/* Bind the socket */
if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0)
errexit("can't bind to %s port: %s\n", service,
strerror(errno));
if (type == SOCK_STREAM && listen(s, qlen) < 0)
errexit("can't listen on %s port: %s\n", service,
strerror(errno));
return s;
}
int passiveTCP(const char *service,int qlen){
return passivesock(service,"tcp",qlen);
}
三、针对TIME服务的UDP客户软件的实现
1.网络拓扑结构：
2.源码：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdarg.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <time.h>
#include <errno.h>
#define BUFSIZE 64
#define UNIXEPOCH 2208988800UL
#define MSG "what time is it?\n"
extern int errno;
int errexit(const char *format,...);
int connectsock(const char *host, const char *service, const char *transport );
int connectUDP(const char *host, const char *service);
int main(int argc, char *argv[]){
char *host= "localhost";
char *service= "time";
time_t now;
int s,n;
switch(argc){
case 1:
host = "localhost";
break;
case 3:
service = argv[2];
case 2:
host=argv[1];
break;
default:
fprintf(stderr,"usage: UDPtime[host[port]]\n");
exit(1);
}
s=connectUDP(host,service);
(void)write(s,MSG,strlen(MSG));
n=read(s,(char *)&now,sizeof(now));
if(n<0) errexit("read failed: %s\n",strerror(errno));
now=ntohl((unsigned long)now);
now-=UNIXEPOCH;
printf("%s",ctime(&now));
exit(0);
}
int errexit(const char *format,...){
va_list arg;
va_start(arg, format);
vfprintf(stderr,format,arg);
va_end(arg);
exit(1);
}
int connectsock(const char *host, const char *service, const char *transport )
/*
* Arguments:
* host - name of host to which connection is desired
* service - service associated with the desired port
* transport - name of transport protocol to use ("tcp" or "udp")
*/
{
struct hostent *phe; /* pointer to host information entry */
struct servent *pse; /* pointer to service information entry */
struct protoent *ppe; /* pointer to protocol information entry*/
struct sockaddr_in sin; /* an Internet endpoint address */
int s, type; /* socket descriptor and socket type */
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
/* Map service name to port number */
if ( pse = getservbyname(service, transport) )
sin.sin_port = pse->s_port;
else if ((sin.sin_port=htons((unsigned short)atoi(service))) == 0)
errexit("can't get \"%s\" service entry\n", service);
/* Map host name to IP address, allowing for dotted decimal */
if ( phe = gethostbyname(host) )
memcpy(&sin.sin_addr, phe->h_addr, phe->h_length);
else if ( (sin.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE )
errexit("can't get \"%s\" host entry\n", host);
/* Map transport protocol name to protocol number */
if ( (ppe = getprotobyname(transport)) == 0)
errexit("can't get \"%s\" protocol entry\n", transport);
/* Use protocol to choose a socket type */
if (strcmp(transport, "udp") == 0)
type = SOCK_DGRAM;
else
type = SOCK_STREAM;
/* Allocate a socket */
s = socket(PF_INET, type, ppe->p_proto);
if (s < 0)
errexit("can't create socket: %s\n", strerror(errno));