D-GSM 1/n: add mslookup server in osmo-hlr

Implement the mslookup server to service remote mslookup requests.

This patch merely adds the logic to answer incoming mslookup requests, an
actual method to receive requests (mDNS) follows in a subsequent patch.

- API to configure service names and addresses for the local site (per MSC).
- determine whether a subscriber is on a local MSC
  (checking the local proxy will be added in subsequent patch that adds proxy
  capability).
- VTY config follows in a subsequent patch.

For a detailed overview of the D-GSM and mslookup related files, please see the
elaborate comment at the top of mslookup.c (already added in an earlier patch).

Change-Id: Ife4a61d71926d08f310a1aeed9d9f1974f64178b

1 files changed, 53 insertions, 0 deletions

diff --git a/src/timestamp.c b/src/timestamp.c
new file mode 100644
index 0000000..002857d
--- /dev/null
+++ b/src/timestamp.c
@@ -0,0 +1,53 @@
+/* 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 Affero General Public License as published by
+ * the Free Software Foundation; either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <osmocom/core/timer.h>
+#include <osmocom/hlr/timestamp.h>
+
+/* Central implementation to set a timestamp to the current time, in case we want to modify this in the future. */
+void timestamp_update(timestamp_t *timestamp)
+{
+	struct timeval tv;
+	time_t raw;
+	struct tm utc;
+	/* The simpler way would be just time(&raw), but by using osmo_gettimeofday() we can also use
+	 * osmo_gettimeofday_override for unit tests independent from real time. */
+	osmo_gettimeofday(&tv, NULL);
+	raw = tv.tv_sec;
+	gmtime_r(&raw, &utc);
+	*timestamp = mktime(&utc);
+}
+
+/* Calculate seconds since a given timestamp was taken. Return true for a valid age returned in age_p, return false if
+ * the timestamp is either in the future or the age surpasses uint32_t range. When false is returned, *age_p is set to
+ * UINT32_MAX. */
+bool timestamp_age(const timestamp_t *timestamp, uint32_t *age_p)
+{
+	int64_t age64;
+	timestamp_t now;
+	timestamp_update(&now);
+	age64 = (int64_t)now - (int64_t)(*timestamp);
+	if (age64 < 0 || age64 > UINT32_MAX) {
+		*age_p = UINT32_MAX;
+		return false;
+	}
+	*age_p = (uint32_t)age64;
+	return true;
+}
+