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/include/osmocom/mslookup/mdns_sock.h b/include/osmocom/mslookup/mdns_sock.h
new file mode 100644
index 0000000..615e971
--- /dev/null
+++ b/include/osmocom/mslookup/mdns_sock.h
@@ -0,0 +1,33 @@
+/* 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/>.
+ */
+
+#pragma once
+#include <netdb.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/select.h>
+
+struct osmo_mdns_sock {
+ struct osmo_fd osmo_fd;
+ struct addrinfo *ai;
+};
+
+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);
+int osmo_mdns_sock_send(const struct osmo_mdns_sock *mdns_sock, struct msgb *msg);
+void osmo_mdns_sock_cleanup(struct osmo_mdns_sock *mdns_sock);