/*
 * "$Id: scandir_posix.c 9832 2013-03-06 22:15:01Z ianmacarthur $"
 *
 * This implementation of 'scandir()' is intended to be POSIX.1-2008 compliant.
 * A POSIX.1-1990 compliant system is required as minimum base.
 * Note:
 * The 'const' declarations were removed to match FLTK 1.3 wrapper (STR #2931)
 *
 * Copyright (c) 2013 by Michael Baeuerle
 *
 * This library is free software. Distribution and use rights are outlined in
 * the file "COPYING" which should have been included with this file. If this
 * file is missing or damaged, see the license at:
 *
 *     http://www.fltk.org/COPYING.php
 *
 * Please report all bugs and problems on the following page:
 *
 *     http://www.fltk.org/str.php
 *
 * It is required that 'SIZE_MAX' is at least 'INT_MAX'.
 * Don't use a C++ compiler to build this module.
 *
 * The build system must define 'HAVE_PTHREAD' and link against a potentially
 * required library to switch this implementation into thread-safe mode.
 * The POSIX.1c-1995 extension is required if 'HAVE_PTHREAD' is defined.
 *
 * Note:
 * In theory, a system that provide threads should also provide 'readdir_r()',
 * a thread-safe version of 'readdir()'. In reality this is not always the case.
 * In addition there may be a race condition that can lead to a buffer overflow:
 * http://womble.decadent.org.uk/readdir_r-advisory.html
 */

#ifndef HAVE_PTHREAD
   /* Switch system headers into POSIX.1-1990 mode */
#  define _POSIX_SOURCE
#else  /* HAVE_PTHREAD */
   /* Switch system headers into POSIX.1c-1995 mode */
#  define _POSIX_C_SOURCE  199506L
#endif  /* HAVE_PTHREAD */

#include <sys/types.h>        /* XPG2 require this for '*dir()' functions */
#include <dirent.h>
#include <errno.h>
#include <stdlib.h>           /* For 'malloc()', 'realloc()' and 'qsort()' */
#include <stddef.h>           /* For 'offsetof()', 'NULL' and 'size_t' */
#include <limits.h>           /* For 'INT_MAX' */
#include <string.h>           /* For 'memcpy()' */
#if defined(HAVE_PTHREAD) && defined(HAVE_PTHREAD_H)
#  include <pthread.h>
#endif  /* HAVE_PTHREAD */


/* ========================================================================== */
/* At startup allocate memory for this number of result array elements */
#define ENTRIES_MIN  (size_t) 32


/* ========================================================================== */
#ifdef HAVE_PTHREAD
static pthread_mutex_t scandir_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif  /* HAVE_PTHREAD */


/* ========================================================================== */
/*
 * This function reads the next entry from the directory referenced by 'dirp',
 * allocate a buffer for the entry and copy it into this buffer.
 * A pointer to this buffer is written to 'entryp' and the size of the buffer is
 * written to 'len'.
 * Success and a NULL pointer is returned for 'entryp' if there are no more
 * entries in the directory.
 * On sucess zero is returned and the caller is responsible for 'free()'ing the
 * buffer after use.
 * On error the return value is nonzero, 'entryp' and 'len' are invalid.
 *
 * Should be declared as 'static inline' if the compiler support that.
 */
static int
readentry(DIR *dirp, struct dirent **entryp, size_t *len)
{
  int result = -1;
  struct dirent *e;

#ifdef HAVE_PTHREAD
  if (!pthread_mutex_lock(&scandir_mutex))
  {
    /* Ensure that there is no code path that bypass the '_unlock()' call! */
#endif  /* HAVE_PTHREAD */
    errno = 0;
    e = readdir(dirp);
    if (NULL == e)
    {
      if (!errno)
      {
        /* No more entries in directory */
        *entryp = NULL;
        *len = 0;
        result = 0;
      }
    }
    else
    {
      /* Entry found, allocate local buffer */
      *len = offsetof(struct dirent, d_name) + strlen(e->d_name) + (size_t) 1;
      *entryp = (struct dirent *) malloc(*len);
      if (NULL != *entryp)
      {
        memcpy((void *) *entryp, (void *) e, *len);
        /* Force NUL termination at end of buffer */
        ((char *) *entryp)[*len - (size_t) 1] = 0;
        result = 0;
      }
    }
#ifdef HAVE_PTHREAD
    /*
     * In a multithreading environment the systems dirent buffer may be shared
     * between all threads. Therefore the mutex must stay locked until we have
     * copied the data to our thread local buffer.
     */
    pthread_mutex_unlock(&scandir_mutex);
  }
#endif  /* HAVE_PTHREAD */

  return result;
}


/* ========================================================================== */
int
fl_scandir(const char *dir, struct dirent ***namelist,
           int (*sel)(struct dirent *),
           int (*compar)(struct dirent **, struct dirent **))
{
  int result = -1;
  DIR *dirp;
  size_t len, num = 0, max = ENTRIES_MIN;
  struct dirent *entryp, **entries, **p;

  entries = (struct dirent **) malloc(sizeof(*entries) * max);
  if (NULL != entries)
  {
    /* Open directory 'dir' (and verify that it really is a directory) */
    dirp = opendir(dir);
    if (NULL != dirp)
    {
      /* Read next directory entry */
      while (!readentry(dirp, &entryp, &len))
      {
        if (NULL == entryp)
        {
          /* EOD => Return number of directory entries */
          result = (int) num;
          break;
        }
        /* Apply select function if there is one provided */
        if (NULL != sel)  { if (!sel(entryp))  continue; }
        entries[num++] = entryp;
        if (num >= max)
        {
          /* Allocate exponentially increasing sized memory chunks */
          if (INT_MAX / 2 >= (int) max)  { max *= (size_t) 2; }
          else
          {
            errno = ENOMEM;
            break;
          }
          p = (struct dirent **) realloc((void *) entries,
                                         sizeof(*entries) * max);
          if (NULL != p)  { entries = p; }
          else  break;
        }
      }
      closedir(dirp);
      /*
       * A standard compliant 'closedir()' is allowed to fail with 'EINTR', but
       * the state of the directory structure is undefined in this case.
       * Therefore we ignore the return value because we can't call 'closedir()'
       * again and must hope that the system has released all ressources.
       */
    }
    /* Sort entries in array if there is a compare function provided */
    if (NULL != compar)
    {
      qsort((void *) entries, num, sizeof(*entries),
            (int (*)(const void *, const void *)) compar);
    }
    *namelist = entries;
  }

  /* Check for error */
  if (-1 == result)
  {
    /* Free all memory we have allocated */
    while (num--)  { free(entries[num]); }
    free(entries);
  }

  return result;
}

/*
 * End of "$Id: scandir_posix.c 9832 2013-03-06 22:15:01Z ianmacarthur $".
 */
