lib/config, lib/fs: Make junction behaviour configurable (ref #6606) (#6907)

lib/fs/basicfs.go

@@ -23,13 +23,24 @@ var (
 	ErrNotRelative     = errors.New("not a relative path")
 )
 
+func WithJunctionsAsDirs() Option {
+	return func(fs Filesystem) {
+		if basic, ok := fs.(*BasicFilesystem); !ok {
+			l.Warnln("WithJunctionsAsDirs must only be used with FilesystemTypeBasic")
+		} else {
+			basic.junctionsAsDirs = true
+		}
+	}
+}
+
 // The BasicFilesystem implements all aspects by delegating to package os.
 // All paths are relative to the root and cannot (should not) escape the root directory.
 type BasicFilesystem struct {
-	root string
+	root            string
+	junctionsAsDirs bool
 }
 
-func newBasicFilesystem(root string) *BasicFilesystem {
+func newBasicFilesystem(root string, opts ...Option) *BasicFilesystem {
 	if root == "" {
 		root = "." // Otherwise "" becomes "/" below
 	}
@@ -64,7 +75,13 @@ func newBasicFilesystem(root string) *BasicFilesystem {
 		root = longFilenameSupport(root)
 	}
 
-	return &BasicFilesystem{root}
+	fs := &BasicFilesystem{
+		root: root,
+	}
+	for _, opt := range opts {
+		opt(fs)
+	}
+	return fs
 }
 
 // rooted expands the relative path to the full path that is then used with os
@@ -145,7 +162,7 @@ func (f *BasicFilesystem) Lstat(name string) (FileInfo, error) {
 	if err != nil {
 		return nil, err
 	}
-	fi, err := underlyingLstat(name)
+	fi, err := f.underlyingLstat(name)
 	if err != nil {
 		return nil, err
 	}

lib/fs/basicfs_lstat_broken.go

@@ -16,7 +16,7 @@ import (
 
 // Lstat is like os.Lstat, except lobotomized for Android. See
 // https://forum.syncthing.net/t/2395
-func underlyingLstat(name string) (fi os.FileInfo, err error) {
+func (*BasicFilesystem) underlyingLstat(name string) (fi os.FileInfo, err error) {
 	for i := 0; i < 10; i++ { // We have to draw the line somewhere
 		fi, err = os.Lstat(name)
 		if err, ok := err.(*os.PathError); ok && err.Err == syscall.EINTR {

lib/fs/basicfs_lstat_regular.go

@@ -10,6 +10,6 @@ package fs
 
 import "os"
 
-func underlyingLstat(name string) (fi os.FileInfo, err error) {
+func (*BasicFilesystem) underlyingLstat(name string) (fi os.FileInfo, err error) {
 	return os.Lstat(name)
 }

lib/fs/basicfs_lstat_windows.go

@@ -66,12 +66,12 @@ func (fi *dirJunctFileInfo) IsDir() bool {
 	return true
 }
 
-func underlyingLstat(name string) (os.FileInfo, error) {
+func (f *BasicFilesystem) underlyingLstat(name string) (os.FileInfo, error) {
 	var fi, err = os.Lstat(name)
 
-	// NTFS directory junctions are treated as ordinary directories,
+	// NTFS directory junctions can be treated as ordinary directories,
 	// see https://forum.syncthing.net/t/option-to-follow-directory-junctions-symbolic-links/14750
-	if err == nil && fi.Mode()&os.ModeSymlink != 0 {
+	if err == nil && f.junctionsAsDirs && fi.Mode()&os.ModeSymlink != 0 {
 		var isJunct bool
 		isJunct, err = isDirectoryJunction(name)
 		if err == nil && isJunct {

lib/fs/fakefs.go

@@ -66,7 +66,7 @@ var (
 	fakefsFs  = make(map[string]*fakefs)
 )
 
-func newFakeFilesystem(rootURI string) *fakefs {
+func newFakeFilesystem(rootURI string, _ ...Option) *fakefs {
 	fakefsMut.Lock()
 	defer fakefsMut.Unlock()
 

lib/fs/filesystem.go

@@ -178,13 +178,15 @@ var IsPermission = os.IsPermission
 // IsPathSeparator is the equivalent of os.IsPathSeparator
 var IsPathSeparator = os.IsPathSeparator
 
-func NewFilesystem(fsType FilesystemType, uri string) Filesystem {
+type Option func(Filesystem)
+
+func NewFilesystem(fsType FilesystemType, uri string, opts ...Option) Filesystem {
 	var fs Filesystem
 	switch fsType {
 	case FilesystemTypeBasic:
-		fs = newBasicFilesystem(uri)
+		fs = newBasicFilesystem(uri, opts...)
 	case FilesystemTypeFake:
-		fs = newFakeFilesystem(uri)
+		fs = newFakeFilesystem(uri, opts...)
 	default:
 		l.Debugln("Unknown filesystem", fsType, uri)
 		fs = &errorFilesystem{

lib/fs/walkfs_test.go

@@ -57,7 +57,7 @@ func testWalkTraverseDirJunct(t *testing.T, fsType FilesystemType, uri string) {
 		t.Skip("Directory junctions are available and tested on windows only")
 	}
 
-	fs := NewFilesystem(fsType, uri)
+	fs := NewFilesystem(fsType, uri, WithJunctionsAsDirs())
 
 	if err := fs.MkdirAll("target/foo", 0); err != nil {
 		t.Fatal(err)
@@ -90,7 +90,7 @@ func testWalkInfiniteRecursion(t *testing.T, fsType FilesystemType, uri string)
 		t.Skip("Infinite recursion detection is tested on windows only")
 	}
 
-	fs := NewFilesystem(fsType, uri)
+	fs := NewFilesystem(fsType, uri, WithJunctionsAsDirs())
 
 	if err := fs.MkdirAll("target/foo", 0); err != nil {
 		t.Fatal(err)