前言

本章节是用基本的Linux/Unix基本函数加上poll调用编写一个完整的服务器和客户端例子，可在Linux(ubuntu)和Unix(freebsd)上运行，客户端和服务端的功能如下:

客户端从标准输入读入一行，发送到服务端

服务端从网络读取一行，然后输出到客户端

客户端收到服务端的响应，输出这一行到标准输出

服务端

代码如下:

#include  <unistd.h>
#include  <sys/types.h>       /* basic system data types */
#include  <sys/socket.h>      /* basic socket definitions */
#include  <netinet/in.h>      /* sockaddr_in{} and other Internet defns */
#include  <arpa/inet.h>       /* inet(3) functions */

#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>


#include <poll.h> /* poll function */
#include <limits.h>

#define MAXLINE 10240

#ifndef OPEN_MAX
#define OPEN_MAX 40960
#endif

void handle(struct pollfd* clients, int maxClient, int readyClient);

int  main(int argc, char **argv)
{
    int servPort = 6888;
    int listenq = 1024;
    int listenfd, connfd;
    struct pollfd clients[OPEN_MAX];
    int  maxi;
    socklen_t socklen = sizeof(struct sockaddr_in);
    struct sockaddr_in cliaddr, servaddr;
    char buf[MAXLINE];
    int nready;

    bzero(&servaddr, socklen);
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(servPort);

    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    if (listenfd < 0) {
        perror("socket error");
    }

    int opt = 1;
    if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt)) < 0) {
        perror("setsockopt error");
    }

    if(bind(listenfd, (struct sockaddr *) &servaddr, socklen) == -1) {
        perror("bind error");
        exit(-1);
    }
    if (listen(listenfd, listenq) < 0) {
        perror("listen error");    
    }

    clients[0].fd = listenfd;
    clients[0].events = POLLIN;
    int i;
    for (i = 1; i< OPEN_MAX; i++) 
        clients[i].fd = -1; 
    maxi = listenfd + 1;

    printf("pollechoserver startup, listen on port:%d\n", servPort);
    printf("max connection is %d\n", OPEN_MAX);

    for ( ; ; )  {
        nready = poll(clients, maxi + 1, -1);
        //printf("nready is %d\n", nready);
        if (nready == -1) {
            perror("poll error");
        }
        if (clients[0].revents & POLLIN) {
            connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &socklen);
            sprintf(buf, "accept form %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port);
            printf(buf, "");

            for (i = 0; i < OPEN_MAX; i++) {
                if (clients[i].fd == -1) {
                    clients[i].fd = connfd;
                    clients[i].events = POLLIN;
                    break;
                }
            }

            if (i == OPEN_MAX) {
                fprintf(stderr, "too many connection, more than %d\n", OPEN_MAX);
                close(connfd);
                continue;
            }

            if (i > maxi)
                maxi = i;

            --nready;
        }

        handle(clients, maxi, nready);
    }
}

void handle(struct pollfd* clients, int maxClient, int nready) {
    int connfd;
    int i, nread;
    char buf[MAXLINE];

    if (nready == 0)
        return;

    for (i = 1; i< maxClient; i++) {
        connfd = clients[i].fd;
        if (connfd == -1) 
            continue;
        if (clients[i].revents & (POLLIN | POLLERR)) {
            nread = read(connfd, buf, MAXLINE);//读取客户端socket流
            if (nread < 0) {
                perror("read error");
                close(connfd);
                clients[i].fd = -1;
                continue;
            }
            if (nread == 0) {
                printf("client close the connection");
                close(connfd);
                clients[i].fd = -1;
                continue;
            }

            write(connfd, buf, nread);//响应客户端  
            if (--nready <= 0)//没有连接需要处理，退出循环
                break;
        }
    }
}

编译和启动服务端

gcc pollechoserver.c -o pollechoserver
./pollechoserver

至于客户端可以参考本文的Linux/Unix服务端和客户端Socket编程入门实例的echoclient例子下载编译。

标签：listenfd,int,clients,Unix,源码,IO,connfd,include,nready
来源： https://blog.csdn.net/daocaokafei/article/details/113813464