/****************************************************************************
 * fileutils.c                                                              *
 *                                                                          *
 * LocalGate Local Filesystem -> WWW Gateway                                *
 *                                                                          *
 * LocalGate allows a user to access HTML files on the local filesystem     *
 * as if they had a web server to access the files.                         *
 *                                                                          *
 * fileutils.c: file access routines for LocalGate.                         *
 *                                                                          *
 * Copyright (C) 1997  Michael Chu                                          *
 * This file is part of the LocalGate local filesystem -> WWW gateway.      *
 *                                                                          *
 * This program 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.                                      *
 *                                                                          *
 * This program 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, write to the Free Software              *
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.                *
 *                                                                          *
 * Contact information:      Michael Chu                                    *
 *                           mmchu@pobox.com                                *
 ****************************************************************************/


/*********************************** INCLUDES *******************************/

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>
#include "fileutils.h"


/********************************** FUNCTIONS *******************************/

/****************************************************************************
 * readFromFile:                                                            *
 *                                                                          *
 * Summary: Reads the given number of bytes from the given file into the    *
 *          given buffer.                                                   *
 *                                                                          *
 * Input:   fileId: file id to read from.                                   *
 *          buffer: buffer to which to write to.                            *
 *          maxBytes: maximum number of bytes to read from file.            *
 *                                                                          *
 * Returns: Actual number of bytes read from the file.                      *
 *                                                                          *
 * Global State Affected:                                                   *
 *          Given number of bytes is read from the given file.              *
 ****************************************************************************/
int readFromFile(int fileId, char *buffer, int maxBytes) {
  int numBytesRead = 0;               /* number of bytes read. */

  /* make sure that file id is non-negative. */
  assert(fileId >= 0);

  /* make sure that buffer is not NULL. */
  assert(buffer != NULL);

  /* make sure that number of bytes to read is non-negative. */
  assert(maxBytes >= 0);

  /* try to read bytes. */
  numBytesRead = read(fileId, buffer, maxBytes);

  /* if we had an error reading from the file, show it. */
  if (numBytesRead < 0) {
    /* show error. */
    fprintf(stderr, "Error reading from file! (errno = %d)\n", errno);

    /* return error. */
    return(-1);
  }

  /* return the number of bytes read. */
  return(numBytesRead);
}


/****************************************************************************
 * readFromFileOffset:                                                      *
 *                                                                          *
 * Summary: Reads the given number of bytes from the given file at the      *
 *          given offset into the given buffer.                             *
 *                                                                          *
 * Input:   fileId: file id to read from.                                   *
 *          fileOffset: file offset to read from.                           *
 *          buffer: buffer to which to write to.                            *
 *          maxBytes: maximum number of bytes to read from file.            *
 *                                                                          *
 * Returns: Actual number of bytes read from the file.                      *
 *                                                                          *
 * Global State Affected:                                                   *
 *          Given number of bytes is read from the given file.              *
 ****************************************************************************/
int readFromFileOffset(int fileId, long fileOffset, char *buffer, 
		       int maxBytes) {
  int numBytesRead = 0;               /* number of bytes read. */

  /* make sure that file id is non-negative. */
  assert(fileId >= 0);

  /* make sure that file offset is non-negative. */
  assert(fileOffset >= 0);

  /* make sure that buffer is not NULL. */
  assert(buffer != NULL);

  /* make sure that number of bytes to read is non-negative. */
  assert(maxBytes >= 0);

  /* try to seek to given file offset. */
  if ((lseek(fileId, fileOffset, SEEK_SET)) < 0) {
    /* show error. */
    fprintf(stderr, "Error seeking to location %ld in file! (errno = %d)\n",
	    fileOffset, errno);

    /* return error. */
    return(-1);
  }

  /* try to read bytes. */
  numBytesRead = read(fileId, buffer, maxBytes);

  /* if we had an error reading from the file, show it. */
  if (numBytesRead < 0) {
    /* show error. */
    fprintf(stderr, "Error reading from file! (errno = %d)\n", errno);

    /* return error. */
    return(-1);
  }

  /* return the number of bytes read. */
  return(numBytesRead);
}