libevent编写echo服务器

逃离我推掉我的手 2022-06-17 02:18 164阅读 0赞

为了使用libevent，编写一个echo回射服务器程序。

### 1. 准备工作 ###

在深入浅出Libevent一书上提到，如果是源码学习的话使用libevent1.4版本，如果是使用的话一般用libevent2.x版本。  
因此，在libevent.org上将libevent2.0.20-stable版本的源码下载下来，编译，安装：

./configure --prefix=INSTALL_DIR
    make
    make install

### 2. 编写Makefile ###

在Makefile中，需要指定libevent安装的头文件目录（gcc中-I选项）和库文件目录（gcc中-L选项），以及加上编译标志`-levent`

PROGS=echo 
    CLEANFILES = core core.* *.core *.o temp.* *.out typescript* \
            *.lc *.lh *.bsdi *.sparc *.uw
    
    
    LIBEVENT_DIRECTORY = /home/zhangxiao/libevent/src/src2 ### INSTALL DIR
    LIBEVENT_INCLUDE = $(LIBEVENT_DIRECTORY)/include
    LIBEVENT_LIBRARY = $(LIBEVENT_DIRECTORY)/lib
    
    SRC=${shell pwd}/src
    
    OUTPUT:=${shell pwd}/bin
    MAKE_BIN_DIR := ${shell mkdir -p $(OUTPUT) }
    
    
    
    all : ${PROGS}
    
    
    CFLAGS+=-g  -I${LIBEVENT_INCLUDE} 
    LDFLAGS+=-L${LIBEVENT_LIBRARY} -levent -lpthread -lrt
    
    echo:${SRC}/echo.o
        @${CC} ${CFLAGS}  -o ${OUTPUT}/$@   $^  ${LDFLAGS}
    
    clean:
        @rm -rf ${OUTPUT} \
            @rm -rf ${SRC}/*.o
    
    
    .PHONY: all clean

### 3. 编写echo server ###

由于libevent的Reactor设计模式，我们需要为网络事件编写回调函数（Handler），例如onAccept,onRead等等

#include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <assert.h>
    
    #include <event2/event.h>
    #include <event2/bufferevent.h>
    
    #define LISTEN_PORT 9999
    #define LISTEN_BACKLOG 32
    
    void do_accept(evutil_socket_t listener, short event,void *arg);
    void read_cb(struct bufferevent *bev,void *arg);
    void error_cb(struct bufferevent*bev,short event,void *arg);
    void write_cb(struct bufferevent*bev,void *arg);
    
    int main(int argc,char **argv)
    {
        int ret;
        evutil_socket_t listener;
        listener=socket(AF_INET,SOCK_STREAM,0);
        assert(listener>0);
    
        evutil_make_listen_socket_reuseable(listener);
    
        struct sockaddr_in sin;
        sin.sin_family=AF_INET;
        sin.sin_addr.s_addr=0;
        sin.sin_port=htons(LISTEN_PORT);
    
        if (bind(listener, (struct sockaddr *)&sin, sizeof(sin)) < 0) 
        {
        perror("bind");
        return 1;
        }
    
        if (listen(listener, LISTEN_BACKLOG) < 0) 
        {
        perror("listen");
        return 1;
        }
    
        printf ("Listening...\r\n");
        evutil_make_socket_nonblocking(listener);
        struct event_base *base = event_base_new();
        assert(base != NULL);
    
        struct event *listen_event;
        listen_event = event_new(base, //base
            listener, //fd
            EV_READ|EV_PERSIST,//event
            do_accept, //call back
            (void*)base);//args
    
        event_add(listen_event,NULL);
        event_base_dispatch(base);
    
        printf("The End.\r\n");
        return 0;
    
    }
    
    void do_accept(evutil_socket_t listener, short event, void *arg)
    {
        struct event_base *base = (struct event_base *)arg;
        evutil_socket_t fd;
        struct sockaddr_in sin;
        socklen_t slen = sizeof(sin);
        fd = accept(listener, (struct sockaddr *)&sin, &slen);
        if (fd < 0) {
        perror("accept");
        return;
        }
        if (fd > FD_SETSIZE) { //这个if是参考了那个ROT13的例子，貌似是官方的疏漏，从select-based例子里抄过来忘了改
        perror("fd > FD_SETSIZE\n");
        return;
        }
    
        printf("ACCEPT: fd = %u\n", fd);
    
        struct bufferevent *bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
        bufferevent_setcb(bev, read_cb, NULL, error_cb, arg);
        bufferevent_enable(bev, EV_READ|EV_WRITE|EV_PERSIST);
    }
    
    void read_cb(struct bufferevent *bev, void *arg)
    {
    #define MAX_LINE    256
        char line[MAX_LINE+1];
        int n;
        evutil_socket_t fd = bufferevent_getfd(bev);
    
        while (n = bufferevent_read(bev, line, MAX_LINE), n > 0) {
        line[n] = '\0';
        printf("fd=%u, read line: %s\n", fd, line);
    
        bufferevent_write(bev, line, n);
        }
    }
    
    void write_cb(struct bufferevent *bev, void *arg) {}
    
    void error_cb(struct bufferevent *bev, short event, void *arg)
    {
        evutil_socket_t fd = bufferevent_getfd(bev);
        printf("fd = %u, ", fd);
        if (event & BEV_EVENT_TIMEOUT) {
        printf("Timed out\n"); //if bufferevent_set_timeouts() called
        }
        else if (event & BEV_EVENT_EOF) {
        printf("connection closed\n");
        }
        else if (event & BEV_EVENT_ERROR) {
        printf("some other error\n");
        }
        bufferevent_free(bev);
    }

### 4. 测试 ###

使用`nc`测试即可

### 5. 参考 ###

深入浅出 Libevent  
Programming with libevent