Unix Network Programming Episode 82

#include "unp.h"
#include <time.h>

int main(int argc, char **argv)
{
    int listenfd, connfd;
    socklen_t len;
    char buff[MAXLINE];
    time_t ticks;
    strct sockaddr_storage clientaddr;

    if(argc==2)
        listenfd=Tcp_listen(NULL,argv[1],&addrlen);
    else if(argc==3)
        listenfd=Tcp_listen(argv[1], argv[2], &addrlen);
    else 
        err_quit("usage: daytimetcpsrv2 [ <host> ] service or port>");
    
    for(;;)
    {
        len=sizeof(clientaddr);
        connfd=Accept(listenfd, (SA *)&clientaddr, &len);
        printf("connection from %s\n", Sock_ntop((SA *)&clientaddr,len));

        ticks=time(NULL);
        snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
        Write(connfd, buff, strlen(buff));

        Close(connfd);
    }

}

Protocol-independent daytime server that uses tcp_listen

‘udp_client’ Function

Our functions that provide a simpler interface to getaddrinfo change with UDP because we provide one client function that creates an unconnected UDP socket, and another in the next section that creates a connected UDP socket.

#include "unp.h"
int udp_client (const char *hostname, const char *service, struct sockaddr **saptr, socklen_t *lenp);

#include "unp.h"
int udp_client(const char *host, const char *serv, SA *saptr, socklen_t *lenp)
{
    int sockfd, n;
    struct addrinfo, *res, *ressave;

    bzero(&hints, sizeof(struct addrinfo));
    hints.ai_family=AF_UNSPEC;
    hints.ai_socktype=SOCK_DGRAM;
    
    if((n=getaddrinfo(host, serv, &hints, &res))!=0)
        err_quit("udp_client error for %s, %s: %s", host, serv, gai_strerror(n));
    
    ressave=res;

    do
    {
        sockfd=socket(res->ai_family, res->ai_socktype, res->ai_protocol);
        if(sockfd>=0)
            break;
    }while((res=res->ai_next)!=NULL);

    if(res==NULL)
        err_sys("udp_client error for %s, %s", host, serv);
    
    *saptr=Malloc(res->ai_addrlen);
    memcpy(*saptr, res->ai_addr, res->ai_addrlen);
    *lenp=res->ai_addrlen;

    freeaddrinfo(ressave);

    return sockfd;
}

udp_client function: creates an unconnected UDP socket