Only make necessary system calls.

[mLib] / fwatch.c

/* -*-c-*-
 *
 * $Id: fwatch.c,v 1.2 2004/04/08 01:36:11 mdw Exp $
 *
 * Watch a file for changes
 *
 * (c) 2001 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * mLib 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 Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with mLib; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

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

#include <errno.h>

#include <sys/types.h>
#include <sys/stat.h>

#include "fwatch.h"

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

/* --- @doupdate@ --- *
 *
 * Arguments:	@fwatch *f@ = pointer to an @fwatch@ structure
 *		@struct stat *st@ = pointer to file state
 *		@int err@ = whether there was an error
 *
 * Returns:	Nonzero if the file has changed.
 *
 * Use:		Updates the information in an @fwatch@ block.
 */

static void copy(fwatch *f, struct stat *st)
{
  f->dev = st->st_dev; f->ino = st->st_ino;
  f->mtime = st->st_mtime; f->size = st->st_size;
  f->mode = st->st_mode;
  f->uid = st->st_uid; f->gid = st->st_gid;
}

static int doupdate(fwatch *f, struct stat *st, int err)
{
  /* --- Fiddle with the error state --- *
   *
   * Only the presence or absence of error is interesting to someone wanting
   * to read the file.
   */

  if (err)
    err = errno;
  if (err || f->err) {
    if (!err != !f->err) {
      f->err = err;
      if (!err)
	copy(f, st);
      return (1);
    }
    return (0);
  }

  /* --- Check everything else --- */

  if (st->st_dev != f->dev || st->st_ino != f->ino ||
      st->st_mtime != f->mtime || st->st_size != f->size ||
      st->st_mode != f->mode ||
      st->st_uid != f->uid || st->st_gid != f->gid) {
    copy(f, st);
    return (1);
  }
  return (0);
}

/* --- @fwatch_init@, @fwatch_update@, etc --- *
 *
 * Arguments:	@fwatch *f@ = pointer to an @fwatch@ structure
 *		@const char *name@ = name of the file to watch
 *		@int fd@ = a file descriptor to watch
 *
 * Returns:	The @update@ functions return nonzero if the file has
 *		changed.
 *
 * Use:		Stores information about a file which can be used to watch
 *		for changes.  The structures may be freed without telling
 *		anyone.
 */

void fwatch_init(fwatch *f, const char *name)
{
  struct stat st;
  memset(f, 0, sizeof(*f));
  doupdate(f, &st, stat(name, &st));
}

void fwatch_initfd(fwatch *f, int fd)
{
  struct stat st;
  memset(f, 0, sizeof(*f));
  doupdate(f, &st, fstat(fd, &st));
}

int fwatch_update(fwatch *f, const char *name)
{
  struct stat st;
  return (doupdate(f, &st, stat(name, &st)));
}

int fwatch_updatefd(fwatch *f, int fd)
{
  struct stat st;
  return (doupdate(f, &st, fstat(fd, &st)));
}

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