libevent笔记4：Filter_bufferevent过滤器
Filter_bufferevent是一种基于bufferevent的过滤器，其本身也是一个bufferevent。能够对底层bufferevent输入缓存区中的数据进行操作（加/解密等）后再读取，同样也能在一定的操作后再将数据写入底层bufferevent的输出缓存区。需要注意的是，在创建Filter_bufferevent后，底层bufferevent的读写回调函数就不会再生效了，而缓存区的回调函数依旧有效。
Filter_bufferevent相关函数
struct bufferevent *bufferevent_filter_new (struct bufferevent underlying, bufferevent_filter_cb input_filter, bufferevent_filter_cb output_filter, int options, void(free_context)(void *), void *ctx)：创建一个过滤器，参数列表如下：
- struct bufferevent *underlying：需要过滤的底层bufferevent；
- bufferevent_filter_cb input_filter/bufferevent_filter_cb output_filter：对底层bufferevent的输入/输出缓存器进行操作的过滤器函数，这两个过滤器函数会在其源缓存区中有数据时触发；
- int option：关于bufferevent的设置；
- void(*free_context)(void *)：释放时调用的函数，返回值及参数列表均为空；
- void *ctx：传递给过滤器函数的参数；
typedef enum bufferevent_filter_result(* bufferevent_filter_cb)(struct evbuffer *src, struct evbuffer *dst, ev_ssize_t dst_limit, enum bufferevent_flush_mode mode, void *ctx)：需要自定义，并传送给bufferevent_filter_new()的过滤器函数，参数列表如下：
- struct evbuffer *src：需要处理的数据的源缓存区，即从这个缓存中取需要过滤的数据；
- struct evbuffer *dst：需要处理的数据的目的缓存区，即将处理后的数据放入这个缓存中；
- ev_ssize_t dst_limit：目标缓存区的长度，过滤器可以忽略这个参数；
- enum bufferevent_flush_mode mode：过滤模式，来告诉过滤器数据是因为什么进过滤器的。
- void *ctx：上一个函数中给定的参数；
- typedef enum bufferevent_filter_result：过滤函数的返回值，包括：BEV_OK(正常)；BEV_NEED_MORE(需要继续读数据)；BEV_ERROR(发生错误)；
过滤器的源/目缓存区
过滤器函数的参数列表中包含了过滤器的源/目的缓存区。而对于输入/输出过滤器，源/目缓存区是不同，而这对理解过滤器至关重要。可以使用一段简单的程序来确定过滤器的参数与底层bufferevent及Filter_bufferevent的关系，客户端正常连接服务器并发生数据，服务器创建一个Filter_bufferevent并两个bufferevent的一共4个缓存区，过滤器则输出源/目的缓存区的地址。
- 客户端：
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <event2/event.h>
#include <event2/bufferevent.h>
void read_cb(struct bufferevent *bev, void *arg)
{
char buf[1024] = {0};
bufferevent_read(bev, buf, sizeof(buf));
printf(buf);
}
void write_cb(struct bufferevent *bev, void *arg)
{
printf("我是写缓冲区的回调函数...您已发送\n");
}
void event_cb(struct bufferevent *bev, short events, void *arg)
{
if (events & BEV_EVENT_EOF)
{
printf("connection closed\n");
}
else if(events & BEV_EVENT_ERROR)
{
printf("some other error\n");
}
else if(events & BEV_EVENT_CONNECTED)
{
printf("服务器已连接\n");
return;
}
bufferevent_free(bev);
printf("free bufferevent...\n");
}
void send_cb(evutil_socket_t fd, short what, void *arg)
{
char buf[1024] = {0};
struct bufferevent* bev = (struct bufferevent*)arg;
read(fd, buf, sizeof(buf));
bufferevent_write(bev, buf, strlen(buf)-1);
}
void signal_cb(evutil_socket_t sig, short events, void *user_data)
{
struct event_base *base = user_data;
struct timeval delay = { 2, 0 };
printf("Caught an interrupt signal; exiting cleanly in two seconds.\n");
event_base_loopexit(base, &delay);
}
int main(int argc, const char* argv[])
{
struct event_base* base;
base = event_base_new();
struct bufferevent* bev;
bev = bufferevent_socket_new(base, -1, BEV_OPT_CLOSE_ON_FREE);
// 连接服务器
struct sockaddr_in serv;
memset(&serv, 0, sizeof(serv));
serv.sin_family = AF_INET;
serv.sin_port = htons(9995);
evutil_inet_pton(AF_INET, "127.0.0.1", &serv.sin_addr.s_addr);
bufferevent_socket_connect(bev, (struct sockaddr*)&serv, sizeof(serv));
// 设置回调
bufferevent_setcb(bev, read_cb, NULL, event_cb, NULL);
bufferevent_enable(bev, EV_READ | EV_PERSIST);
// 创建一个事件
struct event* ev = event_new(base, STDIN_FILENO,
EV_READ|EV_PERSIST, send_cb, bev);
//for Ctrl+C
struct event *signal_event;
signal_event = evsignal_new(base, SIGINT, signal_cb, (void *)base);
event_add(signal_event, NULL);
event_add(ev, NULL);
event_base_dispatch(base);
event_base_free(base);
return 0;
}
- 服务端：
#include <event2/bufferevent.h>
#include <event2/event.h>
#include <event2/buffer.h>
#include <arpa/inet.h>// interner address
#include <unistd.h>//os
#include <stdio.h>
#include <malloc.h>
#include <string.h>
#include <event2/listener.h>
#include <sys/types.h>
#include <errno.h>
enum bufferevent_filter_result input_cb(struct evbuffer *src, struct evbuffer *dst,
ev_ssize_t dst_limit, enum bufferevent_flush_mode mode, void *ctx)
{
//输出缓存区的地址
printf("the src and dst in fun input_cb: %ld, %ld\n", src, dst);
//清空源缓存区，避免被一直调用
evbuffer_drain(src, 1024);
return BEV_OK;
}
enum bufferevent_filter_result output_cb(struct evbuffer *src, struct evbuffer *dst,
ev_ssize_t dst_limit, enum bufferevent_flush_mode mode, void *ctx)
{
//输出缓存区的地址
printf("the src and dst in fun output_cb: %ld, %ld\n", src, dst);
//清空源缓存区，避免被一直调用
evbuffer_drain(src, 1024);
return BEV_OK;
}
void read_cb(struct bufferevent *bev, void *arg)
{
char buf[1024] = {0};
bufferevent_read(bev, buf, 1024);
printf("%s\n", buf);
}
void write_cb(struct bufferevnet *bev, void *arg)
{
printf("write_cb\n");
}
void listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
struct sockaddr *addr, int len, void *ptr)
{
struct sockaddr_in *caddr = (struct sockaddr_in *)addr;
struct event_base *base = (struct event_base *)ptr;
//init bufferevent
struct bufferevent *bev;
bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, NULL, NULL, NULL, NULL);
bufferevent_enable(bev, EV_WRITE | EV_READ);
//bufferevent_write(bev, "Hello client!", strlen("Hello client!")+1);
struct bufferevent *filter_bev = bufferevent_filter_new(bev, input_cb, output_cb, BEV_OPT_CLOSE_ON_FREE, NULL, NULL);
//设置Filter_bufferevent的读写函数
bufferevent_setcb(filter_bev, read_cb, write_cb, NULL, NULL);
bufferevent_enable(filter_bev, EV_READ|EV_WRITE);
//输出底层bufferevent的缓存区地址
printf("the input evbuffer and output evbuffer of underlying bufferevent: %ld, %ld\n", bufferevent_get_input(bev), bufferevent_get_output(bev));
//输出Filter_bufferevent的缓存区地址
printf("the input evbuffer and output evbuffer of filter bufferevent: %ld, %ld\n", bufferevent_get_input(filter_bev), bufferevent_get_output(filter_bev));
//先Filter_bufferevent写
bufferevent_write(filter_bev, "abc", sizeof("abc"));
}
int main(int argc, const char *argv[])
{
//init server
struct sockaddr_in servaddr;
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(9995);
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
//init event_base
struct event_base *base;
base = event_base_new();
//init linstener
struct evconnlistener *listener;
listener = evconnlistener_new_bind(base, listener_cb, base,
LEV_OPT_CLOSE_ON_FREE|LEV_OPT_REUSEABLE_PORT, 36,
(struct socketaddr *)&servaddr, sizeof(servaddr));
event_base_dispatch(base);
evconnlistener_free(listener);
event_base_free(base);
}
服务端运行结果：
sunminming@sunminming:~/libevent/filter$ ./addrdemo
the input evbuffer and output evbuffer of underlying bufferevent: 94493149330208, 94493149330352
the input evbuffer and output evbuffer of filter bufferevent: 94493149331184, 94493149331328
the src and dst in fun output_cb: 94493149331328, 94493149330352
the src and dst in fun input_cb: 94493149330208, 94493149331184
可以看出来：
- 输入过滤器中的源缓存区与底层buferevent的输入缓存区地址一致，目的缓存区与Filter_bufferevent的输入缓存区地址一致。
- 输出过滤器中的源缓存区与Filter_bufferevent的输出缓存区地址一致，目的缓存区与底层bufferevent的输出缓存区地址一致。
因此，4个缓存区与2个过滤器函数的关系可以画成下图：
Demo
之后就是过滤器正常使用的Demo：输入过滤器会将底层bufferevent的接受到的数据加1处理，而输出过滤器则会将输出的数据复制一份加在原数据的末尾。
- 服务端：
#include <event2/bufferevent.h>
#include <event2/event.h>
#include <event2/buffer.h>
#include <arpa/inet.h>// interner address
#include <unistd.h>//os
#include <stdio.h>
#include <malloc.h>
#include <string.h>
#include <event2/listener.h>
#include <sys/types.h>
#include <errno.h>
enum bufferevent_filter_result input_cb(struct evbuffer *src, struct evbuffer *dst,
ev_ssize_t dst_limit, enum bufferevent_flush_mode mode, void *ctx)
{
//处理输入的数据：从源缓存区读，并加1后放入目的缓存区
char buf[1024];
memset(buf, '\0', sizeof(buf));
evbuffer_remove(src, buf, sizeof(buf));
int len = strlen(buf);
printf("%d", len);
for(int i = 0; i < len; ++i)
{
++buf[i];
}
buf[2*len] = '\n';
evbuffer_add(dst, buf, len);
return BEV_OK;
}
enum bufferevent_filter_result output_cb(struct evbuffer *src, struct evbuffer *dst,
ev_ssize_t dst_limit, enum bufferevent_flush_mode mode, void *ctx)
{
//处理输出的数据：从源缓存区读，复制后放入目的缓存区
char buf[1024] = {0};
memset(buf, '\0', sizeof(buf));
evbuffer_remove(src, buf, sizeof(buf));
int len = strlen(buf);
for(int i = len; i < 2*len; ++i)
{
buf[i] = buf[i - len];
}
evbuffer_add(dst, buf, 2*len);
return BEV_OK;
}
void read_cb(struct bufferevent *bev, void *arg)
{
char buf[1024] = {0};
bufferevent_read(bev, buf, 1024);
printf("%s\n", buf);
}
void listener_cb(struct evconnlistener *listener, evutil_socket_t fd,
struct sockaddr *addr, int len, void *ptr)
{
struct sockaddr_in *caddr = (struct sockaddr_in *)addr;
struct event_base *base = (struct event_base *)ptr;
//init bufferevent
struct bufferevent *bev;
bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, NULL, NULL, NULL, NULL);
bufferevent_enable(bev, EV_WRITE | EV_READ);
struct bufferevent *filter_bev = bufferevent_filter_new(bev, input_cb, output_cb, BEV_OPT_CLOSE_ON_FREE, NULL, NULL);
bufferevent_setcb(filter_bev, read_cb, NULL, NULL, NULL);
bufferevent_enable(filter_bev, EV_READ|EV_WRITE);
bufferevent_write(filter_bev, "abc", sizeof("abc"));
}
int main(int argc, const char *argv[])
{
//init server
struct sockaddr_in servaddr;
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(9995);
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
//init event_base
struct event_base *base;
base = event_base_new();
//init linstener
struct evconnlistener *listener;
listener = evconnlistener_new_bind(base, listener_cb, base,
LEV_OPT_CLOSE_ON_FREE|LEV_OPT_REUSEABLE_PORT, 36,
(struct socketaddr *)&servaddr, sizeof(servaddr));
event_base_dispatch(base);
evconnlistener_free(listener);
event_base_free(base);
}
客户端与上一节相同。流程见注释。
