Unix Network Programming Episode 83

#include "unp.h"

int main(int argc, char **argv)
{
    int sockfd, n;
    char recvline[MAXLINE+1];
    socklen_t salen;
    struct sockaddr *sa;

    if(argc!=3)
        err_quit("usage: daytimeudpclil ");
    
    sockfd=Udp_client(argv[1], argv[2], (void **)&sa, &salen);
    printf("sending to %s\n", Sock_ntop_host(sa, salen));
    Sendto(sockfd, "", 1 ,0, sa ,salen);
    n=Recvfrom(sockfd, recvlien, MAXLINE, 0, NULL,NULL);
    recvlien[n]='\0';
    Fputs(recvline, stdout);
    
    return 0;
}

UDP daytime client using our udp_client function

‘udp_connect’ Function

Our udp_connect function creates a connected UDP socket.

#include "unp.h"
int udp_connect (const char *hostname, const char *service);

#include "unp.h"

int udp_connect(const char *host, const char *serv)
{
    int sockfd, n;
    struct addrinfo hints, *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_connect 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)
            continue;
        if(connect(sockfd, res->ai_addr, res->ai_addrlen)==0)
            break;
        
        Close(sockfd);

    }while((res=res->ai_next)!=NULL);

    if(res==NULL)
        err_sys("udp_connect error for %s, %s", host, serv);
    
    freeaddrinfo(ressave);
    return sockfd;
}

udp_connect function: creates a connected UDP socket

‘udp_server’ Function

Our final UDP function that provides a simpler interface to getaddrinfo is udp_server.

#include "unp.h"
int udp_server (const char *hostname, const char *service, socklen_t *lenptr);

#include "unp.h"

int udp_server(const char *host, const char *serv, soclen_t *addrlenp)
{
    int sockfd, n;
    struct addrinfo hints, *res, *ressave;

    bzero(&hints, sizeof(struct addrinfo));
    hints.ai_flags=Ai_PASSIVE;
    hints.ai_family=AF_UNSPEC;
    hints.ai_socktype=SOCK_DGRAM;
    if((n=getaddrinfo(host, serv, &hints, &res))!=0)
        err_quit("udp_server 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)
            contnue;
        if(bind(sockfd, res->ai_addr, res->ai_addrlen)==0)
            break;
        
        Close(socfd);
    }while((res=res->ai_next)!=NULL);

    if(res==NULL)
        err_sys("udp_server error for %s, %s", host, serv);

    if(addrlenp)
        *addrlenp=res->ai_addrlen;

    freeaddrinfo(ressave);

    return sockfd;
}

udp_server function: creates an unconnected socket for a UDP server