#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>   /* for getservbyname */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>

int main(int argc, char **argv)
{
	int s;                        /* file descriptor */
	struct sockaddr_in address;
	char buffer[INET_ADDRSTRLEN]; /* for inet_pton */
	struct hostent *entry;        /* for gethostbyname, gethostbyaddr */
	pid_t pid;
	int c;                        /* return value of getchar is int, not char */
	int status;

	bzero((char *)&address, sizeof address);
	address.sin_family = AF_INET;

	if (argc == 2) {   /* one command line argument */
		const struct servent *const p = getservbyname("telnet", "tcp");
		if (p == NULL) {
			fprintf(stderr, "%s: couldn't find telnet port number\n",
				argv[0]);
			return 1;
		}
		address.sin_port = p->s_port; /* doesn't need htons */
	}

	else if (argc == 3) {   /* two command line arguments */
		/* %hd for "short decimal": a port number is 16 bits */
		if (sscanf(argv[2], "%hd", &address.sin_port) != 1) {
			fprintf(stderr, "%s: %s is not a legal port number\n",
				argv[0], argv[2]);
			return 2;
		}
		address.sin_port = htons(address.sin_port);
	}

	else {
		fprintf(stderr, "%s: usage hostname [port]\n", argv[0]);
		return 3;
	}

	entry = gethostbyname(argv[1]);
	if (entry == NULL) {
		fprintf(stderr, "%s: gethostbyname, h_errno == %d\n",
			argv[0], h_errno);
		return 4;
	}
	address.sin_addr.s_addr = *(in_addr_t *)entry->h_addr_list[0];

	s = socket(AF_INET, SOCK_STREAM, 0);
	if (s < 0) {
		perror(argv[0]);
		return 5;
	}

	if (inet_ntop(AF_INET, &address.sin_addr, buffer, sizeof buffer) == NULL) {
		perror(argv[0]);
		return 6;
	}
	printf("Trying %s...\n", buffer);

	if (connect(s, (struct sockaddr *)&address, sizeof address) != 0) {
		perror(argv[0]);
		return 7;
	}

	entry = gethostbyaddr((char *)&address.sin_addr, sizeof address.sin_addr,
		AF_INET);
	if (entry == NULL) {
		fprintf(stderr, "%s: gethostbyaddr, h_errno == %d\n",
			argv[0], h_errno);
		return 8;
	}
	printf("Connected to %s.\n", entry->h_name);

	pid = fork();
	if (pid < 0) {
		perror(argv[0]);
		return 9;
	}

	if (pid == 0) {
		/* Arrive here if I am the child.
		Copy from the server to the stdout. */

		char c;
		int n;
		while ((n = read(s, &c, 1)) == 1) {
			putchar(c);
		}
		if (n < 0) {
			perror(argv[0]);
			return 1;
		}
		return EXIT_SUCCESS;
	}

	/* Arrive here if I am the parent.
	Copy from the stdin to the server. */

	while ((c = getchar()) != EOF) {
		char ch = c;
		if (write(s, &ch, 1) != 1) {
			perror(argv[0]);
			return 10;
		}
	}

	if (shutdown(s, SHUT_RDWR) != 0) {
		perror(argv[0]);
		return 11;
	}

	pid = wait(&status);
	if (!WIFEXITED(status) || WEXITSTATUS(status) != EXIT_SUCCESS) {
		fprintf(stderr, "%s: child did not return exit status 0.\n",
			argv[0]);
		return 12;
	}

	return EXIT_SUCCESS;
}