From: Guus Sliepen <guus@meshlink.io>
Date: Thu, 13 Aug 2020 21:29:06 +0000 (+0200)
Subject: Set SO_REUSEPORT on the multicast sockets.
X-Git-Url: https://git.meshlink.io/?a=commitdiff_plain;h=e7086ece14ba7e10f701af465c04c77d2b060f2a;p=meshlink

Set SO_REUSEPORT on the multicast sockets.

On Linux this doesn't make any difference, but on macOS this is required
if any other process has already opened an mDNS multicast socket locally,
otherwise bind() will fail.
---

diff --git a/src/discovery.c b/src/discovery.c
index eb29c735..439bcbef 100644
--- a/src/discovery.c
+++ b/src/discovery.c
@@ -669,28 +669,48 @@ bool discovery_start(meshlink_handle_t *mesh) {
 	static const uint8_t ttl8 = 255;
 
 	int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+
+	if(fd == -1) {
+		logger(mesh, MESHLINK_ERROR, "Error creating IPv4 socket: %s", strerror(errno));
+	}
+
 	sockaddr_t sa4 = {
 		.in.sin_family = AF_INET,
 		.in.sin_port = ntohs(5353),
 	};
 	setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+	setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one));
 	setsockopt(fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one8, sizeof(one8));
 	setsockopt(fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl8, sizeof(ttl8));
-	bind(fd, &sa4.sa, SALEN(sa4.sa));
-	io_add(&mesh->loop, &mesh->discovery.sockets[0], mdns_io_handler, &mesh->discovery.sockets[0], fd, IO_READ);
+
+	if(bind(fd, &sa4.sa, SALEN(sa4.sa)) == -1) {
+		logger(mesh, MESHLINK_ERROR, "Error binding to IPv4 multicast socket: %s", strerror(errno));
+	} else {
+		io_add(&mesh->loop, &mesh->discovery.sockets[0], mdns_io_handler, &mesh->discovery.sockets[0], fd, IO_READ);
+	}
 
 	sockaddr_t sa6 = {
 		.in6.sin6_family = AF_INET6,
 		.in6.sin6_port = ntohs(5353),
 	};
 	fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);
+
+	if(fd == -1) {
+		logger(mesh, MESHLINK_ERROR, "Error creating IPv6 socket: %s", strerror(errno));
+	}
+
 	setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+	setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one));
 	setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 	setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
 	setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
 	setsockopt(fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
-	bind(fd, &sa6.sa, SALEN(sa6.sa));
-	io_add(&mesh->loop, &mesh->discovery.sockets[1], mdns_io_handler, &mesh->discovery.sockets[1], fd, IO_READ);
+
+	if(bind(fd, &sa6.sa, SALEN(sa6.sa)) == -1) {
+		logger(mesh, MESHLINK_ERROR, "Error binding to IPv4 multicast socket: %s", strerror(errno));
+	} else {
+		io_add(&mesh->loop, &mesh->discovery.sockets[1], mdns_io_handler, &mesh->discovery.sockets[1], fd, IO_READ);
+	}
 
 #if defined(__linux)
 	int sock = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);