一、问题引入

UNIX网络编程 卷1：套接字联网API（第三版） 第6章 介绍了I/O复用可以通过select()的单进程服务器与多客户端通信。

UNIX下可用的5中I/O模型：

• 阻塞式I/O
• 非阻塞式I/O
• I/O复用（select和poll）
• 信号驱动式I/O（SIGIO）
• 异步I/O（POSIX的aio_系列函数）

其中前面4种可以分为同步I/O，第五种为异步I/O。

二、解决过程

2-1 client 代码

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

#include <unistd.h>

#define IP "10.8.198.227"
#define PORT 8887
#define BUF_MAX_SIZE 1024

#define	min(a,b)	((a) < (b) ? (a) : (b))
#define	max(a,b)	((a) > (b) ? (a) : (b))

static int handle(int connect_fd, const char *socket)
{
    char buf[BUF_MAX_SIZE], read_buf[BUF_MAX_SIZE];
    int n;
    int maxfdp1, stdineof = 0;
    fd_set rset;

    FD_ZERO(&rset);
    while (1)
    {
        if (stdineof == 0)
            FD_SET(fileno(stdin), &rset);
        FD_SET(connect_fd, &rset);
        maxfdp1 = max(fileno(stdin), connect_fd) + 1;
        if (select(maxfdp1, &rset, NULL, NULL, NULL) < 0)
        {
            perror("select error");
            exit(1);
        }

        memset(buf, 0, BUF_MAX_SIZE);
        if (FD_ISSET(connect_fd, &rset)) // socket is readable
        {
            n = read(connect_fd, buf, BUF_MAX_SIZE);
            if (n == -1)
            {
                perror("read error");
                exit(1);
            }
            else if (n == 0)
            {
                if (stdineof == 1)
                    return 1;
                else
                {
                    perror("server terminated prematurely");
                    exit(1);
                }
            }
            memset(read_buf, 0, BUF_MAX_SIZE);
            sprintf(read_buf, "%s:%s(%d Byte)\n", socket, buf, n);
            write(fileno(stdout), read_buf, strlen(read_buf));
        }
        if (FD_ISSET(fileno(stdin), &rset)) // input is readable
        {
            n = read(fileno(stdin), buf, BUF_MAX_SIZE);
            if (n == -1)
            {
                perror("read error");
                exit(1);
            }
            else if (n == 0)
            {
                stdineof = 1;
                shutdown(connect_fd, SHUT_WR);
                FD_CLR(fileno(stdin), &rset);
                continue;
            }
            if (buf[n-1] == '\n') // remove the character '\n'
            {
                buf[n-1] = '\n';
                n = n - 1;
            }
            write(connect_fd, buf, n);
        }
    }
    return 0;
}

int main(void)
{
    int sockfd;
    char buf[1024];
    struct sockaddr_in server_addr;
    char server_socket[128];

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    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 = inet_addr(IP);
    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) < 0)
    {
        printf("connect error \n");
        return -1;
    }
    printf("server addr:%s por:%d\n",
           inet_ntop(AF_INET, &server_addr.sin_addr, buf, sizeof(buf)),
             ntohs(server_addr.sin_port));
    snprintf(server_socket, sizeof(server_socket), "server socket (%s:%d)",
             inet_ntop(AF_INET, &server_addr.sin_addr, buf, sizeof(buf)),
             ntohs(server_addr.sin_port));
    handle(sockfd, server_socket);
    close(sockfd);

    return EXIT_SUCCESS;
}

2-2 server 代码

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

#define MYPORT 8887
#define BACKLOG 5
#define BUF_SIZE 1024

typedef struct CLIENT_CONN_ST
{
    int connfd;
    char socket[128];
    struct sockaddr_in cliaddr;
} CLIENT_CONN_ST;

static CLIENT_CONN_ST g_client_conn[BACKLOG];

stat