org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/DeltaEncoder.java - sop/jgit - Git at Google

 /*
  * Copyright (C) 2010, Google Inc.
  * and other copyright owners as documented in the project's IP log.
  *
  * This program and the accompanying materials are made available
  * under the terms of the Eclipse Distribution License v1.0 which
  * accompanies this distribution, is reproduced below, and is
  * available at http://www.eclipse.org/org/documents/edl-v10.php
  *
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or
  * without modification, are permitted provided that the following
  * conditions are met:
  *
  * - Redistributions of source code must retain the above copyright
  *   notice, this list of conditions and the following disclaimer.
  *
  * - Redistributions in binary form must reproduce the above
  *   copyright notice, this list of conditions and the following
  *   disclaimer in the documentation and/or other materials provided
  *   with the distribution.
  *
  * - Neither the name of the Eclipse Foundation, Inc. nor the
  *   names of its contributors may be used to endorse or promote
  *   products derived from this software without specific prior
  *   written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 package org.eclipse.jgit.internal.storage.pack;

 import java.io.IOException;
 import java.io.OutputStream;

 import org.eclipse.jgit.lib.Constants;

 /** Encodes an instruction stream for {@link BinaryDelta}. */
 public class DeltaEncoder {
 	/**
 	 * Maximum number of bytes to be copied in pack v2 format.
 	 * <p>
 	 * Historical limitations have this at 64k, even though current delta
 	 * decoders recognize larger copy instructions.
 	 */
 	private static final int MAX_V2_COPY = 0x10000;

 	/*
 	 * Maximum number of bytes to be copied in pack v3 format.
 	 *
 	 * Current delta decoders can recognize a copy instruction with a count that
 	 * is this large, but the historical limitation of {@link MAX_V2_COPY} is
 	 * still used.
 	 */
 	// private static final int MAX_V3_COPY = (0xff << 16) | (0xff << 8) | 0xff;

 	/** Maximum number of bytes used by a copy instruction. */
 	private static final int MAX_COPY_CMD_SIZE = 8;

 	/** Maximum length that an an insert command can encode at once. */
 	private static final int MAX_INSERT_DATA_SIZE = 127;

 	private final OutputStream out;

 	private final byte[] buf = new byte[MAX_COPY_CMD_SIZE * 4];

 	private final int limit;

 	private int size;

 	/**
 	 * Create an encoder with no upper bound on the instruction stream size.
 	 *
 	 * @param out
 	 *            buffer to store the instructions written.
 	 * @param baseSize
 	 *            size of the base object, in bytes.
 	 * @param resultSize
 	 *            size of the resulting object, after applying this instruction
 	 *            stream to the base object, in bytes.
 	 * @throws IOException
 	 *             the output buffer cannot store the instruction stream's
 	 *             header with the size fields.
 	 */
 	public DeltaEncoder(OutputStream out, long baseSize, long resultSize)
 			throws IOException {
 		this(out, baseSize, resultSize, 0);
 	}

 	/**
 	 * Create an encoder with an upper limit on the instruction size.
 	 *
 	 * @param out
 	 *            buffer to store the instructions written.
 	 * @param baseSize
 	 *            size of the base object, in bytes.
 	 * @param resultSize
 	 *            size of the resulting object, after applying this instruction
 	 *            stream to the base object, in bytes.
 	 * @param limit
 	 *            maximum number of bytes to write to the out buffer declaring
 	 *            the stream is over limit and should be discarded. May be 0 to
 	 *            specify an infinite limit.
 	 * @throws IOException
 	 *             the output buffer cannot store the instruction stream's
 	 *             header with the size fields.
 	 */
 	public DeltaEncoder(OutputStream out, long baseSize, long resultSize,
 			int limit) throws IOException {
 		this.out = out;
 		this.limit = limit;
 		writeVarint(baseSize);
 		writeVarint(resultSize);
 	}

 	private void writeVarint(long sz) throws IOException {
 		int p = 0;
 		while (sz >= 0x80) {
 			buf[p++] = (byte) (0x80 | (((int) sz) & 0x7f));
 			sz >>>= 7;
 		}
 		buf[p++] = (byte) (((int) sz) & 0x7f);
 		size += p;
 		if (limit == 0 || size < limit)
 			out.write(buf, 0, p);
 	}

 	/** @return current size of the delta stream, in bytes. */
 	public int getSize() {
 		return size;
 	}

 	/**
 	 * Insert a literal string of text, in UTF-8 encoding.
 	 *
 	 * @param text
 	 *            the string to insert.
 	 * @return true if the insert fits within the limit; false if the insert
 	 *         would cause the instruction stream to exceed the limit.
 	 * @throws IOException
 	 *             the instruction buffer can't store the instructions.
 	 */
 	public boolean insert(String text) throws IOException {
 		return insert(Constants.encode(text));
 	}

 	/**
 	 * Insert a literal binary sequence.
 	 *
 	 * @param text
 	 *            the binary to insert.
 	 * @return true if the insert fits within the limit; false if the insert
 	 *         would cause the instruction stream to exceed the limit.
 	 * @throws IOException
 	 *             the instruction buffer can't store the instructions.
 	 */
 	public boolean insert(byte[] text) throws IOException {
 		return insert(text, 0, text.length);
 	}

 	/**
 	 * Insert a literal binary sequence.
 	 *
 	 * @param text
 	 *            the binary to insert.
 	 * @param off
 	 *            offset within {@code text} to start copying from.
 	 * @param cnt
 	 *            number of bytes to insert.
 	 * @return true if the insert fits within the limit; false if the insert
 	 *         would cause the instruction stream to exceed the limit.
 	 * @throws IOException
 	 *             the instruction buffer can't store the instructions.
 	 */
 	public boolean insert(byte[] text, int off, int cnt)
 			throws IOException {
 		if (cnt <= 0)
 			return true;
 		if (limit != 0) {
 			int hdrs = cnt / MAX_INSERT_DATA_SIZE;
 			if (cnt % MAX_INSERT_DATA_SIZE != 0)
 				hdrs++;
 			if (limit < size + hdrs + cnt)
 				return false;
 		}
 		do {
 			int n = Math.min(MAX_INSERT_DATA_SIZE, cnt);
 			out.write((byte) n);
 			out.write(text, off, n);
 			off += n;
 			cnt -= n;
 			size += 1 + n;
 		} while (0 < cnt);
 		return true;
 	}

 	/**
 	 * Create a copy instruction to copy from the base object.
 	 *
 	 * @param offset
 	 *            position in the base object to copy from. This is absolute,
 	 *            from the beginning of the base.
 	 * @param cnt
 	 *            number of bytes to copy.
 	 * @return true if the copy fits within the limit; false if the copy
 	 *         would cause the instruction stream to exceed the limit.
 	 * @throws IOException
 	 *             the instruction buffer cannot store the instructions.
 	 */
 	public boolean copy(long offset, int cnt) throws IOException {
 		if (cnt == 0)
 			return true;

 		int p = 0;

 		// We cannot encode more than MAX_V2_COPY bytes in a single
 		// command, so encode that much and start a new command.
 		// This limit is imposed by the pack file format rules.
 		//
 		while (MAX_V2_COPY < cnt) {
 			p = encodeCopy(p, offset, MAX_V2_COPY);
 			offset += MAX_V2_COPY;
 			cnt -= MAX_V2_COPY;

 			if (buf.length < p + MAX_COPY_CMD_SIZE) {
 				if (limit != 0 && limit < size + p)
 					return false;
 				out.write(buf, 0, p);
 				size += p;
 				p = 0;
 			}
 		}

 		p = encodeCopy(p, offset, cnt);
 		if (limit != 0 && limit < size + p)
 			return false;
 		out.write(buf, 0, p);
 		size += p;
 		return true;
 	}

 	private int encodeCopy(int p, long offset, int cnt) {
 		int cmd = 0x80;
 		final int cmdPtr = p++; // save room for the command
 		byte b;

 		if ((b = (byte) (offset & 0xff)) != 0) {
 			cmd |= 0x01;
 			buf[p++] = b;
 		}
 		if ((b = (byte) ((offset >>> 8) & 0xff)) != 0) {
 			cmd |= 0x02;
 			buf[p++] = b;
 		}
 		if ((b = (byte) ((offset >>> 16) & 0xff)) != 0) {
 			cmd |= 0x04;
 			buf[p++] = b;
 		}
 		if ((b = (byte) ((offset >>> 24) & 0xff)) != 0) {
 			cmd |= 0x08;
 			buf[p++] = b;
 		}

 		if (cnt != MAX_V2_COPY) {
 			if ((b = (byte) (cnt & 0xff)) != 0) {
 				cmd |= 0x10;
 				buf[p++] = b;
 			}
 			if ((b = (byte) ((cnt >>> 8) & 0xff)) != 0) {
 				cmd |= 0x20;
 				buf[p++] = b;
 			}
 			if ((b = (byte) ((cnt >>> 16) & 0xff)) != 0) {
 				cmd |= 0x40;
 				buf[p++] = b;
 			}
 		}

 		buf[cmdPtr] = (byte) cmd;
 		return p;
 	}
 }
	/*
	* Copyright (C) 2010, Google Inc.
	* and other copyright owners as documented in the project's IP log.
	*
	* This program and the accompanying materials are made available
	* under the terms of the Eclipse Distribution License v1.0 which
	* accompanies this distribution, is reproduced below, and is
	* available at http://www.eclipse.org/org/documents/edl-v10.php
	*
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or
	* without modification, are permitted provided that the following
	* conditions are met:
	*
	* - Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	*
	* - Redistributions in binary form must reproduce the above
	* copyright notice, this list of conditions and the following
	* disclaimer in the documentation and/or other materials provided
	* with the distribution.
	*
	* - Neither the name of the Eclipse Foundation, Inc. nor the
	* names of its contributors may be used to endorse or promote
	* products derived from this software without specific prior
	* written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
	* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
	* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
	* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
	* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	package org.eclipse.jgit.internal.storage.pack;

	import java.io.IOException;
	import java.io.OutputStream;

	import org.eclipse.jgit.lib.Constants;

	/** Encodes an instruction stream for {@link BinaryDelta}. */
	public class DeltaEncoder {
	/**
	* Maximum number of bytes to be copied in pack v2 format.
	* <p>
	* Historical limitations have this at 64k, even though current delta
	* decoders recognize larger copy instructions.
	*/
	private static final int MAX_V2_COPY = 0x10000;

	/*
	* Maximum number of bytes to be copied in pack v3 format.
	*
	* Current delta decoders can recognize a copy instruction with a count that
	* is this large, but the historical limitation of {@link MAX_V2_COPY} is
	* still used.
	*/
	// private static final int MAX_V3_COPY = (0xff << 16) \| (0xff << 8) \| 0xff;

	/** Maximum number of bytes used by a copy instruction. */
	private static final int MAX_COPY_CMD_SIZE = 8;

	/** Maximum length that an an insert command can encode at once. */
	private static final int MAX_INSERT_DATA_SIZE = 127;

	private final OutputStream out;

	private final byte[] buf = new byte[MAX_COPY_CMD_SIZE * 4];

	private final int limit;

	private int size;

	/**
	* Create an encoder with no upper bound on the instruction stream size.
	*
	* @param out
	* buffer to store the instructions written.
	* @param baseSize
	* size of the base object, in bytes.
	* @param resultSize
	* size of the resulting object, after applying this instruction
	* stream to the base object, in bytes.
	* @throws IOException
	* the output buffer cannot store the instruction stream's
	* header with the size fields.
	*/
	public DeltaEncoder(OutputStream out, long baseSize, long resultSize)
	throws IOException {
	this(out, baseSize, resultSize, 0);
	}

	/**
	* Create an encoder with an upper limit on the instruction size.
	*
	* @param out
	* buffer to store the instructions written.
	* @param baseSize
	* size of the base object, in bytes.
	* @param resultSize
	* size of the resulting object, after applying this instruction
	* stream to the base object, in bytes.
	* @param limit
	* maximum number of bytes to write to the out buffer declaring
	* the stream is over limit and should be discarded. May be 0 to
	* specify an infinite limit.
	* @throws IOException
	* the output buffer cannot store the instruction stream's
	* header with the size fields.
	*/
	public DeltaEncoder(OutputStream out, long baseSize, long resultSize,
	int limit) throws IOException {
	this.out = out;
	this.limit = limit;
	writeVarint(baseSize);
	writeVarint(resultSize);
	}

	private void writeVarint(long sz) throws IOException {
	int p = 0;
	while (sz >= 0x80) {
	buf[p++] = (byte) (0x80 \| (((int) sz) & 0x7f));
	sz >>>= 7;
	}
	buf[p++] = (byte) (((int) sz) & 0x7f);
	size += p;
	if (limit == 0 \|\| size < limit)
	out.write(buf, 0, p);
	}

	/** @return current size of the delta stream, in bytes. */
	public int getSize() {
	return size;
	}

	/**
	* Insert a literal string of text, in UTF-8 encoding.
	*
	* @param text
	* the string to insert.
	* @return true if the insert fits within the limit; false if the insert
	* would cause the instruction stream to exceed the limit.
	* @throws IOException
	* the instruction buffer can't store the instructions.
	*/
	public boolean insert(String text) throws IOException {
	return insert(Constants.encode(text));
	}

	/**
	* Insert a literal binary sequence.
	*
	* @param text
	* the binary to insert.
	* @return true if the insert fits within the limit; false if the insert
	* would cause the instruction stream to exceed the limit.
	* @throws IOException
	* the instruction buffer can't store the instructions.
	*/
	public boolean insert(byte[] text) throws IOException {
	return insert(text, 0, text.length);
	}

	/**
	* Insert a literal binary sequence.
	*
	* @param text
	* the binary to insert.
	* @param off
	* offset within {@code text} to start copying from.
	* @param cnt
	* number of bytes to insert.
	* @return true if the insert fits within the limit; false if the insert
	* would cause the instruction stream to exceed the limit.
	* @throws IOException
	* the instruction buffer can't store the instructions.
	*/
	public boolean insert(byte[] text, int off, int cnt)
	throws IOException {
	if (cnt <= 0)
	return true;
	if (limit != 0) {
	int hdrs = cnt / MAX_INSERT_DATA_SIZE;
	if (cnt % MAX_INSERT_DATA_SIZE != 0)
	hdrs++;
	if (limit < size + hdrs + cnt)
	return false;
	}
	do {
	int n = Math.min(MAX_INSERT_DATA_SIZE, cnt);
	out.write((byte) n);
	out.write(text, off, n);
	off += n;
	cnt -= n;
	size += 1 + n;
	} while (0 < cnt);
	return true;
	}

	/**
	* Create a copy instruction to copy from the base object.
	*
	* @param offset
	* position in the base object to copy from. This is absolute,
	* from the beginning of the base.
	* @param cnt
	* number of bytes to copy.
	* @return true if the copy fits within the limit; false if the copy
	* would cause the instruction stream to exceed the limit.
	* @throws IOException
	* the instruction buffer cannot store the instructions.
	*/
	public boolean copy(long offset, int cnt) throws IOException {
	if (cnt == 0)
	return true;

	int p = 0;

	// We cannot encode more than MAX_V2_COPY bytes in a single
	// command, so encode that much and start a new command.
	// This limit is imposed by the pack file format rules.
	//
	while (MAX_V2_COPY < cnt) {
	p = encodeCopy(p, offset, MAX_V2_COPY);
	offset += MAX_V2_COPY;
	cnt -= MAX_V2_COPY;

	if (buf.length < p + MAX_COPY_CMD_SIZE) {
	if (limit != 0 && limit < size + p)
	return false;
	out.write(buf, 0, p);
	size += p;
	p = 0;
	}
	}

	p = encodeCopy(p, offset, cnt);
	if (limit != 0 && limit < size + p)
	return false;
	out.write(buf, 0, p);
	size += p;
	return true;
	}

	private int encodeCopy(int p, long offset, int cnt) {
	int cmd = 0x80;
	final int cmdPtr = p++; // save room for the command
	byte b;

	if ((b = (byte) (offset & 0xff)) != 0) {
	cmd \|= 0x01;
	buf[p++] = b;
	}
	if ((b = (byte) ((offset >>> 8) & 0xff)) != 0) {
	cmd \|= 0x02;
	buf[p++] = b;
	}
	if ((b = (byte) ((offset >>> 16) & 0xff)) != 0) {
	cmd \|= 0x04;
	buf[p++] = b;
	}
	if ((b = (byte) ((offset >>> 24) & 0xff)) != 0) {
	cmd \|= 0x08;
	buf[p++] = b;
	}

	if (cnt != MAX_V2_COPY) {
	if ((b = (byte) (cnt & 0xff)) != 0) {
	cmd \|= 0x10;
	buf[p++] = b;
	}
	if ((b = (byte) ((cnt >>> 8) & 0xff)) != 0) {
	cmd \|= 0x20;
	buf[p++] = b;
	}
	if ((b = (byte) ((cnt >>> 16) & 0xff)) != 0) {
	cmd \|= 0x40;
	buf[p++] = b;
	}
	}

	buf[cmdPtr] = (byte) cmd;
	return p;
	}
	}