/*      $NetBSD: bufferevent_pair.c,v 1.1.1.4 2021/04/07 02:43:13 christos Exp $        */
/*
* 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 <sys/cdefs.h>
__RCSID("$NetBSD: bufferevent_pair.c,v 1.1.1.4 2021/04/07 02:43:13 christos Exp $");
#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;
       if (!BEV_IS_PAIR(bev))
               return NULL;
       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() -> finilizers -> 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;
       bev_p = upcast(bev);
       if (! bev_p)
               return NULL;

       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 */
};

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