Originální popis anglicky:
rtime - get time from a remote machine
Návod, kniha: RPC time function
#include <rpc/des_crypt.h>
int rtime(struct sockaddr_in *addrp, struct rpc_timeval
*timep, struct rpc_timeval *timeout);
This function uses the Time Server Protocol as described in RFC 868 to obtain
the time from a remote machine.
The Time Server Protocol gives the time in seconds since midnight 1900-01-01,
and this function subtracts the appropriate constant in order to convert the
result to seconds since midnight 1970-01-01, the Unix epoch.
When
timeout is non-NULL, the udp/time socket (port 37) is used.
Otherwise, the tcp/time socket (port 37) is used.
On success, 0 is returned, and the obtained 32-bit time value is stored in
timep->tv_sec. In case of error -1 is returned, and
errno is
set appropriately.
All errors for underlying functions (sendto, poll, recvfrom, connect, read) can
occur. Moreover:
- EIO
- The number of returned bytes is not 4.
- ETIMEDOUT
- The waiting time as defined in timeout has expired.
This example requires that port 37 is up and open. You may check that the time
entry within
/etc/inetd.conf is not commented out.
The program connects to a computer called 'linux'. Using 'localhost' does not
work. The result is the localtime of the computer 'linux'.
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <time.h>
#include <rpc/auth_des.h>
#include <netdb.h>
int use_tcp = 0;
char *servername = "linux";
int main() {
struct sockaddr_in name;
struct rpc_timeval time1 = {0,0};
struct rpc_timeval timeout = {1,0};
struct hostent *hent;
int ret;
memset((char *)&name, 0, sizeof(name));
sethostent(1);
hent = gethostbyname(servername);
memcpy((char *)&name.sin_addr, hent->h_addr, hent->h_length);
ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
if (ret < 0)
perror("rtime error");
else
printf("%s", ctime((time_t *)&time1.tv_sec));
return 0;
}
Only IPV4 is supported.
Some
in.timed versions only support TCP. Try the above example program
with
use_tcp set to 1.
Libc5 uses the prototype
int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);
and requires
<sys/time.h> instead of
<rpc/auth_des.h>.
rtime() in glibc <= 2.2.5 does not work properly on 64bit machines.
netdate(1),
ntpdate(1),
rdate(1),
inetd(8)
