Advanced Programming in the UNIX® Environment

ptg10805159

620 Network IPC: Sockets Chapter 16

The other choice we have is to deal with the error by letting the user retry the

command. For simple applications this might be adequate, but for complex

applications it usually isn’t a viable alternative. Thus, it is generally better to use

connection-oriented sockets in this case.

The drawbacks to connection-oriented sockets arethat morework and time are

needed to establish a connection, and each connection consumes moreresources from

the operating system.

Example — Connectionless Client

The program in Figure16.19 is a version of theuptimeclient command that uses the

datagram socket interface.

#include "apue.h"

#include <netdb.h>

#include <errno.h>

#include <sys/socket.h>

#define BUFLEN 128

#define TIMEOUT 20

void

sigalrm(int signo)

{

}

void

print_uptime(int sockfd, struct addrinfo *aip)

{

int n;

char buf[BUFLEN];

buf[0] = 0;

if (sendto(sockfd, buf, 1, 0, aip->ai_addr, aip->ai_addrlen) < 0)

err_sys("sendto error");

alarm(TIMEOUT);

if ((n = recvfrom(sockfd, buf, BUFLEN, 0, NULL, NULL)) < 0) {

if (errno != EINTR)

alarm(0);

err_sys("recv error");

}

alarm(0);

write(STDOUT_FILENO, buf, n);

}

int

main(int argc, char *argv[])

{

struct addrinfo *ailist, *aip;

struct addrinfo hint;