dns: add common dns_timestamp util functions

The dns structs have an unsigned 32 bit timestamp in hours since the
beginning of 1601. In a number of places we need to convert from unix
time to this timestamp, or from the timestamp to NTTIME.

You'll see subsequent patches that make use of these functions.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Jeremy Allison <jra@samba.org>

diff --git a/source4/dns_server/dnsserver_common.c b/source4/dns_server/dnsserver_common.c
index afd8df20194456b55dd819007f0c742e26497e2d..6142d2af406787a64c643ca3680cc73ef114cf62 100644 (file)
--- a/source4/dns_server/dnsserver_common.c
+++ b/source4/dns_server/dnsserver_common.c
@@ -1394,3 +1394,84 @@ bool dns_name_equal(const char *name1, const char *name2)
        }
        return strncasecmp(name1, name2, len1) == 0;
 }
+
+
+/*
+ * Convert unix time to a DNS timestamp
+ * uint32 hours in the NTTIME epoch
+ *
+ * This uses unix_to_nt_time() which can return special flag NTTIMEs like
+ * UINT64_MAX (0xFFF...) or NTTIME_MAX (0x7FF...), which will convert to
+ * distant future timestamps; or 0 as a flag value, meaning a 1601 timestamp,
+ * which is used to indicate a record does not expire.
+ *
+ * As we don't generally check for these special values in NTTIME conversions,
+ * we also don't check here, but for the benefit of people encountering these
+ * timestamps and searching for their origin, here is a list:
+ *
+ **  TIME_T_MAX
+ *
+ * Even if time_t is 32 bit, this will become NTTIME_MAX (a.k.a INT64_MAX,
+ * 0x7fffffffffffffff) in 100ns units. That translates to 256204778 hours
+ * since 1601, which converts back to 9223372008000000000 or
+ * 0x7ffffff9481f1000. It will present as 30828-09-14 02:00:00, around 48
+ * minutes earlier than NTTIME_MAX.
+ *
+ **  0, the start of the unix epoch, 1970-01-01 00:00:00
+ *
+ * This is converted into 0 in the Windows epoch, 1601-01-01 00:00:00 which is
+ * clearly the same whether you count in 100ns units or hours. In DNS record
+ * timestamps this is a flag meaning the record will never expire.
+ *
+ **  (time_t)-1, such as what *might* mean 1969-12-31 23:59:59
+ *
+ * This becomes (NTTIME)-1ULL a.k.a. UINT64_MAX, 0xffffffffffffffff thence
+ * 512409557 in hours since 1601. That in turn is 0xfffffffaf2028800 or
+ * 18446744052000000000 in NTTIME (rounded to the hour), which might be
+ * presented as -21709551616 or -0x50dfd7800, because NTITME is not completely
+ * dedicated to being unsigned. If it gets shown as a year, it will be around
+ * 60055.
+ *
+ **  Other negative time_t values (e.g. 1969-05-29).
+ *
+ * The meaning of these is somewhat undefined, but in any case they will
+ * translate perfectly well into the same dates in NTTIME.
+ *
+ **  Notes
+ *
+ * There are dns timestamps that exceed the range of NTTIME (up to 488356 AD),
+ * but it is not possible for this function to produce them.
+ *
+ * It is plausible that it was at midnight on 1601-01-01, in London, that
+ * Shakespeare wrote:
+ *
+ *  The time is out of joint. O cursed spite
+ *  That ever I was born to set it right!
+ *
+ * and this is why we have this epoch and time zone.
+ */
+uint32_t unix_to_dns_timestamp(time_t t)
+{
+       NTTIME nt;
+       unix_to_nt_time(&nt, t);
+       nt /= NTTIME_TO_HOURS;
+       return (uint32_t) nt;
+}
+
+/*
+ * Convert a DNS timestamp into NTTIME.
+ *
+ * Because DNS timestamps cover a longer time period than NTTIME, and these
+ * would wrap to an arbitrary NTTIME, we saturate at NTTIME_MAX and return an
+ * error in this case.
+ */
+NTSTATUS dns_timestamp_to_nt_time(NTTIME *_nt, uint32_t t)
+{
+       NTTIME nt = t;
+       if (nt > NTTIME_MAX / NTTIME_TO_HOURS) {
+               *_nt = NTTIME_MAX;
+               return NT_STATUS_INTEGER_OVERFLOW;
+       }
+       *_nt = nt * NTTIME_TO_HOURS;
+       return NT_STATUS_OK;
+}

diff --git a/source4/dns_server/dnsserver_common.h b/source4/dns_server/dnsserver_common.h
index 9d634fc1b7dd47c6a3cc98f794b58de1d73a063f..98af0a9a274f51edbdf88571078aa36c4a9c8063 100644 (file)
--- a/source4/dns_server/dnsserver_common.h
+++ b/source4/dns_server/dnsserver_common.h
@@ -119,4 +119,18 @@ bool dns_zoneinfo_load_zone_property(struct dnsserver_zoneinfo *zoneinfo,
                        dt == NULL ? "" : dt); \
        }
 
+/* There are this many nttime jiffies in an hour */
+#define NTTIME_TO_HOURS (3600ULL * 10ULL * 1000ULL * 1000ULL)
+
+/*
+ * convert unix time to a DNS timestamp
+ * (hours in the NTTIME epoch, 32 bit).
+ */
+uint32_t unix_to_dns_timestamp(time_t t);
+
+/*
+ * Convert a DNS timestamp into NTTIME.
+ */
+NTSTATUS dns_timestamp_to_nt_time(NTTIME *_nt, uint32_t t);
+
 #endif /* __DNSSERVER_COMMON_H__ */