/*

 * Copyright (c) 2009-2012 Niels Provos, Nick Mathewson

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. The name of the author may not be used to endorse or promote products

 *    derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "event2/event-config.h"

#include "evconfig-private.h"

#include <sys/types.h>

#ifdef _WIN32

#include <winsock2.h>

#endif

#include "event2/util.h"

#include "event2/buffer.h"

#include "event2/bufferevent.h"

#include "event2/bufferevent_struct.h"

#include "event2/event.h"

#include "defer-internal.h"

#include "bufferevent-internal.h"

#include "mm-internal.h"

#include "util-internal.h"

struct bufferevent_pair {

  struct bufferevent_private bev;

  struct bufferevent_pair *partner;

  /* For ->destruct() lock checking */

  struct bufferevent_pair *unlinked_partner;

};

/* Given a bufferevent that's really a bev part of a bufferevent_pair,

 * return that bufferevent_filtered. Returns NULL otherwise.*/

static inline struct bufferevent_pair *

upcast(struct bufferevent *bev)

{

  struct bufferevent_pair *bev_p;

  bev_p = EVUTIL_UPCAST(bev, struct bufferevent_pair, bev.bev);

  EVUTIL_ASSERT(BEV_IS_PAIR(&bev_p->bev.bev));

  return bev_p;

}

#define downcast(bev_pair) (&(bev_pair)->bev.bev)

static inline void

incref_and_lock(struct bufferevent *b)

{

  struct bufferevent_pair *bevp;

  bufferevent_incref_and_lock_(b);

  bevp = upcast(b);

  if (bevp->partner)

    bufferevent_incref_and_lock_(downcast(bevp->partner));

}

static inline void

decref_and_unlock(struct bufferevent *b)

{

  struct bufferevent_pair *bevp = upcast(b);

  if (bevp->partner)

    bufferevent_decref_and_unlock_(downcast(bevp->partner));

  bufferevent_decref_and_unlock_(b);

}

/* XXX Handle close */

static void be_pair_outbuf_cb(struct evbuffer *,

    const struct evbuffer_cb_info *, void *);

static struct bufferevent_pair *

bufferevent_pair_elt_new(struct event_base *base,

    int options)

{

  struct bufferevent_pair *bufev;

  if (! (bufev = mm_calloc(1, sizeof(struct bufferevent_pair))))

    return NULL;

  if (bufferevent_init_common_(&bufev->bev, base, &bufferevent_ops_pair,

    options)) {

    mm_free(bufev);

    return NULL;

  }

  if (!evbuffer_add_cb(bufev->bev.bev.output, be_pair_outbuf_cb, bufev)) {

    bufferevent_free(downcast(bufev));

    return NULL;

  }

  bufferevent_init_generic_timeout_cbs_(&bufev->bev.bev);

  return bufev;

}

int

bufferevent_pair_new(struct event_base *base, int options,

    struct bufferevent *pair[2])

{

  struct bufferevent_pair *bufev1 = NULL, *bufev2 = NULL;

  int tmp_options;

  options |= BEV_OPT_DEFER_CALLBACKS;

  tmp_options = options & ~BEV_OPT_THREADSAFE;

  bufev1 = bufferevent_pair_elt_new(base, options);

  if (!bufev1)

    return -1;

  bufev2 = bufferevent_pair_elt_new(base, tmp_options);

  if (!bufev2) {

    bufferevent_free(downcast(bufev1));

    return -1;

  }

  if (options & BEV_OPT_THREADSAFE) {

    /*XXXX check return */

    bufferevent_enable_locking_(downcast(bufev2), bufev1->bev.lock);

  }

  bufev1->partner = bufev2;

  bufev2->partner = bufev1;

  evbuffer_freeze(downcast(bufev1)->input, 0);

  evbuffer_freeze(downcast(bufev1)->output, 1);

  evbuffer_freeze(downcast(bufev2)->input, 0);

  evbuffer_freeze(downcast(bufev2)->output, 1);

  pair[0] = downcast(bufev1);

  pair[1] = downcast(bufev2);

  return 0;

}

static void

be_pair_transfer(struct bufferevent *src, struct bufferevent *dst,

    int ignore_wm)

{

  size_t dst_size;

  size_t n;

  evbuffer_unfreeze(src->output, 1);

  evbuffer_unfreeze(dst->input, 0);

  if (dst->wm_read.high) {

    dst_size = evbuffer_get_length(dst->input);

    if (dst_size < dst->wm_read.high) {

      n = dst->wm_read.high - dst_size;

      evbuffer_remove_buffer(src->output, dst->input, n);

    } else {

      if (!ignore_wm)

        goto done;

      n = evbuffer_get_length(src->output);

      evbuffer_add_buffer(dst->input, src->output);

    }

  } else {

    n = evbuffer_get_length(src->output);

    evbuffer_add_buffer(dst->input, src->output);

  }

  if (n) {

    BEV_RESET_GENERIC_READ_TIMEOUT(dst);

    if (evbuffer_get_length(dst->output))

      BEV_RESET_GENERIC_WRITE_TIMEOUT(dst);

    else

      BEV_DEL_GENERIC_WRITE_TIMEOUT(dst);

  }

  bufferevent_trigger_nolock_(dst, EV_READ, 0);

  bufferevent_trigger_nolock_(src, EV_WRITE, 0);

done:

  evbuffer_freeze(src->output, 1);

  evbuffer_freeze(dst->input, 0);

}

static inline int

be_pair_wants_to_talk(struct bufferevent_pair *src,

    struct bufferevent_pair *dst)

{

  return (downcast(src)->enabled & EV_WRITE) &&

      (downcast(dst)->enabled & EV_READ) &&

      !dst->bev.read_suspended &&

      evbuffer_get_length(downcast(src)->output);

}

static void

be_pair_outbuf_cb(struct evbuffer *outbuf,

    const struct evbuffer_cb_info *info, void *arg)

{

  struct bufferevent_pair *bev_pair = arg;

  struct bufferevent_pair *partner = bev_pair->partner;

  incref_and_lock(downcast(bev_pair));

  if (info->n_added > info->n_deleted && partner) {

    /* We got more data.  If the other side's reading, then

       hand it over. */

    if (be_pair_wants_to_talk(bev_pair, partner)) {

      be_pair_transfer(downcast(bev_pair), downcast(partner), 0);

    }

  }

  decref_and_unlock(downcast(bev_pair));

}

static int

be_pair_enable(struct bufferevent *bufev, short events)

{

  struct bufferevent_pair *bev_p = upcast(bufev);

  struct bufferevent_pair *partner = bev_p->partner;

  incref_and_lock(bufev);

  if (events & EV_READ) {

    BEV_RESET_GENERIC_READ_TIMEOUT(bufev);

  }

  if ((events & EV_WRITE) && evbuffer_get_length(bufev->output))

    BEV_RESET_GENERIC_WRITE_TIMEOUT(bufev);

  /* We're starting to read! Does the other side have anything to write?*/

  if ((events & EV_READ) && partner &&

      be_pair_wants_to_talk(partner, bev_p)) {

    be_pair_transfer(downcast(partner), bufev, 0);

  }

  /* We're starting to write! Does the other side want to read? */

  if ((events & EV_WRITE) && partner &&

      be_pair_wants_to_talk(bev_p, partner)) {

    be_pair_transfer(bufev, downcast(partner), 0);

  }

  decref_and_unlock(bufev);

  return 0;

}

static int

be_pair_disable(struct bufferevent *bev, short events)

{

  if (events & EV_READ) {

    BEV_DEL_GENERIC_READ_TIMEOUT(bev);

  }

  if (events & EV_WRITE) {

    BEV_DEL_GENERIC_WRITE_TIMEOUT(bev);

  }

  return 0;

}

static void

be_pair_unlink(struct bufferevent *bev)

{

  struct bufferevent_pair *bev_p = upcast(bev);

  if (bev_p->partner) {

    bev_p->unlinked_partner = bev_p->partner;

    bev_p->partner->partner = NULL;

    bev_p->partner = NULL;

  }

}

/* Free *shared* lock in the latest be (since we share it between two of them). */

static void

be_pair_destruct(struct bufferevent *bev)

{

  struct bufferevent_pair *bev_p = upcast(bev);

  /* Transfer ownership of the lock into partner, otherwise we will use

   * already free'd lock during freeing second bev, see next example:

   *

   * bev1->own_lock = 1

   * bev2->own_lock = 0

   * bev2->lock = bev1->lock

   *

   * bufferevent_free(bev1) # refcnt == 0 -> unlink

   * bufferevent_free(bev2) # refcnt == 0 -> unlink

   *

   * event_base_free() -> finalizers -> EVTHREAD_FREE_LOCK(bev1->lock)

   *                                 -> BEV_LOCK(bev2->lock) <-- already freed

   *

   * Where bev1 == pair[0], bev2 == pair[1].

   */

  if (bev_p->unlinked_partner && bev_p->bev.own_lock) {

    bev_p->unlinked_partner->bev.own_lock = 1;

    bev_p->bev.own_lock = 0;

  }

  bev_p->unlinked_partner = NULL;

}

static int

be_pair_flush(struct bufferevent *bev, short iotype,

    enum bufferevent_flush_mode mode)

{

  struct bufferevent_pair *bev_p = upcast(bev);

  struct bufferevent *partner;

  if (!bev_p->partner)

    return -1;

  if (mode == BEV_NORMAL)

    return 0;

  incref_and_lock(bev);

  partner = downcast(bev_p->partner);

  if ((iotype & EV_READ) != 0)

    be_pair_transfer(partner, bev, 1);

  if ((iotype & EV_WRITE) != 0)

    be_pair_transfer(bev, partner, 1);

  if (mode == BEV_FINISHED) {

    short what = BEV_EVENT_EOF;

    if (iotype & EV_READ)

      what |= BEV_EVENT_WRITING;

    if (iotype & EV_WRITE)

      what |= BEV_EVENT_READING;

    bufferevent_run_eventcb_(partner, what, 0);

  }

  decref_and_unlock(bev);

  return 0;

}

struct bufferevent *

bufferevent_pair_get_partner(struct bufferevent *bev)

{

  struct bufferevent_pair *bev_p;

  struct bufferevent *partner = NULL;

  if (!BEV_IS_PAIR(bev))

    return NULL;

  bev_p = upcast(bev);

  incref_and_lock(bev);

  if (bev_p->partner)

    partner = downcast(bev_p->partner);

  decref_and_unlock(bev);

  return partner;

}

const struct bufferevent_ops bufferevent_ops_pair = {

  "pair_elt",

  evutil_offsetof(struct bufferevent_pair, bev.bev),

  be_pair_enable,

  be_pair_disable,

  be_pair_unlink,

  be_pair_destruct,

  bufferevent_generic_adj_timeouts_,

  be_pair_flush,

  NULL, /* ctrl */

};