--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2010-01-09  Bruno Haible  <bruno@clisp.org>
+
+	getlogin_r: Support for native Windows.
+	* lib/getlogin_r.c: Include <windows.h>
+	(getlogin_r): Implement for native Windows.
+	* tests/test-getlogin_r.c (main): Also test with a huge buffer.
+	Reported by <tmacchant5@yahoo.co.jp> via John W. Eaton <jwe@gnu.org>.
+
 2010-01-09  Bruno Haible  <bruno@clisp.org>
 
 	getlogin_r: Small fixes.

--- a/lib/getlogin_r.c
+++ b/lib/getlogin_r.c
@@ -16,7 +16,7 @@
    along with this program; if not, write to the Free Software Foundation,
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
-/* written by Paul Eggert and Derek Price */
+/* Written by Paul Eggert, Derek Price, and Bruno Haible.  */
 
 #include <config.h>
 
@@ -26,14 +26,41 @@
 #include <errno.h>
 #include <string.h>
 
-#if !HAVE_DECL_GETLOGIN
-char *getlogin (void);
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+#else
+# if !HAVE_DECL_GETLOGIN
+extern char *getlogin (void);
+# endif
 #endif
 
 /* See unistd.in.h for documentation.  */
 int
 getlogin_r (char *name, size_t size)
 {
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+  /* Native Windows platform.  */
+  DWORD sz;
+
+  /* When size > 0x7fff, the doc says that GetUserName will fail.
+     Actually, on Windows XP SP3, it succeeds.  But let's be safe,
+     for the sake of older Windows versions.  */
+  if (size > 0x7fff)
+    size = 0x7fff;
+  sz = size;
+  if (!GetUserName (name, &sz))
+    {
+      if (GetLastError () == ERROR_INSUFFICIENT_BUFFER)
+        /* In this case, the doc says that sz contains the required size, but
+           actually, on Windows XP SP3, it contains 2 * the required size.  */
+        return ERANGE;
+      else
+        return ENOENT;
+    }
+  return 0;
+#else
+  /* Platform with a getlogin() function.  */
   char *n;
   size_t nlen;
 
@@ -48,4 +75,5 @@
     return ERANGE;
   memcpy (name, n, nlen + 1);
   return 0;
+#endif
 }

--- a/tests/test-getlogin_r.c
+++ b/tests/test-getlogin_r.c
@@ -69,5 +69,13 @@
       ASSERT (getlogin_r (smallbuf, i) == ERANGE);
   }
 
+  /* Test with a huge buffer.  */
+  {
+    static char hugebuf[70000];
+
+    ASSERT (getlogin_r (hugebuf, sizeof (hugebuf)) == 0);
+    ASSERT (strcmp (hugebuf, buf) == 0);
+  }
+
   return 0;
 }