void reaper(int);
int TCPechod(int fd);
int errexit(const char *format,...);
int passivesock(const char *service, const char *transport, int qlen);
int passiveTCP(const char *service,int qlen);

int main(int argc, char *argv[]){
? ? char *service= "echo";
? ? struct sockaddr_in fsin;
? ? unsigned int alen;
? ? int msock,ssock;
? ? switch(argc){
case 1:
? ? break;
case 2:
? ? service=argv[1];
? ? break;
default:
? ? errexit("usage: TCPechod [port]\n");
? ? }

? ? msock=passiveTCP(service,QLEN);
? ? (void)signal(SIGCHLD,(__sighandler_t)QLEN);

? ? while(1){
? ? ? ? alen=sizeof(fsin);
? ? ? ? ssock=accept(msock,(struct sockaddr *)&fsin,&alen);
? ? ? ? if(ssock<0){
? ? ? ? ? ? if(errno==EINTR)? ? continue;
? ? ? ? ? ? errexit("accept: %s\n",strerror(errno));
? ? ? ? }
? ? ? ? switch(fork()){
? ? case 0:
? ? ? ? (void)close(msock);
? ? ? ? exit(TCPechod(ssock));
? ? default:
? ? ? ? (void)close(ssock);
? ? ? ? break;
? ? case -1:
? ? ? ? errexit("fork: %s\n",strerror(errno));
? ? ? ? }
? ? }
}

void reaper(int sig){
? ? int status;
? ? while(wait3(&status,WNOHANG,(struct rusage *)0)>=0) ;
}
int TCPechod(int fd){
? ? char buf[BUFSIZ];
? ? int cc;

? ? while(cc=read(fd,buf,sizeof(buf))){
? ? ? ? if(cc<0)
? ? ? ? ? ? errexit("echo read: %s\n",strerror(errno));
? ? ? ? if(write(fd,buf,cc)<0)
? ? ? ? ? ? errexit("echo write: %s\n",strerror(errno));
? ? }
? ? return 0;
}
int errexit(const char *format,...){
? ? va_list arg;
? ? va_start(arg, format);
? ? vfprintf(stderr,format,arg);
? ? va_end(arg);
? ? exit(1);
}
int passivesock(const char *service, const char *transport, int qlen)
/*
?* Arguments:
?*? ? ? service? - service associated with the desired port
?*? ? ? transport - transport protocol to use ("tcp" or "udp")
?*? ? ? qlen? ? ? - maximum server request queue length
?*/
{

? ? 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;
? ? sin.sin_addr.s_addr = INADDR_ANY;

? ? ? ? /* Map service name to port number */
? ? if ( pse = getservbyname(service, transport) )
? ? sin.sin_port = htons(ntohs((unsigned short)pse->s_port)+ portbase);
? ? else
? ? ? ? ? ? ? if ((sin.sin_port=htons((unsigned short)atoi(service)+portbase)) == 0)
? ? errexit("can't create passive service %d \n",sin.sin_port);

? ? ? ? /* Map 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));

? ? ? ? /* 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
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include