SideBandOutputStream.java

/*
 * Copyright (C) 2008-2010, Google Inc. 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 java.io.IOException;
import java.io.OutputStream;
import java.text.MessageFormat;

import org.eclipse.jgit.internal.JGitText;

/**
 * Multiplexes data and progress messages.
 * <p>
 * This stream is buffered at packet sizes, so the caller doesn't need to wrap
 * it in yet another buffered stream.
 *
 * @since 2.0
 */
public class SideBandOutputStream extends OutputStream {
    /** Channel used for pack data. */
    public static final int CH_DATA = SideBandInputStream.CH_DATA;

    /** Channel used for progress messages. */
    public static final int CH_PROGRESS = SideBandInputStream.CH_PROGRESS;

    /** Channel used for error messages. */
    public static final int CH_ERROR = SideBandInputStream.CH_ERROR;

    /** Default buffer size for a small amount of data. */
    public static final int SMALL_BUF = 1000;

    /** Maximum buffer size for a single packet of sideband data. */
    public static final int MAX_BUF = 65520;

    static final int HDR_SIZE = 5;

    private final OutputStream out;

    private final byte[] buffer;

    /**
     * Number of bytes in {@link #buffer} that are valid data.
     * <p>
     * Initialized to {@link #HDR_SIZE} if there is no application data in the
     * buffer, as the packet header always appears at the start of the buffer.
     */
    private int cnt;

    /**
     * Create a new stream to write side band packets.
     *
     * @param chan
     *            channel number to prefix all packets with, so the remote side
     *            can demultiplex the stream and get back the original data.
     *            Must be in the range [1, 255].
     * @param sz
     *            maximum size of a data packet within the stream. The remote
     *            side needs to agree to the packet size to prevent buffer
     *            overflows. Must be in the range [HDR_SIZE + 1, MAX_BUF).
     * @param os
     *            stream that the packets are written onto. This stream should
     *            be attached to a SideBandInputStream on the remote side.
     */
    public SideBandOutputStream(int chan, int sz, OutputStream os) {
        if (chan <= 0 || chan > 255)
            throw new IllegalArgumentException(MessageFormat.format(
                    JGitText.get().channelMustBeInRange1_255,
                    Integer.valueOf(chan)));
        if (sz <= HDR_SIZE)
            throw new IllegalArgumentException(MessageFormat.format(
                    JGitText.get().packetSizeMustBeAtLeast,
                    Integer.valueOf(sz), Integer.valueOf(HDR_SIZE)));
        else if (MAX_BUF < sz)
            throw new IllegalArgumentException(MessageFormat.format(
                    JGitText.get().packetSizeMustBeAtMost, Integer.valueOf(sz),
                    Integer.valueOf(MAX_BUF)));

        out = os;
        buffer = new byte[sz];
        buffer[4] = (byte) chan;
        cnt = HDR_SIZE;
    }

    void flushBuffer() throws IOException {
        if (HDR_SIZE < cnt)
            writeBuffer();
    }

    /** {@inheritDoc} */
    @Override
    public void flush() throws IOException {
        flushBuffer();
        out.flush();
    }

    /** {@inheritDoc} */
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        while (0 < len) {
            int capacity = buffer.length - cnt;
            if (cnt == HDR_SIZE && capacity < len) {
                // Our block to write is bigger than the packet size,
                // stream it out as-is to avoid unnecessary copies.
                PacketLineOut.formatLength(buffer, buffer.length);
                out.write(buffer, 0, HDR_SIZE);
                out.write(b, off, capacity);
                off += capacity;
                len -= capacity;

            } else {
                if (capacity == 0)
                    writeBuffer();

                int n = Math.min(len, capacity);
                System.arraycopy(b, off, buffer, cnt, n);
                cnt += n;
                off += n;
                len -= n;
            }
        }
    }

    /** {@inheritDoc} */
    @Override
    public void write(int b) throws IOException {
        if (cnt == buffer.length)
            writeBuffer();
        buffer[cnt++] = (byte) b;
    }

    private void writeBuffer() throws IOException {
        PacketLineOut.formatLength(buffer, cnt);
        out.write(buffer, 0, cnt);
        cnt = HDR_SIZE;
    }
}