#include <stdio.h>
#include <stdlib.h>
#include <string.h>        //for strlen, strspn
#include <unistd.h>        //for fork

#include <sys/types.h>     //for socket, fork, wait
#include <sys/socket.h>    //for socket, shutdown
#include <sys/wait.h>

#include <netdb.h>         //for gethostbyname, getservbyname
#include <netinet/in.h>    //for inet_ntop
#include <arpa/inet.h>      //for inet_ntop

int main(int argc, char **argv)
{
	struct hostent *host;
	int s;
	struct sockaddr_in echo;
	char buffer[INET6_ADDRSTRLEN];

	pid_t pid;
	int status;

	int i;    /* getchar requires an int: KR p. 16 */
	char c;   /* write requires a char: KR p. 170 */

	if (argc < 2 || argc > 3) {
		fprintf(stderr, "%s: requires hostname and optional port number\n",
			argv[0]);
		return 1;
	}

	host = gethostbyname(argv[1]);
	if (host == NULL) {
		fprintf(stderr, "%s: %s: Unknown host\n", argv[0], argv[1]);
		return 2;
	}

	s = socket(AF_INET, SOCK_STREAM, 0);
	if (s < 0) {
		perror(argv[0]);
		return 3;
	}

	bzero((char *)&echo, sizeof echo);
	echo.sin_family = AF_INET;
	echo.sin_addr.s_addr = *(in_addr_t *)*host->h_addr_list;

	if (argc < 3) {
		struct servent *server = getservbyname("telnet", "tcp");
		if (server == NULL) {
			perror(argv[0]);
			return 4;
		}
		echo.sin_port = htons(server->s_port);
	}

	else {
		const size_t length = strlen(argv[2]);
		if (length <= 0) {
			fprintf(stderr, "%s: second argument must be port number\n", argv[0]);
			return 5;
		}

		if (strspn(argv[2], "0123456789") != length) {
			fprintf(stderr, "%s: second argument must be all digits\n", argv[0]);
			return 6;
		}

		echo.sin_port = htons(atoi(argv[2]));
	}

	if (inet_ntop(AF_INET, &echo.sin_addr, buffer, sizeof buffer) == NULL) {
		perror(argv[0]);
		return 7;
	}
	printf("Trying %s...\n", buffer);

	if (connect(s, (struct sockaddr *)&echo, sizeof echo) != 0) {
		perror(argv[0]);
		return 8;
	}

	printf("Connected to %s.\n"
		"Escape character is '^d'.\n", buffer);

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

	if (pid == 0) {
		/* The child will copy from the server to the stdout. */
		while (read(s, &c, 1) == 1) {
			putchar(c);
		}

		fprintf(stderr, "Connection closed by foreign host.\n");
		return EXIT_SUCCESS;
	}

	/* The parent will copy from the stdin to the server. */
	while ((i = getchar()) != EOF) {
		c = i;
		if (write(s, &c, 1) != 1) {
			perror(argv[0]);
			return 10;
		}
	}

	if (shutdown(s, SHUT_RDWR) != 0) {	/* terminate while loop in line 95 */
		perror(argv[0]);
		return 11;
	}

	wait(&status);
	if (WIFEXITED(status)) {
		printf("My child's exit status was %d.\n", WEXITSTATUS(status));
	}

	else if (WIFSIGNALED(status)) {
		printf("My child was terminated by signal number%d.\n", WTERMSIG(status));
	}

	else if (WIFSTOPPED(status)) {
		printf("My child was stopped by signal number%d.\n", WSTOPSIG(status));
	}

	else {
		fprintf(stderr, "%s: couldn't find out how child ended up.\n", argv[0]);
	}

	return EXIT_SUCCESS;
}