line echo server with libevent

echo-server.c

#include <event2/listener.h>
#include <event2/bufferevent.h>
#include <event2/buffer.h>

#include <arpa/inet.h>
#include <netinet/tcp.h>

#include <assert.h>
#include <signal.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#define MAX_LINE_LENGTH 10240
#define MAX_OUTPUT_BUFFER 102400

static void set_tcp_no_delay(evutil_socket_t fd)
{
  int one = 1;
  setsockopt(fd, IPPROTO_TCP, TCP_NODELAY,
      &one, sizeof one);
}

static void signal_cb(evutil_socket_t fd, short what, void *arg)
{
  struct event_base *base = arg;
  printf("stop\n");

  event_base_loopexit(base, NULL);
}

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);

  while (1)
  {
    size_t eol_len = 0;
    struct evbuffer_ptr eol = evbuffer_search_eol(input, NULL, &eol_len, EVBUFFER_EOL_LF);
    if (eol.pos < 0)
    {
      size_t readable = evbuffer_get_length(input);
      if (readable > MAX_LINE_LENGTH)
      {
        printf("input is too long %zd\n", readable);
        bufferevent_free(bev);
      }
      break;
    }
    else if (eol.pos > MAX_LINE_LENGTH)
    {
      printf("line is too long %zd\n", eol.pos);
      bufferevent_free(bev);
      break;
    }
    else
    {
      assert(eol_len == 1);
      // int nr = evbuffer_remove_buffer(input, output, eol.pos+1);

      // read
      char request[MAX_LINE_LENGTH+1];
      assert(eol.pos+1 <= sizeof(request));
      int req_len = evbuffer_remove(input, request, eol.pos+1);
      assert(req_len == eol.pos+1);

      // business logic
      char response[MAX_LINE_LENGTH+1];
      int resp_len = req_len;
      memcpy(response, request, req_len);

      // write
      int succeed = evbuffer_add(output, response, resp_len);
      assert(succeed == 0);
      if (evbuffer_get_length(output) > MAX_OUTPUT_BUFFER)
      {
        printf("output buffer is too long\n");
        bufferevent_free(bev);
        break;
      }
    }
  }
}

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);
  set_tcp_no_delay(fd);

  bufferevent_setcb(bev, echo_read_cb, NULL, echo_event_cb, NULL);

  bufferevent_enable(bev, EV_READ|EV_WRITE);
}

int main(int argc, char **argv)
{
  struct event_base *base;
  struct evconnlistener *listener;
  struct sockaddr_in sin;
  struct event *evstop;

  int port = 9876;

  if (argc > 1) {
    port = atoi(argv[1]);
  }
  if (port<=0 || port>65535) {
    puts("Invalid port");
    return 1;
  }

  signal(SIGPIPE, SIG_IGN);

  base = event_base_new();
  if (!base) {
    puts("Couldn't open event base");
    return 1;
  }

  evstop = evsignal_new(base, SIGHUP, signal_cb, base);
  evsignal_add(evstop, NULL);

  memset(&sin, 0, sizeof(sin));
  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = htonl(0); /* Listen on 0.0.0.0 */
  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;
  }

  event_base_dispatch(base);

  evconnlistener_free(listener);
  event_free(evstop);
  event_base_free(base);
  return 0;
}