网络编程-select模型

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <pthread.h>
#include <unistd.h>
#define BUFFER_LENGTH 128
int main()
{
    int listenfd = socket(AF_INET, SOCK_STREAM, 0);
    if (listenfd == -1) return -1;
    struct sockaddr_in servaddr;
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(9999);
    if (-1 == bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)))
    {
        return -2;
    }
#if 0 //nonblock
    int flag = fcntl(listenfd, F_GETFL, 0);
    flag |= O_NONBLOCK;
    fcntl(listenfd, F_SETFL, flag);
#endif
    listen(listenfd, 10);
#if 0
    struct sockaddr_in client;
    socklen_t len = sizeof(client);
    int clientfd = accept(listenfd, (struct sockaddr*)&client, &len);
    printf("clientfd: %d\n", clientfd);
    while(1){
        unsigned char buffer[BUFFER_LENGTH] = {0};
        int ret = recv(clientfd, buffer, BUFFER_LENGTH, 0);
        printf("buffer : %s, ret: %d\n", buffer, ret);
        send(clientfd, buffer, ret, 0);
    }
#else
    //rfds,wfds用来设置，rset,wset用来检测
    fd_set rfds, wfds, rset, wset;
    FD_ZERO(&rfds);
    FD_SET(listenfd, &rfds);
    FD_ZERO(&wfds);
    int maxfd = listenfd;
    unsigned char buffer[BUFFER_LENGTH] = {0};
    while (1) {
        rset = rfds;
        wset = wfds;
        select(maxfd + 1, &rset, &wset, NULL, NULL);
        if (FD_ISSET(listenfd, &rset)) {
            printf("listenfd->\n");
            struct sockaddr_in client;
            socklen_t len = sizeof(client);
            int clientfd = accept(listenfd, (struct sockaddr*)&client, &len);
            printf("clientfd: %d\n", clientfd);
            FD_SET(clientfd, &rfds);
            if (clientfd > maxfd) maxfd = clientfd;
        }
        int ret;
        for (int i = listenfd + 1; i <= maxfd; i++) {
            if (FD_ISSET(i, &rset)) {
                ret = recv(i, buffer, BUFFER_LENGTH, 0);
                if (ret == 0) {
                    close(i);
                    FD_CLR(i, &rfds);
                } else if (ret > 0) {
                    printf("buffer : %s, ret: %d\n", buffer, ret);
                    FD_SET(i, &wfds);
                }
            } else if (FD_ISSET(i, &wset)) {
                send(i, buffer, ret, 0);
                FD_CLR(i, &wfds);
                FD_SET(i, &rfds);
            }
        }
    }
#endif
    return 0;
}