PacketLineOut.java

/*
 * Copyright (C) 2008, 2010 Google Inc.
 * Copyright (C) 2008, 2009 Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2008, 2020 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.transport;

import static java.nio.charset.StandardCharsets.UTF_8;

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

import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.util.RawParseUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Write Git style pkt-line formatting to an output stream.
 * <p>
 * This class is not thread safe and may issue multiple writes to the underlying
 * stream for each method call made.
 * <p>
 * This class performs no buffering on its own. This makes it suitable to
 * interleave writes performed by this class with writes performed directly
 * against the underlying OutputStream.
 */
public class PacketLineOut {

    private static final Logger log = LoggerFactory.getLogger(PacketLineOut.class);

    private final OutputStream out;

    private final byte[] lenbuffer;

    private final boolean logEnabled;

    private boolean flushOnEnd;

    private boolean usingSideband;

    /**
     * Create a new packet line writer.
     *
     * @param outputStream
     *            stream.
     */
    public PacketLineOut(OutputStream outputStream) {
        this(outputStream, true);
    }

    /**
     * Create a new packet line writer that potentially doesn't log.
     *
     * @param outputStream
     *            stream.
     * @param enableLogging
     *            {@code false} to suppress all logging; {@code true} to log
     *            normally
     * @since 5.11
     */
    public PacketLineOut(OutputStream outputStream, boolean enableLogging) {
        out = outputStream;
        lenbuffer = new byte[5];
        flushOnEnd = true;
        logEnabled = enableLogging;
    }

    /**
     * Set the flush behavior during {@link #end()}.
     *
     * @param flushOnEnd
     *            if true, a flush-pkt written during {@link #end()} also
     *            flushes the underlying stream.
     */
    public void setFlushOnEnd(boolean flushOnEnd) {
        this.flushOnEnd = flushOnEnd;
    }

    /**
     * @return whether to add a sideband designator to each non-flush and
     *     non-delim packet
     * @see #setUsingSideband
     * @since 5.5
     */
    public boolean isUsingSideband() {
        return usingSideband;
    }

    /**
     * @param value If true, when writing packet lines, add, as the first
     *     byte, a sideband designator to each non-flush and non-delim
     *     packet. See pack-protocol.txt and protocol-v2.txt from the Git
     *     project for more information, specifically the "side-band" and
     *     "sideband-all" sections.
     * @since 5.5
     */
    public void setUsingSideband(boolean value) {
        this.usingSideband = value;
    }

    /**
     * Write a UTF-8 encoded string as a single length-delimited packet.
     *
     * @param s
     *            string to write.
     * @throws java.io.IOException
     *             the packet could not be written, the stream is corrupted as
     *             the packet may have been only partially written.
     */
    public void writeString(String s) throws IOException {
        writePacket(Constants.encode(s));
    }

    /**
     * Write a binary packet to the stream.
     *
     * @param packet
     *            the packet to write; the length of the packet is equal to the
     *            size of the byte array.
     * @throws java.io.IOException
     *             the packet could not be written, the stream is corrupted as
     *             the packet may have been only partially written.
     */
    public void writePacket(byte[] packet) throws IOException {
        writePacket(packet, 0, packet.length);
    }

    /**
     * Write a binary packet to the stream.
     *
     * @param buf
     *            the packet to write
     * @param pos
     *            first index within {@code buf}.
     * @param len
     *            number of bytes to write.
     * @throws java.io.IOException
     *             the packet could not be written, the stream is corrupted as
     *             the packet may have been only partially written.
     * @since 4.5
     */
    public void writePacket(byte[] buf, int pos, int len) throws IOException {
        if (usingSideband) {
            formatLength(len + 5);
            out.write(lenbuffer, 0, 4);
            out.write(1);
        } else {
            formatLength(len + 4);
            out.write(lenbuffer, 0, 4);
        }
        out.write(buf, pos, len);
        if (logEnabled && log.isDebugEnabled()) {
            // Escape a trailing \n to avoid empty lines in the log.
            if (len > 0 && buf[pos + len - 1] == '\n') {
                log.debug(
                        "git> " + RawParseUtils.decode(UTF_8, buf, pos, len - 1) //$NON-NLS-1$
                                + "\\n"); //$NON-NLS-1$
            } else {
                log.debug("git> " + RawParseUtils.decode(UTF_8, buf, pos, len)); //$NON-NLS-1$
            }
        }
    }

    /**
     * Write a packet delim marker (0001).
     *
     * @throws java.io.IOException
     *             the marker could not be written, the stream is corrupted
     *             as the marker may have been only partially written.
     * @since 5.0
     */
    public void writeDelim() throws IOException {
        formatLength(1);
        out.write(lenbuffer, 0, 4);
        if (logEnabled && log.isDebugEnabled()) {
            log.debug("git> 0001"); //$NON-NLS-1$
        }
    }

    /**
     * Write a packet end marker, sometimes referred to as a flush command.
     * <p>
     * Technically this is a magical packet type which can be detected
     * separately from an empty string or an empty packet.
     * <p>
     * Implicitly performs a flush on the underlying OutputStream to ensure the
     * peer will receive all data written thus far.
     *
     * @throws java.io.IOException
     *             the end marker could not be written, the stream is corrupted
     *             as the end marker may have been only partially written.
     */
    public void end() throws IOException {
        formatLength(0);
        out.write(lenbuffer, 0, 4);
        if (logEnabled && log.isDebugEnabled()) {
            log.debug("git> 0000"); //$NON-NLS-1$
        }
        if (flushOnEnd) {
            flush();
        }
    }

    /**
     * Flush the underlying OutputStream.
     * <p>
     * Performs a flush on the underlying OutputStream to ensure the peer will
     * receive all data written thus far.
     *
     * @throws java.io.IOException
     *             the underlying stream failed to flush.
     */
    public void flush() throws IOException {
        out.flush();
    }

    private static final byte[] hexchar = { '0', '1', '2', '3', '4', '5', '6',
            '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

    private void formatLength(int w) {
        formatLength(lenbuffer, w);
    }

    static void formatLength(byte[] lenbuffer, int w) {
        int o = 3;
        while (o >= 0 && w != 0) {
            lenbuffer[o--] = hexchar[w & 0xf];
            w >>>= 4;
        }
        while (o >= 0)
            lenbuffer[o--] = '0';
    }
}