From af60e5f5164b28495c4a441f38c86e8f6b184a38 Mon Sep 17 00:00:00 2001
From: Guus Sliepen <guus@meshlink.io>
Date: Wed, 30 Dec 2020 14:50:56 +0100
Subject: [PATCH] Use the canonical address during UDP probes.

It is possible that a node has a canonical address, but due to NAT or other
reasons, the meta-connections with that node use other addresses. If UDP is
only possible to the canonical address, then we need to include that during
the initial UDP probing phase.
---
 src/net_packet.c | 21 +++++++++++++++++++--
 src/netutl.c     | 40 ++++++++++++++++++++++++++++++++++++++++
 src/netutl.h     |  1 +
 3 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/src/net_packet.c b/src/net_packet.c
index b32c78f7..ce1eb626 100644
--- a/src/net_packet.c
+++ b/src/net_packet.c
@@ -305,7 +305,7 @@ static void send_sptps_packet(meshlink_handle_t *mesh, node_t *n, vpn_packet_t *
 	return;
 }
 
-static void choose_udp_address(meshlink_handle_t *mesh, const node_t *n, const sockaddr_t **sa, int *sock) {
+static void choose_udp_address(meshlink_handle_t *mesh, const node_t *n, const sockaddr_t **sa, int *sock, sockaddr_t *sa_buf) {
 	/* Latest guess */
 	*sa = &n->address;
 	*sock = n->sock;
@@ -330,6 +330,22 @@ static void choose_udp_address(meshlink_handle_t *mesh, const node_t *n, const s
 		goto check_socket;
 	}
 
+	/* Else, if we have a canonical address, try this once every batch */
+	if(mesh->udp_choice == 1 && n->canonical_address) {
+		char *host = xstrdup(n->canonical_address);
+		char *port = strchr(host, ' ');
+
+		if(port) {
+			*port++ = 0;
+			*sa_buf = str2sockaddr_random(mesh, host, port);
+			*sa = sa_buf;
+			free(host);
+			goto check_socket;
+		}
+
+		free(host);
+	}
+
 	/* Otherwise, address are found in edges to this node.
 	   So we pick a random edge and a random socket. */
 
@@ -422,13 +438,14 @@ bool send_sptps_data(void *handle, uint8_t type, const void *data, size_t len) {
 
 	/* Otherwise, send the packet via UDP */
 
+	sockaddr_t sa_buf;
 	const sockaddr_t *sa;
 	int sock;
 
 	if(to->status.broadcast) {
 		choose_broadcast_address(mesh, to, &sa, &sock);
 	} else {
-		choose_udp_address(mesh, to, &sa, &sock);
+		choose_udp_address(mesh, to, &sa, &sock, &sa_buf);
 	}
 
 	if(sendto(mesh->listen_socket[sock].udp.fd, data, len, 0, &sa->sa, SALEN(sa->sa)) < 0 && !sockwouldblock(sockerrno)) {
diff --git a/src/netutl.c b/src/netutl.c
index 5406bbb8..9988b123 100644
--- a/src/netutl.c
+++ b/src/netutl.c
@@ -19,6 +19,7 @@
 
 #include "system.h"
 
+#include "meshlink_internal.h"
 #include "net.h"
 #include "netutl.h"
 #include "logger.h"
@@ -77,6 +78,45 @@ sockaddr_t str2sockaddr(const char *address, const char *port) {
 	return result;
 }
 
+sockaddr_t str2sockaddr_random(struct meshlink_handle *mesh, const char *address, const char *port) {
+	struct addrinfo *ai;
+	sockaddr_t result;
+	int err;
+
+	memset(&result, 0, sizeof(result));
+
+	struct addrinfo hint = {
+		.ai_family = AF_UNSPEC,
+		.ai_flags = NI_NUMERICHOST | NI_NUMERICSERV,
+		.ai_socktype = SOCK_STREAM,
+	};
+
+	err = getaddrinfo(address, port, &hint, &ai);
+
+	if(err || !ai) {
+		logger(NULL, MESHLINK_DEBUG, "Unknown type address %s port %s", address, port);
+		result.sa.sa_family = AF_UNKNOWN;
+		result.unknown.address = xstrdup(address);
+		result.unknown.port = xstrdup(port);
+		return result;
+	}
+
+	int count = 0;
+
+	for(struct addrinfo *aip = ai; aip; aip = aip->ai_next) {
+		count++;
+	}
+
+	struct addrinfo *aip = ai;
+
+	for(count = prng(mesh, count); count--; aip = aip->ai_next);
+
+	memcpy(&result, aip->ai_addr, aip->ai_addrlen);
+	freeaddrinfo(ai);
+
+	return result;
+}
+
 void sockaddr2str(const sockaddr_t *sa, char **addrstr, char **portstr) {
 	char address[NI_MAXHOST];
 	char port[NI_MAXSERV];
diff --git a/src/netutl.h b/src/netutl.h
index bce0aaee..69346bca 100644
--- a/src/netutl.h
+++ b/src/netutl.h
@@ -25,6 +25,7 @@
 
 struct addrinfo *str2addrinfo(const char *, const char *, int) __attribute__((__malloc__));
 sockaddr_t str2sockaddr(const char *, const char *);
+sockaddr_t str2sockaddr_random(struct meshlink_handle *mesh, const char *, const char *);
 void sockaddr2str(const sockaddr_t *, char **, char **);
 char *sockaddr2hostname(const sockaddr_t *) __attribute__((__malloc__));
 int sockaddrcmp(const sockaddr_t *, const sockaddr_t *) __attribute__((__warn_unused_result__));
-- 
2.39.5