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The Enterprise Security API (ESAPI) project is an OWASP project to create simple strong security controls for every web platform. Security controls are not simple to build. You can read about the hundreds of pitfalls for unwary developers on the OWASP website. By providing developers with a set of strong controls, we aim to eliminate some of the complexity of creating secure web applications. This can result in significant cost savings across the SDLC.

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/**
 * OWASP Enterprise Security API (ESAPI)
 *
 * This file is part of the Open Web Application Security Project (OWASP)
 * Enterprise Security API (ESAPI) project. For details, please see
 * http://www.owasp.org/index.php/ESAPI.
 *
 * Copyright (c) 2008 - The OWASP Foundation
 *
 * The ESAPI is published by OWASP under the BSD license. You should read and accept the
 * LICENSE before you use, modify, and/or redistribute this software.
 *
 * @author Arshan Dabirsiaghi Aspect Security
 * @created 2008
 */
package org.owasp.esapi;

import java.io.File;
import java.net.URI;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.owasp.esapi.errors.ValidationException;

/**
 * Extension to java.io.File to prevent against null byte injections and
 * other unforeseen problems resulting from unprintable characters
 * causing problems in path lookups. This does _not_ prevent against
 * directory traversal attacks.
 */
public class SafeFile extends File {

    private static final long serialVersionUID = 1L;
    private static final Pattern PERCENTS_PAT = Pattern.compile("(%)([0-9a-fA-F])([0-9a-fA-F])");
    private static final Pattern FILE_BLACKLIST_PAT = Pattern.compile("([\\\\/:*?<>|^])");
    private static final Pattern DIR_BLACKLIST_PAT = Pattern.compile("([*?<>|^])");

    public SafeFile(String path) throws ValidationException {
        super(path);
        doDirCheck(this.getParent());
        doFileCheck(this.getName());
    }

    public SafeFile(String parent, String child) throws ValidationException {
        super(parent, child);
        doDirCheck(this.getParent());
        doFileCheck(this.getName());
    }

    public SafeFile(File parent, String child) throws ValidationException {
        super(parent, child);
        doDirCheck(this.getParent());
        doFileCheck(this.getName());
    }

    public SafeFile(URI uri) throws ValidationException {
        super(uri);
        doDirCheck(this.getParent());
        doFileCheck(this.getName());
    }


    private void doDirCheck(String path) throws ValidationException {
        Matcher m1 = DIR_BLACKLIST_PAT.matcher( path );
        if ( null != m1 && m1.find() ) {
            throw new ValidationException( "Invalid directory", "Directory path (" + path + ") contains illegal character: " + m1.group() );
        }

        Matcher m2 = PERCENTS_PAT.matcher( path );
        if (null != m2 &&  m2.find() ) {
            throw new ValidationException( "Invalid directory", "Directory path (" + path + ") contains encoded characters: " + m2.group() );
        }

        int ch = containsUnprintableCharacters(path);
        if (ch != -1) {
            throw new ValidationException("Invalid directory", "Directory path (" + path + ") contains unprintable character: " + ch);
        }
    }

    private void doFileCheck(String path) throws ValidationException {
        Matcher m1 = FILE_BLACKLIST_PAT.matcher( path );
        if ( m1.find() ) {
            throw new ValidationException( "Invalid directory", "Directory path (" + path + ") contains illegal character: " + m1.group() );
        }

        Matcher m2 = PERCENTS_PAT.matcher( path );
        if ( m2.find() ) {
            throw new ValidationException( "Invalid file", "File path (" + path + ") contains encoded characters: " + m2.group() );
        }

        int ch = containsUnprintableCharacters(path);
        if (ch != -1) {
            throw new ValidationException("Invalid file", "File path (" + path + ") contains unprintable character: " + ch);
        }
    }

    private int containsUnprintableCharacters(String s) {
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (((int) ch) < 32 || ((int) ch) > 126) {
                return (int) ch;
            }
        }
        return -1;
    }

}