Improve File.expand_path performance in Windows

0-proposal.md

Background

While investigating the performance issues of File.expand_path on Windows, Usaku Nakamura and Nobuyoshi Nakada on [ruby-core:39504] pointed out that due security concerns, accessing files on Windows required normalized paths.

This was covered in the security update of March 2008, WEBrick file-access vulnerability.

After closer inspection of WEBrick code (mentioned by the security update), I noticed it uses File.expand_path to perform the heavy lifting of path normalization in the request.

The code around this can be inspected in prevent_directory_traversal and shift_path_info methods.

This approach performs a hit into the filesystem, contrary to its implementation in any other operating system.

File.expand_path is heavily used by require, on both lookup for files and check if files were loaded before.

This result in slow application startup, depending on the application size or number of gems it depends on.

While File.expand_path behavior can't be changed, we agreed that internal usage do not need to hit the filesystem when expanding paths or looking for files.

With Hiroshi Shirosaki help, we worked on a patch that:

• Limit filesystem hit only when using File.expand_path (and File.absolute_path)
• Internally require no longer hit the filesystem, improving file loading
• No longer hit the filesystem when checking every single path in $LOAD_PATH
• Use a Windows-specific API to normalize paths

Performance

To demonstrate the benefits of this patch, I've used measurements project and both core_require_empty and core_require_nested workloads, obtained the following results:

ruby 2.0.0dev (2012-08-23 trunk 36786) [i386-mingw32]
Rehearsal ------------------------------------------------------
core_require_empty   1.264000   3.151000   4.415000 (  4.446254)
--------------------------------------------- total: 4.415000sec

                         user     system      total        real
core_require_empty   1.154000   3.229000   4.383000 (  4.432253)

Rehearsal -------------------------------------------------------
core_require_nested   1.248000   3.447000   4.695000 (  4.707269)
---------------------------------------------- total: 4.695000sec

                          user     system      total        real
core_require_nested   1.467000   3.214000   4.681000 (  4.699268)

With patch applied:

ruby 2.0.0dev (2012-08-23 trunk 36786) [i386-mingw32]
Rehearsal ------------------------------------------------------
core_require_empty   0.593000   0.936000   1.529000 (  1.595091)
--------------------------------------------- total: 1.529000sec

                         user     system      total        real
core_require_empty   0.624000   0.936000   1.560000 (  1.577090)

ruby 2.0.0dev (2012-08-23 trunk 36786) [i386-mingw32]
Rehearsal -------------------------------------------------------
core_require_nested   0.843000   0.998000   1.841000 (  1.855106)
---------------------------------------------- total: 1.841000sec

                          user     system      total        real
core_require_nested   0.764000   1.061000   1.825000 (  1.838106)

Benchmarks were performed all on the same hardware and OS:

• CPU: Core 2 Duo T7500 @ 2.20Ghz
• RAM: 4GB
• HDD: 1.5GB RAMdisk (ImDisk)
• OS: Windows 7 Ultimate x64

Additional tests that exercise specific aspects of new function were added.

All tests (existing and added) pass.

Patch has been tested also against Visual Studio build of Ruby, so changes are compatible.

You can see the individual commits of this patch here:

https://github.com/luislavena/ruby/compare/improve-require-and-file-expand_path

Real life impact: Rails

The biggest Ruby project affected by this is Rails applications.

An empty Rails application on startup requires more than 700 files from different gems:

V:\emptyapp>ruby script\rails runner -e production "p $LOADED_FEATURES.size"
771

When benchmark startup using w32time:

V:\emptyapp>timer ruby script\rails runner -e production "0"
real    7.491
system  4.680
user    2.761

And patched Ruby:

V:\emptyapp>timer ruby script\rails runner -e production "0"
real    2.345
system  0.733
user    1.591

(best result taken from several warm ups).

Now, a mid-sized application like Enki which loads 1146 files in production mode, result in:

V:\enki>timer ruby script\rails runner -e production "p $LOADED_FEATURES.size"
1135
real    22.710
system  11.013
user    11.575

Almost 23 seconds, compared to patched version:

V:\enki>timer ruby script\rails runner -e production "0"
real    10.735
system  1.716
user    8.923

This change also improves performance of rake, from:

V:\enki>timer rake -T
...
real    8.868
system  0.031
user    0.000

To:

V:\enki>timer rake -T
...
real    3.068
system  0.015
user    0.015

Making normal operations more accessible.

1-complete.diff

diff --git a/configure.in b/configure.in
index e8b1cc7..8463bf7 100644
--- a/configure.in
+++ b/configure.in
@@ -1186,7 +1186,7 @@ main()
 		AC_CHECK_FUNCS(cygwin_conv_path)
 		AC_LIBOBJ([langinfo])
 		],
-[mingw*], [	LIBS="-lshell32 -lws2_32 -limagehlp $LIBS"
+[mingw*], [	LIBS="-lshell32 -lws2_32 -limagehlp -lshlwapi $LIBS"
 		ac_cv_header_a_out_h=no
 		ac_cv_header_pwd_h=no
 		ac_cv_header_utime_h=no
diff --git a/file.c b/file.c
index 4050067..c30e3b2 100644
--- a/file.c
+++ b/file.c
@@ -2882,8 +2882,9 @@ append_fspath(VALUE result, VALUE fname, char *dir, rb_encoding **enc, rb_encodi
     return buf + dirlen;
 }
 
-static VALUE
-file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
+#ifndef _WIN32
+VALUE
+rb_file_expand_path_internal(VALUE fname, VALUE dname, int abs_mode, int long_name, VALUE result)
 {
     const char *s, *b, *fend;
     char *buf, *p, *pend, *root;
@@ -2945,7 +2946,7 @@ file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
 	    /* specified drive, but not full path */
 	    int same = 0;
 	    if (!NIL_P(dname) && !not_same_drive(dname, s[0])) {
-		file_expand_path(dname, Qnil, abs_mode, result);
+		rb_file_expand_path_internal(dname, Qnil, abs_mode, long_name, result);
 		BUFINIT();
 		if (has_drive_letter(p) && TOLOWER(p[0]) == TOLOWER(s[0])) {
 		    /* ok, same drive */
@@ -2969,7 +2970,7 @@ file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
 #endif
     else if (!rb_is_absolute_path(s)) {
 	if (!NIL_P(dname)) {
-	    file_expand_path(dname, Qnil, abs_mode, result);
+	    rb_file_expand_path_internal(dname, Qnil, abs_mode, long_name, result);
 	    rb_enc_associate(result, rb_enc_check(result, fname));
 	    BUFINIT();
 	    p = pend;
@@ -3222,6 +3223,7 @@ file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
     ENC_CODERANGE_CLEAR(result);
     return result;
 }
+#endif /* _WIN32 */
 
 #define EXPAND_PATH_BUFFER() rb_usascii_str_new(0, MAXPATHLEN + 2)
 
@@ -3232,14 +3234,21 @@ file_expand_path(VALUE fname, VALUE dname, int abs_mode, VALUE result)
 static VALUE
 file_expand_path_1(VALUE fname)
 {
-    return file_expand_path(fname, Qnil, 0, EXPAND_PATH_BUFFER());
+    return rb_file_expand_path_internal(fname, Qnil, 0, 0, EXPAND_PATH_BUFFER());
 }
 
 VALUE
 rb_file_expand_path(VALUE fname, VALUE dname)
 {
     check_expand_path_args(fname, dname);
-    return file_expand_path(fname, dname, 0, EXPAND_PATH_BUFFER());
+    return rb_file_expand_path_internal(fname, dname, 0, 1, EXPAND_PATH_BUFFER());
+}
+
+VALUE
+rb_file_expand_path_fast(VALUE fname, VALUE dname)
+{
+    check_expand_path_args(fname, dname);
+    return rb_file_expand_path_internal(fname, dname, 0, 0, EXPAND_PATH_BUFFER());
 }
 
 /*
@@ -3276,7 +3285,7 @@ VALUE
 rb_file_absolute_path(VALUE fname, VALUE dname)
 {
     check_expand_path_args(fname, dname);
-    return file_expand_path(fname, dname, 1, EXPAND_PATH_BUFFER());
+    return rb_file_expand_path_internal(fname, dname, 1, 1, EXPAND_PATH_BUFFER());
 }
 
 /*
@@ -5250,7 +5259,7 @@ rb_find_file_ext_safe(VALUE *filep, const char *const *ext, int safe_level)
 
 	    RB_GC_GUARD(str) = rb_get_path_check(str, safe_level);
 	    if (RSTRING_LEN(str) == 0) continue;
-	    file_expand_path(fname, str, 0, tmp);
+	    rb_file_expand_path_internal(fname, str, 0, 0, tmp);
 	    if (rb_file_load_ok(RSTRING_PTR(tmp))) {
 		*filep = copy_path_class(tmp, *filep);
 		return (int)(j+1);
@@ -5309,7 +5318,7 @@ rb_find_file_safe(VALUE path, int safe_level)
 	    VALUE str = RARRAY_PTR(load_path)[i];
 	    RB_GC_GUARD(str) = rb_get_path_check(str, safe_level);
 	    if (RSTRING_LEN(str) > 0) {
-		file_expand_path(path, str, 0, tmp);
+		rb_file_expand_path_internal(path, str, 0, 0, tmp);
 		f = RSTRING_PTR(tmp);
 		if (rb_file_load_ok(f)) goto found;
 	    }
@@ -5544,4 +5553,8 @@ Init_File(void)
     rb_define_method(rb_cStat, "setuid?",  rb_stat_suid, 0);
     rb_define_method(rb_cStat, "setgid?",  rb_stat_sgid, 0);
     rb_define_method(rb_cStat, "sticky?",  rb_stat_sticky, 0);
+
+#ifdef _WIN32
+    rb_w32_init_file();
+#endif
 }
diff --git a/internal.h b/internal.h
index c091a1c..ed4864c 100644
--- a/internal.h
+++ b/internal.h
@@ -105,8 +105,15 @@ VALUE rb_home_dir(const char *user, VALUE result);
 VALUE rb_realpath_internal(VALUE basedir, VALUE path, int strict);
 void rb_file_const(const char*, VALUE);
 int rb_file_load_ok(const char *);
+VALUE rb_file_expand_path_fast(VALUE, VALUE);
+VALUE rb_file_expand_path_internal(VALUE, VALUE, int, int, VALUE);
 void Init_File(void);
 
+#ifdef _WIN32
+/* file.c, win32/file.c */
+void rb_w32_init_file(void);
+#endif
+
 /* gc.c */
 void Init_heap(void);
 void *ruby_mimmalloc(size_t size);
diff --git a/load.c b/load.c
index fd5f862..b21d17c 100644
--- a/load.c
+++ b/load.c
@@ -43,7 +43,7 @@ rb_get_expanded_load_path(void)
 
     ary = rb_ary_new2(RARRAY_LEN(load_path));
     for (i = 0; i < RARRAY_LEN(load_path); ++i) {
-	VALUE path = rb_file_expand_path(RARRAY_PTR(load_path)[i], Qnil);
+	VALUE path = rb_file_expand_path_fast(RARRAY_PTR(load_path)[i], Qnil);
 	rb_str_freeze(path);
 	rb_ary_push(ary, path);
     }
@@ -233,7 +233,7 @@ rb_feature_provided(const char *feature, const char **loading)
 
     if (*feature == '.' &&
 	(feature[1] == '/' || strncmp(feature+1, "./", 2) == 0)) {
-	fullpath = rb_file_expand_path(rb_str_new2(feature), Qnil);
+	fullpath = rb_file_expand_path_fast(rb_str_new2(feature), Qnil);
 	feature = RSTRING_PTR(fullpath);
     }
     if (ext && !strchr(ext, '/')) {
diff --git a/test/ruby/test_file_exhaustive.rb b/test/ruby/test_file_exhaustive.rb
index 7467bff..1523823 100644
--- a/test/ruby/test_file_exhaustive.rb
+++ b/test/ruby/test_file_exhaustive.rb
@@ -14,6 +14,7 @@ class TestFileExhaustive < Test::Unit::TestCase
 
   def setup
     @dir = Dir.mktmpdir("rubytest-file")
+    @rootdir = "#{DRIVE}/"
     File.chown(-1, Process.gid, @dir)
     @file = make_tmp_filename("file")
     @zerofile = make_tmp_filename("zerofile")
@@ -450,9 +451,24 @@ class TestFileExhaustive < Test::Unit::TestCase
       assert_equal(expected.force_encoding(cp), File.expand_path(a.dup.force_encoding(cp)), cp)
     end
 
+    path = "\u3042\u3044\u3046\u3048\u304a".encode("EUC-JP")
+    assert_equal("#{Dir.pwd}/#{path}".encode("CP932"), File.expand_path(path).encode("CP932"))
+
+    path = "\u3042\u3044\u3046\u3048\u304a".encode("CP51932")
+    assert_equal("#{Dir.pwd}/#{path}", File.expand_path(path))
+
     assert_incompatible_encoding {|d| File.expand_path(d)}
   end
 
+  def test_expand_path_encoding_filesystem
+    path = "~".encode("US-ASCII")
+    dir = "C:/".encode("IBM437")
+    fs = Encoding.find("filesystem")
+
+    assert_equal fs, File.expand_path(path).encoding
+    assert_equal fs, File.expand_path(path, dir).encoding
+  end
+
   def test_expand_path_home
     assert_kind_of(String, File.expand_path("~")) if ENV["HOME"]
     assert_raise(ArgumentError) { File.expand_path("~foo_bar_baz_unknown_user_wahaha") }
@@ -460,7 +476,13 @@ class TestFileExhaustive < Test::Unit::TestCase
     begin
       bug3630 = '[ruby-core:31537]'
       home = ENV["HOME"]
+      home_drive = ENV["HOMEDRIVE"]
+      home_path = ENV["HOMEPATH"]
+      user_profile = ENV["USERPROFILE"]
       ENV["HOME"] = nil
+      ENV["HOMEDRIVE"] = nil
+      ENV["HOMEPATH"] = nil
+      ENV["USERPROFILE"] = nil
       assert_raise(ArgumentError) { File.expand_path("~") }
       ENV["HOME"] = "~"
       assert_raise(ArgumentError, bug3630) { File.expand_path("~") }
@@ -468,9 +490,193 @@ class TestFileExhaustive < Test::Unit::TestCase
       assert_raise(ArgumentError, bug3630) { File.expand_path("~") }
     ensure
       ENV["HOME"] = home
+      ENV["HOMEDRIVE"] = home_drive
+      ENV["HOMEPATH"] = home_path
+      ENV["USERPROFILE"] = user_profile
+    end
+  end
+
+  def test_expand_path_remove_trailing_alternative_data
+    assert_equal File.join(@rootdir, "aaa"), File.expand_path("#{@rootdir}/aaa::$DATA")
+    assert_equal File.join(@rootdir, "aa:a"), File.expand_path("#{@rootdir}/aa:a:$DATA")
+    assert_equal File.join(@rootdir, "aaa:$DATA"), File.expand_path("#{@rootdir}/aaa:$DATA")
+  end if DRIVE
+
+  def test_expand_path_resolve_empty_string_current_directory
+    assert_equal(Dir.pwd, File.expand_path(""))
+  end
+
+  def test_expand_path_resolve_dot_current_directory
+    assert_equal(Dir.pwd, File.expand_path("."))
+  end
+
+  def test_expand_path_resolve_file_name_relative_current_directory
+    assert_equal(File.join(Dir.pwd, "foo"), File.expand_path("foo"))
+  end
+
+  def test_ignore_nil_dir_string
+    assert_equal(File.join(Dir.pwd, "foo"), File.expand_path("foo", nil))
+  end
+
+  def test_expand_path_resolve_file_name_and_dir_string_relative
+    assert_equal(File.join(Dir.pwd, "bar", "foo"),
+      File.expand_path("foo", "bar"))
+  end
+
+  def test_expand_path_cleanup_dots_file_name
+    bug = "[ruby-talk:18512]"
+
+    assert_equal(File.join(Dir.pwd, ".a"), File.expand_path(".a"), bug)
+    assert_equal(File.join(Dir.pwd, "..a"), File.expand_path("..a"), bug)
+
+    if DRIVE
+      # cleanup dots only on Windows
+      assert_equal(File.join(Dir.pwd, "a"), File.expand_path("a."), bug)
+      skip "FIXME"
+      assert_equal(File.join(Dir.pwd, "a"), File.expand_path("a.."), bug)
+    else
+      assert_equal(File.join(Dir.pwd, "a."), File.expand_path("a."), bug)
+      assert_equal(File.join(Dir.pwd, "a.."), File.expand_path("a.."), bug)
+    end
+  end
+
+  def test_expand_path_converts_a_pathname_to_an_absolute_pathname_using_a_complete_path
+    assert_equal(@dir, File.expand_path("", "#{@dir}"))
+    assert_equal(File.join(@dir, "a"), File.expand_path("a", "#{@dir}"))
+    assert_equal(File.join(@dir, "a"), File.expand_path("../a", "#{@dir}/xxx"))
+    assert_equal(@rootdir, File.expand_path(".", "#{@rootdir}"))
+  end
+
+  def test_expand_path_ignores_supplied_dir_if_path_contains_a_drive_letter
+    assert_equal(@rootdir, File.expand_path(@rootdir, "D:/"))
+  end if DRIVE
+
+  def test_expand_path_removes_trailing_slashes_from_absolute_path
+    assert_equal(File.join(@rootdir, "foo"), File.expand_path("#{@rootdir}foo/"))
+    assert_equal(File.join(@rootdir, "foo.rb"), File.expand_path("#{@rootdir}foo.rb/"))
+  end
+
+  def test_expand_path_removes_trailing_spaces_from_absolute_path
+    assert_equal(File.join(@rootdir, "a"), File.expand_path("#{@rootdir}a "))
+  end if DRIVE
+
+  def test_expand_path_converts_a_pathname_which_starts_with_a_slash_using_dir_s_drive
+    assert_match(%r"\Az:/foo\z"i, File.expand_path('/foo', "z:/bar"))
+  end if DRIVE
+
+  def test_expand_path_converts_a_pathname_which_starts_with_a_slash_and_unc_pathname
+    assert_equal("//foo", File.expand_path('//foo', "//bar"))
+    assert_equal("//bar/foo", File.expand_path('/foo', "//bar"))
+    assert_equal("//foo", File.expand_path('//foo', "/bar"))
+  end if DRIVE
+
+  def test_expand_path_converts_a_dot_with_unc_dir
+    assert_equal("//", File.expand_path('.', "//"))
+  end
+
+  def test_expand_path_preserves_unc_path_root
+    assert_equal("//", File.expand_path("//"))
+    assert_equal("//", File.expand_path("//."))
+    assert_equal("//", File.expand_path("//.."))
+  end
+
+  def test_expand_path_converts_a_pathname_which_starts_with_a_slash_using_host_share
+    assert_match(%r"\A//host/share/foo\z"i, File.expand_path('/foo', "//host/share/bar"))
+  end if DRIVE
+
+  def test_expand_path_converts_a_pathname_which_starts_with_a_slash_using_a_current_drive
+    assert_match(%r"\A#{DRIVE}/foo\z"i, File.expand_path('/foo'))
+  end
+
+  def test_expand_path_returns_tainted_strings_or_not
+    assert_equal(true, File.expand_path('foo').tainted?)
+    assert_equal(true, File.expand_path('foo'.taint).tainted?)
+    assert_equal(true, File.expand_path('/foo'.taint).tainted?)
+    assert_equal(true, File.expand_path('foo', 'bar').tainted?)
+    assert_equal(true, File.expand_path('foo', '/bar'.taint).tainted?)
+    assert_equal(true, File.expand_path('foo'.taint, '/bar').tainted?)
+    assert_equal(true, File.expand_path('~').tainted?)
+
+    if DRIVE
+      assert_equal(true, File.expand_path('/foo').tainted?)
+      assert_equal(false, File.expand_path('//foo').tainted?)
+      assert_equal(true, File.expand_path('C:/foo'.taint).tainted?)
+      assert_equal(false, File.expand_path('C:/foo').tainted?)
+      assert_equal(true, File.expand_path('foo', '/bar').tainted?)
+      assert_equal(true, File.expand_path('foo', 'C:/bar'.taint).tainted?)
+      assert_equal(true, File.expand_path('foo'.taint, 'C:/bar').tainted?)
+      assert_equal(false, File.expand_path('foo', 'C:/bar').tainted?)
+      assert_equal(false, File.expand_path('C:/foo/../bar').tainted?)
+      assert_equal(false, File.expand_path('foo', '//bar').tainted?)
+    else
+      assert_equal(false, File.expand_path('/foo').tainted?)
+      assert_equal(false, File.expand_path('foo', '/bar').tainted?)
     end
   end
 
+  def test_expand_path_converts_a_pathname_to_an_absolute_pathname_using_home_as_base
+    old_home = ENV["HOME"]
+    home = ENV["HOME"] = "#{DRIVE}/UserHome"
+    assert_equal(home, File.expand_path("~"))
+    assert_equal(home, File.expand_path("~", "C:/FooBar"))
+    assert_equal(File.join(home, "a"), File.expand_path("~/a", "C:/FooBar"))
+  ensure
+    ENV["HOME"] = old_home
+  end
+
+  def test_expand_path_converts_a_pathname_to_an_absolute_pathname_using_unc_home
+    old_home = ENV["HOME"]
+    unc_home = ENV["HOME"] = "//UserHome"
+    assert_equal(unc_home, File.expand_path("~"))
+  ensure
+    ENV["HOME"] = old_home
+  end if DRIVE
+
+  def test_expand_path_does_not_modify_a_home_string_argument
+    old_home = ENV["HOME"]
+    home = ENV["HOME"] = "#{DRIVE}/UserHome"
+    str = "~/a"
+    assert_equal("#{home}/a", File.expand_path(str))
+    assert_equal("~/a", str)
+  ensure
+    ENV["HOME"] = old_home
+  end
+
+  def test_expand_path_raises_argument_error_for_any_supplied_username
+    bug = '[ruby-core:39597]'
+    assert_raise(ArgumentError, bug) { File.expand_path("~anything") }
+  end if DRIVE
+
+  def test_expand_path_raises_a_type_error_if_not_passed_a_string_type
+    assert_raise(TypeError) { File.expand_path(1) }
+    assert_raise(TypeError) { File.expand_path(nil) }
+    assert_raise(TypeError) { File.expand_path(true) }
+  end
+
+  def test_expand_path_expands_dot_dir
+    assert_equal("#{DRIVE}/dir", File.expand_path("#{DRIVE}/./dir"))
+  end
+
+  def test_expand_path_does_not_modify_the_string_argument
+    str = "./a/b/../c"
+    assert_equal("#{Dir.pwd}/a/c", File.expand_path(str, Dir.pwd))
+    assert_equal("./a/b/../c", str)
+  end
+
+  def test_expand_path_returns_a_string_when_passed_a_string_subclass
+    sub = Class.new(String)
+    str = sub.new "./a/b/../c"
+    path = File.expand_path(str, Dir.pwd)
+    assert_equal("#{Dir.pwd}/a/c", path)
+    assert_instance_of(String, path)
+  end
+
+  def test_expand_path_accepts_objects_that_have_a_to_path_method
+    klass = Class.new { def to_path; "a/b/c"; end }
+    obj = klass.new
+    assert_equal("#{Dir.pwd}/a/b/c", File.expand_path(obj))
+  end
+
   def test_basename
     assert_equal(File.basename(@file).sub(/\.test$/, ""), File.basename(@file, ".test"))
     assert_equal("", s = File.basename(""))
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index c0cdfa9..979890d 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -226,7 +226,7 @@ EXTLIBS =
 EXTSOLIBS =
 !endif
 !if !defined(LIBS)
-LIBS = oldnames.lib user32.lib advapi32.lib shell32.lib ws2_32.lib imagehlp.lib $(EXTLIBS)
+LIBS = oldnames.lib user32.lib advapi32.lib shell32.lib ws2_32.lib imagehlp.lib shlwapi.lib $(EXTLIBS)
 !endif
 !if !defined(MISSING)
 MISSING = acosh.obj cbrt.obj crypt.obj erf.obj ffs.obj langinfo.obj lgamma_r.obj strlcat.obj strlcpy.obj tgamma.obj win32/win32.obj win32/file.obj setproctitle.obj
diff --git a/win32/file.c b/win32/file.c
index 955f91b..c8bb445 100644
--- a/win32/file.c
+++ b/win32/file.c
@@ -1,10 +1,630 @@
 #include "ruby/ruby.h"
+#include "ruby/encoding.h"
 #include <winbase.h>
+#include <wchar.h>
+#include <shlwapi.h>
 
 #ifndef INVALID_FILE_ATTRIBUTES
 # define INVALID_FILE_ATTRIBUTES ((DWORD)-1)
 #endif
 
+/* cache 'encoding name' => 'code page' into a hash */
+static VALUE rb_code_page;
+
+#define IS_DIR_SEPARATOR_P(c) (c == L'\\' || c == L'/')
+#define IS_DIR_UNC_P(c) (IS_DIR_SEPARATOR_P(c[0]) && IS_DIR_SEPARATOR_P(c[1]))
+
+/* MultiByteToWideChar() doesn't work with code page 51932 */
+#define INVALID_CODE_PAGE 51932
+#define PATH_BUFFER_SIZE MAX_PATH * 2
+
+#define insecure_obj_p(obj, level) ((level) >= 4 || ((level) > 0 && OBJ_TAINTED(obj)))
+
+static inline void
+replace_wchar(wchar_t *s, int find, int replace)
+{
+    while (*s != 0) {
+	if (*s == find)
+	    *s = replace;
+	s++;
+    }
+}
+
+/* Convert str from multibyte char to wchar with specified code page */
+static inline void
+convert_mb_to_wchar(VALUE str, wchar_t **wstr, wchar_t **wstr_pos, size_t *wstr_len, UINT code_page)
+{
+    size_t len;
+
+    if (NIL_P(str))
+	return;
+
+    len = MultiByteToWideChar(code_page, 0, RSTRING_PTR(str), -1, NULL, 0) + 1;
+    *wstr = (wchar_t *)xmalloc(len * sizeof(wchar_t));
+    if (wstr_pos)
+	*wstr_pos = *wstr;
+
+    MultiByteToWideChar(code_page, 0, RSTRING_PTR(str), -1, *wstr, len);
+    *wstr_len = len - 2;
+}
+
+static inline void
+convert_wchar_to_mb(const wchar_t *wstr, char **str, size_t *str_len, UINT code_page)
+{
+    size_t len;
+
+    len = WideCharToMultiByte(code_page, 0, wstr, -1, NULL, 0, NULL, NULL);
+    *str = (char *)xmalloc(len * sizeof(char));
+    WideCharToMultiByte(code_page, 0, wstr, -1, *str, len, NULL, NULL);
+
+    /* do not count terminator as part of the string length */
+    *str_len = len - 1;
+}
+
+/*
+  Return user's home directory using environment variables combinations.
+  Memory allocated by this function should be manually freeded afterwards.
+
+  Try:
+  HOME, HOMEDRIVE + HOMEPATH and USERPROFILE environment variables
+  TODO: Special Folders - Profile and Personal
+*/
+static wchar_t *
+home_dir()
+{
+    wchar_t *buffer = NULL;
+    size_t buffer_len = 0, len = 0;
+    size_t home_env = 0;
+
+    /*
+      GetEnvironmentVariableW when used with NULL will return the required
+      buffer size and its terminating character.
+      http://msdn.microsoft.com/en-us/library/windows/desktop/ms683188(v=vs.85).aspx
+    */
+
+    if (len = GetEnvironmentVariableW(L"HOME", NULL, 0)) {
+	buffer_len = len;
+	home_env = 1;
+    }
+    else if (len = GetEnvironmentVariableW(L"HOMEDRIVE", NULL, 0)) {
+	buffer_len = len;
+	if (len = GetEnvironmentVariableW(L"HOMEPATH", NULL, 0)) {
+	    buffer_len += len;
+	    home_env = 2;
+	}
+	else {
+	    buffer_len = 0;
+	}
+    }
+    else if (len = GetEnvironmentVariableW(L"USERPROFILE", NULL, 0)) {
+	buffer_len = len;
+	home_env = 3;
+    }
+
+    /* allocate buffer */
+    if (home_env)
+	buffer = (wchar_t *)xmalloc(buffer_len * sizeof(wchar_t));
+
+    switch (home_env) {
+	case 1:
+	    /* HOME */
+	    GetEnvironmentVariableW(L"HOME", buffer, buffer_len);
+	    break;
+	case 2:
+	    /* HOMEDRIVE + HOMEPATH */
+	    len = GetEnvironmentVariableW(L"HOMEDRIVE", buffer, buffer_len);
+	    GetEnvironmentVariableW(L"HOMEPATH", buffer + len, buffer_len - len);
+	    break;
+	case 3:
+	    /* USERPROFILE */
+	    GetEnvironmentVariableW(L"USERPROFILE", buffer, buffer_len);
+	    break;
+	default:
+	    break;
+	}
+
+    if (home_env) {
+	/* sanitize backslashes with forwardslashes */
+	replace_wchar(buffer, L'\\', L'/');
+
+	return buffer;
+    }
+
+    return NULL;
+}
+
+/* Remove trailing invalid ':$DATA' of the path. */
+static inline size_t
+remove_invalid_alternative_data(wchar_t *wfullpath, size_t size) {
+    static const wchar_t prime[] = L":$DATA";
+    enum { prime_len = (sizeof(prime) / sizeof(wchar_t)) -1 };
+
+    if (size <= prime_len || _wcsnicmp(wfullpath + size - prime_len, prime, prime_len) != 0)
+	return size;
+
+    /* alias of stream */
+    /* get rid of a bug of x64 VC++ */
+    if (wfullpath[size - (prime_len + 1)] == ':') {
+	/* remove trailing '::$DATA' */
+	size -= prime_len + 1; /* prime */
+	wfullpath[size] = L'\0';
+    }
+    else {
+	/* remove trailing ':$DATA' of paths like '/aa:a:$DATA' */
+	wchar_t *pos = wfullpath + size - (prime_len + 1);
+	while (!IS_DIR_SEPARATOR_P(*pos) && pos != wfullpath) {
+	    if (*pos == L':') {
+		size -= prime_len; /* alternative */
+		wfullpath[size] = L'\0';
+		break;
+	    }
+	    pos--;
+	}
+    }
+    return size;
+}
+
+/* Return system code page. */
+static inline UINT
+system_code_page() {
+    return AreFileApisANSI() ? CP_ACP : CP_OEMCP;
+}
+
+/*
+  Return code page number of the encoding.
+  Cache code page into a hash for performance since finding the code page in
+  Encoding#names is slow.
+*/
+static UINT
+code_page(rb_encoding *enc)
+{
+    VALUE code_page_value, name_key;
+    VALUE encoding, names_ary = Qundef, name;
+    char *enc_name;
+    struct RString fake_str;
+    ID names;
+    long i;
+
+    if (!enc)
+	return system_code_page();
+
+    enc_name = (char *)rb_enc_name(enc);
+
+    fake_str.basic.flags = T_STRING|RSTRING_NOEMBED;
+    fake_str.basic.klass = rb_cString;
+    fake_str.as.heap.len = strlen(enc_name);
+    fake_str.as.heap.ptr = enc_name;
+    fake_str.as.heap.aux.capa = fake_str.as.heap.len;
+    name_key = (VALUE)&fake_str;
+    ENCODING_CODERANGE_SET(name_key, rb_usascii_encindex(), ENC_CODERANGE_7BIT);
+
+    code_page_value = rb_hash_lookup(rb_code_page, name_key);
+    if (code_page_value != Qnil)
+	return (UINT)FIX2INT(code_page_value);
+
+    name_key = rb_usascii_str_new2(enc_name);
+
+    encoding = rb_enc_from_encoding(enc);
+    if (!NIL_P(encoding)) {
+	CONST_ID(names, "names");
+	names_ary = rb_funcall(encoding, names, 0);
+    }
+
+    /* map US-ASCII and ASCII-8bit as code page 20127 (us-ascii) */
+    if (enc == rb_usascii_encoding() || enc == rb_ascii8bit_encoding()) {
+	UINT code_page = 20127;
+	rb_hash_aset(rb_code_page, name_key, INT2FIX(code_page));
+	return code_page;
+    }
+
+    if (names_ary != Qundef) {
+	for (i = 0; i < RARRAY_LEN(names_ary); i++) {
+	    name = RARRAY_PTR(names_ary)[i];
+	    if (strncmp("CP", RSTRING_PTR(name), 2) == 0) {
+		int code_page = atoi(RSTRING_PTR(name) + 2);
+		if (code_page != 0) {
+		    rb_hash_aset(rb_code_page, name_key, INT2FIX(code_page));
+		    return (UINT)code_page;
+		}
+	    }
+	}
+    }
+
+    rb_hash_aset(rb_code_page, name_key, INT2FIX(INVALID_CODE_PAGE));
+    return INVALID_CODE_PAGE;
+}
+
+static inline VALUE
+fix_string_encoding(VALUE str, rb_encoding *encoding)
+{
+    VALUE result, tmp;
+
+    tmp = rb_enc_str_new(RSTRING_PTR(str), RSTRING_LEN(str), encoding);
+    result = rb_str_encode(tmp, rb_enc_from_encoding(rb_utf8_encoding()), 0, Qnil);
+
+    return result;
+}
+
+/*
+  Replace the last part of the path to long name.
+  We try to avoid to call FindFirstFileW() since it takes long time.
+*/
+static inline size_t
+replace_to_long_name(wchar_t **wfullpath, size_t size, int heap) {
+    WIN32_FIND_DATAW find_data;
+    HANDLE find_handle;
+
+    /*
+      Skip long name conversion if the path is already long name.
+      Short name is 8.3 format.
+      http://en.wikipedia.org/wiki/8.3_filename
+      This check can be skipped for directory components that have file
+      extensions longer than 3 characters, or total lengths longer than
+      12 characters.
+      http://msdn.microsoft.com/en-us/library/windows/desktop/aa364980(v=vs.85).aspx
+    */
+    size_t const max_short_name_size = 8 + 1 + 3;
+    size_t const max_extension_size = 3;
+    size_t path_len = 1, extension_len = 0;
+    wchar_t *pos = *wfullpath;
+
+    if (size == 3 && pos[1] == L':' && pos[2] == L'\\' && pos[3] == L'\0') {
+	/* root path doesn't need short name expansion */
+	return size;
+    }
+
+    pos = *wfullpath + size - 1;
+    while (!IS_DIR_SEPARATOR_P(*pos) && pos != *wfullpath) {
+	if (!extension_len && *pos == L'.') {
+	    extension_len = path_len - 1;
+	}
+	if (path_len > max_short_name_size || extension_len > max_extension_size) {
+	    return size;
+	}
+	path_len++;
+	pos--;
+    }
+
+    find_handle = FindFirstFileW(*wfullpath, &find_data);
+    if (find_handle != INVALID_HANDLE_VALUE) {
+	size_t trail_pos = wcslen(*wfullpath);
+	size_t file_len = wcslen(find_data.cFileName);
+
+	FindClose(find_handle);
+	while (trail_pos > 0) {
+	    if (IS_DIR_SEPARATOR_P((*wfullpath)[trail_pos]))
+		break;
+	    trail_pos--;
+	}
+	size = trail_pos + 1 + file_len;
+	if ((size + 1) > sizeof(*wfullpath) / sizeof((*wfullpath)[0])) {
+	    wchar_t *buf = (wchar_t *)xmalloc((size + 1) * sizeof(wchar_t));
+	    wcsncpy(buf, *wfullpath, trail_pos + 1);
+	    if (heap)
+		xfree(*wfullpath);
+	    *wfullpath = buf;
+	}
+	wcsncpy(*wfullpath + trail_pos + 1, find_data.cFileName, file_len + 1);
+    }
+    return size;
+}
+
+VALUE
+rb_file_expand_path_internal(VALUE fname, VALUE dname, int abs_mode, int long_name, VALUE result)
+{
+    size_t size = 0, wpath_len = 0, wdir_len = 0, whome_len = 0;
+    size_t buffer_len = 0;
+    char *fullpath = NULL;
+    wchar_t *wfullpath = NULL, *wpath = NULL, *wpath_pos = NULL, *wdir = NULL;
+    wchar_t *whome = NULL, *buffer = NULL, *buffer_pos = NULL;
+    UINT path_cp, cp;
+    VALUE path = fname, dir = dname;
+    wchar_t wfullpath_buffer[PATH_BUFFER_SIZE];
+    wchar_t path_drive = L'\0', dir_drive = L'\0';
+    int ignore_dir = 0;
+    rb_encoding *path_encoding;
+    int tainted = 0;
+
+    /* tainted if path is tainted */
+    tainted = OBJ_TAINTED(path);
+
+    /* get path encoding */
+    if (NIL_P(dir)) {
+	path_encoding = rb_enc_get(path);
+    }
+    else {
+	path_encoding = rb_enc_check(path, dir);
+    }
+
+    cp = path_cp = code_page(path_encoding);
+
+    /* workaround invalid codepage */
+    if (path_cp == INVALID_CODE_PAGE) {
+	cp = CP_UTF8;
+	if (!NIL_P(path)) {
+	    path = fix_string_encoding(path, path_encoding);
+	}
+    }
+
+    /* convert char * to wchar_t */
+    convert_mb_to_wchar(path, &wpath, &wpath_pos, &wpath_len, cp);
+
+    /* determine if we need the user's home directory */
+    /* expand '~' only if NOT rb_file_absolute_path() where `abs_mode` is 1 */
+    if (abs_mode == 0 && ((wpath_len == 1 && wpath_pos[0] == L'~') ||
+	(wpath_len >= 2 && wpath_pos[0] == L'~' && IS_DIR_SEPARATOR_P(wpath_pos[1])))) {
+	/* tainted if expanding '~' */
+	tainted = 1;
+
+	whome = home_dir();
+	if (whome == NULL) {
+	    xfree(wpath);
+	    rb_raise(rb_eArgError, "couldn't find HOME environment -- expanding `~'");
+	}
+	whome_len = wcslen(whome);
+
+	if (PathIsRelativeW(whome) && !(whome_len >= 2 && IS_DIR_UNC_P(whome))) {
+	    xfree(wpath);
+	    rb_raise(rb_eArgError, "non-absolute home");
+	}
+
+	/* use filesystem encoding if expanding home dir */
+	path_encoding = rb_filesystem_encoding();
+	cp = path_cp = system_code_page();
+
+	/* ignores dir since we are expading home */
+	ignore_dir = 1;
+
+	/* exclude ~ from the result */
+	wpath_pos++;
+	wpath_len--;
+
+	/* exclude separator if present */
+	if (wpath_len && IS_DIR_SEPARATOR_P(wpath_pos[0])) {
+	    wpath_pos++;
+	    wpath_len--;
+	}
+    }
+    else if (wpath_len >= 2 && wpath_pos[1] == L':') {
+	if (wpath_len >= 3 && IS_DIR_SEPARATOR_P(wpath_pos[2])) {
+	    /* ignore dir since path contains a drive letter and a root slash */
+	    ignore_dir = 1;
+	}
+	else {
+	    /* determine if we ignore dir or not later */
+	    path_drive = wpath_pos[0];
+	}
+    }
+    else if (abs_mode == 0 && wpath_len >= 2 && wpath_pos[0] == L'~') {
+	wchar_t *wuser = wpath_pos + 1;
+	wchar_t *pos = wuser;
+	char *user;
+
+	/* tainted if expanding '~' */
+	tainted = 1;
+
+	while (!IS_DIR_SEPARATOR_P(*pos) && *pos != '\0')
+	    pos++;
+
+	*pos = '\0';
+	convert_wchar_to_mb(wuser, &user, &size, cp);
+
+	/* convert to VALUE and set the path encoding */
+	if (path_cp == INVALID_CODE_PAGE) {
+	    VALUE tmp = rb_enc_str_new(user, size, rb_utf8_encoding());
+	    result = rb_str_encode(tmp, rb_enc_from_encoding(path_encoding), 0, Qnil);
+	    rb_str_resize(tmp, 0);
+	}
+	else {
+	    result = rb_enc_str_new(user, size, path_encoding);
+	}
+
+	xfree(wpath);
+	if (user)
+	    xfree(user);
+
+	rb_raise(rb_eArgError, "can't find user %s", StringValuePtr(result));
+    }
+
+    /* convert dir */
+    if (!ignore_dir && !NIL_P(dir)) {
+	/* fix string encoding */
+	if (path_cp == INVALID_CODE_PAGE) {
+	    dir = fix_string_encoding(dir, path_encoding);
+	}
+
+	/* convert char * to wchar_t */
+	convert_mb_to_wchar(dir, &wdir, NULL, &wdir_len, cp);
+
+	if (wdir_len >= 2 && wdir[1] == L':') {
+	    dir_drive = wdir[0];
+	    if (wpath_len && IS_DIR_SEPARATOR_P(wpath_pos[0])) {
+		wdir_len = 2;
+	    }
+	}
+	else if (wdir_len >= 2 && IS_DIR_UNC_P(wdir)) {
+	    /* UNC path */
+	    if (wpath_len && IS_DIR_SEPARATOR_P(wpath_pos[0])) {
+		/* cut the UNC path tail to '//host/share' */
+		size_t separators = 0;
+		size_t pos = 2;
+		while (pos < wdir_len && separators < 2) {
+		    if (IS_DIR_SEPARATOR_P(wdir[pos])) {
+			separators++;
+		    }
+		    pos++;
+		}
+		if (separators == 2)
+		    wdir_len = pos - 1;
+	    }
+	}
+    }
+
+    /* determine if we ignore dir or not */
+    if (!ignore_dir && path_drive && dir_drive) {
+	if (towupper(path_drive) == towupper(dir_drive)) {
+	    /* exclude path drive letter to use dir */
+	    wpath_pos += 2;
+	    wpath_len -= 2;
+	}
+	else {
+	    /* ignore dir since path drive is different from dir drive */
+	    ignore_dir = 1;
+	    wdir_len = 0;
+	}
+    }
+
+    if (!ignore_dir && wpath_len >= 2 && IS_DIR_UNC_P(wpath)) {
+	/* ignore dir since path has UNC root */
+	ignore_dir = 1;
+	wdir_len = 0;
+    }
+    else if (!ignore_dir && wpath_len >= 1 && IS_DIR_SEPARATOR_P(wpath[0]) &&
+	!dir_drive && !(wdir_len >= 2 && IS_DIR_UNC_P(wdir))) {
+	/* ignore dir since path has root slash and dir doesn't have drive or UNC root */
+	ignore_dir = 1;
+	wdir_len = 0;
+    }
+
+    buffer_len = wpath_len + 1 + wdir_len + 1 + whome_len + 1;
+
+    buffer = buffer_pos = (wchar_t *)xmalloc((buffer_len + 1) * sizeof(wchar_t));
+
+    /* add home */
+    if (whome_len) {
+	wcsncpy(buffer_pos, whome, whome_len);
+	buffer_pos += whome_len;
+    }
+
+    /* Add separator if required */
+    if (whome_len && wcsrchr(L"\\/:", buffer_pos[-1]) == NULL) {
+	buffer_pos[0] = L'\\';
+	buffer_pos++;
+    }
+
+    if (wdir_len) {
+	/* tainted if dir is used and dir is tainted */
+	if (!tainted && OBJ_TAINTED(dir))
+	    tainted = 1;
+
+	wcsncpy(buffer_pos, wdir, wdir_len);
+	buffer_pos += wdir_len;
+    }
+
+    /* add separator if required */
+    if (wdir_len && wcsrchr(L"\\/:", buffer_pos[-1]) == NULL) {
+	buffer_pos[0] = L'\\';
+	buffer_pos++;
+    }
+
+    /* now deal with path */
+    if (wpath_len) {
+	wcsncpy(buffer_pos, wpath_pos, wpath_len);
+	buffer_pos += wpath_len;
+    }
+
+    /* GetFullPathNameW requires at least "." to determine current directory */
+    if (wpath_len == 0) {
+	buffer_pos[0] = L'.';
+	buffer_pos++;
+    }
+
+    /* Ensure buffer is NULL terminated */
+    buffer_pos[0] = L'\0';
+
+    /* tainted if path is relative */
+    if (!tainted && PathIsRelativeW(buffer) && !(buffer_len >= 2 && IS_DIR_UNC_P(buffer)))
+	tainted = 1;
+
+    /* FIXME: Make this more robust */
+    /* Determine require buffer size */
+    size = GetFullPathNameW(buffer, PATH_BUFFER_SIZE, wfullpath_buffer, NULL);
+    if (size > PATH_BUFFER_SIZE) {
+	/* allocate more memory than alloted originally by PATH_BUFFER_SIZE */
+	wfullpath = (wchar_t *)xmalloc(size * sizeof(wchar_t));
+	size = GetFullPathNameW(buffer, size, wfullpath, NULL);
+    }
+    else {
+	wfullpath = wfullpath_buffer;
+    }
+
+    /* Remove any trailing slashes */
+    if (IS_DIR_SEPARATOR_P(wfullpath[size - 1]) &&
+	wfullpath[size - 2] != L':' &&
+	!(size == 2 && IS_DIR_UNC_P(wfullpath))) {
+	size -= 1;
+	wfullpath[size] = L'\0';
+    }
+
+    /* Remove any trailing dot */
+    if (wfullpath[size - 1] == L'.') {
+	size -= 1;
+	wfullpath[size] = L'\0';
+    }
+
+    /* removes trailing invalid ':$DATA' */
+    size = remove_invalid_alternative_data(wfullpath, size);
+
+    /* Replace the trailing path to long name */
+    if (long_name)
+	size = replace_to_long_name(&wfullpath, size, (wfullpath != wfullpath_buffer));
+
+    /* sanitize backslashes with forwardslashes */
+    replace_wchar(wfullpath, L'\\', L'/');
+
+    /* convert to char * */
+    size = WideCharToMultiByte(cp, 0, wfullpath, size, NULL, 0, NULL, NULL);
+    if (size > (size_t)RSTRING_LEN(result)) {
+	rb_str_modify(result);
+	rb_str_resize(result, size);
+    }
+
+    WideCharToMultiByte(cp, 0, wfullpath, size, RSTRING_PTR(result), size, NULL, NULL);
+    rb_str_set_len(result, size);
+
+    /* convert to VALUE and set the path encoding */
+    if (path_cp == INVALID_CODE_PAGE) {
+	VALUE tmp;
+	size_t len;
+
+	rb_enc_associate(result, rb_utf8_encoding());
+	ENC_CODERANGE_CLEAR(result);
+	tmp = rb_str_encode(result, rb_enc_from_encoding(path_encoding), 0, Qnil);
+	len = RSTRING_LEN(tmp);
+	rb_str_modify(result);
+	rb_str_resize(result, len);
+	memcpy(RSTRING_PTR(result), RSTRING_PTR(tmp), len);
+	rb_str_resize(tmp, 0);
+    }
+    rb_enc_associate(result, path_encoding);
+    ENC_CODERANGE_CLEAR(result);
+
+    /* makes the result object tainted if expanding tainted strings or returning modified path */
+    if (tainted)
+	OBJ_TAINT(result);
+
+    /* TODO: better cleanup */
+    if (buffer)
+	xfree(buffer);
+
+    if (wpath)
+	xfree(wpath);
+
+    if (wdir)
+	xfree(wdir);
+
+    if (whome)
+	xfree(whome);
+
+    if (wfullpath && wfullpath != wfullpath_buffer)
+	xfree(wfullpath);
+
+    if (fullpath)
+	xfree(fullpath);
+
+    return result;
+}
+
 int
 rb_file_load_ok(const char *path)
 {
@@ -27,3 +647,12 @@ rb_file_load_ok(const char *path)
     }
     return ret;
 }
+
+void
+rb_w32_init_file(void)
+{
+    rb_code_page = rb_hash_new();
+
+    /* prevent GC removing rb_code_page */
+    rb_gc_register_mark_object(rb_code_page);
+}

This was submitted to Ruby-Core as Bug #6836