Allow binding a listener to a specific network interface

Signed-off-by: Steven Lawrance <stl@koffein.net>

man/mosquitto.conf.5.xml

@@ -803,6 +803,16 @@
 						<para>Not reloaded on reload signal.</para>
 					</listitem>
 				</varlistentry>
+				<varlistentry>
+					<term><option>bind_interface</option> <replaceable>device</replaceable></term>
+					<listitem>
+						<para>Listen for incoming network connections only on
+							the specified interface. This is similar to the
+							preceding option but useful when an interface has
+							multiple addresses or the address may change.</para>
+						<para>Not reloaded on reload signal.</para>
+					</listitem>
+				</varlistentry>
 				<varlistentry>
 					<term><option>http_dir</option> <replaceable>directory</replaceable></term>
 					<listitem>

mosquitto.conf

@@ -207,6 +207,11 @@
 # Port to use for the default listener.
 #port 1883
 
+# Bind the listener to a specific interface. This is similar to
+# bind_address above but useful when an interface has multiple
+# addresses or the address may change. Only available on Linux.
+#bind_interface eth0
+
 # The maximum number of client connections to allow. This is 
 # a per listener setting.
 # Default is -1, which means unlimited connections.

src/conf.c

@@ -291,6 +291,7 @@ void config__cleanup(struct mosquitto__config *config)
 	if(config->listeners){
 		for(i=0; i<config->listener_count; i++){
 			mosquitto__free(config->listeners[i].host);
+			mosquitto__free(config->listeners[i].bind_interface);
 			mosquitto__free(config->listeners[i].mount_point);
 			mosquitto__free(config->listeners[i].socks);
 			mosquitto__free(config->listeners[i].security_options.auto_id_prefix);
@@ -915,6 +916,14 @@ int config__read_file_core(struct mosquitto__config *config, bool reload, struct
 					if(conf__attempt_resolve(config->default_listener.host, "bind_address", MOSQ_LOG_ERR, "Error")){
 						return MOSQ_ERR_INVAL;
 					}
+				}else if(!strcmp(token, "bind_interface")){
+#ifdef SO_BINDTODEVICE
+					if(reload) continue; // Listeners not valid for reloading.
+					if(conf__parse_string(&token, "bind_interface", &cur_listener->bind_interface, saveptr)) return MOSQ_ERR_INVAL;
+#else
+					log__printf(NULL, MOSQ_LOG_ERR, "Error: bind_interface specified but socket option not available.");
+					return MOSQ_ERR_INVAL;
+#endif
 				}else if(!strcmp(token, "bridge_attempt_unsubscribe")){
 #ifdef WITH_BRIDGE
 					if(reload) continue; // FIXME

src/mosquitto_broker_internal.h

@@ -212,6 +212,7 @@ struct mosquitto__listener {
 	int fd;
 	uint16_t port;
 	char *host;
+	char *bind_interface;
 	int max_connections;
 	char *mount_point;
 	mosq_sock_t *socks;

src/net.c

@@ -22,6 +22,7 @@ Contributors:
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <netinet/tcp.h>
+#include <net/if.h>
 #else
 #include <winsock2.h>
 #include <ws2tcpip.h>
@@ -395,6 +396,9 @@ int net__socket_listen(struct mosquitto__listener *listener)
 	X509_LOOKUP *lookup;
 	ENGINE *engine = NULL;
 #endif
+#ifdef SO_BINDTODEVICE
+	struct ifreq ifr;
+#endif
 
 	if(!listener) return MOSQ_ERR_INVAL;
 
@@ -446,6 +450,20 @@ int net__socket_listen(struct mosquitto__listener *listener)
 			return 1;
 		}
 
+#ifdef SO_BINDTODEVICE
+		if(listener->bind_interface){
+			memset(&ifr, 0, sizeof(ifr));
+			strncpy(ifr.ifr_name, listener->bind_interface, sizeof(ifr.ifr_name)-1);
+			ifr.ifr_name[sizeof(ifr.ifr_name)-1] = '\0';
+			log__printf(NULL, MOSQ_LOG_INFO, "Binding listener to interface \"%s\".", ifr.ifr_name);
+			if(setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0) {
+				net__print_error(MOSQ_LOG_ERR, "Error: %s");
+				COMPAT_CLOSE(sock);
+				return 1;
+			}
+		}
+#endif
+
 		if(bind(sock, rp->ai_addr, rp->ai_addrlen) == -1){
 			net__print_error(MOSQ_LOG_ERR, "Error: %s");
 			COMPAT_CLOSE(sock);