sd-dhcp6-lease: Add helper function to compute remaining expiry time

Create a helper function to compute the remaining time in seconds from
time T2 to the IPv6 address with the longest lifetime. The computed
time is used as the Maximum Retransmission Duration in Rebinding state.
See RFC 3315, section 18.1.4. for details.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/libsystemd-network/sd-dhcp6-lease.c b/src/libsystemd-network/sd-dhcp6-lease.c
index cbda7d8c84..17a4b64063 100644
--- a/src/libsystemd-network/sd-dhcp6-lease.c
+++ b/src/libsystemd-network/sd-dhcp6-lease.c
@@ -33,6 +33,28 @@ int dhcp6_lease_clear_timers(DHCP6IA *ia) {
         return 0;
 }
 
+int dhcp6_lease_ia_rebind_expire(const DHCP6IA *ia, uint32_t *expire) {
+        DHCP6Address *addr;
+        uint32_t valid = 0, t;
+
+        assert_return(ia, -EINVAL);
+        assert_return(expire, -EINVAL);
+
+        LIST_FOREACH(addresses, addr, ia->addresses) {
+                t = be32toh(addr->lifetime_valid);
+                if (valid < t)
+                        valid = t;
+        }
+
+        t = be32toh(ia->lifetime_t2);
+        if (t > valid)
+                return -EINVAL;
+
+        *expire = valid - t;
+
+        return 0;
+}
+
 DHCP6IA *dhcp6_lease_free_ia(DHCP6IA *ia) {
         DHCP6Address *address;