrinfo(destaddr, "80", &hint, &rai) || !rai)
+               return false;
+
+       int sock = socket(rai->ai_family, rai->ai_socktype, rai->ai_protocol);
+       if(sock == -1) {
+               freeaddrinfo(rai);
+               return false;
+       }
+
+       if(connect(sock, rai->ai_addr, rai->ai_addrlen) && !sockwouldblock(errno)) {
+               freeaddrinfo(rai);
+               return false;
+       }
+
+       freeaddrinfo(rai);
+
+       struct sockaddr_storage sn;
+       socklen_t sl = sizeof sn;
+
+       if(getsockname(sock, (struct sockaddr *)&sn, &sl))
+               return false;
+
+       if(getnameinfo((struct sockaddr *)&sn, sl, host, hostlen, NULL, 0, NI_NUMERICHOST | NI_NUMERICSERV))
+               return false;
+
+       return true;
+}
+
+// Get our local address(es) by simulating connecting to an Internet host.
+static void add_local_addresses(meshlink_handle_t *mesh) {
+       char host[NI_MAXHOST];
+       char entry[MAX_STRING_SIZE];
+
+       // IPv4 example.org
+
+       if(getlocaladdrname("93.184.216.34", host, sizeof host)) {
+               snprintf(entry, sizeof entry, "%s %s", host, mesh->myport);
+               append_config_file(mesh, mesh->name, "Address", entry);
+       }
+
+       // IPv6 example.org
+
+       if(getlocaladdrname("2606:2800:220:1:248:1893:25c8:1946", host, sizeof host)) {
+               snprintf(entry, sizeof entry, "%s %s", host, mesh->myport);
+               append_config_file(mesh, mesh->name, "Address", entry);
+       }
+}
+
 static bool meshlink_setup(meshlink_handle_t *mesh) {
        if(mkdir(mesh->confbase, 0777) && errno != EEXIST) {
                logger(mesh, MESHLINK_DEBUG, "Could not create directory %s: %s\n", mesh->confbase, strerror(errno));
@@ -853,6 +912,8 @@ meshlink_handle_t *meshlink_open(const char *confbase, const char *name, const c
                return NULL;
        }
 
+       add_local_addresses(mesh);
+
        idle_set(&mesh->loop, idle, mesh);
 
        logger(NULL, MESHLINK_DEBUG, "meshlink_open returning\n");