1 files changed, 150 insertions, 0 deletions
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/AbbrevConfig.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/AbbrevConfig.java
new file mode 100644
index 0000000000..9109cfd769
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/AbbrevConfig.java
@@ -0,0 +1,150 @@
+/*
+ * 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);
+	}
+}
+\ No newline at end of file