bundles/org.eclipse.core.runtime/src/org/eclipse/core/internal/content/TextContentDescriber.java

/*******************************************************************************
 * Copyright (c) 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.internal.content;

import java.io.*;
import org.eclipse.core.runtime.QualifiedName;
import org.eclipse.core.runtime.content.IContentDescription;
import org.eclipse.core.runtime.content.ITextContentDescriber;

/**
 * This class provides internal basis for text-based content describers. 
 * 
 * <p>
 * Note: do not add protected/public members to this class if you don't intend to 
 * make them public API.
 * </p>  
 * 
 * @see org.eclipse.core.runtime.content.XMLRootElementContentDescriber
 * @since 3.0
 */
public class TextContentDescriber implements ITextContentDescriber {

	private final static QualifiedName[] SUPPORTED_OPTIONS = {IContentDescription.BYTE_ORDER_MARK};

	/*
	 *  (non-Javadoc)
	 * @see org.eclipse.core.runtime.content.ITextContentDescriber#describe(java.io.Reader, org.eclipse.core.runtime.content.IContentDescription)
	 */
	public int describe(Reader contents, IContentDescription description) throws IOException {
		// we want to be pretty loose on detecting the text content type  
		return INDETERMINATE;
	}

	/*
	 *  (non-Javadoc)
	 * @see org.eclipse.core.runtime.content.IContentDescriber#describe(java.io.InputStream, org.eclipse.core.runtime.content.IContentDescription)
	 */
	public int describe(InputStream contents, IContentDescription description) throws IOException {
		if (description == null || !description.isRequested(IContentDescription.BYTE_ORDER_MARK))
			return INDETERMINATE;
		byte[] bom = getByteOrderMark(contents);
		if (bom != null)
			description.setProperty(IContentDescription.BYTE_ORDER_MARK, bom);
		// we want to be pretty loose on detecting the text content type  		
		return INDETERMINATE;
	}

	/*
	 *  (non-Javadoc)
	 * @see org.eclipse.core.runtime.content.IContentDescriber#getSupportedOptions()
	 */
	public QualifiedName[] getSupportedOptions() {
		return SUPPORTED_OPTIONS;
	}

	byte[] getByteOrderMark(InputStream input) throws IOException {
		int first = (input.read() & 0xFF);//converts unsigned byte to int
		int second = (input.read() & 0xFF);
		if (first == -1 || second == -1)
			return null;
		//look for the UTF-16 Byte Order Mark (BOM)
		if (first == 0xFE && second == 0xFF)
			return IContentDescription.BOM_UTF_16BE;
		if (first == 0xFF && second == 0xFE)
			return IContentDescription.BOM_UTF_16LE;
		int third = (input.read() & 0xFF);
		if (third == -1)
			return null;
		//look for the UTF-8 BOM
		if (first == 0xEF && second == 0xBB && third == 0xBF)
			return IContentDescription.BOM_UTF_8;
		return null;
	}

}