CS473 - Computer Networks

Displaying exercises/e4/solution/listen.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <signal.h>

#include <sys/wait.h>

#define BUFSIZE	4096

char *sock_path = "/tmp/listen";

void clear(void)
{
  pid_t pid = fork();
  if (pid < 0) perror("fork");
  else if (pid == 0) {
    execlp("clear", "clear", NULL);
    perror("execlp");
    exit(0);
  } else {
    wait(NULL);
  }
}

void cleanup(int sig)
{
  unlink(sock_path);
  exit(0);
}


int main(int argc, char *argv[])
{
  struct sockaddr_un name;
  char buf[BUFSIZE];
  int r;

  if (argc > 1) sock_path = strdup(argv[1]);

  signal(SIGINT, cleanup);
  
  /* Create socket, initially un-connected. */
  int sock = socket(AF_UNIX, SOCK_DGRAM, 0);
  if (sock < 0) {
    perror("socket");
    exit(1);
  }
  
  /* Create name (filesystem socket file) */
  name.sun_family = AF_UNIX;
  strcpy(name.sun_path, sock_path);

  /* Abort if socket file is present */
  if (access(sock_path, F_OK) == 0) {
    printf("Socket file %s already exists, aborting.\n", sock_path);
    exit(0);
  }

  /* Bind socket to name: */
  if (bind(sock, (struct sockaddr *)&name, sizeof(struct sockaddr_un))) {
    perror("bind");
    exit(1);
  }

  clear();
  gethostname(buf, BUFSIZE);
  printf("Login to %s and say at %s\n", buf, sock_path);

  while((r = read(sock, buf, BUFSIZE)) > 0) {
    write(STDOUT_FILENO, buf, r);
  }
  return 0;
}