From a9f0659f2f4bf910f82b652fd27a864074ec7ab8 Mon Sep 17 00:00:00 2001
From: Jakob Borg <jakob@kastelo.net>
Date: Fri, 29 Dec 2017 21:23:06 +0000
Subject: [PATCH] lib/fs: Handle deduplicated files on NTFS (fixes #1845)

These files always have the symlink bit set, because they are reparse
points. Nonetheless they are not symlinks, and Lstat reports a size for
them. We use this fact to disambiguate, and hope fervently that nothing
else matches this description so it comes back to bite us...

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4622
---
 lib/fs/basicfs.go            | 12 +++++-------
 lib/fs/filesystem.go         |  2 ++
 lib/fs/fsfileinfo_unix.go    | 13 +++++++++++++
 lib/fs/fsfileinfo_windows.go | 21 +++++++++++++++++++++
 4 files changed, 41 insertions(+), 7 deletions(-)
 create mode 100644 lib/fs/fsfileinfo_unix.go
 create mode 100644 lib/fs/fsfileinfo_windows.go

diff --git a/lib/fs/basicfs.go b/lib/fs/basicfs.go
index 4a0dc0919..8736d621b 100644
--- a/lib/fs/basicfs.go
+++ b/lib/fs/basicfs.go
@@ -322,14 +322,12 @@ type fsFileInfo struct {
 	os.FileInfo
 }
 
-func (e fsFileInfo) Mode() FileMode {
-	return FileMode(e.FileInfo.Mode())
+func (e fsFileInfo) IsSymlink() bool {
+	// Must use fsFileInfo.Mode() because it may apply magic.
+	return e.Mode()&ModeSymlink != 0
 }
 
 func (e fsFileInfo) IsRegular() bool {
-	return e.FileInfo.Mode().IsRegular()
-}
-
-func (e fsFileInfo) IsSymlink() bool {
-	return e.FileInfo.Mode()&os.ModeSymlink == os.ModeSymlink
+	// Must use fsFileInfo.Mode() because it may apply magic.
+	return e.Mode()&ModeType == 0
 }
diff --git a/lib/fs/filesystem.go b/lib/fs/filesystem.go
index fe267ac00..346dd2548 100644
--- a/lib/fs/filesystem.go
+++ b/lib/fs/filesystem.go
@@ -126,6 +126,8 @@ const ModePerm = FileMode(os.ModePerm)
 const ModeSetgid = FileMode(os.ModeSetgid)
 const ModeSetuid = FileMode(os.ModeSetuid)
 const ModeSticky = FileMode(os.ModeSticky)
+const ModeSymlink = FileMode(os.ModeSymlink)
+const ModeType = FileMode(os.ModeType)
 const PathSeparator = os.PathSeparator
 const OptAppend = os.O_APPEND
 const OptCreate = os.O_CREATE
diff --git a/lib/fs/fsfileinfo_unix.go b/lib/fs/fsfileinfo_unix.go
new file mode 100644
index 000000000..96b1a392f
--- /dev/null
+++ b/lib/fs/fsfileinfo_unix.go
@@ -0,0 +1,13 @@
+// Copyright (C) 2017 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+// +build !windows
+
+package fs
+
+func (e fsFileInfo) Mode() FileMode {
+	return FileMode(e.FileInfo.Mode())
+}
diff --git a/lib/fs/fsfileinfo_windows.go b/lib/fs/fsfileinfo_windows.go
new file mode 100644
index 000000000..fdd524d1c
--- /dev/null
+++ b/lib/fs/fsfileinfo_windows.go
@@ -0,0 +1,21 @@
+// Copyright (C) 2017 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package fs
+
+import (
+	"os"
+)
+
+func (e fsFileInfo) Mode() FileMode {
+	m := e.FileInfo.Mode()
+	if m&os.ModeSymlink != 0 && e.Size() > 0 {
+		// "Symlinks" with nonzero size are in fact "hard" links, such as
+		// NTFS deduped files. Remove the symlink bit.
+		m &^= os.ModeSymlink
+	}
+	return FileMode(m)
+}