New module: mreadlink-with-size.

* MODULES.html.sh: Add mreadlink-with-size.
* modules/mreadlink-with-size: New module
* modules/canonicalize (Depends-on): Depend on mreadlink-with-size,
not xreadlink-with-size.
* lib/mreadlink-with-size.c, lib/mreadlink.h: New files.

ChangeLog

@@ -1,3 +1,12 @@
+2007-06-18  Jim Meyering  <jim@meyering.net>
+
+	New module: mreadlink-with-size.
+	* MODULES.html.sh: Add mreadlink-with-size.
+	* modules/mreadlink-with-size: New module
+	* modules/canonicalize (Depends-on): Depend on mreadlink-with-size,
+	not xreadlink-with-size.
+	* lib/mreadlink-with-size.c, lib/mreadlink.h: New files.
+
 2007-06-16  Bruno Haible  <bruno@clisp.org>
 
 	* m4/frexpl.m4 (gl_FUNC_FREXPL_WORKS): Catch the MacOS X 10.4 bug.

MODULES.html.sh

@@ -2149,6 +2149,7 @@ func_all_modules ()
   func_module mkdir-p
   func_module modechange
   func_module mountlist
+  func_module mreadlink-with-size
   func_module openat
   func_module pathmax
   func_module same

lib/mreadlink-with-size.c

@@ -0,0 +1,110 @@
+/* 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>  */
+
+#include <config.h>
+
+#include "mreadlink.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)
+
+/* 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, malloc fails, or if the link value is longer
+   than SSIZE_MAX, return NULL (caller may use errno to diagnose).  */
+
+char *
+mreadlink_with_size (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)
+    {
+      ssize_t r;
+      size_t link_length;
+      char *buffer = malloc (buf_size);
+
+      if (buffer == NULL)
+	return NULL;
+      r = readlink (file, buffer, buf_size);
+      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
+	{
+	  errno = ENOMEM;
+	  return NULL;
+	}
+    }
+}

lib/mreadlink.h

@@ -0,0 +1,24 @@
+/* Read symbolic links without size limitation.
+
+   Copyright (C) 2001, 2003, 2004, 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>  */
+
+#include <stddef.h>
+
+extern char *mreadlink_with_size (char const *filename, size_t size_hint);

modules/canonicalize

@@ -13,7 +13,7 @@ filenamecat
 sys_stat
 xalloc
 xgetcwd
-xreadlink-with-size
+mreadlink-with-size
 
 configure.ac:
 AC_FUNC_CANONICALIZE_FILE_NAME

modules/mreadlink-with-size

@@ -0,0 +1,25 @@
+Description:
+Return the contents of a symbolic link, without size limitations.
+
+Files:
+lib/mreadlink.h
+lib/mreadlink-with-size.c
+
+Depends-on:
+readlink
+ssize_t
+unistd
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += mreadlink-with-size.c
+
+Include:
+"mreadlink.h"
+
+License:
+GPL
+
+Maintainer:
+Jim Meyering