Programming

#include <stdio.h>
#include <string.h>
#include <stdlib.h> /* exit() */
#include <errno.h> /* herror() */
#include <netdb.h> /* gethostbyname() */
#include <sys/types.h> /* bind() accept() */
#include <sys/socket.h> /* bind() accept() */

#define PORT 3490

main(int argc, char *argv[]) {
	int sockfd, n_sockfd, sin_size, len;
	char *host_addr, *recv_msg;
	struct hostent *host;
	struct sockaddr_in my_addr;
	struct sockaddr_in their_addr;

	if (argc != 3) {
		fprintf(stderr, "usage: %s [hostname] [ip address]\n",
		        argv[0]);
		exit(1);
	}
	if ((host = gethostbyname(argv[1])) == NULL) {
		herror("gethostbyname");
		exit(1);
	}
	if ((sockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1) {
		perror("socket");
		exit(1);
	}

	my_addr.sin_family = AF_INET;
	my_addr.sin_port = htons(PORT);
	my_addr.sin_addr.s_addr = inet_addr(argv[2]);
	memset(my_addr.sin_zero, '\0', sizeof my_addr.sin_zero);

	if ((bind(sockfd, (struct sockaddr *)&my_addr,
	     sizeof(struct sockaddr))) == -1) {
		perror("bind");
		exit(1);
	}
	if ((listen(sockfd, 10)) == -1) {
		perror("socket");
		exit(1);
	}
	sin_size = sizeof(struct sockaddr_in);
	if ((n_sockfd = accept(sockfd, (struct sockaddr *)&their_addr,
	    &sin_size)) == -1) {
		perror("accept");
		exit(1);
	}
	close(sockfd);

	host_addr = inet_ntoa(*((struct in_addr *)host->h_addr));

	len = strlen(host_addr);
	send(n_sockfd, host_addr, len, 0);
	len = strlen("\n");
	send(n_sockfd, "\n", len, 0);

	recv(n_sockfd, recv_msg, 10, 0);
	printf("%s\n", recv_msg);

	close(n_sockfd);
}

~/c/network/testing $ ./hostinfo google.com 127.0.0.1
hello
� +������F��V��f��v����
                       ~/c/network/testing $

~ $ telnet 127.0.0.1 3490
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
64.233.167.99
hello
Connection closed by foreign host.
~ $

bytes = recv(n_sockfd, recv_msg, 10, 0);
recv_msg[bytes] = '\0';
printf("%s\n", recv_msg);