Re: [PR] Amend description of FilenameUtils#getFullPathNoEndSeparator(String) to reflect correct named user result with trailing slash [commons-io]

["govind-gupta-tfs (via GitHub)" <gi...@apache.org>]

govind-gupta-tfs commented on PR #553:
URL: https://github.com/apache/commons-io/pull/553#issuecomment-3380782150

   `package com.thermofisher.gsd.archive;
   
   import org.apache.commons.lang3.Validate;
   import java.net.URLDecoder;
   import java.nio.charset.StandardCharsets;
   import java.nio.file.InvalidPathException;
   import java.nio.file.Path;
   import java.util.Locale;
   import java.util.Set;
   
   public class PathValidator {
   
       private static final Set<String> RESERVED_NAMES = Set.of(
               "CON", "PRN", "AUX", "NUL", "COM1", "COM2", "COM3", "COM4", "COM5", "COM6",
               "COM7", "COM8", "COM9", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6",
               "LPT7", "LPT8", "LPT9"
       );
   
       public static void validateSafePathComponent(String component) {
           // --- 1. Basic Checks (Using Apache Commons Lang) ---
           Validate.notBlank(component, "Path component must not be blank");
           Validate.isTrue(component.length() <= 255, "Path component too long");
   
           // Pre-decode raw dangerous percent encodings
           String lower = component.toLowerCase(Locale.ROOT);
           if (lower.contains("%2f") || lower.contains("%5c") || lower.contains("%00")) {
               throw new IllegalArgumentException("Encoded separator/null not allowed: " + component);
           }
   
           // --- 2. Decoding ---
           String decoded;
           try {
               decoded = URLDecoder.decode(component, StandardCharsets.UTF_8);
           } catch (IllegalArgumentException ex) {
               throw new IllegalArgumentException("Invalid percent encoding: " + component);
           }
   
           // --- 3. Path Traversal/Normalization Check (Using Path API) ---
           Path p;
           try {
               p = Path.of(decoded);
           } catch (InvalidPathException e) {
               throw new IllegalArgumentException("Invalid path syntax: " + component);
           }
   
           // Critical Path Traversal check: must be a single name and not contain '..' or '.'
           if (p.isAbsolute() || p.getNameCount() != 1 || !p.normalize().equals(p)) {
               throw new IllegalArgumentException("Traversal/dot segments or absolute path not allowed: " + component);
           }
   
           String name = p.getFileName().toString();
   
           // --- 4. Final Name/Custom Policy Checks ---
   
           // Basic character / separator checks
           if (name.contains("/") || name.contains("\\") || name.indexOf('\0') >= 0 || name.contains("+")) {
               throw new IllegalArgumentException("Unsafe characters (separators/null/plus): " + component);
           }
   
           // Control chars
           for (int i = 0; i < name.length(); i++) {
               char c = name.charAt(i);
               if (c < 0x20 || c == 0x7F) {
                   throw new IllegalArgumentException("Control character present: " + component);
               }
           }
   
           // Dot-only or reserved dot forms & Trailing space/dot
           if (name.equals(".") || name.equals("..") || name.matches("\\.{2,}") ||
                   name.endsWith(" ") || name.endsWith(".")) {
               throw new IllegalArgumentException("Invalid dot sequence or trailing space/dot: " + component);
           }
   
           // Allowlist
           if (!name.matches("[A-Za-z0-9._-]+")) {
               throw new IllegalArgumentException("Disallowed characters: " + component);
           }
   
           // Windows reserved device names
           if (RESERVED_NAMES.contains(name.toUpperCase(Locale.ROOT))) {
               throw new IllegalArgumentException("Reserved device name: " + component);
           }
       }
   }`
   
   
   @garydgregory  can we use the above code to avoid path injection in user provided paths in windows machine. 
   It can further be optimized for other OS


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