Reuse blacklisting code in exp_archive.

client/internal/common/filesystem_view.go

 // Copyright 2017 The LUCI Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 package common
 
 import (
         "fmt"
+        "os"
         "path/filepath"
 )
 
 // FilesystemView provides a filtered "view" of a filesystem.
 // It translates absolute paths to relative paths based on its configured root path.
 // It also hides any paths which match a blacklist entry.
 type FilesystemView struct {
         root      string
         blacklist []string
 }
@@ skipping 43 matching lines @@
         }
 
         return false
 }
 
 // match is equivalent to filepath.Match, but assumes that pattern is valid.
 func match(pattern, name string) bool {
         matched, _ := filepath.Match(pattern, name)
         return matched
 }
+
+// WalkFuncSkipFile is a helper for implemenations of filepath.WalkFunc. The
+// value that it returns may in turn be returned by the WalkFunc implementaiton
+// to indicate that file should be skipped.
+func WalkFuncSkipFile(file os.FileInfo) error {
+        if file.IsDir() {
+                return filepath.SkipDir
+        }
+        // If we were to return SkipDir for a file, it would cause
+        // filepath.Walk to skip the file's containing directory, which we do
+        // not want (see https://golang.org/pkg/path/filepath/#WalkFunc).
+        return nil
+}