telnet.cpp

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <unistd.h>

#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define BUFLEN	10U
unsigned char buf[BUFLEN];
const unsigned short PORT(8888);
#define BACKLOG	16U

void errpro(int condition, const char *errmsg) {
	if (condition) {
		perror(errmsg);
		exit(EXIT_FAILURE);
	}
}

int clientpro(int fda[], unsigned int idx) {
	int ret(0);
	int cnt = recv(fda[idx], buf, BUFLEN-1, 0);
	errpro(-1 == cnt, "recv");
	if (0 == cnt) { // client go off
		printf("client[%u] goes off\n", idx);
	} else {
		ret = cnt;
		printf("-->[0x%x]\n", buf[0]);
		switch (buf[0]) {
			case 0x04:
				printf("^D\n");
				break;
			case 0x73:
				printf("getstatus\n");
				break;
			case 0xff:
				printf("client[%u] logout\n", idx);
				return 0;
				break;
			default:
				break;
		}
		buf[cnt] = '\0';
		printf("message from client[%u]:\n%s", idx, buf);
		while (BUFLEN-1 == cnt) {
			cnt = recv(fda[idx], buf, BUFLEN-1, 0);
			ret += cnt;
			errpro(-1 == cnt, "recv");
			buf[cnt] = '\0';
			printf("%s", buf);
		}
		char msg[] = "Hello, client x\n";
		msg[strlen(msg)-2] = idx + '0';
		errpro(-1 == send(fda[idx], msg, strlen(msg)+1, 0), "send");
	}
	return ret;
}

int main(int argc, char *argv[]) {
	struct sockaddr_in server_addr, client_addr;
	socklen_t sin_size(sizeof(server_addr));
	int sockfd;
	errpro(-1 == (sockfd = socket(AF_INET, SOCK_STREAM, 0)), "socket");
	int opval = 1;
	errpro(-1 == setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &opval,
				sizeof(opval)), "setsockopt");
	server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(PORT);
	server_addr.sin_addr.s_addr = INADDR_ANY;
	memset(server_addr.sin_zero, 0, sizeof(server_addr.sin_zero));

	errpro(-1 == bind(sockfd, (struct sockaddr *)&server_addr,
				sin_size), "bind");
	errpro(-1 == listen(sockfd, BACKLOG), "listen");
	printf("listen on port: %u\n", PORT);

	int maxsockfd(sockfd);
	struct timeval tv;
	unsigned int conn_cnt(0);
	int fda[BACKLOG]; // accepted connection fds
	memset(fda, 0, sizeof(fda));
	fd_set fds;
	while (1) {
		// init file descriptor set
		FD_ZERO(&fds);
		FD_SET(sockfd, &fds);
		// set timeout
		tv.tv_sec = 10;
		tv.tv_usec = 0;
		// add active connection to fd set
		for (unsigned int i = 0; i < BACKLOG; ++i) {
			if (fda[i] != 0) {
				FD_SET(fda[i], &fds);
			}
		}
		switch (select(maxsockfd+1, &fds, NULL, NULL, &tv)) {
			case -1:
				errpro(EXIT_FAILURE, "select");
				break;
			case 0:
				printf("timeout\n");
				continue;
				break;
			default:
				break;
		}
		// check every fd in the set
		for (unsigned int i = 0; i < conn_cnt; ++i) {
			if (FD_ISSET(fda[i], &fds)) {
				if (0 == clientpro(fda, i)) {
					--conn_cnt;
					close(fda[i]);
					FD_CLR(fda[i], &fds);
					fda[i] = 0;
				}
			}
		}

		// check whether a new connection comes
		if (FD_ISSET(sockfd, &fds)) {
			int fd = accept(sockfd, (struct sockaddr *)&client_addr, &sin_size);
			errpro(-1 == fd, "accept");

			// add fd to queue
			if (conn_cnt < BACKLOG) {
				fda[conn_cnt++] = fd;
				printf("new connection client[%u] %s:%u\n", conn_cnt,
						inet_ntoa(client_addr.sin_addr),
						ntohs(client_addr.sin_port));
				maxsockfd = fd > maxsockfd ? fd : maxsockfd;
			} else {
				printf("max connections reached, ignore new connection\n");
				char msg[] = "sorry, server is busy, please try later\n";
				errpro(-1 == send(fd, msg, strlen(msg)+1, 0), "send");
				close(fd);
			}
		}
		printf("client count: %u\n", conn_cnt);
	}
	// close active connections
	for (unsigned int i = 0; i < BACKLOG; ++i) {
		fda[i] != 0 ? close(fda[i]) : 0;
	}

	return 0;
}