X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Fxreadlink.c;h=2aba2654780912fa86c299fdff4b20a554a05385;hb=8badccbd46d6cbd0f1fa2014e01ce8a7cae2b272;hp=2e66c07f240791c8c1b05609da58ca58e6dd3b34;hpb=a62be9f4039b4499cfbb76e394cad2259d03fa84;p=gnulib.git

diff --git a/lib/xreadlink.c b/lib/xreadlink.c
index 2e66c07f2..2aba26547 100644
--- a/lib/xreadlink.c
+++ b/lib/xreadlink.c
@@ -1,6 +1,6 @@
 /* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
 
-   Copyright (C) 2001, 2003, 2004 Free Software Foundation, Inc.
+   Copyright (C) 2001, 2003-2007 Free Software Foundation, Inc.
 
    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
@@ -15,24 +15,23 @@
    You should have received a copy of the GNU General Public License
    along with this program; see the file COPYING.
    If not, write to the Free Software Foundation,
-   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
+   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
-/* Written by Jim Meyering <jim@meyering.net>  */
+/* Written by Jim Meyering <jim@meyering.net>
+   and Bruno Haible <bruno@clisp.org>.  */
 
-#if HAVE_CONFIG_H
-# include <config.h>
-#endif
+#include <config.h>
 
+/* Specification.  */
 #include "xreadlink.h"
 
 #include <stdio.h>
+#include <string.h>
 #include <errno.h>
 #include <limits.h>
 #include <sys/types.h>
 #include <stdlib.h>
-#if HAVE_UNISTD_H
-# include <unistd.h>
-#endif
+#include <unistd.h>
 
 #ifndef SIZE_MAX
 # define SIZE_MAX ((size_t) -1)
@@ -41,45 +40,92 @@
 # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
 #endif
 
-#include "xalloc.h"
+#ifdef NO_XMALLOC
+# define xmalloc malloc
+#else
+# include "xalloc.h"
+#endif
 
 /* Call readlink to get the symbolic link value of FILENAME.
-   SIZE is a hint as to how long the link is expected to be;
-   typically it is taken from st_size.  It need not be correct.
    Return a pointer to that NUL-terminated string in malloc'd storage.
    If readlink fails, return NULL (caller may use errno to diagnose).
-   If malloc fails, or if the link value is longer than SSIZE_MAX :-),
+   If realloc fails, or if the link value is longer than SIZE_MAX :-),
    give a diagnostic and exit.  */
 
 char *
-xreadlink (char const *filename, size_t size)
+xreadlink (char const *filename)
 {
   /* The initial buffer size for the link value.  A power of 2
      detects arithmetic overflow earlier, but is not required.  */
-  size_t buf_size = size + 1;
+#define INITIAL_BUF_SIZE 1024
+
+  /* Allocate the initial buffer on the stack.  This way, in the common
+     case of a symlink of small size, we get away with a single small malloc()
+     instead of a big malloc() followed by a shrinking realloc().  */
+  char initial_buf[INITIAL_BUF_SIZE];
+
+  char *buffer = initial_buf;
+  size_t buf_size = sizeof (initial_buf);
 
   while (1)
     {
-      char *buffer = xmalloc (buf_size);
+      /* Attempt to read the link into the current buffer.  */
       ssize_t link_length = readlink (filename, buffer, buf_size);
 
-      if (link_length < 0)
+      /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
+	 with errno == ERANGE if the buffer is too small.  */
+      if (link_length < 0 && errno != ERANGE)
 	{
-	  int saved_errno = errno;
-	  free (buffer);
-	  errno = saved_errno;
+	  if (buffer != initial_buf)
+	    {
+	      int saved_errno = errno;
+	      free (buffer);
+	      errno = saved_errno;
+	    }
 	  return NULL;
 	}
 
       if ((size_t) link_length < buf_size)
 	{
-	  buffer[link_length] = 0;
+	  buffer[link_length++] = '\0';
+
+	  /* Return it in a chunk of memory as small as possible.  */
+	  if (buffer == initial_buf)
+	    {
+	      buffer = (char *) xmalloc (link_length);
+#ifdef NO_XMALLOC
+	      if (buffer == NULL)
+		return NULL;
+#endif
+	      memcpy (buffer, initial_buf, link_length);
+	    }
+	  else
+	    {
+	      /* Shrink buffer before returning it.  */
+	      if ((size_t) link_length < buf_size)
+		{
+		  char *smaller_buffer = (char *) realloc (buffer, link_length);
+
+		  if (smaller_buffer != NULL)
+		    buffer = smaller_buffer;
+		}
+	    }
 	  return buffer;
 	}
 
-      free (buffer);
+      if (buffer != initial_buf)
+	free (buffer);
       buf_size *= 2;
-      if (! (0 < buf_size && buf_size <= SSIZE_MAX))
+      if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
+#ifdef NO_XMALLOC
+	return NULL;
+#else
 	xalloc_die ();
+#endif
+      buffer = (char *) xmalloc (buf_size);
+#ifdef NO_XMALLOC
+      if (buffer == NULL)
+	return NULL;
+#endif
     }
 }