libevent::bufferevent

#include <cstdio>
#include <netinet/in.h>  
#include <sys/socket.h>   
#include <fcntl.h> 
#include <event2/event.h>  
#include <event2/buffer.h> 
#include <event2/bufferevent.h>
#include <assert.h>  
#include <unistd.h>  
#include <string.h>   
#include <stdlib.h> 
#include <stdio.h>   
#include <errno.h>  

#define MAX_LINE 16384

struct fd_state
{
    char buffer[MAX_LINE];
    size_t buffer_used;
    size_t n_written;
    size_t write_upto;
    struct event*read_event;
    struct event*write_event;
};

void run(void);
void do_accept(evutil_socket_t listener, short event, void*arg);
void readcb(struct bufferevent* bev, void * ctx);
void errorcb(struct bufferevent* bev, short error, void * ctx);

char rot13_char(char c)
{
    if ((c >= ‘a‘  &&  c <= ‘m ‘) || (c >= ‘A ‘ && c <= ‘M ‘))
        return c + 13;
    else if ((c >= ‘n‘ && c <= ‘z‘) || (c >= ‘N‘ && c <= ‘Z‘))
        return c - 13;
    else
        return c;
}

int main(int c, char**v)
{
    run();
    return 0;
}

void run(void)
{
    evutil_socket_t listener;
    struct sockaddr_in sin;
    struct event_base*base;
    struct event*listener_event;
    base = event_base_new();
    if (!base)
        return;

    sin.sin_family = AF_INET; sin.sin_addr.s_addr = 0;
    sin.sin_port = htons(9090);
    listener = socket(AF_INET, SOCK_STREAM, 0);
    evutil_make_socket_nonblocking(listener);
    /*#ifndef WIN32
        {
            int one = 1;
            setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
        }
    #endif    */
    if (bind(listener, (struct sockaddr*) &sin, sizeof(sin)) < 0)
    {
        perror("bind"); return;
    }
    if (listen(listener, 16) < 0)
    {
        perror("listen");
        return;
    }
    listener_event = event_new(base, listener, EV_READ | EV_PERSIST, do_accept, (void*)base);

    event_add(listener_event, NULL);
    event_base_dispatch(base);
}

void do_accept(evutil_socket_t listener, short event, void*arg)
{
    struct event_base*base = (event_base*)(arg);
    struct sockaddr_storage ss;
    socklen_t slen = sizeof(ss);
    int fd = accept(listener, (struct sockaddr*) &ss, &slen);
    if (fd < 0)
    {
        perror("accept");
    }
    else if (fd > FD_SETSIZE)
    {
        close(fd);
    }
    else
    {
        struct bufferevent* bev;
        evutil_make_socket_nonblocking(fd);
        bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);
        bufferevent_setcb(bev, readcb, NULL, errorcb, NULL);
        bufferevent_setwatermark(bev, EV_READ, 0, MAX_LINE);
        bufferevent_enable(bev, EV_READ | EV_WRITE);
    }
}
void readcb(struct bufferevent* bev, void * ctx)
{
    struct evbuffer* input, *output;
    char* line;
    size_t n;
    int i;
    input = bufferevent_get_input(bev);
    output = bufferevent_get_output(bev);
    while ((line = evbuffer_readln(input, &n, EVBUFFER_EOL_LF)))
    {
        printf("str = %s \n", line);

        for (i = 0; i < n; ++i)
            line[i] = rot13_char(line[i]);

        evbuffer_add(output, line, n);
        evbuffer_add(output, "\n", 1);
        free(line);
    }

    if (evbuffer_get_length(input) >= MAX_LINE)
    {
        char buf[1024];
        while (evbuffer_get_length(input))
        {
            int n = evbuffer_remove(input, buf, sizeof(buf));
            for (i = 0; i < n; ++i)
                buf[i] = rot13_char(buf[i]);

            evbuffer_add(output, buf, n);
        }
        evbuffer_add(output, "\n", 1);
    }
}
void errorcb(struct bufferevent* bev, short error, void * ctx)
{
    if (error & BEV_EVENT_EOF)
    {
        /* connection has been closed, do any clean up here*/
    }
    else if (error & BEV_EVENT_ERROR)
    {
        /* check errno to see what error occurred*/
    }
    else if (error & BEV_EVENT_TIMEOUT)
    {
        /* must be a timeout event handle, handle it*/
    }
    bufferevent_free(bev);
}