1 files changed, 78 insertions, 0 deletions
diff --git a/src/mscorlib/shared/System/IO/FileStream.WinRT.cs b/src/mscorlib/shared/System/IO/FileStream.WinRT.cs
new file mode 100644
index 0000000000..062b160b57
--- /dev/null
+++ b/src/mscorlib/shared/System/IO/FileStream.WinRT.cs
@@ -0,0 +1,78 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.Win32.SafeHandles;
+using System.Runtime.InteropServices;
+
+namespace System.IO
+{
+    public partial class FileStream : Stream
+    {
+        private unsafe SafeFileHandle OpenHandle(FileMode mode, FileShare share, FileOptions options)
+        {
+            Interop.Kernel32.SECURITY_ATTRIBUTES secAttrs = GetSecAttrs(share);
+
+            int fAccess =
+                ((_access & FileAccess.Read) == FileAccess.Read ? GENERIC_READ : 0) |
+                ((_access & FileAccess.Write) == FileAccess.Write ? GENERIC_WRITE : 0);
+
+            // Our Inheritable bit was stolen from Windows, but should be set in
+            // the security attributes class.  Don't leave this bit set.
+            share &= ~FileShare.Inheritable;
+
+            // Must use a valid Win32 constant here...
+            if (mode == FileMode.Append)
+                mode = FileMode.OpenOrCreate;
+
+            Interop.Kernel32.CREATEFILE2_EXTENDED_PARAMETERS parameters = new Interop.Kernel32.CREATEFILE2_EXTENDED_PARAMETERS();
+            parameters.dwSize = (uint)sizeof(Interop.Kernel32.CREATEFILE2_EXTENDED_PARAMETERS);
+            parameters.dwFileFlags = (uint)options;
+            parameters.lpSecurityAttributes = &secAttrs;
+
+            SafeFileHandle fileHandle = Interop.Kernel32.CreateFile2(
+                lpFileName: _path,
+                dwDesiredAccess: fAccess,
+                dwShareMode: share,
+                dwCreationDisposition: mode,
+                pCreateExParams: &parameters);
+
+            fileHandle.IsAsync = _useAsyncIO;
+
+            if (fileHandle.IsInvalid)
+            {
+                // Return a meaningful exception with the full path.
+
+                // NT5 oddity - when trying to open "C:\" as a Win32FileStream,
+                // we usually get ERROR_PATH_NOT_FOUND from the OS.  We should
+                // probably be consistent w/ every other directory.
+                int errorCode = Marshal.GetLastWin32Error();
+
+                if (errorCode == Interop.Errors.ERROR_PATH_NOT_FOUND && _path.Length == PathInternal.GetRootLength(_path))
+                    errorCode = Interop.Errors.ERROR_ACCESS_DENIED;
+
+                throw Win32Marshal.GetExceptionForWin32Error(errorCode, $"{_path} {options} {fAccess} {share} {mode}");
+            }
+
+            return fileHandle;
+        }
+
+#if PROJECTN
+        // TODO: These internal methods should be removed once we start consuming updated CoreFX builds
+        public static FileStream InternalOpen(string path, int bufferSize = 4096, bool useAsync = true)
+        {
+            return new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize, useAsync);
+        }
+
+        public static FileStream InternalCreate(string path, int bufferSize = 4096, bool useAsync = true)
+        {
+            return new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read, bufferSize, useAsync);
+        }
+
+        public static FileStream InternalAppend(string path, int bufferSize = 4096, bool useAsync = true)
+        {
+            return new FileStream(path, FileMode.Append, FileAccess.Write, FileShare.Read, bufferSize, useAsync);
+        }
+#endif
+    }
+}