Question

我只是使用libevent编写一个echo服务器，但似乎永远不会触发read事件。代码是：

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <netinet/tcp.h>
#include <event.h>
#include <event2/event.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <arpa/inet.h>

static short ListenPort = 19999;
static long ListenAddr = INADDR_ANY;//任意地址，值就是0
static int   MaxConnections = 1024;

static int ServerSocket;
static struct event ServerEvent;

int SetNonblock(int fd)
{
    int flags;
    if ((flags = fcntl(fd, F_GETFL)) == -1) {
            return -1;
    }

    if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
            return -1;
    }
    return 0;
}

void ServerRead(int fd, short ev, void *arg)
{
    //1)when telnet on 1999 and send a string,this never prints,help!
    printf("client readble\n");
    fflush(stdout);
            struct client *client = (struct client *)arg;
    u_char buf[8196];
    int len, wlen;

    len = read(fd, buf, sizeof(buf));
    if (len == 0) {
            printf("disconnected\n");
            close(fd);
            event_del(&ServerEvent);
            free(client);
            return;
    } else if (len < 0) {
            printf("socket fail %s\n", strerror(errno));
            close(fd);
            event_del(&ServerEvent);
            free(client);
            return;
    }

    wlen = write(fd, buf, len);//1)client str never echo back
    if (wlen < len) {
            printf("not all data write back to client\n");
    }
}

void ServerWrite(int fd, short ev, void *arg)
{
//2)to be simple,let writer do nothing
/*  if(!arg)
    {
            printf("ServerWrite err!arg null\n");
            return;
    }
    int len=strlen(arg);
    if(len <= 0)
    {
            printf("ServerWrite err!len:%d\n",len);
            return;
    }
            int wlen = write(fd, arg, len);
        if (wlen<len) {
                printf("not all data write back to client!wlen:%d len:%d \n",wlen,len);
        }
*/
    return;
}


void ServerAccept(int fd, short ev, void *arg)
{
    int cfd;
    struct sockaddr_in addr;
    socklen_t addrlen = sizeof(addr);
    int yes = 1;

    cfd = accept(fd, (struct sockaddr *)&addr, &addrlen);
    if (cfd == -1) {
    //3)this prints ok
            printf("accept(): can not accept client connection");
            return;
    }
    if (SetNonblock(cfd) == -1) {
            close(cfd);
            return;
    }

    if (setsockopt(cfd, IPPROTO_TCP, TCP_NODELAY, &yes, sizeof(yes)) == -1) {
            printf("setsockopt(): TCP_NODELAY %s\n", strerror(errno));
            close(cfd);
            return;
    }

    event_set(&ServerEvent, cfd, EV_READ | EV_PERSIST, ServerRead, NULL);
    event_set(&ServerEvent, cfd, EV_WRITE| EV_PERSIST, ServerWrite,NULL);
    event_add(&ServerEvent, NULL);

    printf("Accepted connection from %s \n", (char *)inet_ntoa(addr.sin_addr));
}
int NewSocket(void)
{
    struct sockaddr_in sa;

    ServerSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (ServerSocket == -1) {
            printf("socket(): can not create server socket\n");
            return -1;
    }
    if (SetNonblock(ServerSocket) == -1) {
            return -1;
    }

    memset(&sa, 0, sizeof(sa));
    sa.sin_family = AF_INET;
    sa.sin_port = htons(ListenPort);
    sa.sin_addr.s_addr = htonl(ListenAddr);

    if (bind(ServerSocket, (struct sockaddr*)&sa, sizeof(sa)) == -1) {
            close(ServerSocket);
            printf("bind(): can not bind server socket");
            return -1;
    }

    if (listen(ServerSocket, MaxConnections) == -1) {
            printf("listen(): can not listen server socket");
            close(ServerSocket);
            return -1;
    }
    event_set(&ServerEvent, ServerSocket, EV_READ | EV_PERSIST, ServerAccept, NULL);
    if (event_add(&ServerEvent, 0) == -1) {
            printf("event_add(): can not add accept event into libevent");
            close(ServerSocket);
            return -1;
    }
    return 0;
}

int main(int argc, char *argv[])
{
    int retval;
    event_init();
    retval = NewSocket();
    if (retval == -1) {
       exit(-1);
    }
    event_dispatch();
    return 0;
}

服务器使用Telnet进行测试，但客户端什么都没有收到问题详细信息在上面的代码中作为注释发布，在1），2），3）。有人可以帮我找出为什么永远不会触发读取事件？

Answer 1

基本上你不应该将接受的套接字设置为EV_WRITE，直到你真正想要写入套接字。你告诉libevent＆＃34;让我知道什么时候我可以写这个socket＃34;这几乎总是如此。所以ServerWrite是在紧密循环中调用的。实际上，只有在编写缓冲区时才需要EV_WRITE，但是不写入所有字节。然后，您需要保存缓冲区的未写入部分，并使用EV_WRITE发出信号，以便再次写入套接字。

读取事件从未触发，使用libevent

1 个答案: