util: add the perverse SNMP 'string' time format

/var/lib/mibs/ietf/SNMPv2-TC

DateAndTime ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "2d-1d-1d,1d:1d:1d.1d,1a1d:1d"
    STATUS       current
    DESCRIPTION
            "A date-time specification.

            field  octets  contents                  range
            -----  ------  --------                  -----
              1      1-2   year*                     0..65536
              2       3    month                     1..12
              3       4    day                       1..31
              4       5    hour                      0..23
              5       6    minutes                   0..59
              6       7    seconds                   0..60
                           (use 60 for leap-second)
              7       8    deci-seconds              0..9
              8       9    direction from UTC        '+' / '-'
              9      10    hours from UTC*           0..13
             10      11    minutes from UTC          0..59

            * Notes:
            - the value of year is in network-byte order
            - daylight saving time in New Zealand is +13

            For example, Tuesday May 26, 1992 at 1:30:15 PM EDT would be
            displayed as:

                             1992-5-26,13:30:15.0,-4:0

            Note that if only local time is known, then timezone
            information (fields 8-10) is not present."
    SYNTAX       OCTET STRING (SIZE (8 | 11))

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

include/util.h

@@ -20,6 +20,7 @@ char *format_time(uint64_t sec, int format);
 #define TIME_FORMAT_LEGACY 0
 #define TIME_FORMAT_SYSLOG 1
 #define TIME_FORMAT_SORTED 2
+#define TIME_FORMAT_SNMP   3
 
 /* Color printf() variant. */
 void cprintf(int color, const char *fmt, ...);

lib/util.c

@@ -85,6 +85,18 @@ char *format_time(uint64_t sec, int format)
 			t.tm_year + YEAR0, t.tm_mon + 1, t.tm_mday,
 			t.tm_hour, t.tm_min, t.tm_sec);
 		break;
+	case TIME_FORMAT_SNMP: /* See "DateAndTime" in mibs/ietf/SNMPv2-TC */
+		t.tm_year += YEAR0;
+		buf[0] = t.tm_year >> 8;
+		buf[1] = t.tm_year & 0xff;
+		buf[2] = t.tm_mon;
+		buf[3] = t.tm_mday;
+		buf[4] = t.tm_hour;
+		buf[5] = t.tm_min;
+		buf[6] = t.tm_sec;
+		buf[7] = 0;
+		/* we stop here, no time zone. Size is 8 */
+		break;
 	}
 
 	return buf;