telnet.c

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

char* logo = 
"   ____  ____  ____  ____\n"
"  /\\   \\/\\   \\/\\   \\/\\   \\\n"
" /  \\___\\ \\___\\ \\___\\ \\___\\\n"
" \\  / __/_/   / /   / /   /\n"
"  \\/_/\\   \\__/\\/___/\\/___/\n"
"    /  \\___\\    /  \\___\\\n"
"    \\  / __/_  _\\  /   /\n"
"     \\/_/\\   \\/\\ \\/___/\n"
"       /  \\__/  \\___\\\n"
"       \\  / _\\  /   /\n"
"        \\/_/\\ \\/___/\n"
"          /  \\___\\\n"
"          \\  /   /\n"
"           \\/___/\n";

void telnet_session(FILE* in, FILE* out) {
	fputs("\e[0;44m\e[2J\e[H", out);
	fputs("\e[30m", out);
	fputs(logo, out);
	fputs("\e[3;40HLogin:\e[4;40H", out);
	fflush(out);
	char buf[256];
	fscanf(in, "%s", buf);
	fprintf(out, "\e[4;40H\e[K\e[3;40H\e[0KHello %s!", buf);
	fflush(out);
	sleep(3);
	fprintf(out, "\e[0m\e[2J\e[HGoodbye!\n");
	fflush(out);

	fclose(out);
	fclose(in);
}

int main() {
	struct sockaddr_in sa, sr;
	socklen_t addrsize = sizeof(sr);
	memset(&sa, 0, sizeof(sa));
	int sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (sock == -1) return 1;
	int yes = 1;
	if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
		perror("setsockopt"); return 4; }
	sa.sin_family = AF_INET;
	sa.sin_port = htons(23000);
	sa.sin_addr.s_addr = inet_addr("127.0.0.1");
	if (bind(sock, (struct sockaddr*)&sa, sizeof(sa)) == -1) { perror("bind"); return 2; }
	if (listen(sock, 5) == -1) return 3;
	for(;;) {
		int in_sock = accept(sock, (struct sockaddr*)&sr, &addrsize);
		if (in_sock == -1) { perror("accept"); return 7; }
		int pid = fork();
		if (pid == 0) {
			FILE *sinfile, *soutfile;
			sinfile = fdopen(in_sock, "r");
			soutfile = fdopen(in_sock, "w");
			if (sinfile == 0 || soutfile == 0) { perror("fdopen"); return 5; }
			telnet_session(sinfile, soutfile);
			close(in_sock);
			return 0;
		} else 
			close(in_sock);
	}
	close(sock);
	return 0;
}