lib/fs: The interface and basicfs

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3748

lib/fs/basicfs_walk.go

@@ -0,0 +1,81 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This part copied directly from golang.org/src/path/filepath/path.go (Go
+// 1.6) and lightly modified to be methods on BasicFilesystem.
+
+// In our Walk() all paths given to a WalkFunc() are relative to the
+// filesystem root.
+
+package fs
+
+import "path/filepath"
+
+// WalkFunc is the type of the function called for each file or directory
+// visited by Walk. The path argument contains the argument to Walk as a
+// prefix; that is, if Walk is called with "dir", which is a directory
+// containing the file "a", the walk function will be called with argument
+// "dir/a". The info argument is the FileInfo for the named path.
+//
+// If there was a problem walking to the file or directory named by path, the
+// incoming error will describe the problem and the function can decide how
+// to handle that error (and Walk will not descend into that directory). If
+// an error is returned, processing stops. The sole exception is when the function
+// returns the special value SkipDir. If the function returns SkipDir when invoked
+// on a directory, Walk skips the directory's contents entirely.
+// If the function returns SkipDir when invoked on a non-directory file,
+// Walk skips the remaining files in the containing directory.
+type WalkFunc func(path string, info FileInfo, err error) error
+
+// walk recursively descends path, calling walkFn.
+func (f *BasicFilesystem) walk(path string, info FileInfo, walkFn WalkFunc) error {
+	err := walkFn(path, info, nil)
+	if err != nil {
+		if info.IsDir() && err == SkipDir {
+			return nil
+		}
+		return err
+	}
+
+	if !info.IsDir() {
+		return nil
+	}
+
+	names, err := f.DirNames(path)
+	if err != nil {
+		return walkFn(path, info, err)
+	}
+
+	for _, name := range names {
+		filename := filepath.Join(path, name)
+		fileInfo, err := f.Lstat(filename)
+		if err != nil {
+			if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
+				return err
+			}
+		} else {
+			err = f.walk(filename, fileInfo, walkFn)
+			if err != nil {
+				if !fileInfo.IsDir() || err != SkipDir {
+					return err
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// Walk walks the file tree rooted at root, calling walkFn for each file or
+// directory in the tree, including root. All errors that arise visiting files
+// and directories are filtered by walkFn. The files are walked in lexical
+// order, which makes the output deterministic but means that for very
+// large directories Walk can be inefficient.
+// Walk does not follow symbolic links.
+func (f *BasicFilesystem) Walk(root string, walkFn WalkFunc) error {
+	info, err := f.Lstat(root)
+	if err != nil {
+		return walkFn(root, nil, err)
+	}
+	return f.walk(root, info, walkFn)
+}