add mDNS lookup method to libosmo-mslookup
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.
Related: OS#4237
Patch-by: osmith, nhofmeyr
Change-Id: I03a0ffa1d4dc1b24ac78a5ad0975bca90a49c728
diff --git a/include/osmocom/mslookup/mdns.h b/include/osmocom/mslookup/mdns.h
new file mode 100644
index 0000000..b62e95f
--- /dev/null
+++ b/include/osmocom/mslookup/mdns.h
@@ -0,0 +1,39 @@
+/* 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/>.
+ */
+
+/*! \file mdns.h */
+
+#pragma once
+
+#include <osmocom/core/msgb.h>
+#include <osmocom/mslookup/mslookup.h>
+
+#define OSMO_MDNS_DOMAIN_SUFFIX_DEFAULT "mdns.osmocom.org"
+
+struct msgb *osmo_mdns_query_encode(void *ctx, uint16_t packet_id, const struct osmo_mslookup_query *query,
+ const char *domain_suffix);
+
+struct osmo_mslookup_query *osmo_mdns_query_decode(void *ctx, const uint8_t *data, size_t data_len,
+ uint16_t *packet_id, const char *domain_suffix);
+
+struct msgb *osmo_mdns_result_encode(void *ctx, uint16_t packet_id, const struct osmo_mslookup_query *query,
+ const struct osmo_mslookup_result *result, const char *domain_suffix);
+
+int osmo_mdns_result_decode(void *ctx, const uint8_t *data, size_t data_len, uint16_t *packet_id,
+ struct osmo_mslookup_query *query, struct osmo_mslookup_result *result,
+ const char *domain_suffix);