Ensure last Win32 error is preserved for IO operations (case 1047186)

Author: joncham

mono/metadata/w32file-win32.c

@@ -12,6 +12,7 @@
 #include <windows.h>
 #include "mono/metadata/w32file-win32-internals.h"
 #include "mono/metadata/profiler-private.h"
+#include "mono/metadata/w32error.h"
 
 void
 mono_w32file_init (void)
@@ -97,12 +98,17 @@ mono_w32file_read (gpointer handle, gpointer buffer, guint32 numbytes, guint32 *
 	mono_thread_info_install_interrupt (cancel_w32_io, handle, &interrupted);
 	if (!interrupted)
 	{
+		guint32 last_error;
 		MONO_ENTER_GC_SAFE;
 		res = ReadFile (handle, buffer, numbytes, bytesread, NULL);
 		MONO_PROFILER_RAISE (fileio, (1, *bytesread));
 		MONO_EXIT_GC_SAFE;
 
+		/* need to save and restore since clients expect error code set for
+		 * failed IO calls and mono_thread_info_uninstall_interrupt overwrites value */
+		last_error = mono_w32error_get_last ();
 		mono_thread_info_uninstall_interrupt (&interrupted);
+		mono_w32error_set_last (last_error);
 	}
 
 	return res;
@@ -117,12 +123,17 @@ mono_w32file_write (gpointer handle, gconstpointer buffer, guint32 numbytes, gui
 	mono_thread_info_install_interrupt (cancel_w32_io, handle, &interrupted);
 	if (!interrupted)
 	{
+		guint32 last_error;
 		MONO_ENTER_GC_SAFE;
 		res = WriteFile (handle, buffer, numbytes, byteswritten, NULL);
 		MONO_PROFILER_RAISE (fileio, (0, *byteswritten));
 		MONO_EXIT_GC_SAFE;
 
+		/* need to save and restore since clients expect error code set for
+		* failed IO calls and mono_thread_info_uninstall_interrupt overwrites value */
+		last_error = mono_w32error_get_last ();
 		mono_thread_info_uninstall_interrupt (&interrupted);
+		mono_w32error_set_last (last_error);
 	}
 
 	return res;