用select实现多客户端连接

server.c

把accept也看成是一个read类型的函数, 于是我们可以把sockfd也放入到select中
maxi标记当前客户端连接数组的最大下标
select返回值为当前已经准备就绪的fd总数

#include <unistd.h>
#include <netdb.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
 
#define MAX(a,b) a>b?a:b;
 
void err_quit(const char *s){
    perror(s);
    exit(1);
}
 
ssize_t readn(int fd,void *buff,size_t count){
    char *buffp;
    ssize_t nread;
    size_t nleft;
 
    buffp=(char *)buff;
    nleft=count;
    while(nleft > 0){
        if((nread = read(fd,buffp,nleft)) < 0){
            if(errno == EINTR)
                continue;
            else
                return -1;
        }else if(nread == 0)
            break;
        nleft -= nread;
        buffp += nread;
    }
    return count-nleft;
}
 
ssize_t writen(int fd,const void *buff,size_t n){
    size_t nleft;
    ssize_t nwritten;
    const char *ptr;
 
    ptr=buff;
    nleft=n;
    while(nleft > 0){
        if((nwritten=write(fd,ptr,nleft)) < 0){
            if(nwritten < 0 && errno == EINTR)
                continue;
            else
                return -1;
        }else if(nwritten == 0)
            break;
        nleft -= nwritten;
        ptr += nwritten;
    }
    return n-nleft;
}
 
ssize_t recv_peek(int fd,void *buf,size_t len){
    ssize_t ret;
    while(1){
        ret=recv(fd,buf,len,MSG_PEEK);
        if(ret == -1 && errno == EINTR)
            continue;
        return ret;
    }
}
 
ssize_t readline(int fd,void *buf,size_t maxline){
    ssize_t ret;
    size_t nread;
    size_t nleft;
    char *bufp;
 
    bufp=buf;
    nleft=maxline;
    while(1){
        ret=recv_peek(fd,buf,nleft);
        if(ret < 0)
            return ret;
        else if(ret == 0)
            return ret;
 
        nread=ret;
        int i;
        for(i=0;i<nread;i++){
            if(bufp[i] == '\n'){
                ret=readn(fd,bufp,i+1);
                if(ret != i+1)
                    err_quit("readn");
 
                return ret;
            }
        }
 
        if(nread > nleft)
            err_quit("readn");
 
        nleft -= nread;
        ret=readn(fd,bufp,nread);
        if(ret != nread)
            err_quit("readn");
 
        bufp += nread;
    }
 
    return -1;
}
 
int main(int argc,char *argv[]){
    int i,maxi,maxfd,tmpfd,sockfd,connfd;
    socklen_t len;
    struct sockaddr_in addr,client;
    fd_set rset,allset;
    int nready,clientfd[FD_SETSIZE];
    ssize_t n;
    char buf[1024];
 
    if((sockfd=socket(PF_INET,SOCK_STREAM,0)) < 0)
        err_quit("sockfd");
 
    bzero(&addr,sizeof(addr));
    addr.sin_family=AF_INET;
    addr.sin_addr.s_addr=htonl(INADDR_ANY);
    addr.sin_port=htons(5566);
 
    int on=1;
    if(setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)) <0)
        err_quit("setsockopt");
 
    if(bind(sockfd,(struct sockaddr *)&addr,sizeof(addr))<0)
        err_quit("bind");
 
    if(listen(sockfd,10)<0)
        err_quit("listen");
 
    maxfd=sockfd;
    maxi=-1;
    for(i=0;i<FD_SETSIZE;i++)
        clientfd[i]=-1;
    FD_ZERO(&allset);
    FD_SET(sockfd,&allset);
    while(1){
        rset=allset;
        nready=select(maxfd+1,&rset,NULL,NULL,NULL);
 
        if(nready == -1){
            if(errno == EINTR)
                continue;
            else
                err_quit("select");
        }
 
        if(FD_ISSET(sockfd,&rset)){
            len=sizeof(client);
            connfd=accept(sockfd,(struct sockaddr *)&client,&len);
            if(connfd < 0)
                err_quit("accept");
 
            for(i=0;i<FD_SETSIZE;i++){
                if(clientfd[i] < 0){
                    clientfd[i]=connfd;
                    break;
                }
            }
            if(i == FD_SETSIZE)
                err_quit("too many clients");
 
            FD_SET(connfd,&allset);
            if(connfd > maxfd)
                maxfd=connfd;
            if(i>maxi)
                maxi=i;
            if(--nready <= 0)
                continue;
        }
 
 
        for(i=0;i<=maxi;i++){
            if((tmpfd=clientfd[i]) < 0)
                continue;
            if(FD_ISSET(tmpfd,&rset)){
                bzero(buf,sizeof(buf));
                if((n=readline(tmpfd,buf,sizeof(buf))) == 0){
                    close(tmpfd);
                    FD_CLR(tmpfd,&allset);
                    clientfd[i]=-1;
                }
                write(STDOUT_FILENO,buf,n);
                writen(tmpfd,buf,n);
 
                if(--nready <= 0)
                    break;
            }
        }
    }
}

client.c

fileno函数的作用把FILE *型转换电脑int fd型
此实例用了shutdown方法

#include <unistd.h>
#include <signal.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netinet/in.h>
 
#define MAX(a,b) a>b?a:b;
 
void err_quit(const char *s){
    perror(s);
    exit(1);
}
 
ssize_t readn(int fd,void *buff,size_t count){
    size_t nleft;
    ssize_t nread;
    char *ptr;
 
    nleft=count;
    ptr=(char *)buff;
    while(nleft > 0){
        if((nread=read(fd,ptr,nleft)) < 0){
            if(errno == EINTR)
                continue;
            else
                return -1;
        }else if(nread == 0)
            break;
 
        ptr += nread;
        nleft -= nread;
    }
 
    return count - nleft;
}
 
ssize_t writen(int fd,const void *buff,size_t n){
    size_t nleft;
    ssize_t nwritten;
    const char *ptr;
 
    nleft=n;
    while(n > 0){
        if((nwritten=write(fd,buff,nleft)) < 0){
            if(errno == EINTR)
                continue;
            else
                return -1;
        }else if(nwritten == 0)
            break;
 
        nleft -= nwritten;
        ptr += nwritten;
    }
 
    return n-nleft;
}
/* if have any data then return */
ssize_t recv_peek(int fd,void *buf,size_t len){
    ssize_t ret;
    while(1){
        ret=recv(fd,buf,len,MSG_PEEK);
        if(ret == -1 && errno == EINTR)
            continue;
        return ret;
    }
}
 
ssize_t readline(int fd,void *buf,size_t maxline){
    ssize_t ret;
    size_t nread;
    size_t nleft;
    char *bufp;
 
    bufp=buf;
    nleft=maxline;
    while(1){
        ret=recv_peek(fd,buf,nleft);
        if(ret < 0)
            return ret;
        else if(ret == 0)
            return ret;
 
        nread=ret;
        int i;
        for(i=0;i<nread;i++){
            if(bufp[i] == '\n'){
                ret=readn(fd,bufp,i+1);
                if(ret != i+1)
                    err_quit("readn");
 
                return ret;
            }
        }
 
        if(nread > nleft)
            err_quit("nread");
 
        nleft -= nread;
        ret=readn(fd,bufp,nread);
        if(ret != nread)
            err_quit("readn");
 
        bufp += nread;
    }
 
    return -1;
}
 
int main(int argc,char *argv[]){
    int sockfd,maxfd;
    int nready;
    struct sockaddr_in servaddr;
    fd_set fileset;
    char buf[1024];
    int stdineof;
 
    if((sockfd=socket(PF_INET,SOCK_STREAM,0)) < 0)
        err_quit("socket");
 
    bzero(&servaddr,sizeof(servaddr));
    servaddr.sin_family=AF_INET;
    servaddr.sin_addr.s_addr=inet_addr("127.0.0.1");
    servaddr.sin_port=htons(5566);
 
    if(connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr)) <0)
        err_quit("connect");
 
    bzero(buf,sizeof(buf));
 
    FD_ZERO(&fileset);
    stdineof=0;
    while(1){
        if(stdineof == 0)
            FD_SET(fileno(stdin),&fileset);
        FD_SET(sockfd,&fileset);
 
        maxfd=MAX(fileno(stdin),sockfd);
        nready=select(maxfd+1,&fileset,NULL,NULL,NULL);
 
        if(nready == -1){
            if(errno == EINTR)
                continue;
            else
                err_quit("select");
        }
 
        if(FD_ISSET(fileno(stdin),&fileset)){
            if(fgets(buf,sizeof(buf),stdin) == NULL){
                stdineof=1;
                shutdown(sockfd,SHUT_WR);
                FD_CLR(fileno(stdin),&fileset);
                continue;
            }else{
                writen(sockfd,buf,strlen(buf));
                bzero(buf,sizeof(buf));
            }
        }
 
        if(FD_ISSET(sockfd,&fileset)){
            int ret=readline(sockfd,buf,sizeof(buf));
            if(ret == -1)
                err_quit("read");
            if(ret == 0){
                if(stdineof == 1)
                    exit(0);
                else
                    err_quit("readline");
            }
            fputs(buf,stdout);
            bzero(buf,sizeof(buf));
        }
    }
}