# ExecutionDataWriter.java

    /*******************************************************************************
     * Copyright (c) 2009, 2013 Mountainminds GmbH & Co. KG and Contributors
     * All rights reserved. This program and the accompanying materials
     * are made available under the terms of the Eclipse Public License v1.0
     * which accompanies this distribution, and is available at
     * http://www.eclipse.org/legal/epl-v10.html
     *
     * Contributors:
     *    Marc R. Hoffmann - initial API and implementation
     *
     *******************************************************************************/
    package org.jacoco.core.data;

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

    import org.jacoco.core.internal.data.CompactDataOutput;

    /**
     * Serialization of execution data into binary streams.
     */
    public class ExecutionDataWriter implements ISessionInfoVisitor,
    		IExecutionDataVisitor {

    	/** File format version, will be incremented for each incompatible change. */
    	public static final char FORMAT_VERSION = 0x1006;

    	/** Magic number in header for file format identification. */
    	public static final char MAGIC_NUMBER = 0xC0C0;

    	/** Block identifier for file headers. */
    	public static final byte BLOCK_HEADER = 0x01;

    	/** Block identifier for session information. */
    	public static final byte BLOCK_SESSIONINFO = 0x10;

    	/** Block identifier for execution data of a single class. */
    	public static final byte BLOCK_EXECUTIONDATA = 0x11;

    	/** Underlying data output */
    	protected final CompactDataOutput out;

    	/**
    	 * Creates a new writer based on the given output stream. Depending on the
    	 * nature of the underlying stream output should be buffered as most data is
    	 * written in single bytes.
    	 *
    	 * @param output
    	 *            binary stream to write execution data to
    	 * @throws IOException
    	 *             if the header can't be written
    	 */
    	public ExecutionDataWriter(final OutputStream output) throws IOException {
    		this.out = new CompactDataOutput(output);
    		writeHeader();
    	}

    	/**
    	 * Writes an file header to identify the stream and its protocol version.
    	 *
    	 * @throws IOException
    	 *             if the header can't be written
    	 */
    	private void writeHeader() throws IOException {
    		out.writeByte(BLOCK_HEADER);
    		out.writeChar(MAGIC_NUMBER);
    		out.writeChar(FORMAT_VERSION);
    	}

    	/**
    	 * Flushes the underlying stream.
    	 *
    	 * @throws IOException
    	 *             if the underlying stream can't be flushed
    	 */
    	public void flush() throws IOException {
    		out.flush();
    	}

    	public void visitSessionInfo(final SessionInfo info) {
    		try {
    			out.writeByte(BLOCK_SESSIONINFO);
    			out.writeUTF(info.getId());
    			out.writeLong(info.getStartTimeStamp());
    			out.writeLong(info.getDumpTimeStamp());
    		} catch (final IOException e) {
    			throw new RuntimeException(e);
    		}
    	}

    	public void visitClassExecution(final ExecutionData data) {
    		try {
    			out.writeByte(BLOCK_EXECUTIONDATA);
    			out.writeLong(data.getId());
    			out.writeUTF(data.getName());
    			out.writeBooleanArray(data.getProbes());
    		} catch (final IOException e) {
    			throw new RuntimeException(e);
    		}
    	}

    	/**
    	 * Returns the first bytes of a file that represents a valid execution data
    	 * file. In any case every execution data file starts with the three bytes
    	 * <code>0x01 0xC0 0xC0</code>.
    	 *
    	 * @return first bytes of a execution data file
    	 */
    	public static final byte[] getFileHeader() {
    		final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    		try {
    			new ExecutionDataWriter(buffer);
    		} catch (final IOException e) {
    			// Must not happen with ByteArrayOutputStream
    			throw new AssertionError(e);
    		}
    		return buffer.toByteArray();
    	}

    }