Re: [Libevent-users] Line-based evbuffer?

[Ãystein SchÃnning-Johansen <oysteijo@xxxxxxxxx>]

It is probably a misconception on my side. I'm pretty good at misconceptions. :-)

To illustrate, I set up a really naive server in python:

>>> import socket

>>> s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

>>> s.bind(('', 8888))

>>> s.listen(10)

>>> while 1:

... Â Âconn, addr = s.accept()

... Â Âconn.send(b"Line 1\nLine 2\nLine 3\nLast line\n")

... Â Âconn.close()

telnet-ing to this will send back

Line 1

Line 2

Line 3

Last Line

OK, then I code a simple client. (There are som short-cuts to avoid a lot of code, but this compiles and runs with -std=gnu99)

#include <event2/dns.h>

#include <event2/bufferevent.h>

#include <event2/buffer.h>

#include <event2/util.h>

#include <event2/event.h>

#include <stdlib.h>

#include <stdio.h>

void buffercb(struct evbuffer *input, const struct evbuffer_cb_info *info, void *ptr)

{

#if 1

  char *request_line;

  size_t len;

  request_line = evbuffer_readln( input, &len, EVBUFFER_EOL_CRLF );

  if ( request_line ){

    printf("%s\n", request_line ); fflush( stdout );

    free( request_line );

  }

#else

  char buf[1024];

  int n;

  while ((n = evbuffer_remove(input, buf, sizeof(buf))) > 0) {

    fwrite(buf, 1, n, stdout);

  }

#endif

}

int main(int argc, char **argv)

{

  struct event_base *base;

  struct evdns_base *dns_base;

  struct bufferevent *bev;

  if( argc != 3 ){

    printf("Usage: %s host port", argv[0]);

    return -1;

  }

  base = event_base_new();

  dns_base = evdns_base_new(base, 1);

  bev = bufferevent_socket_new(base, -1, BEV_OPT_CLOSE_ON_FREE);

  bufferevent_setcb(bev, NULL, NULL, NULL, base);

  bufferevent_enable(bev, EV_READ|EV_WRITE);

  bufferevent_socket_connect_hostname(

    bev, dns_base, AF_UNSPEC, argv[1], atoi(argv[2]));

  evbuffer_add_cb( bufferevent_get_input(bev), buffercb, NULL );

  event_base_dispatch(base);

  return 0;

}

If I compile that code and run it against the python server, I get:

$ ./testclient localhost 8888

Last line

Line 3

Line 2

Line 1

How come? I still think the problem is in my conception of the buffer. At least, I can still not get it working as expected with evbuffer_readln(). :-)

Thanks,

On Tue, Feb 2, 2016 at 12:54 PM, Azat Khuzhin <a3at.mail@xxxxxxxxx> wrote:

On Tue, Feb 2, 2016 at 1:50 PM, Ãystein SchÃnning-Johansen
<oysteijo@xxxxxxxxx> wrote:
> Thanks, I'm aware of that function. However, the reads from the socket comes
> in with several lines at a time and the buffer does not necessarily begin
> with the start of a new line or end at the end of a line. In these cases the

Even if it will end with new line, no guarantee that you will receive
this like the sender send, since this is network and you have
non-blocking IO.

> callback handler will handle the last full line first. I'm not sure if this
> is a bug in evbuffer_readln() or not?

I'm not sure that I understand you, it can't work like this,
it must process buffer from begin->end not in the reverse order.

Can you please provide a sample, that will show this behavior?

And of course evbuffer have buffering, IOW if you have something like this:
recv(4, "foo")
recv(4, "bar\n")

Then evbuffer_readln() will return "foobar\n", and will return empty
if you will call it between this two recv().

Am I missing something?

***********************************************************************
To unsubscribe, send an e-mail to majordomo@xxxxxxxxxxxxx with
unsubscribe libevent-users  in the body.