Until now it is not possible to give absolute timestamps in odhcpd.
This means that on every new RA or request, the timestamp is renewed.
Further, the valid and preferred lifetimes are not synced between all
devices.

There are several usecases when it is needed to have absolute timestamp
that needed to be synced across all devices, e.g. your ISP delegates
you a prefix for some certain time, or you want to change to another
prefix.

The purpose of having this as a absolute timestamp is to make it easier
to track. An example configuration is

  option absolute_lifetime '1'
  option valid_lifetime '05 Jan 2021 23:00:00'
  option preferred_lifetime '05 Jan 2021 23:00:00'

If the valid_lifetime is in the past, the preferred lifetime and valid
lifetime are set to 1 minute.

Signed-off-by: Nick Hainke <[email protected]>
---
 README          |  8 ++++--
 src/config.c    | 69 ++++++++++++++++++++++++++++++++++---------------
 src/dhcpv6-ia.c | 10 +++++++
 src/odhcpd.h    |  1 +
 4 files changed, 65 insertions(+), 23 deletions(-)

diff --git a/README b/README
index f9cbb11..0af5c75 100644
--- a/README
+++ b/README
@@ -107,11 +107,13 @@ dns_service               bool    1                       
Announce the address of interface as DNS service
                                                        if the list of dns is 
empty
 domain                 list    <local search domain>   Search domains to 
announce
 
-leasetime              string  12h                     DHCPv4 address leasetime
+leasetime              string  12h                     DHCPv4 address 
leasetime. If absolute_lifetime is
+                                                       set the value can be 
given as a date, e.g. "10 Jan 2020 00:00:00".
 start                  integer 100                     DHCPv4 pool start
 limit                  integer 150                     DHCPv4 pool size
 preferred_lifetime     string  12h                     Value for the preferred 
lifetime
-                                                       for a prefix
+                                                       for a prefix. If 
absolute_lifetime is set the value can
+                                                       be given as a date, 
e.g. "10 Jan 2020 00:00:00".
 ra_default             integer 0                       Override default route
                        0: default, 1: ignore no public address, 2: ignore all
 ra_flags               list    other-config            List of RA flags to be
@@ -145,6 +147,8 @@ ndproxy_slave               bool    0                       
NDProxy external slave
 prefix_filter          string  ::/0                    Only advertise on-link 
prefixes within
                        [IPv6 prefix]                   the provided IPv6 
prefix; others are
                                                        filtered out.
+absolute_lifetime              bool    0                       Interpret 
configured lifetime as
+                                                       absolute timestamps. 
The format has to be "10 Jan 2020 00:00:00".
 
 
 Sections of type host (static leases)
diff --git a/src/config.c b/src/config.c
index 78b5855..42f73a1 100644
--- a/src/config.c
+++ b/src/config.c
@@ -8,6 +8,7 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <syslog.h>
+#include <time.h>
 
 #include <uci.h>
 #include <uci_blob.h>
@@ -83,6 +84,7 @@ enum {
        IFACE_ATTR_NDPROXY_SLAVE,
        IFACE_ATTR_PREFIX_FILTER,
        IFACE_ATTR_PREFERRED_LIFETIME,
+       IFACE_ATTR_ABSOLUTE_LIFETIME,
        IFACE_ATTR_MAX
 };
 
@@ -132,6 +134,7 @@ static const struct blobmsg_policy 
iface_attrs[IFACE_ATTR_MAX] = {
        [IFACE_ATTR_NDPROXY_SLAVE] = { .name = "ndproxy_slave", .type = 
BLOBMSG_TYPE_BOOL },
        [IFACE_ATTR_PREFIX_FILTER] = { .name = "prefix_filter", .type = 
BLOBMSG_TYPE_STRING },
        [IFACE_ATTR_PREFERRED_LIFETIME] = { .name = "preferred_lifetime", .type 
= BLOBMSG_TYPE_STRING },
+       [IFACE_ATTR_ABSOLUTE_LIFETIME] = { .name = "absolute_lifetime", .type = 
BLOBMSG_TYPE_BOOL },
 };
 
 static const struct uci_blob_param_info iface_attr_info[IFACE_ATTR_MAX] = {
@@ -212,6 +215,7 @@ static void set_interface_defaults(struct interface *iface)
        iface->ra_mininterval = iface->ra_maxinterval/3;
        iface->ra_lifetime = -1;
        iface->ra_dns = true;
+       iface->absolute_lifetime = false;
 }
 
 static void clean_interface(struct interface *iface)
@@ -321,29 +325,48 @@ static void set_config(struct uci_section *s)
        }
 }
 
-static double parse_leasetime(struct blob_attr *c) {
+static double parse_leasetime(struct blob_attr *c, bool absolute) {
        char *val = blobmsg_get_string(c), *endptr = NULL;
-       double time = strcmp(val, "infinite") ? strtod(val, &endptr) : 
UINT32_MAX;
-
-       if (time && endptr && endptr[0]) {
-               if (endptr[0] == 's')
-                       time *= 1;
-               else if (endptr[0] == 'm')
-                       time *= 60;
-               else if (endptr[0] == 'h')
-                       time *= 3600;
-               else if (endptr[0] == 'd')
-                       time *= 24 * 3600;
-               else if (endptr[0] == 'w')
-                       time *= 7 * 24 * 3600;
-               else
+       double ret_time = strcmp(val, "infinite") ? strtod(val, &endptr) : 
UINT32_MAX;
+
+       if (absolute)
+       {
+               // "10 Jan 2020 00:00:00"
+               // Parse absolut time
+               struct tm tm = {0};
+               char *s = strptime(val, "%d %b %Y %H:%M:%S", &tm);
+               if (s == NULL) {
+                       syslog(LOG_ERR, "Failed to Parse Date: %s", val);
                        goto err;
+               }
+
+               time_t now = odhcpd_time();
+               time_t wall_time = time(NULL);
+               time_t t = mktime(&tm);
+
+               double diff = difftime(t,wall_time);
+               ret_time += now + diff;
+       } else {
+               if (ret_time && endptr && endptr[0]) {
+                       if (endptr[0] == 's')
+                               ret_time *= 1;
+                       else if (endptr[0] == 'm')
+                               ret_time *= 60;
+                       else if (endptr[0] == 'h')
+                               ret_time *= 3600;
+                       else if (endptr[0] == 'd')
+                               ret_time *= 24 * 3600;
+                       else if (endptr[0] == 'w')
+                               ret_time *= 7 * 24 * 3600;
+                       else
+                               goto err;
+               }
        }
 
-       if (time < 60)
-               time = 60;
+       if (ret_time < 60)
+               ret_time = 60;
 
-       return time;
+       return ret_time;
 
 err:
        return -1;
@@ -409,7 +432,7 @@ int set_lease_from_blobmsg(struct blob_attr *ba)
        }
 
        if ((c = tb[LEASE_ATTR_LEASETIME])) {
-               double time = parse_leasetime(c);
+               double time = parse_leasetime(c, false); // do not support 
absolute timestamps for now
                if (time < 0)
                        goto err;
 
@@ -520,8 +543,12 @@ int config_parse_interface(void *data, size_t len, const 
char *name, bool overwr
        if ((c = tb[IFACE_ATTR_DYNAMICDHCP]))
                iface->no_dynamic_dhcp = !blobmsg_get_bool(c);
 
+
+       if ((c = tb[IFACE_ATTR_ABSOLUTE_LIFETIME]))
+               iface->absolute_lifetime = blobmsg_get_bool(c);
+
        if ((c = tb[IFACE_ATTR_LEASETIME])) {
-               double time = parse_leasetime(c);
+               double time = parse_leasetime(c, iface->absolute_lifetime);
                if (time < 0)
                        goto err;
 
@@ -529,7 +556,7 @@ int config_parse_interface(void *data, size_t len, const 
char *name, bool overwr
        }
 
        if ((c = tb[IFACE_ATTR_PREFERRED_LIFETIME])) {
-               double time = parse_leasetime(c);
+               double time = parse_leasetime(c, iface->absolute_lifetime);
                if (time < 0)
                        goto err;
 
diff --git a/src/dhcpv6-ia.c b/src/dhcpv6-ia.c
index a59fc20..78be8b8 100644
--- a/src/dhcpv6-ia.c
+++ b/src/dhcpv6-ia.c
@@ -865,6 +865,16 @@ static size_t build_ia(uint8_t *buf, size_t buflen, 
uint16_t status,
                        if (prefix_valid > leasetime)
                                prefix_valid = leasetime;
 
+                       if (iface->absolute_lifetime) {
+                               if ((long int) iface->dhcp_leasetime > now) {
+                                       prefix_valid = iface->dhcp_leasetime - 
now;
+                                       prefix_pref = iface->preferred_lifetime 
- now;
+                               } else { // if we have a timestamp in the past 
set pref and valid to 60s
+                                       prefix_valid = 60;
+                                       prefix_pref = 60;
+                               }
+                       }
+
                        if (a->flags & OAF_DHCPV6_PD) {
                                struct dhcpv6_ia_prefix o_ia_p = {
                                        .type = htons(DHCPV6_OPT_IA_PREFIX),
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 45b6784..98673a8 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -288,6 +288,7 @@ struct interface {
        uint32_t ra_hoplimit;
        int ra_mtu;
        uint32_t preferred_lifetime;
+       bool absolute_lifetime;
 
        // DHCP
        uint32_t dhcp_leasetime;
-- 
2.30.0


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