From: Guus Sliepen <guus@meshlink.io>
Date: Tue, 13 Oct 2015 12:14:08 +0000 (+0200)
Subject: Determine the local node's address(es) and add them to its host config file.
X-Git-Url: https://git.meshlink.io/?a=commitdiff_plain;h=ff72e68fcde755cddd425599c83dc052aeff6efb;p=meshlink

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 addb4900..cbbb64d3 100644
--- 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");