AbbrevConfig.java

/*
 * Copyright (C) 2022,  Matthias Sohn <matthias.sohn@sap.com> 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.lib;

import static org.eclipse.jgit.lib.Constants.OBJECT_ID_ABBREV_STRING_LENGTH;
import static org.eclipse.jgit.lib.TypedConfigGetter.UNSET_INT;

import java.text.MessageFormat;

import org.eclipse.jgit.api.errors.InvalidConfigurationException;
import org.eclipse.jgit.internal.JGitText;

/**
 * Git configuration option <a
 * href=https://git-scm.com/docs/git-config#Documentation/git-config.txt-coreabbrev">
 * core.abbrev</a>
 *
 * @since 6.1
 */
public final class AbbrevConfig {
    private static final String VALUE_NO = "no"; //$NON-NLS-1$

    private static final String VALUE_AUTO = "auto"; //$NON-NLS-1$

    /**
     * The minimum value of abbrev
     */
    public static final int MIN_ABBREV = 4;

    /**
     * Cap configured core.abbrev to range between minimum of 4 and number of
     * hex-digits of a full object id.
     *
     * @param len
     *            configured number of hex-digits to abbreviate object ids to
     * @return core.abbrev capped to range between minimum of 4 and number of
     *         hex-digits of a full object id
     */
    public static int capAbbrev(int len) {
        return Math.min(Math.max(MIN_ABBREV, len),
                Constants.OBJECT_ID_STRING_LENGTH);
    }

    /**
     * No abbreviation
     */
    public final static AbbrevConfig NO = new AbbrevConfig(
            Constants.OBJECT_ID_STRING_LENGTH);

    /**
     * Parse string value of core.abbrev git option for a given repository
     *
     * @param repo
     *            repository
     * @return the parsed AbbrevConfig
     * @throws InvalidConfigurationException
     *             if value of core.abbrev is invalid
     */
    public static AbbrevConfig parseFromConfig(Repository repo)
            throws InvalidConfigurationException {
        Config config = repo.getConfig();
        String value = config.getString(ConfigConstants.CONFIG_CORE_SECTION,
                null, ConfigConstants.CONFIG_KEY_ABBREV);
        if (value == null || value.equalsIgnoreCase(VALUE_AUTO)) {
            return auto(repo);
        }
        if (value.equalsIgnoreCase(VALUE_NO)) {
            return NO;
        }
        try {
            int len = config.getIntInRange(ConfigConstants.CONFIG_CORE_SECTION,
                    ConfigConstants.CONFIG_KEY_ABBREV, MIN_ABBREV,
                    Constants.OBJECT_ID_STRING_LENGTH, UNSET_INT);
            if (len == UNSET_INT) {
                // Unset was checked above. If we get UNSET_INT here, then
                // either the value was UNSET_INT, or it was an invalid value
                // (not an integer, or out of range), and EGit's
                // ReportingTypedGetter caught the exception and has logged a
                // warning. In either case we should fall back to some sane
                // default.
                len = OBJECT_ID_ABBREV_STRING_LENGTH;
            }
            return new AbbrevConfig(len);
        } catch (IllegalArgumentException e) {
            throw new InvalidConfigurationException(MessageFormat
                    .format(JGitText.get().invalidCoreAbbrev, value), e);
        }
    }

    /**
     * An appropriate value is computed based on the approximate number of
     * packed objects in a repository, which hopefully is enough for abbreviated
     * object names to stay unique for some time.
     *
     * @param repo
     * @return appropriate value computed based on the approximate number of
     *         packed objects in a repository
     */
    private static AbbrevConfig auto(Repository repo) {
        long count = repo.getObjectDatabase().getApproximateObjectCount();
        if (count == -1) {
            return new AbbrevConfig(OBJECT_ID_ABBREV_STRING_LENGTH);
        }
        // find msb, round to next power of 2
        int len = 63 - Long.numberOfLeadingZeros(count) + 1;
        // With the order of 2^len objects, we expect a collision at
        // 2^(len/2). But we also care about hex chars, not bits, and
        // there are 4 bits per hex. So all together we need to divide
        // by 2; but we also want to round odd numbers up, hence adding
        // one before dividing.
        len = (len + 1) / 2;
        // for small repos use at least fallback length
        return new AbbrevConfig(Math.max(len, OBJECT_ID_ABBREV_STRING_LENGTH));
    }

    /**
     * All other possible abbreviation lengths. Valid range 4 to number of
     * hex-digits of an unabbreviated object id (40 for SHA1 object ids, jgit
     * doesn't support SHA256 yet).
     */
    private int abbrev;

    /**
     * @param abbrev
     */
    private AbbrevConfig(int abbrev) {
        this.abbrev = capAbbrev(abbrev);
    }

    /**
     * Get the configured abbreviation length for object ids.
     *
     * @return the configured abbreviation length for object ids
     */
    public int get() {
        return abbrev;
    }

    @Override
    public String toString() {
        return Integer.toString(abbrev);
    }
}