int server_sock;
int client_sock;

struct sockaddr_in server_addr;
struct sockaddr_in client_addr;

socklen_t client_size;

server_sock = socket(AF_INET, SOCK_STREAM, 0);

memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
server_addr.sin_port = htons(atoi(argv[1]));
bind(server_sock, (struct sockaddr *)&server_addr, sizeof(server_addr));

listen(server_sock, 5);

fd_set reads;
fd_set read_init;
int fd_max;
int fd_num;
struct timeval timeout;

char buf[BUF_SIZE+1];
int str_len;

fd_max = server_sock;
FD_ZERO(&read_init);
FD_SET(server_sock, &read_init);

while (1) {
        reads = read_init;
        timeout.tv_sec = 5;
        timeout.tv_usec = 0;
        fd_num = select(fd_max+1, &reads, 0, 0, &timeout);
        if (fd_num < 0) { // select error
                break;
        } else if (fd_num == 0) {
                printf("timeout ...\n");
                continue;
        }

        for (int i = 0; i < fd_max+1; i++) {
                if (FD_ISSET(i, &reads)) {
                        if (server_sock == i) { // 表示有客户端发起连接请求
                                client_size = sizeof(client_addr);
                                client_sock = accept(server_sock, (struct sockaddr *)&client_addr, &client_size);

                                FD_SET(client_sock, &read_init);

                                if (fd_max < client_sock) {
                                        fd_max = client_sock;
                                }

                                printf("client connect: %d\n", client_sock);

                        } else { // 表示有客户端发送信息来了
                                str_len = read(i, buf, BUF_SIZE);
                                buf[str_len] = 0;
                                if (str_len == 0) {
                                        FD_CLR(i, &read_init);
                                        close(i);
                                        printf("client closed: %d\n", i);
                                } else {
                                        write(i, buf, str_len);
                                }
                        }
                }
        }
}

close(server_sock);
close(client_sock);