9-7-server.c

#define _GNU_SOURCE       1
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <poll.h>

#define USER_LIMIT    5 /*最大用户数量*/
#define BUFFER_SIZE   1024
#define FD_LIMIT      65535

/*客户数据：客户端socket地址、待写到客户端的数据的位置、从客户端读入的数据 */
struct client_data
{
    sockaddr_in address;
    char *write_buf;
    char buf[BUFFER_SIZE];
};

int setnonblocking(int fd)
{
    int old_option = fcntl(fd, F_GETFL);
    int new_option = old_option | O_NONBLOCK;
    fcntl(fd, F_SETFL, new_option);
    return old_option;
}

int main(int argc, const char *argv[])
{
    if (argc < 2) 
    {
        fprintf(stderr, "usage: %s ip_address port_number\n", basename(argv[0]));
        return 1;
    }

    const char *ip = argv[1];
    int port       = atoi(argv[2]);

    int ret = 0;
    struct sockaddr_in  address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port = htons(port);

    int listenfd = socket(PF_INET, SOCK_STREAM, 0);
    assert(listenfd >= 0);

    ret = bind(listenfd, (struct sockaddr *)&address, sizeof(address));
    assert(ret != -1);
    ret = listen(listenfd, 5);
    assert(ret != -1);

    /*创建users数组，
     * 分配FD_LIMIT个client_data对象。可以预期：每个可能的socket
     * 连接可以获得一个这样的对象，
     * 并且socket的值可以直接用来索引（作为数组的下标)socket连接对应的client_data对象，
     * 这是将socket和客户数据关系的简单而高效的方式
     */
    client_data *users = new client_data[FD_LIMIT];
    
    /*尽管我们分配了足够的client_data 对象, 但为了提高poll的性能，
     * 仍然有必要限制用户的数量
     * */
    pollfd fds[USER_LIMIT + 1];
    int user_counter = 0;
    for(int i = 0; i <= USER_LIMIT; i++) 
    {
        fds[i].fd = -1;
        fds[i].events = 0;
    }

    fds[0].fd = listenfd;
    fds[0].events = POLLIN | POLLERR;
    fds[0].revents = 0;
    
    while(1)
    {
        ret = poll(fds, user_counter + 1, -1);
        if (ret < 1) 
        {
            fprintf(stderr, "poll failure\n");
            break;
        }

        for(int i = 0; i < user_counter + 1; i++) 
        {
            if ((fds[i].fd == listenfd) && (fds[i].revents & POLLIN )) 
            {
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof(client_address);
                int connfd = accept(listenfd, (struct sockaddr *)&client_address, &client_addrlength);
                if (connfd < 0) 
                {
                    fprintf(stderr, "accept error, errno is:%d\n", errno);
                    continue;
                }

                /*如果请求太多， 则关闭新到的连接 */
                if (user_counter >= USER_LIMIT) 
                {
                    const char *info = "too many users\n";
                    fprintf(stdout, "%s\n", info);
                    send(connfd, info, strlen(info), 0);
                    close(connfd);
                    continue;
                }
                
                /*对于新的连接，同时修改fds和users数组，前文已经提到，users[connnfd]
                 * 对应于新连接文件描述符connfd的客户数据
                 */
                user_counter ++;
                users[connfd].address = client_address;
                setnonblocking(connfd);
                fds[user_counter].fd = connfd;
                fds[user_counter].events = POLLIN | POLLRDHUP | POLLERR;
                fds[user_counter].revents= 0;
                fprintf(stdout, "comes a new user, now here %d users\n", user_counter);
            }
            else if (fds[i].revents & POLLERR) 
            {
                fprintf(stderr, "get an error from %d\n", fds[i].fd);
                char errors[100];
                memset(errors, '\0', 100);
                socklen_t length = sizeof(errors);
                if (getsockopt(fds[i].fd, SOL_SOCKET, SO_ERROR, &errors, &length) < 0) 
                {
                    fprintf(stderr, "get socket option failed\n");
                }
                continue;
            }
            else if (fds[i].revents & POLLIN) 
            {
                int connfd = fds[i].fd;
                memset(users[connfd].buf, '\0', BUFFER_SIZE);
                ret = recv(connfd, users[connfd].buf, BUFFER_SIZE - 1, 0);
                fprintf(stdout, "get %d bytes of client data %s from %d\n", ret, users[connfd].buf, connfd);
                if (ret < 0) 
                {
                    if (errno != EAGAIN) 
                    {
                        close(connfd);
                        users[fds[i].fd] = users[fds[user_counter].fd];
                        fds[i] = fds[user_counter];
                        i --;
                        user_counter -- ;
                    }
                }
                else if (ret == 0) 
                {
                }
                else
                {
                    for(int j = 0; j <= user_counter; ++j)
                    {
                        if(fds[j].fd == connfd)
                        {
                            continue;
                        }
                        fds[j].events |= ~POLLIN;
                        fds[j].events |= POLLOUT;
                        users[fds[j].fd].write_buf = users[connfd].buf;
                    }
                }
            }
            else if (fds[i].revents & POLLOUT) 
            {
                int connfd = fds[i].fd;
                if (!users[connfd].write_buf) 
                {
                    continue;
                }
                ret = send(connfd, users[connfd].write_buf, strlen(users[connfd].write_buf), 0);
                users[connfd].write_buf = NULL;
                fds[i].events |= ~POLLOUT;
                fds[i].events |= POLLIN;
            }
        }
    }
    
    delete [] users;
    close(listenfd);

    return 0;
}