From: Bruno Haible <bruno@clisp.org>
Date: Tue, 18 Sep 2007 22:03:42 +0000 (+0000)
Subject: New module 'areadlink'. File based on lib/xreadlink.c.
X-Git-Tag: cvs-readonly~1
X-Git-Url: http://erislabs.net/gitweb/?a=commitdiff_plain;h=9e1c363a5e3c4ccc9c44ac40e90c811af52c7a63;p=gnulib.git

New module 'areadlink'. File based on lib/xreadlink.c.
---

diff --git a/lib/areadlink.c b/lib/areadlink.c
new file mode 100644
index 000000000..1b01d6f8b
--- /dev/null
+++ b/lib/areadlink.c
@@ -0,0 +1,122 @@
+/* areadlink.c -- readlink wrapper to return the link name in malloc'd storage
+   Unlike xreadlink and xreadlink_with_size, don't ever call exit.
+
+   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
+   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>
+   and Bruno Haible <bruno@clisp.org>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "areadlink.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
+#ifndef SSIZE_MAX
+# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
+#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 and set errno.
+   If realloc fails, or if the link value is longer than SIZE_MAX :-),
+   return NULL and set errno to ENOMEM.  */
+
+char *
+areadlink (char const *filename)
+{
+  /* 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)
+    {
+      /* 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)
+	{
+	  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';
+
+	  /* Return it in a chunk of memory as small as possible.  */
+	  if (buffer == initial_buf)
+	    {
+	      buffer = (char *) malloc (link_length);
+	      if (buffer == NULL)
+		/* errno is ENOMEM.  */
+		return NULL;
+	      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 (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
+	{
+	  errno = ENOMEM;
+	  return NULL;
+	}
+      buffer = (char *) malloc (buf_size);
+      if (buffer == NULL)
+	/* errno is ENOMEM.  */
+	return NULL;
+    }
+}