How to close socket after writing in libevent with bufferevents? - c++

Question

Here is an example of echo TCP server from libevent book.
How can I modify it to close a socket after each write. I know that I can close a socket connection by calling bufferevent_free(), but I don't understand how use it to close connection every time I send an echo to the socket.
#include <event2/listener.h>
#include <event2/bufferevent.h>
#include <event2/buffer.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
static void
echo_read_cb(struct bufferevent *bev, void *ctx)
{
/* This callback is invoked when there is data to read on bev. */
struct evbuffer *input = bufferevent_get_input(bev);
struct evbuffer *output = bufferevent_get_output(bev);
/* Copy all the data from the input buffer to the output buffer. */
evbuffer_add_buffer(output, input);
}
static void
echo_event_cb(struct bufferevent *bev, short events, void *ctx)
{
if (events & BEV_EVENT_ERROR)
perror("Error from bufferevent");
if (events & (BEV_EVENT_EOF | BEV_EVENT_ERROR)) {
bufferevent_free(bev);
}
}
static void
accept_conn_cb(struct evconnlistener *listener,
evutil_socket_t fd, struct sockaddr *address, int socklen,
void *ctx)
{
/* We got a new connection! Set up a bufferevent for it. */
struct event_base *base = evconnlistener_get_base(listener);
struct bufferevent *bev = bufferevent_socket_new(
base, fd, BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, echo_read_cb, NULL, echo_event_cb, NULL);
bufferevent_enable(bev, EV_READ|EV_WRITE);
}
static void
accept_error_cb(struct evconnlistener *listener, void *ctx)
{
struct event_base *base = evconnlistener_get_base(listener);
int err = EVUTIL_SOCKET_ERROR();
fprintf(stderr, "Got an error %d (%s) on the listener. "
"Shutting down.\n", err, evutil_socket_error_to_string(err));
event_base_loopexit(base, NULL);
}
int
main(int argc, char **argv)
{
struct event_base *base;
struct evconnlistener *listener;
struct sockaddr_in sin;
int port = 9876;
if (argc > 1) {
port = atoi(argv[1]);
}
if (port<=0 || port>65535) {
puts("Invalid port");
return 1;
}
base = event_base_new();
if (!base) {
puts("Couldn't open event base");
return 1;
}
/* Clear the sockaddr before using it, in case there are extra
* platform-specific fields that can mess us up. */
memset(&sin, 0, sizeof(sin));
/* This is an INET address */
sin.sin_family = AF_INET;
/* Listen on 0.0.0.0 */
sin.sin_addr.s_addr = htonl(0);
/* Listen on the given port. */
sin.sin_port = htons(port);
listener = evconnlistener_new_bind(base, accept_conn_cb, NULL,
LEV_OPT_CLOSE_ON_FREE|LEV_OPT_REUSEABLE, -1,
(struct sockaddr*)&sin, sizeof(sin));
if (!listener) {
perror("Couldn't create listener");
return 1;
}
evconnlistener_set_error_cb(listener, accept_error_cb);
event_base_dispatch(base);
return 0;
}

Answer 1

From my understanding of documentation - you should put bufferevent_free(bev); at the end of echo_event_cb() function, this should close the connection after echoing user data back w/o waiting the client to close it. This should work this way till you use BEV_OPT_CLOSE_ON_FREE when creating bev buffer event.