Linux下的I/O复用

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

int main( int argc, char **argv )
{
    //判断输入参数的合法性
    if ( argc <= 1 )
    {
        printf("usage: %s port\n", argv[0]);
        return -1;
    }

    int port = atoi(argv[1]);
    printf("listen at port:%d.\n", port);

    //服务端地址
    struct sockaddr_in server_addr;
    memset( &server_addr, 0, sizeof(server_addr) );
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port);
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);

    //创建套接字
    int server_fd = socket( AF_INET, SOCK_STREAM, 0 );
    if ( -1 == server_fd )
    {
        printf("create socket failed.\n");
        return -1;
    }

    //绑定套接字
    int ret = bind( server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr) );
    if ( -1 == ret )
    {
        printf("bind failed.\n");
        return -1;
    }

    //监听
    ret = listen( server_fd, 5 );
    if ( -1 == ret )
    {
        printf("listen failed.\n");
        return -1;
    }

    //客户端地址
    struct sockaddr_in client_addr;
    memset( &client_addr, 0, sizeof(client_addr) );
    socklen_t client_addr_len = sizeof(client_addr);

    //接收客户端连接 为了方便此处只接收一个来自客户端的请求
    int talk_fd = accept( server_fd, (struct sockaddr*)&client_addr, &client_addr_len );
    if ( -1 == talk_fd )
    {
        printf("accept failed.\n");
        close( server_fd );
        return -1;
    }

    //接收信息缓冲区
    char buff[1204];
    memset( buff, 0, sizeof(buff) );


    fd_set read_fd;         //关注的可读文件描述符集合
    fd_set exception_fd;    //关注的异常文件描述符集合
    FD_ZERO( &read_fd );    //清空可读文件描述符集合的所有位
    FD_ZERO( &exception_fd );   //清空异常文件描述符集合的所有位

    while(1)
    {
        //清空信息缓冲区
        memset( buff, 0, sizeof(buff) );
        //每次调用select前需要重新设置文件描述符集合 因为事件发生之后文件描述符集合将被内核修改
        FD_SET( talk_fd, &read_fd );     //将客户端、服务端的socket描述符加入可读描述符集合
        FD_SET( talk_fd, &exception_fd );//将客户端、服务端的socket描述符加入异常描述符集合

        //阻塞在select调用 直到可读、异常描述符集合发生状态变化
        ret = select( talk_fd + 1, &read_fd, NULL, &exception_fd, NULL );
        if ( -1 == ret )
        {
            printf("select failed.\n");
            return -1;
        }
        
        //对于可读事件 采用普通的recv函数读取数据
        if ( FD_ISSET( talk_fd, &read_fd ) )
        {
            ret = recv( talk_fd, buff, sizeof(buff) - 1, 0 );
            
            if ( ret < 0 )
            {
                printf("recv read_fd failed.\n");
                break;
            }

            //输出接收到的普通数据
            printf( "get %d bytes of normal data: %s\n", ret, buff );
        }

        //对于异常事件 采用带MSG_OOB标志的recv函数接收数据
        if ( FD_ISSET( talk_fd, &exception_fd ) )
        {
            ret = recv( talk_fd, buff, sizeof(buff) - 1, MSG_OOB );
            if ( ret < 0 )
            {
                printf("recv exception_fd failed.\n");
                break;
            }

            //输出接收到的异常数据
            printf( "get %d bytes of oob data: %s\n", ret, buff );
        }
    }

    close( talk_fd );
    close( server_fd );
    return 0;
}