lrealpath.c

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/*

@deftypefn Replacement {const char*} lrealpath (const char *@var{name})

Given a pointer to a string containing a pathname, returns a canonical
version of the filename.  Symlinks will be resolved, and ``.'' and ``..''
components will be simplified.  The returned value will be allocated using
@code{malloc}, or @code{NULL} will be returned on a memory allocation error.

@end deftypefn

*/

#include "config.h"
#include "lrealpath.h"

#ifdef HAVE_LIMITS_H
#include <limits.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif

/* On GNU libc systems the declaration is only visible with _GNU_SOURCE.  */
#if defined(HAVE_CANONICALIZE_FILE_NAME) \
    && defined(NEED_DECLARATION_CANONICALIZE_FILE_NAME)
extern char *canonicalize_file_name (const char *);
#endif

#if defined(HAVE_REALPATH)
# if defined (PATH_MAX)
#  define REALPATH_LIMIT PATH_MAX
# else
#  if defined (MAXPATHLEN)
#   define REALPATH_LIMIT MAXPATHLEN
#  endif
# endif
#else
  /* cygwin has realpath, so it won't get here.  */ 
# if defined (_WIN32)
#  define WIN32_LEAN_AND_MEAN
#  include <windows.h> /* for GetFullPathName */
# endif
#endif

char *
lrealpath (const char *filename)
{
  /* Method 1: The system has a compile time upper bound on a filename
     path.  Use that and realpath() to canonicalize the name.  This is
     the most common case.  Note that, if there isn't a compile time
     upper bound, you want to avoid realpath() at all costs.  */
#if defined(REALPATH_LIMIT)
  {
    char buf[REALPATH_LIMIT];
    const char *rp = realpath (filename, buf);
    if (rp == NULL)
      rp = filename;
    return strdup (rp);
  }
  /* REALPATH_LIMIT */

  /* Method 2: The host system (i.e., GNU) has the function
     canonicalize_file_name() which malloc's a chunk of memory and
     returns that, use that.  */
#elif defined(HAVE_CANONICALIZE_FILE_NAME)
  {
    char *rp = canonicalize_file_name (filename);
    if (rp == NULL)
      return strdup (filename);
    else
      return rp;
  }
  /* HAVE_CANONICALIZE_FILE_NAME */

  /* Method 3: Now we're getting desperate!  The system doesn't have a
     compile time buffer size and no alternative function.  Query the
     OS, using pathconf(), for the buffer limit.  Care is needed
     though, some systems do not limit PATH_MAX (return -1 for
     pathconf()) making it impossible to pass a correctly sized buffer
     to realpath() (it could always overflow).  On those systems, we
     skip this.  */
#elif defined (HAVE_REALPATH) && defined (HAVE_UNISTD_H)
  {
    /* Find out the max path size.  */
    long path_max = pathconf ("/", _PC_PATH_MAX);
    if (path_max > 0)
      {
        /* PATH_MAX is bounded.  */
        char *buf, *rp, *ret;
        buf = (char *) malloc (path_max);
        if (buf == NULL)
          return NULL;
        rp = realpath (filename, buf);
        ret = strdup (rp ? rp : filename);
        free (buf);
        return ret;
      }
  }
  /* HAVE_REALPATH && HAVE_UNISTD_H */

  /* The MS Windows method.  If we don't have realpath, we assume we
     don't have symlinks and just canonicalize to a Windows absolute
     path.  GetFullPath converts ../ and ./ in relative paths to
     absolute paths, filling in current drive if one is not given
     or using the current directory of a specified drive (eg, "E:foo").
     It also converts all forward slashes to back slashes.  */
#elif defined (_WIN32)
  {
    char buf[MAX_PATH];
    char* basename;
    DWORD len = GetFullPathName (filename, MAX_PATH, buf, &basename);
    if (len == 0 || len > MAX_PATH - 1)
      return strdup (filename);
    else
      {
        /* The file system is case-preserving but case-insensitive,
           Canonicalize to lowercase, using the codepage associated
           with the process locale.  */
        CharLowerBuff (buf, len);
        return strdup (buf);
      }
  }
#else

  /* This system is a lost cause, just duplicate the filename.  */
  return strdup (filename);
#endif
}