X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Fxreadlink-with-size.c;fp=lib%2Fxreadlink-with-size.c;h=baea5b9cfbdb7b2204f39b1036c693afe9e96033;hb=0b4f797cac54f402a07eccb83e2f3321a98cf71c;hp=0000000000000000000000000000000000000000;hpb=91ae88c7c924074ad64d5191e62cf56dc5854030;p=gnulib.git

diff --git a/lib/xreadlink-with-size.c b/lib/xreadlink-with-size.c
new file mode 100644
index 000000000..baea5b9cf
--- /dev/null
+++ b/lib/xreadlink-with-size.c
@@ -0,0 +1,105 @@
+/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
+
+   Copyright (C) 2001, 2003, 2004, 2005, 2006 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
+   the Free Software Foundation; either version 2, 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; see the file COPYING.
+   If not, write to the Free Software Foundation,
+   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Written by Jim Meyering <jim@meyering.net>  */
+
+#include <config.h>
+
+#include "xreadlink.h"
+
+#include <stdio.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
+#ifndef SSIZE_MAX
+# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
+#endif
+
+/* SYMLINK_MAX is used only for an initial memory-allocation sanity
+   check, so it's OK to guess too small on hosts where there is no
+   arbitrary limit to symbolic link length.  */
+#ifndef SYMLINK_MAX
+# define SYMLINK_MAX 1024
+#endif
+
+#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
+
+#include "xalloc.h"
+
+/* Call readlink to get the symbolic link value of FILE.
+   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 :-),
+   give a diagnostic and exit.  */
+
+char *
+xreadlink (char const *file, size_t size)
+{
+  /* Some buggy file systems report garbage in st_size.  Defend
+     against them by ignoring outlandish st_size values in the initial
+     memory allocation.  */
+  size_t symlink_max = SYMLINK_MAX;
+  size_t INITIAL_LIMIT_BOUND = 8 * 1024;
+  size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND
+			  ? symlink_max + 1
+			  : INITIAL_LIMIT_BOUND);
+
+  /* The initial buffer size for the link value.  */
+  size_t buf_size = size < initial_limit ? size + 1 : initial_limit;
+
+  while (1)
+    {
+      char *buffer = xmalloc (buf_size);
+      ssize_t r = readlink (file, buffer, buf_size);
+      size_t link_length = r;
+
+      /* 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 (r < 0 && errno != ERANGE)
+	{
+	  int saved_errno = errno;
+	  free (buffer);
+	  errno = saved_errno;
+	  return NULL;
+	}
+
+      if (link_length < buf_size)
+	{
+	  buffer[link_length] = 0;
+	  return buffer;
+	}
+
+      free (buffer);
+      if (buf_size <= MAXSIZE / 2)
+	buf_size *= 2;
+      else if (buf_size < MAXSIZE)
+	buf_size = MAXSIZE;
+      else
+	xalloc_die ();
+    }
+}