luci-go/common/dirwalk: Code for walking a directory tree efficiently

common/dirwalk/callback.go

Index: common/dirwalk/callback.go
diff --git a/common/dirwalk/callback.go b/common/dirwalk/callback.go
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+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package dirwalk
+
+import "io"
+
+// WalkFunc is a callback for receiving the results of walking a directory
+// tree.
+//
+// r.Close() should be called if r is not nil.
+//
+// Callback for a directory will have a nil reader and occur *after* all the
+// paths contained inside the directory have already been provided.
+type WalkFunc func(path string, size int64, r io.ReadCloser, err error)