libevent evbuffer bug

今天发现 libevent 2.0.22 一个坑爹的bug，导致消息混乱。查找问题浪费一天，复现代码如下

#include <event2/buffer.h>
#include <stdio.h>
#include <string.h>

// libevent-2.0.22-stable bug, but libevent 2.0.21 worked well
int main(int argc, char **argv)
{
    evbuffer *buf = evbuffer_new();
    evbuffer_expand(buf, );
    evbuffer_add(buf, ": first line \n", );

    // force to add a new chain
    evbuffer_expand(buf, );
    // add always add to the last chain, but last_with_datap is not changed accordingly
    evbuffer_add(buf, ": second line \n", );

    //evbuffer_expand(buf, 30);
    // printf try expand buffer and return the first chain, then add to the first chain
    evbuffer_add_printf(buf, ": last line\n");

    fprintf(stdout, "%*s\n", evbuffer_get_length(buf), evbuffer_pullup(buf, -));

    return ;
}

结果在 libevent 2.0.22 输出

: first line
: last line
: second line

libevent 2.0.21 正常

: first line
: second line
: last line