server/servutil.c: Add utilities for simple leaky-bucket rate limiting.

[tripe] / server / servutil.c

/* -*-c-*-
 *
 * Various handy server-only utilities
 *
 * (c) 2001 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Trivial IP Encryption (TrIPE).
 *
 * TrIPE 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.
 *
 * TrIPE 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 TrIPE.  If not, see <https://www.gnu.org/licenses/>.
 */

/*----- Header files ------------------------------------------------------*/

#include "tripe.h"

/*----- Global variables --------------------------------------------------*/

octet buf_i[PKBUFSZ], buf_o[PKBUFSZ], buf_t[PKBUFSZ], buf_u[PKBUFSZ];

/*----- Sequence numbers --------------------------------------------------*/

/* --- @seq_reset@ --- *
 *
 * Arguments:	@seqwin *s@ = sequence-checking window
 *
 * Returns:	---
 *
 * Use:		Resets a sequence number window.
 */

void seq_reset(seqwin *s) { s->seq = 0; s->win = 0; }

/* --- @seq_check@ --- *
 *
 * Arguments:	@seqwin *s@ = sequence-checking window
 *		@uint32 q@ = sequence number to check
 *		@const char *service@ = service to report message from
 *
 * Returns:	Zero on success, nonzero if the sequence number was bad.
 *
 * Use:		Checks a sequence number against the window, updating things
 *		as necessary.
 */

int seq_check(seqwin *s, uint32 q, const char *service)
{
  uint32 qbit;
  uint32 n;

  if (q < s->seq) {
    a_warn(service, "replay", "old-sequence", A_END);
    return (-1);
  }
  if (q >= s->seq + SEQ_WINSZ) {
    n = q - (s->seq + SEQ_WINSZ - 1);
    if (n < SEQ_WINSZ)
      s->win >>= n;
    else
      s->win = 0;
    s->seq += n;
  }
  qbit = 1 << (q - s->seq);
  if (s->win & qbit) {
    a_warn(service, "replay", "duplicated-sequence", A_END);
    return (-1);
  }
  s->win |= qbit;
  return (0);
}

/*----- Rate limiting -----------------------------------------------------*/

/* --- @ratelim_init@ --- *
 *
 * Arguments:	@ratelim *r@ = rate-limiting state to fill in
 *		@unsigned persec@ = credit to accumulate per second
 *		@unsigned max@ = maximum credit to retain
 *
 * Returns:	---
 *
 * Use:		Initialize a rate-limiting state.
 */

void ratelim_init(ratelim *r, unsigned persec, unsigned max)
{
  r->n = r->max = max;
  r->persec = persec;
  gettimeofday(&r->when, 0);
}

/* --- @ratelim_withdraw@ --- *
 *
 * Arguments:	@ratelim *r@ = rate-limiting state
 *		@unsigned n@ = credit to withdraw
 *
 * Returns:	Zero if successful; @-1@ if there is unsufficient credit
 *
 * Use:		Updates the state with any accumulated credit.  Then, if
 *		there there are more than @n@ credits available, withdraw @n@
 *		and return successfully; otherwise, report failure.
 */

int ratelim_withdraw(ratelim *r, unsigned n)
{
  struct timeval now, delta;
  unsigned long d;

  gettimeofday(&now, 0);
  TV_SUB(&delta, &now, &r->when);
  d = (unsigned long)r->persec*delta.tv_sec +
    (unsigned long)r->persec*delta.tv_usec/MILLION;
  if (d < r->max - r->n) r->n += d;
  else r->n = r->max;
  r->when = now;

  if (n > r->n) return (-1);
  else { r->n -= n; return (0); }
}

/*----- Random odds and sods ----------------------------------------------*/

/* --- @timestr@ --- *
 *
 * Arguments:	@time_t t@ = a time to convert
 *
 * Returns:	A pointer to a textual representation of the time.
 *
 * Use:		Converts a time to a textual representation.  Corrupts
 *		@buf_u@.
 */

const char *timestr(time_t t)
{
  struct tm *tm;
  if (!t)
    return ("NEVER");
  tm = localtime(&t);
  strftime((char *)buf_u, sizeof(buf_u), "%Y-%m-%dT%H:%M:%S", tm);
  return ((const char *)buf_u);
}

/* --- @mystrieq@ --- *
 *
 * Arguments:	@const char *x, *y@ = two strings
 *
 * Returns:	True if @x@ and @y are equal, up to case.
 */

int mystrieq(const char *x, const char *y)
{
  for (;;) {
    if (!*x && !*y) return (1);
    if (tolower((unsigned char)*x) != tolower((unsigned char)*y))
      return (0);
    x++; y++;
  }
}

/* --- @addrsz@ --- *
 *
 * Arguments:	@const addr *a@ = a network address
 *
 * Returns:	The size of the address, for passing into the sockets API.
 */

socklen_t addrsz(const addr *a)
{
  switch (a->sa.sa_family) {
    case AF_INET: return (sizeof(a->sin));
    default: abort();
  }
}

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