identify.c: Stash a copy of the caller's description string.

[fwd] / endpt.c

/* -*-c-*-
 *
 * Generic endpoint abstraction
 *
 * (c) 1999 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the `fwd' port forwarder.
 *
 * `fwd' is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * `fwd' is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with `fwd'; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include "fwd.h"

/*----- Data structures ---------------------------------------------------*/

/* --- Pairs of channels --- *
 *
 * Channels are always allocated and freed in pairs.  It makes sense to keep
 * the pair together.  (It also wastes less memory.)
 */

typedef struct chanpair {
  struct chanpair *next;
  chan ab, ba;
} chanpair;

/* --- The `private data structure' --- *
 *
 * This is called a @tango@ because it takes two (endpoints).
 */

typedef struct tango {
  struct tango *next, *prev;		/* A big list of all tangos */
  endpt *a, *b;				/* The two endpoints */
  char *desc;				/* Description of the connection */
  unsigned s;				/* State of the connection */
  chanpair *c;				/* The pair of channels */
} tango;

#define EPS_AB 1u
#define EPS_BA 2u

/*----- Static variables --------------------------------------------------*/

static chanpair *chans = 0;		/* List of spare channel pairs */
static tango *tangos = 0;		/* List of tangos */

/*----- Main code ---------------------------------------------------------*/

/* --- @doneab@, @doneba@ --- *
 *
 * Arguments:	@void *p@ = pointer to a tango block
 *
 * Returns:	---
 *
 * Use:		Handles completion of a channel.
 */

static void doneab(void *p)
{
  tango *t = p;
  t->s &= ~EPS_AB;
  t->b->ops->wclose(t->b);
  if (!t->s)
    endpt_kill(t->a);
}

static void doneba(void *p)
{
  tango *t = p;
  t->s &= ~EPS_BA;
  t->a->ops->wclose(t->a);
  if (!t->s)
    endpt_kill(t->a);
}

/* --- @endpt_kill@ --- *
 *
 * Arguments:	@endpt *a@ = an endpoint
 *
 * Returns:	---
 *
 * Use:		Kills an endpoint.  If the endpoint is joined to another, the
 *		other endpoint is also killed, as is the connection between
 *		them (and that's the tricky bit).
 */

void endpt_kill(endpt *a)
{
  tango *t;
  endpt *b;

  /* --- If the endpont is unconnected, just close it --- */

  if (!a->t) {
    a->ops->close(a);
    return;
  }
  t = a->t;
  a = t->a;
  b = t->b;

  /* --- See whether to close channels --- *
   *
   * I'll only have opened channels if both things are files.  Also, the
   * channel from @b@ to @a@ will only be open if @b@ is not pending.
   */

  if (a->f & b->f & EPF_FILE) {
    if (t->c->ab.err)
      fw_log(NOW, "[%s] error: %s", t->desc, strerror(t->c->ab.err));
    else if (t->c->ba.err)
      fw_log(NOW, "[%s] error: %s", t->desc, strerror(t->c->ba.err));
    if (t->s & EPS_AB)
      chan_close(&t->c->ab);
    if (!(b->f & EPF_PENDING) && (t->s & EPS_BA))
      chan_close(&t->c->ba);
    t->c->next = chans;
    chans = t->c;
  }

  /* --- Now just throw the endpoints and tango block away --- */

  a->ops->close(a);
  b->ops->close(b);
  if (t->next)
    t->next->prev = t->prev;
  if (t->prev)
    t->prev->next = t->next;
  else
    tangos = t->next;
  if (t->desc)
    xfree(t->desc);
  DESTROY(t);
}

/* --- @endpt_killall@ --- *
 *
 * Arguments:	---
 *
 * Returns:	---
 *
 * Use:		Destroys all current endpoint connections.  Used when
 *		shutting down.
 */

void endpt_killall(void)
{
  tango *t = tangos;
  while (t) {
    tango *tt = t;
    t = t->next;
    endpt_kill(tt->a);
  }
  tangos = 0;
}

/* --- @endpt_join@ --- *
 *
 * Arguments:	@endpt *a@ = pointer to first endpoint
 *		@endpt *b@ = pointer to second endpoint
 *		@const char *desc@ = description of connection
 *
 * Returns:	---
 *
 * Use:		Joins two endpoints together.  It's OK to join endpoints
 *		which are already joined; in fact, the the right thing to do
 *		when your endpoint decides that it's not pending any more is
 *		to join it to its partner again.
 *
 *		If the endpoints are already connected then the description
 *		string is ignored.  The endpoint manager takes a copy of the
 *		string, so you don't need to keep it around.
 */

void endpt_join(endpt *a, endpt *b, const char *desc)
{
  tango *t = a->t;

  /* --- If there is no tango yet, create one --- */

  if (!t) {
    t = CREATE(tango);
    t->next = tangos;
    t->prev = 0;
    t->a = b->other = a;
    t->b = a->other = b;
    a->t = b->t = t;
    t->s = EPS_AB | EPS_BA;
    t->c = 0;
    t->desc = xstrdup(desc);
    if (tangos)
      tangos->prev = t;
    tangos = t;
  }

  /* --- If both endpoints are unfinished, leave them for a while --- */

  if (a->f & b->f & EPF_PENDING)
    return;

  /* --- At least one endpoint is ready --- *
   *
   * If both endpoints are files then I can speculatively create the
   * channels, which will let data start flowing a bit.  Otherwise, I'll just
   * have to wait some more.
   */

  if ((a->f | b->f) & EPF_PENDING) {

    /* --- Only be interested if both things are files --- */

    if (!t->c && (a->f & b->f & EPF_FILE)) {

      /* --- Allocate a pair of channels --- */

      if (!chans)
	t->c = xmalloc(sizeof(*t->c));
      else {
	t->c = chans;
	chans = chans->next;
      }

      /* --- Make @a@ the endpoint which is ready --- */

      if (a->f & EPF_PENDING) {
	t->b = a; t->a = b;
	a = t->a; b = t->b;
      }

      /* --- Open one channel to read from @a@ --- */

      chan_open(&t->c->ab, a->in->fd, -1, doneab, t);
    }
    return;
  }

  /* --- Both endpoints are now ready --- *
   *
   * There are four cases to consider here.
   */

  /* --- Case 1 --- *
   *
   * Neither endpoint is a file.  I need to make a pair of pipes and tell
   * both endpoints to attach to them.  I can then close the pipes and
   * discard the tango.
   */

  if (!((a->f | b->f) & EPF_FILE)) {
    int pab[2], pba[2];
    reffd *rab, *wab, *rba, *wba;

    /* --- Create the pipes --- */

    if (pipe(pab)) goto tidy_nofile_0;
    if (pipe(pba)) goto tidy_nofile_1;

    /* --- Attach reference counters --- */

    rab = reffd_init(pab[0]); wab = reffd_init(pab[1]);
    rba = reffd_init(pba[0]); wba = reffd_init(pba[1]);
    a->ops->attach(a, rba, wab);
    b->ops->attach(b, rab, wba);
    REFFD_DEC(rab); REFFD_DEC(wab);
    REFFD_DEC(rba); REFFD_DEC(wba);
    goto tidy_nofile_0;

    /* --- Tidy up after a mess --- */

  tidy_nofile_1:
    close(pab[0]); close(pab[1]);
  tidy_nofile_0:
    a->ops->close(a);
    b->ops->close(b);
    if (t->next)
      t->next->prev = t->prev;
    if (t->prev)
      t->prev->next = t->next;
    else
      tangos = t->next;
    DESTROY(t);
    return;
  }

  /* --- Case 2 --- *
   *
   * One endpoint is a file, the other isn't.  I just attach the other
   * endpoint to the file and stand well back.
   */

  if ((a->f ^ b->f) & EPF_FILE) {

    /* --- Let @a@ be the endpoint with the file --- */

    if (b->f & EPF_FILE) {
      endpt *e;
      e = a; a = b; b = e;
    }

    /* --- Attach the non-file endpoint to the file and run away --- *
     *
     * Leave it as the non-file's responsibility to close the other endpoint
     * when it's ready.  It should also close itself at that time.
     */

    b->ops->attach(b, a->in, a->out);
    b->ops->file(b, a);
    if (t->next)
      t->next->prev = t->prev;
    if (t->prev)
      t->prev->next = t->next;
    else
      tangos = t->next;
    DESTROY(t);
    return;
  }

  /* --- Case 3 --- *
   *
   * Both endpoints are files and I have a partially created channel pair.  I
   * need to create the other channel and add a destination to the first one.
   * In this case, @t->b@ is the endpoint which has just finished setting
   * itself up.
   */

  if (t->c) {
    a = t->a; b = t->b;
    chan_open(&t->c->ba, b->in->fd, a->out->fd, doneba, t);
    chan_dest(&t->c->ab, b->out->fd);
    return;
  }

  /* --- Case 4 --- *
   *
   * Both endpoints are files and I don't have a partially created channel
   * pair.  I need to allocate a channel pair and create both channels.
   */

  if (!chans)
    t->c = xmalloc(sizeof(*t->c));
  else {
    t->c = chans;
    chans = chans->next;
  }
  chan_open(&t->c->ab, a->in->fd, b->out->fd, doneab, t);
  chan_open(&t->c->ba, b->in->fd, a->out->fd, doneba, t);
  return;
}

/*----- That's all, folks -------------------------------------------------*/