+struct socket_in_netns_params {
+ int domain;
+ int type;
+ int protocol;
+ int netns;
+ int fd;
+};
+
+static void *socket_in_netns_thread(void *arg) {
+ struct socket_in_netns_params *params = arg;
+
+ if(setns(params->netns, CLONE_NEWNET) == -1) {
+ meshlink_errno = MESHLINK_EINVAL;
+ } else {
+ params->fd = socket(params->domain, params->type, params->protocol);
+ }
+
+ return NULL;
+}
+
+static int socket_in_netns(int domain, int type, int protocol, int netns) {
+ if(netns == -1) {
+ return socket(domain, type, protocol);
+ }
+
+ struct socket_in_netns_params params = {domain, type, protocol, netns, -1};
+
+ pthread_t thr;
+
+ if(pthread_create(&thr, NULL, socket_in_netns_thread, ¶ms) == 0) {
+ pthread_join(thr, NULL);
+ }
+
+ return params.fd;
+}
+
+// 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, int netns) {
+ 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_in_netns(rai->ai_family, rai->ai_socktype, rai->ai_protocol, netns);
+
+ if(sock == -1) {
+ freeaddrinfo(rai);
+ return false;
+ }
+
+ if(connect(sock, rai->ai_addr, rai->ai_addrlen) && !sockwouldblock(errno)) {
+ closesocket(sock);
+ freeaddrinfo(rai);
+ return false;
+ }
+
+ freeaddrinfo(rai);
+
+ struct sockaddr_storage sn;
+ socklen_t sl = sizeof(sn);
+
+ if(getsockname(sock, (struct sockaddr *)&sn, &sl)) {
+ closesocket(sock);
+ return false;
+ }
+
+ closesocket(sock);
+
+ if(getnameinfo((struct sockaddr *)&sn, sl, host, hostlen, NULL, 0, NI_NUMERICHOST | NI_NUMERICSERV)) {
+ return false;
+ }
+
+ return true;
+}
+