add mDNS lookup method to libosmo-mslookup (#2)
Add the first actually useful lookup method to the mslookup library: multicast
DNS.
The server side is added in a subsequent commit, when the mslookup server is
implemented for the osmo-hlr program.
Use custom DNS encoding instead of libc-ares (which we use in OsmoSGSN
already), because libc-ares is only a DNS client implementation and we will
need both client and server.
Resubmit of f10463c5fc6d9e786ab7c648d99f7450f9a25906 after being
reverted in 110a49f69f29fed844d8743b76fd748f4a14812a. This new version
skips the mslookup_client_mdns test if multicast is not supported in the
build environment. I have verified that it doesn't break the build
anymore in my own OBS namespace.
Related: OS#4237, OS#4361
Patch-by: osmith, nhofmeyr
Change-Id: I3c340627181b632dd6a0d577aa2ea2a7cd035c0c
diff --git a/src/mslookup/mdns_sock.c b/src/mslookup/mdns_sock.c
new file mode 100644
index 0000000..5291660
--- /dev/null
+++ b/src/mslookup/mdns_sock.c
@@ -0,0 +1,144 @@
+/* Copyright 2019 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <stdbool.h>
+#include <talloc.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/select.h>
+#include <osmocom/hlr/logging.h>
+#include <osmocom/mslookup/mdns_sock.h>
+
+/*! Open socket to send and receive multicast data.
+ *
+ * The socket is opened with SO_REUSEADDR, so we can bind to the same IP and port multiple times. This socket receives
+ * everything sent to that multicast IP/port, including its own data data sent from osmo_mdns_sock_send(). So whenever
+ * sending something, the receive callback will be called with the same data and should discard it.
+ *
+ * \param[in] ip multicast IPv4 or IPv6 address.
+ * \param[in] port port number.
+ * \param[in] cb callback for incoming data that will be passed to osmo_fd_setup (should read from osmo_fd->fd).
+ * \param[in] data userdata passed to osmo_fd (available in cb as osmo_fd->data).
+ * \param[in] priv_nr additional userdata integer passed to osmo_fd (available in cb as osmo_fd->priv_nr).
+ * \returns allocated osmo_mdns_sock, NULL on error.
+ */
+struct osmo_mdns_sock *osmo_mdns_sock_init(void *ctx, const char *ip, unsigned int port,
+ int (*cb)(struct osmo_fd *fd, unsigned int what),
+ void *data, unsigned int priv_nr)
+{
+ struct osmo_mdns_sock *ret;
+ int sock, rc;
+ struct addrinfo hints = {0};
+ struct ip_mreq multicast_req = {0};
+ in_addr_t iface = INADDR_ANY;
+ char portbuf[10];
+ int y = 1;
+
+ snprintf(portbuf, sizeof(portbuf) -1, "%u", port);
+ ret = talloc_zero(ctx, struct osmo_mdns_sock);
+ OSMO_ASSERT(ret);
+
+ /* Fill addrinfo */
+ hints.ai_family = PF_UNSPEC;
+ hints.ai_socktype = SOCK_DGRAM;
+ hints.ai_flags = (AI_PASSIVE | AI_NUMERICHOST);
+ rc = getaddrinfo(ip, portbuf, &hints, &ret->ai);
+ if (rc != 0) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "osmo_mdns_sock_init: getaddrinfo: %s\n", gai_strerror(rc));
+ ret->ai = NULL;
+ goto error;
+ }
+
+ /* Open socket */
+ sock = socket(ret->ai->ai_family, ret->ai->ai_socktype, 0);
+ if (sock == -1) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "osmo_mdns_sock_init: socket: %s\n", strerror(errno));
+ goto error;
+ }
+
+ /* Set multicast options */
+ rc = setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, (char*)&iface, sizeof(iface));
+ if (rc == -1) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "osmo_mdns_sock_init: setsockopt: %s\n", strerror(errno));
+ goto error;
+ }
+ memcpy(&multicast_req.imr_multiaddr, &((struct sockaddr_in*)(ret->ai->ai_addr))->sin_addr,
+ sizeof(multicast_req.imr_multiaddr));
+ multicast_req.imr_interface.s_addr = htonl(INADDR_ANY);
+ rc = setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&multicast_req, sizeof(multicast_req));
+ if (rc == -1) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "osmo_mdns_sock_init: setsockopt: %s\n", strerror(errno));
+ goto error;
+ }
+
+ /* Always allow binding the same IP and port twice. This is needed in OsmoHLR (where the code becomes cleaner by
+ * just using a different socket for server and client code) and in the mslookup_client_mdns_test. Also for
+ * osmo-mslookup-client if it is running multiple times in parallel (i.e. two incoming calls almost at the same
+ * time need to be resolved with the simple dialplan example that just starts new processes). */
+ rc = setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char *)&y, sizeof(y));
+ if (rc == -1) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "osmo_mdns_sock_init: setsockopt: %s\n", strerror(errno));
+ goto error;
+ }
+
+ /* Bind and register osmo_fd callback */
+ rc = bind(sock, ret->ai->ai_addr, ret->ai->ai_addrlen);
+ if (rc == -1) {
+ LOGP(DMSLOOKUP, LOGL_ERROR, "osmo_mdns_sock_init: bind: %s\n", strerror(errno));
+ goto error;
+ }
+ osmo_fd_setup(&ret->osmo_fd, sock, OSMO_FD_READ, cb, data, priv_nr);
+ if (osmo_fd_register(&ret->osmo_fd) != 0)
+ goto error;
+
+ return ret;
+error:
+ if (ret->ai)
+ freeaddrinfo(ret->ai);
+ talloc_free(ret);
+ return NULL;
+}
+
+/*! Send msgb over mdns_sock and consume msgb.
+ * \returns 0 on success, -1 on error.
+ */
+int osmo_mdns_sock_send(const struct osmo_mdns_sock *mdns_sock, struct msgb *msg)
+{
+ size_t len = msgb_length(msg);
+ int rc = sendto(mdns_sock->osmo_fd.fd, msgb_data(msg), len, 0, mdns_sock->ai->ai_addr,
+ mdns_sock->ai->ai_addrlen);
+ msgb_free(msg);
+ return (rc == len) ? 0 : -1;
+}
+
+/*! Tear down osmo_mdns_sock. */
+void osmo_mdns_sock_cleanup(struct osmo_mdns_sock *mdns_sock)
+{
+ osmo_fd_close(&mdns_sock->osmo_fd);
+ freeaddrinfo(mdns_sock->ai);
+ talloc_free(mdns_sock);
+}