jgit/org.eclipse.jgit/src/org/eclipse/jgit/diff/RawText.java

/*
 * Copyright (C) 2009, Google Inc.
 * Copyright (C) 2008-2009, Johannes E. Schindelin <johannes.schindelin@gmx.de>
 * 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.diff;

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

import org.eclipse.jgit.util.IO;
import org.eclipse.jgit.util.IntList;
import org.eclipse.jgit.util.RawParseUtils;

/**
 * A Sequence supporting UNIX formatted text in byte[] format.
 * <p>
 * Elements of the sequence are the lines of the file, as delimited by the UNIX
 * newline character ('\n'). The file content is treated as 8 bit binary text,
 * with no assumptions or requirements on character encoding.
 * <p>
 * Note that the first line of the file is element 0, as defined by the Sequence
 * interface API. Traditionally in a text editor a patch file the first line is
 * line number 1. Callers may need to subtract 1 prior to invoking methods if
 * they are converting from "line number" to "element index".
 */
public class RawText implements Sequence {
	/** Number of bytes to check for heuristics in {@link #isBinary(byte[])} */
	private static final int FIRST_FEW_BYTES = 8000;

	/** The file content for this sequence. */
	protected final byte[] content;

	/** Map of line number to starting position within {@link #content}. */
	protected final IntList lines;

	/** Hash code for each line, for fast equality elimination. */
	protected final IntList hashes;

	/**
	 * Create a new sequence from an existing content byte array.
	 * <p>
	 * The entire array (indexes 0 through length-1) is used as the content.
	 *
	 * @param input
	 *            the content array. The array is never modified, so passing
	 *            through cached arrays is safe.
	 */
	public RawText(final byte[] input) {
		content = input;
		lines = RawParseUtils.lineMap(content, 0, content.length);
		hashes = computeHashes();
	}

	/**
	 * Create a new sequence from a file.
	 * <p>
	 * The entire file contents are used.
	 *
	 * @param file
	 *            the text file.
	 * @throws IOException if Exceptions occur while reading the file
	 */
	public RawText(File file) throws IOException {
		this(IO.readFully(file));
	}

	public int size() {
		// The line map is always 2 entries larger than the number of lines in
		// the file. Index 0 is padded out/unused. The last index is the total
		// length of the buffer, and acts as a sentinel.
		//
		return lines.size() - 2;
	}

	public boolean equals(final int i, final Sequence other, final int j) {
		return equals(this, i + 1, (RawText) other, j + 1);
	}

	private static boolean equals(final RawText a, final int ai,
			final RawText b, final int bi) {
		if (a.hashes.get(ai) != b.hashes.get(bi))
			return false;

		int as = a.lines.get(ai);
		int bs = b.lines.get(bi);
		final int ae = a.lines.get(ai + 1);
		final int be = b.lines.get(bi + 1);

		if (ae - as != be - bs)
			return false;

		while (as < ae) {
			if (a.content[as++] != b.content[bs++])
				return false;
		}
		return true;
	}

	/**
	 * Write a specific line to the output stream, without its trailing LF.
	 * <p>
	 * The specified line is copied as-is, with no character encoding
	 * translation performed.
	 * <p>
	 * If the specified line ends with an LF ('\n'), the LF is <b>not</b>
	 * copied. It is up to the caller to write the LF, if desired, between
	 * output lines.
	 *
	 * @param out
	 *            stream to copy the line data onto.
	 * @param i
	 *            index of the line to extract. Note this is 0-based, so line
	 *            number 1 is actually index 0.
	 * @throws IOException
	 *             the stream write operation failed.
	 */
	public void writeLine(final OutputStream out, final int i)
			throws IOException {
		final int start = lines.get(i + 1);
		int end = lines.get(i + 2);
		if (content[end - 1] == '\n')
			end--;
		out.write(content, start, end - start);
	}

	/**
	 * Determine if the file ends with a LF ('\n').
	 *
	 * @return true if the last line has an LF; false otherwise.
	 */
	public boolean isMissingNewlineAtEnd() {
		final int end = lines.get(lines.size() - 1);
		if (end == 0)
			return true;
		return content[end - 1] != '\n';
	}

	private IntList computeHashes() {
		final IntList r = new IntList(lines.size());
		r.add(0);
		for (int lno = 1; lno < lines.size() - 1; lno++) {
			final int ptr = lines.get(lno);
			final int end = lines.get(lno + 1);
			r.add(hashLine(content, ptr, end));
		}
		r.add(0);
		return r;
	}

	/**
	 * Compute a hash code for a single line.
	 *
	 * @param raw
	 *            the raw file content.
	 * @param ptr
	 *            first byte of the content line to hash.
	 * @param end
	 *            1 past the last byte of the content line.
	 * @return hash code for the region <code>[ptr, end)</code> of raw.
	 */
	protected int hashLine(final byte[] raw, int ptr, final int end) {
		int hash = 5381;
		for (; ptr < end; ptr++)
			hash = (hash << 5) ^ (raw[ptr] & 0xff);
		return hash;
	}

	/**
	 * Determine heuristically whether a byte array represents binary (as
	 * opposed to text) content.
	 *
	 * @param raw
	 *            the raw file content.
	 * @return true if raw is likely to be a binary file, false otherwise
	 */
	public static boolean isBinary(byte[] raw) {
		// Same heuristic as C Git
		int size = raw.length > FIRST_FEW_BYTES ? FIRST_FEW_BYTES : raw.length;
		for (int ptr = 0; ptr < size; ptr++)
			if (raw[ptr] == '\0')
				return true;

		return false;
	}
}