X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Fxreadlink.c;h=2aba2654780912fa86c299fdff4b20a554a05385;hb=2e7980e7a83a290bfaf0638bd95a9cbfeec0f67d;hp=333551fedabbedb99e71f2043a223a0b3b195de4;hpb=7d7fb7355d5c231ef7b954d5f28f550efa16eaf5;p=gnulib.git

diff --git a/lib/xreadlink.c b/lib/xreadlink.c
index 333551fed..2aba26547 100644
--- a/lib/xreadlink.c
+++ b/lib/xreadlink.c
@@ -1,6 +1,6 @@
-/* exclude.c -- exclude file names
+/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
 
-   Copyright 2001 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
@@ -15,58 +15,117 @@
    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>
-#if HAVE_SYS_TYPES_H
-# include <sys/types.h>
-#endif
-#if HAVE_STDLIB_H
-# include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#ifndef SIZE_MAX
+# define SIZE_MAX ((size_t) -1)
 #endif
-#if HAVE_UNISTD_H
-# include <unistd.h>
+#ifndef SSIZE_MAX
+# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
 #endif
 
-#include "xalloc.h"
-#include "xreadlink.h"
+#ifdef NO_XMALLOC
+# define xmalloc malloc
+#else
+# include "xalloc.h"
+#endif
 
 /* Call readlink to get the symbolic link value of FILENAME.
    Return a pointer to that NUL-terminated string in malloc'd storage.
-   If readlink fails, return NULL (use errno to diagnose).
+   If readlink fails, return NULL (caller may use errno to diagnose).
    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 *link_length_arg)
+xreadlink (char const *filename)
 {
-  size_t buf_size = 128;  /* must be a power of 2 */
-  char *buffer = NULL;
+  /* The initial buffer size for the link value.  A power of 2
+     detects arithmetic overflow earlier, but is not required.  */
+#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)
     {
-      int link_length;
-      buffer = (char *) xrealloc (buffer, buf_size);
-      link_length = readlink (filename, buffer, buf_size);
-      if (link_length < 0)
+      /* Attempt to read the link into the current buffer.  */
+      ssize_t link_length = readlink (filename, buffer, buf_size);
+
+      /* 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)
 	{
-	  free (buffer);
+	  if (buffer != initial_buf)
+	    {
+	      int saved_errno = errno;
+	      free (buffer);
+	      errno = saved_errno;
+	    }
 	  return NULL;
 	}
-      if (link_length < buf_size)
+
+      if ((size_t) link_length < buf_size)
 	{
-	  *link_length_arg = link_length;
-	  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;
 	}
+
+      if (buffer != initial_buf)
+	free (buffer);
       buf_size *= 2;
-      if (buf_size == 0)
+      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
     }
 }