# ContentTypeDetector.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.internal;

    import java.io.BufferedInputStream;
    import java.io.IOException;
    import java.io.InputStream;

    import org.objectweb.asm.Opcodes;

    /**
     * Detector for content types of binary streams based on a magic headers.
     */
    public class ContentTypeDetector {

    	/** Unknown file type */
    	public static final int UNKNOWN = -1;

    	/** File type Java class */
    	public static final int CLASSFILE = 0xcafebabe;

    	/** File type ZIP archive */
    	public static final int ZIPFILE = 0x504b0304;

    	/** File type GZIP compressed Data */
    	public static final int GZFILE = 0x1f8b0000;

    	/** File type Pack200 archive */
    	public static final int PACK200FILE = 0xcafed00d;

    	private static final int BUFFER_SIZE = 8;

    	private final InputStream in;

    	private final int type;

    	/**
    	 * Creates a new detector based on the given input. To process the complete
    	 * original input afterwards use the stream returned by
    	 * {@link #getInputStream()}.
    	 *
    	 * @param in
    	 *            input to read the header from
    	 * @throws IOException
    	 *             if the stream can't be read
    	 */
    	public ContentTypeDetector(final InputStream in) throws IOException {
    		if (in.markSupported()) {
    			this.in = in;
    		} else {
    			this.in = new BufferedInputStream(in, BUFFER_SIZE);
    		}
    		this.in.mark(BUFFER_SIZE);
    		this.type = determineType(this.in);
    		this.in.reset();
    	}

    	private static int determineType(final InputStream in) throws IOException {
    		final int header = readInt(in);
    		switch (header) {
    		case ZIPFILE:
    			return ZIPFILE;
    		case PACK200FILE:
    			return PACK200FILE;
    		case CLASSFILE:
    			// also verify version to distinguish from Mach Object files:
    			switch (readInt(in)) {
    			case Opcodes.V1_1:
    			case Opcodes.V1_2:
    			case Opcodes.V1_3:
    			case Opcodes.V1_4:
    			case Opcodes.V1_5:
    			case Opcodes.V1_6:
    			case Opcodes.V1_7:
    				return CLASSFILE;
    			}
    		}
    		if ((header & 0xffff0000) == GZFILE) {
    			return GZFILE;
    		}
    		return UNKNOWN;
    	}

    	private static int readInt(final InputStream in) throws IOException {
    		return in.read() << 24 | in.read() << 16 | in.read() << 8 | in.read();
    	}

    	/**
    	 * Returns an input stream instance to read the complete content (including
    	 * the header) of the underlying stream.
    	 *
    	 * @return input stream containing the complete content
    	 */
    	public InputStream getInputStream() {
    		return in;
    	}

    	/**
    	 * Returns the detected file type.
    	 *
    	 * @return file type
    	 */
    	public int getType() {
    		return type;
    	}

    }