Paths.java

/*
 * Copyright (C) 2016, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.util;

import static org.eclipse.jgit.lib.FileMode.TYPE_MASK;
import static org.eclipse.jgit.lib.FileMode.TYPE_TREE;

/**
 * Utility functions for paths inside of a Git repository.
 *
 * @since 4.2
 */
public class Paths {
    /**
     * Remove trailing {@code '/'} if present.
     *
     * @param path
     *            input path to potentially remove trailing {@code '/'} from.
     * @return null if {@code path == null}; {@code path} after removing a
     *         trailing {@code '/'}.
     */
    public static String stripTrailingSeparator(String path) {
        if (path == null || path.isEmpty()) {
            return path;
        }

        int i = path.length();
        if (path.charAt(path.length() - 1) != '/') {
            return path;
        }
        do {
            i--;
        } while (path.charAt(i - 1) == '/');
        return path.substring(0, i);
    }

    /**
     * Compare two paths according to Git path sort ordering rules.
     *
     * @param aPath
     *            first path buffer. The range {@code [aPos, aEnd)} is used.
     * @param aPos
     *            index into {@code aPath} where the first path starts.
     * @param aEnd
     *            1 past last index of {@code aPath}.
     * @param aMode
     *            mode of the first file. Trees are sorted as though
     *            {@code aPath[aEnd] == '/'}, even if aEnd does not exist.
     * @param bPath
     *            second path buffer. The range {@code [bPos, bEnd)} is used.
     * @param bPos
     *            index into {@code bPath} where the second path starts.
     * @param bEnd
     *            1 past last index of {@code bPath}.
     * @param bMode
     *            mode of the second file. Trees are sorted as though
     *            {@code bPath[bEnd] == '/'}, even if bEnd does not exist.
     * @return <0 if {@code aPath} sorts before {@code bPath};
     *         0 if the paths are the same;
     *         >0 if {@code aPath} sorts after {@code bPath}.
     */
    public static int compare(byte[] aPath, int aPos, int aEnd, int aMode,
            byte[] bPath, int bPos, int bEnd, int bMode) {
        int cmp = coreCompare(
                aPath, aPos, aEnd, aMode,
                bPath, bPos, bEnd, bMode);
        if (cmp == 0) {
            cmp = lastPathChar(aMode) - lastPathChar(bMode);
        }
        return cmp;
    }

    /**
     * Compare two paths, checking for identical name.
     * <p>
     * Unlike {@code compare} this method returns {@code 0} when the paths have
     * the same characters in their names, even if the mode differs. It is
     * intended for use in validation routines detecting duplicate entries.
     * <p>
     * Returns {@code 0} if the names are identical and a conflict exists
     * between {@code aPath} and {@code bPath}, as they share the same name.
     * <p>
     * Returns {@code <0} if all possibles occurrences of {@code aPath} sort
     * before {@code bPath} and no conflict can happen. In a properly sorted
     * tree there are no other occurrences of {@code aPath} and therefore there
     * are no duplicate names.
     * <p>
     * Returns {@code >0} when it is possible for a duplicate occurrence of
     * {@code aPath} to appear later, after {@code bPath}. Callers should
     * continue to examine candidates for {@code bPath} until the method returns
     * one of the other return values.
     *
     * @param aPath
     *            first path buffer. The range {@code [aPos, aEnd)} is used.
     * @param aPos
     *            index into {@code aPath} where the first path starts.
     * @param aEnd
     *            1 past last index of {@code aPath}.
     * @param bPath
     *            second path buffer. The range {@code [bPos, bEnd)} is used.
     * @param bPos
     *            index into {@code bPath} where the second path starts.
     * @param bEnd
     *            1 past last index of {@code bPath}.
     * @param bMode
     *            mode of the second file. Trees are sorted as though
     *            {@code bPath[bEnd] == '/'}, even if bEnd does not exist.
     * @return &lt;0 if no duplicate name could exist;
     *         0 if the paths have the same name;
     *         &gt;0 other {@code bPath} should still be checked by caller.
     */
    public static int compareSameName(
            byte[] aPath, int aPos, int aEnd,
            byte[] bPath, int bPos, int bEnd, int bMode) {
        return coreCompare(
                aPath, aPos, aEnd, TYPE_TREE,
                bPath, bPos, bEnd, bMode);
    }

    private static int coreCompare(
            byte[] aPath, int aPos, int aEnd, int aMode,
            byte[] bPath, int bPos, int bEnd, int bMode) {
        while (aPos < aEnd && bPos < bEnd) {
            int cmp = (aPath[aPos++] & 0xff) - (bPath[bPos++] & 0xff);
            if (cmp != 0) {
                return cmp;
            }
        }
        if (aPos < aEnd) {
            return (aPath[aPos] & 0xff) - lastPathChar(bMode);
        }
        if (bPos < bEnd) {
            return lastPathChar(aMode) - (bPath[bPos] & 0xff);
        }
        return 0;
    }

    private static int lastPathChar(int mode) {
        if ((mode & TYPE_MASK) == TYPE_TREE) {
            return '/';
        }
        return 0;
    }

    private Paths() {
    }
}