BinaryDelta.java
/*
* Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
* Copyright (C) 2006-2007, Shawn O. Pearce <spearce@spearce.org> 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.internal.storage.pack;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.util.QuotedString;
import org.eclipse.jgit.util.RawParseUtils;
/**
* Recreate a stream from a base stream and a GIT pack delta.
* <p>
* This entire class is heavily cribbed from <code>patch-delta.c</code> in the
* GIT project. The original delta patching code was written by Nicolas Pitre
* (<nico@cam.org>).
* </p>
*/
public class BinaryDelta {
/**
* Length of the base object in the delta stream.
*
* @param delta
* the delta stream, or at least the header of it.
* @return the base object's size.
*/
public static long getBaseSize(byte[] delta) {
int p = 0;
long baseLen = 0;
int c, shift = 0;
do {
c = delta[p++] & 0xff;
baseLen |= ((long) (c & 0x7f)) << shift;
shift += 7;
} while ((c & 0x80) != 0);
return baseLen;
}
/**
* Length of the resulting object in the delta stream.
*
* @param delta
* the delta stream, or at least the header of it.
* @return the resulting object's size.
*/
public static long getResultSize(byte[] delta) {
int p = 0;
// Skip length of the base object.
//
int c;
do {
c = delta[p++] & 0xff;
} while ((c & 0x80) != 0);
long resLen = 0;
int shift = 0;
do {
c = delta[p++] & 0xff;
resLen |= ((long) (c & 0x7f)) << shift;
shift += 7;
} while ((c & 0x80) != 0);
return resLen;
}
/**
* Apply the changes defined by delta to the data in base, yielding a new
* array of bytes.
*
* @param base
* some byte representing an object of some kind.
* @param delta
* a git pack delta defining the transform from one version to
* another.
* @return patched base
*/
public static final byte[] apply(byte[] base, byte[] delta) {
return apply(base, delta, null);
}
/**
* Apply the changes defined by delta to the data in base, yielding a new
* array of bytes.
*
* @param base
* some byte representing an object of some kind.
* @param delta
* a git pack delta defining the transform from one version to
* another.
* @param result
* array to store the result into. If null the result will be
* allocated and returned.
* @return either {@code result}, or the result array allocated.
*/
public static final byte[] apply(final byte[] base, final byte[] delta,
byte[] result) {
int deltaPtr = 0;
// Length of the base object (a variable length int).
//
int baseLen = 0;
int c, shift = 0;
do {
c = delta[deltaPtr++] & 0xff;
baseLen |= (c & 0x7f) << shift;
shift += 7;
} while ((c & 0x80) != 0);
if (base.length != baseLen)
throw new IllegalArgumentException(
JGitText.get().baseLengthIncorrect);
// Length of the resulting object (a variable length int).
//
int resLen = 0;
shift = 0;
do {
c = delta[deltaPtr++] & 0xff;
resLen |= (c & 0x7f) << shift;
shift += 7;
} while ((c & 0x80) != 0);
if (result == null)
result = new byte[resLen];
else if (result.length != resLen)
throw new IllegalArgumentException(
JGitText.get().resultLengthIncorrect);
int resultPtr = 0;
while (deltaPtr < delta.length) {
final int cmd = delta[deltaPtr++] & 0xff;
if ((cmd & 0x80) != 0) {
// Determine the segment of the base which should
// be copied into the output. The segment is given
// as an offset and a length.
//
int copyOffset = 0;
if ((cmd & 0x01) != 0)
copyOffset = delta[deltaPtr++] & 0xff;
if ((cmd & 0x02) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
if ((cmd & 0x04) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
if ((cmd & 0x08) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 24;
int copySize = 0;
if ((cmd & 0x10) != 0)
copySize = delta[deltaPtr++] & 0xff;
if ((cmd & 0x20) != 0)
copySize |= (delta[deltaPtr++] & 0xff) << 8;
if ((cmd & 0x40) != 0)
copySize |= (delta[deltaPtr++] & 0xff) << 16;
if (copySize == 0)
copySize = 0x10000;
System.arraycopy(base, copyOffset, result, resultPtr, copySize);
resultPtr += copySize;
} else if (cmd != 0) {
// Anything else the data is literal within the delta
// itself.
//
System.arraycopy(delta, deltaPtr, result, resultPtr, cmd);
deltaPtr += cmd;
resultPtr += cmd;
} else {
// cmd == 0 has been reserved for future encoding but
// for now its not acceptable.
//
throw new IllegalArgumentException(
JGitText.get().unsupportedCommand0);
}
}
return result;
}
/**
* Format this delta as a human readable string.
*
* @param delta
* the delta instruction sequence to format.
* @return the formatted delta.
*/
public static String format(byte[] delta) {
return format(delta, true);
}
/**
* Format this delta as a human readable string.
*
* @param delta
* the delta instruction sequence to format.
* @param includeHeader
* true if the header (base size and result size) should be
* included in the formatting.
* @return the formatted delta.
*/
public static String format(byte[] delta, boolean includeHeader) {
StringBuilder r = new StringBuilder();
int deltaPtr = 0;
long baseLen = 0;
int c, shift = 0;
do {
c = delta[deltaPtr++] & 0xff;
baseLen |= ((long) (c & 0x7f)) << shift;
shift += 7;
} while ((c & 0x80) != 0);
long resLen = 0;
shift = 0;
do {
c = delta[deltaPtr++] & 0xff;
resLen |= ((long) (c & 0x7f)) << shift;
shift += 7;
} while ((c & 0x80) != 0);
if (includeHeader) {
r.append("DELTA( BASE="); //$NON-NLS-1$
r.append(baseLen);
r.append(" RESULT="); //$NON-NLS-1$
r.append(resLen);
r.append(" )\n"); //$NON-NLS-1$
}
while (deltaPtr < delta.length) {
final int cmd = delta[deltaPtr++] & 0xff;
if ((cmd & 0x80) != 0) {
// Determine the segment of the base which should
// be copied into the output. The segment is given
// as an offset and a length.
//
int copyOffset = 0;
if ((cmd & 0x01) != 0)
copyOffset = delta[deltaPtr++] & 0xff;
if ((cmd & 0x02) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
if ((cmd & 0x04) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
if ((cmd & 0x08) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 24;
int copySize = 0;
if ((cmd & 0x10) != 0)
copySize = delta[deltaPtr++] & 0xff;
if ((cmd & 0x20) != 0)
copySize |= (delta[deltaPtr++] & 0xff) << 8;
if ((cmd & 0x40) != 0)
copySize |= (delta[deltaPtr++] & 0xff) << 16;
if (copySize == 0)
copySize = 0x10000;
r.append(" COPY ("); //$NON-NLS-1$
r.append(copyOffset);
r.append(", "); //$NON-NLS-1$
r.append(copySize);
r.append(")\n"); //$NON-NLS-1$
} else if (cmd != 0) {
// Anything else the data is literal within the delta
// itself.
//
r.append(" INSERT("); //$NON-NLS-1$
r.append(QuotedString.GIT_PATH.quote(RawParseUtils.decode(
delta, deltaPtr, deltaPtr + cmd)));
r.append(")\n"); //$NON-NLS-1$
deltaPtr += cmd;
} else {
// cmd == 0 has been reserved for future encoding but
// for now its not acceptable.
//
throw new IllegalArgumentException(
JGitText.get().unsupportedCommand0);
}
}
return r.toString();
}
}