github.com/google/osv-scalibr@v0.4.1/artifact/image/whiteout/whiteout.go (about)

     1  // Copyright 2025 Google LLC
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package whiteout defines and implements whiteout related functions to be used in the layer
    16  // scanning methods and functions.
    17  package whiteout
    18  
    19  import (
    20  	"fmt"
    21  	"io/fs"
    22  	"path"
    23  	"path/filepath"
    24  	"strings"
    25  
    26  	scalibrfs "github.com/google/osv-scalibr/fs"
    27  )
    28  
    29  const (
    30  	// WhiteoutPrefix is the prefix found on whiteout files.
    31  	WhiteoutPrefix = ".wh."
    32  	// WhiteoutDirPrefix is the prefix found on whiteout directories. This means the directory cannot
    33  	// hold any more files in the current layer, as well as future layers.
    34  	WhiteoutDirPrefix = ".wh..wh..opq."
    35  )
    36  
    37  // Files outputs all of the whiteout files found in an FS.
    38  func Files(scalibrfs scalibrfs.FS) (map[string]struct{}, error) {
    39  	whiteouts := make(map[string]struct{})
    40  
    41  	err := fs.WalkDir(scalibrfs, ".", func(path string, d fs.DirEntry, err error) error {
    42  		if err != nil {
    43  			// Continue walking if there is an error.
    44  			//nolint:nilerr
    45  			return nil
    46  		}
    47  
    48  		base := filepath.Base(path)
    49  
    50  		if d.Type().IsRegular() && strings.HasPrefix(base, WhiteoutPrefix) {
    51  			whiteouts[path] = struct{}{}
    52  		}
    53  
    54  		if d.IsDir() && strings.HasPrefix(base, WhiteoutDirPrefix) {
    55  			whiteouts[path] = struct{}{}
    56  		}
    57  		return nil
    58  	})
    59  
    60  	if err != nil {
    61  		return nil, fmt.Errorf("failed to successfully walk fs to find whiteout files: %w", err)
    62  	}
    63  	return whiteouts, nil
    64  }
    65  
    66  // IsWhiteout returns true if a path is a whiteout path.
    67  func IsWhiteout(p string) bool {
    68  	_, file := path.Split(p)
    69  	return strings.HasPrefix(file, WhiteoutPrefix)
    70  }
    71  
    72  // ToWhiteout returns the whiteout version of a path.
    73  func ToWhiteout(p string) string {
    74  	dir, file := path.Split(p)
    75  	return path.Join(dir, fmt.Sprintf("%s%s", WhiteoutPrefix, file))
    76  }
    77  
    78  // ToPath returns the non whiteout version of a path.
    79  func ToPath(p string) string {
    80  	dir, file := path.Split(p)
    81  
    82  	file = strings.TrimPrefix(file, WhiteoutPrefix)
    83  
    84  	nonWhitoutPath := path.Join(dir, file)
    85  
    86  	if dir != "" && file == "" {
    87  		nonWhitoutPath += "/"
    88  	}
    89  
    90  	return nonWhitoutPath
    91  }