socket编程之并发回射服务器2

承接上文：socket编程之并发回射服务器

为了让服务器进程的终止一经发生，客户端就能检测到，客户端需要能够同时处理两个描述符：套接字和用户输入。

可以使用select达到这一目的：

void str_cli(FILE *fp, int sockfd) {
    int maxfdp1;
    fd_set rset;
    char sendline[MAXLINE], recvline[MAXLINE];
    
    FD_ZERO(&rset);
    for (;;) {
        FD_SET(fileno(fp), &rset);
        FD_SET(sockfd, &rset);
        maxfdp1 = max(fileno(fp), sockfd) + 1;
        select(maxfdp1, &rset, NULL, NULL, NULL);
        
        /* socket is readable */
        if (FD_ISSET(sockfd, &rset)) {
            memset(recvline, 0, sizeof(recvline));
            if (read(sockfd, recvline, MAXLINE) == 0) {
                printf("server terminated prematurely
");
                exit(1);
            }
            fputs(recvline, stdout);
        }
        /* input is readable */
        if (FD_ISSET(fileno(fp), &rset)) {
            memset(sendline, 0, sizeof(sendline));
            if (fgets(sendline, MAXLINE, fp) == NULL) {
                return;
            }
            write(sockfd, sendline, strlen(sendline));
        }
    }
}

函数声明如下：

// 返回：若有就绪描述符则为其数目，若超时则为0，若出错则为-1
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

之前的服务器程序通过多进程的方式来处理并发连接，我们也可以使用select对其进行改造：

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

#define MAXLINE 4096
#define LISTENQ 10

int main(int argc, char **argv) {
    
    int listenfd, connfd, sockfd;
    
    char buf[MAXLINE];
    socklen_t clilen;
    struct sockaddr_in servaddr, cliaddr;
    
    if ( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket error");
        exit(1);
    }
    
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(13);  /* daytime server */
    
    if ( bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0) {
        perror("bind error");
        exit(1);
    }
    
    if ( listen(listenfd, LISTENQ) < 0) {
        perror("listen error");
        exit(1);
    }
    
    int maxfd = listenfd;
    int maxi = -1;
    int nready, client[FD_SETSIZE];
    int i;
    for (i = 0; i < FD_SETSIZE; i++) {
        client[i] = -1;
    }
    fd_set rset, allset;
    FD_ZERO(&allset);
    FD_SET(listenfd, &allset);
    
    for ( ; ; ) {
        rset = allset;
        nready = select(maxfd + 1, &rset, NULL, NULL, NULL);
        // new client connection
        if (FD_ISSET(listenfd, &rset)) {
            clilen = sizeof(cliaddr);
            connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
            
            for (i = 0; i < FD_SETSIZE; i++) {
                if (client[i] < 0) {
                    client[i] = connfd;
                    break;
                }
            }
            if (i == FD_SETSIZE) {
                printf("too many clients
");
                exit(1);
            }
            FD_SET(connfd, &allset);
            if (connfd > maxfd)
                maxfd = connfd;
            if (i > maxi)
                maxi = i;
            if (--nready <= 0)
                continue;
        }
        // check all clients for data
        for (i = 0; i < FD_SETSIZE; i++) {
            if ( (sockfd = client[i]) < 0)
                continue;
            if (FD_ISSET(sockfd, &rset)) {
                memset(buf, 0, sizeof(buf));
                ssize_t n;
                if ( (n = read(sockfd, buf, MAXLINE)) == 0) {
                    close(sockfd);
                    FD_CLR(sockfd, &allset);
                    client[i] = -1;
                } else {
                    write(sockfd, buf, n);
                }
                
                if (--nready <= 0)
                    break;
            }
        }
    }
}

当然了，也可以使用poll对其进行改造：

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

#define MAXLINE 4096
#define LISTENQ 10
#define OPEN_MAX 1024

int main(int argc, char **argv) {
    
    int listenfd, connfd, sockfd;
    
    char buf[MAXLINE];
    socklen_t clilen;
    struct sockaddr_in servaddr, cliaddr;
    
    if ( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket error");
        exit(1);
    }
    
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(13);  /* daytime server */
    
    if ( bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0) {
        perror("bind error");
        exit(1);
    }
    
    if ( listen(listenfd, LISTENQ) < 0) {
        perror("listen error");
        exit(1);
    }
    
    struct pollfd client[OPEN_MAX];
    client[0].fd = listenfd;
    client[0].events = POLLRDNORM;
    int i, maxi, nready;
    for (i = 1; i < OPEN_MAX; i++) {
        client[i].fd = -1;
    }
    maxi = 0;
    
    for ( ; ; ) {
        nready = poll(client, maxi + 1, -1);
        // new client connection
        if (client[0].revents & POLLRDNORM) {
            clilen = sizeof(cliaddr);
            connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
            
            for (i = 1; i < OPEN_MAX; i++) {
                if (client[i].fd < 0) {
                    client[i].fd = connfd;
                    break;
                }
            }
            if (i == OPEN_MAX) {
                printf("too many clients
");
                exit(1);
            }
            
            client[i].events = POLLRDNORM;
            if (i > maxi)
                maxi = i;
            if (--nready <= 0)
                continue;
        }
    
        // check all clients for data
        for (i = 1; i <= maxi; i++) {
            if ( (sockfd = client[i].fd) < 0)
                continue;
            if (client[i].revents & (POLLRDNORM | POLLERR)) {
                memset(buf, 0, sizeof(buf));
                ssize_t n;
                if ( (n = read(sockfd, buf, MAXLINE)) < 0) {
                    if (errno == ECONNRESET) {
                        printf("connection reset by client
");
                        close(sockfd);
                        client[i].fd = -1;
                    } else {
                        perror("read error");
                        exit(1);
                    }
                } else if (n == 0){
                    printf("connection closed by client
");
                    close(sockfd);
                    client[i].fd = -1;
                } else {
                    write(sockfd, buf, n);
                }
                
                if (--nready <= 0)
                    break;
            }
        }
    }
}

函数声明如下：

/*
 * 返回：若有就绪描述符则为其数目，若超时则为0，若出错则为-1
 * nfds：结构数组fds中元素个数
 */
int poll(struct pollfd *fds, nfds_t nfds, int timeout);

struct pollfd {
    int   fd;             /* file descriptor */
    short events;     /* requested events */
    short revents;    /* returned events */
};

最后附上一张图吧：

参考文章：

也谈IO模型