inetutils/telnet/ring.c

/*
  Copyright (C) 1995-2025 Free Software Foundation, Inc.

  This file is part of GNU Inetutils.

  GNU Inetutils 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 3 of the License, or (at
  your option) any later version.

  GNU Inetutils 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 this program.  If not, see `http://www.gnu.org/licenses/'. */

/*
 * Copyright (c) 1988, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * 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. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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 <config.h>

#include <string.h>

/*
 * This defines a structure for a ring buffer.
 *
 * The circular buffer has two parts:
 *(((
 *	full:	[consume, supply)
 *	empty:	[supply, consume)
 *]]]
 *
 */

#include	<stdio.h>
#include	<errno.h>

#ifdef	size_t
# undef	size_t
#endif

#include	<sys/types.h>
#ifndef FILIO_H
# include	<sys/ioctl.h>
#endif
#include	<sys/socket.h>

#include	"ring.h"
#include	"general.h"

/* Internal macros */

#if !defined MIN
# define MIN(a,b)	(((a)<(b))? (a):(b))
#endif /* !defined(MIN) */

#define ring_subtract(d,a,b)	(((a)-(b) >= 0)? \
					(a)-(b): (((a)-(b))+(d)->size))

#define ring_increment(d,a,c)	(((a)+(c) < (d)->top)? \
					(a)+(c) : (((a)+(c))-(d)->size))

#define ring_decrement(d,a,c)	(((a)-(c) >= (d)->bottom)? \
					(a)-(c) : (((a)-(c))-(d)->size))


/*
 * The following is a clock, used to determine full, empty, etc.
 *
 * There is some trickiness here.  Since the ring buffers are initialized
 * to ZERO on allocation, we need to make sure, when interpreting the
 * clock, that when the times are EQUAL, then the buffer is FULL.
 */
static unsigned long ring_clock = 0;


#define ring_empty(d) (((d)->consume == (d)->supply) && \
				((d)->consumetime >= (d)->supplytime))
#define ring_full(d) (((d)->supply == (d)->consume) && \
				((d)->supplytime > (d)->consumetime))





/* Buffer state transition routines */

int
ring_init (Ring *ring, unsigned char *buffer, int count)
{
  memset ((char *) ring, 0, sizeof *ring);

  ring->size = count;

  ring->supply = ring->consume = ring->bottom = buffer;

  ring->top = ring->bottom + ring->size;

#ifdef	ENCRYPTION
  ring->clearto = 0;
#endif /* ENCRYPTION */

  return 1;
}

/* Mark routines */

/*
 * Mark the most recently supplied byte.
 */

void
ring_mark (Ring *ring)
{
  ring->mark = ring_decrement (ring, ring->supply, 1);
}

/*
 * Is the ring pointing to the mark?
 */

int
ring_at_mark (Ring *ring)
{
  if (ring->mark == ring->consume)
    {
      return 1;
    }
  else
    {
      return 0;
    }
}

/*
 * Clear any mark set on the ring.
 */

void
ring_clear_mark (Ring *ring)
{
  ring->mark = 0;
}

/*
 * Add characters from current segment to ring buffer.
 */
void
ring_supplied (Ring *ring, int count)
{
  ring->supply = ring_increment (ring, ring->supply, count);
  ring->supplytime = ++ring_clock;
}

/*
 * We have just consumed "c" bytes.
 */
void
ring_consumed (Ring *ring, int count)
{
  if (count == 0)		/* don't update anything */
    return;

  if (ring->mark && (ring_subtract (ring, ring->mark, ring->consume) < count))
    {
      ring->mark = 0;
    }
#ifdef	ENCRYPTION
  if (ring->consume < ring->clearto && ring->clearto <= ring->consume + count)
    ring->clearto = 0;
  else if (ring->consume + count > ring->top &&
	   ring->bottom <= ring->clearto &&
	   ring->bottom + ((ring->consume + count) - ring->top))
    ring->clearto = 0;
#endif /* ENCRYPTION */
  ring->consume = ring_increment (ring, ring->consume, count);
  ring->consumetime = ++ring_clock;
  /*
   * Try to encourage "ring_empty_consecutive()" to be large.
   */
  if (ring_empty (ring))
    {
      ring->consume = ring->supply = ring->bottom;
    }
}



/* Buffer state query routines */


/* Number of bytes that may be supplied */
int
ring_empty_count (Ring *ring)
{
  if (ring_empty (ring))
    {				/* if empty */
      return ring->size;
    }
  else
    {
      return ring_subtract (ring, ring->consume, ring->supply);
    }
}

/* number of CONSECUTIVE bytes that may be supplied */
int
ring_empty_consecutive (Ring *ring)
{
  if ((ring->consume < ring->supply) || ring_empty (ring))
    {
      /*
       * if consume is "below" supply, or empty, then
       * return distance to the top
       */
      return ring_subtract (ring, ring->top, ring->supply);
    }
  else
    {
      /*
       * else, return what we may.
       */
      return ring_subtract (ring, ring->consume, ring->supply);
    }
}

/* Return the number of bytes that are available for consuming
 * (but don't give more than enough to get to cross over set mark)
 */

int
ring_full_count (Ring *ring)
{
  if ((ring->mark == 0) || (ring->mark == ring->consume))
    {
      if (ring_full (ring))
	{
	  return ring->size;	/* nothing consumed, but full */
	}
      else
	{
	  return ring_subtract (ring, ring->supply, ring->consume);
	}
    }
  else
    {
      return ring_subtract (ring, ring->mark, ring->consume);
    }
}

/*
 * Return the number of CONSECUTIVE bytes available for consuming.
 * However, don't return more than enough to cross over set mark.
 */
int
ring_full_consecutive (Ring *ring)
{
  if ((ring->mark == 0) || (ring->mark == ring->consume))
    {
      if ((ring->supply < ring->consume) || ring_full (ring))
	{
	  return ring_subtract (ring, ring->top, ring->consume);
	}
      else
	{
	  return ring_subtract (ring, ring->supply, ring->consume);
	}
    }
  else
    {
      if (ring->mark < ring->consume)
	{
	  return ring_subtract (ring, ring->top, ring->consume);
	}
      else
	{			/* Else, distance to mark */
	  return ring_subtract (ring, ring->mark, ring->consume);
	}
    }
}

/*
 * Move data into the "supply" portion of of the ring buffer.
 */
void
ring_supply_data (Ring *ring, unsigned char *buffer, int count)
{
  int i;

  while (count)
    {
      i = MIN (count, ring_empty_consecutive (ring));
      memmove (ring->supply, buffer, i);
      ring_supplied (ring, i);
      count -= i;
      buffer += i;
    }
}

#ifdef	ENCRYPTION
void
ring_encrypt (Ring *ring, void (*encryptor) (unsigned char *, int))
{
  unsigned char *s, *c;

  if (ring_empty (ring) || ring->clearto == ring->supply)
    return;

  if (!(c = ring->clearto))
    c = ring->consume;

  s = ring->supply;

  if (s <= c)
    {
      (*encryptor) (c, ring->top - c);
      (*encryptor) (ring->bottom, s - ring->bottom);
    }
  else
    (*encryptor) (c, s - c);

  ring->clearto = ring->supply;
}

void
ring_clearto (Ring *ring)
{
  if (!ring_empty (ring))
    ring->clearto = ring->supply;
  else
    ring->clearto = 0;
}
#endif /* ENCRYPTION */