select實現echo服務器

#include <stdio.h>

#define CLIENTSIZE 50
#define BUFFERSIZE 512

char ch_char(char c) {
    if(c >= 'a' && c <= 'z') 
    return c - 32;
    return c;
}

int main(int argc, char **argv){
    if(argc != 2){
        fprintf(stderr, " usage :%s port !\n", argv[0]);
        exit(1);
    }
    int server_listen, sockfd, max_fd;
    int client[CLIENTSIZE] = {0};
    memset(client, -1, sizeof(client));
    if((server_listen = socket_create(argv[1]))) < 0) {
        perror("socket_create");
        exit(1);
    }
    make_nonblock(server_listen);//轉換爲非阻塞狀態
    fd_set rfds, wfds, efds;
    max_fd = server_listen;

    whiel(1) {
        FD_ZERO(&rfds);
        FD_ZERO(&wfds);
        FD_ZERO(&efds);

        FD_SET(server_listen, &rfds);

        for(int i = 0 ; i < CLIENTSIZE; i++){
            if(client[i] == server_listen){
                continue;
            }
            if(client[i] > 0) {//有效的文件描述符
                if(max_fd < client[i]) max_fd = client[i];
                FD_SET(client[i], &rfds);
            }
        }

        if(select(max_fd + 1, &rfds, NULL, NULL, NULL) < 0){
            perror("select");
            return 1;
        }

        if(FD_ISSET(server_listen, &rfds)) {
            printf("connect ready on server_listen!\n");
            if((fd = accept(server_listen, NULL, NULL)) < 0){
                perror("accept");
                return 1;
            }
            if(sockfd > CLIENTSIZE){
                printf("too many clients!\n");
                close(sockfd);
            }else{
                make_nonblock(sockfd);
                if(client[sockfd] == -1)
                client[sockfd] = sockfd;
            }
        }

        for(int i = 0; i < CLIENTSIZE; i++) {
            if(i == server_listen) continue;
            if(FD_ISSET(i, &rfds)) {
                char buffer[BUFFERSIZE] = {0};
                int retval = recv(i ,buffer, BUFFERSIZE, 0);
                if(retval <= 0){
                    printf("logout!\n");
                    client[i] = -1;
                    close(1);
                    continue;
                }
                printf("recev : %s", buffer);
                for(int j = 0; j < strlen(buffer); j++) {
                    buffer[j] = ch_char(buffer[j]);
                }
                send(i, buffer, strlen(buffer), 0);
            }
        }
    }
    
    return 0;
}