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

common/dirwalk/tests/tools/walkdir/util.go

Index: common/dirwalk/tests/tools/walkdir/util.go
diff --git a/common/dirwalk/tests/tools/walkdir/util.go b/common/dirwalk/tests/tools/walkdir/util.go
new file mode 100644
index 0000000000000000000000000000000000000000..03b38f9cfa593c918130562f0a97838edc877308
--- /dev/null
+++ b/common/dirwalk/tests/tools/walkdir/util.go
@@ -0,0 +1,20 @@
+// 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 main
+
+import (
+	"io"
+
+	"github.com/luci/luci-go/common/isolated"
+)
+
+func hash(src io.Reader) (isolated.HexDigest, uint64, error) {
+	h := isolated.GetHash()
+	bytes, err := io.Copy(h, src)
+	if err != nil {
+		return isolated.HexDigest(""), 0, err
+	}
+	return isolated.Sum(h), uint64(bytes), nil
+}