source: other-projects/rsyntax-textarea/src/java/org/fife/io/UnicodeReader.java@ 25584

/*
 * 09/23/2004
 *
 * UnicodeReader.java - A reader for Unicode input streams that is capable of
 * discerning which particular encoding is being used via the BOM.
 * 
 * This library is distributed under a modified BSD license.  See the included
 * RSyntaxTextArea.License.txt file for details.
 */
package org.fife.io;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PushbackInputStream;
import java.io.Reader;


/**
 * A reader capable of identifying Unicode streams by their BOMs.  This class
 * will recognize the following encodings:
 * <ul>
 *   <li>UTF-8
 *   <li>UTF-16LE
 *   <li>UTF-16BE
 *   <li>UTF-32LE
 *   <li>UTF-32BE
 * </ul>
 * If the stream is not found to be any of the above, then a default encoding
 * is used for reading.  The user can specify this default encoding, or a system
 * default will be used.<p>
 *
 * For optimum performance, it is recommended that you wrap all instances of
 * <code>UnicodeReader</code> with a <code>java.io.BufferedReader</code>.<p>
 *
 * This class is mostly ripped off from the workaround in the description of
 * Java Bug 4508058.
 *
 * @author Robert Futrell
 * @version 0.9
 */
public class UnicodeReader extends Reader {

    /**
     * The input stream from which we're really reading.
     */
    private InputStreamReader internalIn = null;

    /**
     * The encoding being used.  We keep our own instead of using the string
     * returned by <code>java.io.InputStreamReader</code> since that class
     * does not return user-friendly names.
     */
    private String encoding;

    /**
     * The size of a BOM.
     */
    private static final int BOM_SIZE = 4;


    /**
     * This utility constructor is here because you will usually use a
     * <code>UnicodeReader</code> on files.<p>
     * Creates a reader using the encoding specified by the BOM in the file;
     * if there is no recognized BOM, then a system default encoding is used.
     *
     * @param file The file from which you want to read.
     * @throws IOException If an error occurs when checking for/reading the
     *         BOM.
     * @throws FileNotFoundException If the file does not exist, is a
     *         directory, or cannot be opened for reading.
     * @throws SecurityException If a security manager exists and its
     *         checkRead method denies read access to the file.
     */
    public UnicodeReader(String file) throws IOException,
                            FileNotFoundException, SecurityException {
        this(new File(file));
    }


    /**
     * This utility constructor is here because you will usually use a
     * <code>UnicodeReader</code> on files.<p>
     * Creates a reader using the encoding specified by the BOM in the file;
     * if there is no recognized BOM, then a system default encoding is used.
     *
     * @param file The file from which you want to read.
     * @throws IOException If an error occurs when checking for/reading the
     *         BOM.
     * @throws FileNotFoundException If the file does not exist, is a
     *         directory, or cannot be opened for reading.
     * @throws SecurityException If a security manager exists and its
     *         checkRead method denies read access to the file.
     */
    public UnicodeReader(File file) throws IOException, FileNotFoundException,
                                    SecurityException {
        this(new FileInputStream(file));
    }


    /**
     * This utility constructor is here because you will usually use a
     * <code>UnicodeReader</code> on files.<p>
     * Creates a reader using the encoding specified by the BOM in the file;
     * if there is no recognized BOM, then a specified default encoding is
     * used.
     *
     * @param file The file from which you want to read.
     * @param defaultEncoding The encoding to use if no BOM is found.  If
     *        this value is <code>null</code>, a system default is used.
     * @throws IOException If an error occurs when checking for/reading the
     *         BOM.
     * @throws FileNotFoundException If the file does not exist, is a
     *         directory, or cannot be opened for reading.
     * @throws SecurityException If a security manager exists and its
     *         checkRead method denies read access to the file.
     */
    public UnicodeReader(File file, String defaultEncoding)
                        throws IOException, FileNotFoundException,
                                SecurityException {
        this(new FileInputStream(file), defaultEncoding);
    }


    /**
     * Creates a reader using the encoding specified by the BOM in the file;
     * if there is no recognized BOM, then a system default encoding is used.
     *
     * @param in The input stream from which to read.
     * @throws IOException If an error occurs when checking for/reading the
     *         BOM.
     */
    public UnicodeReader(InputStream in) throws IOException {
        this(in, null);
    }


    /**
     * Creates a reader using the encoding specified by the BOM in the file;
     * if there is no recognized BOM, then <code>defaultEncoding</code> is
     * used.
     *
     * @param in The input stream from which to read.
     * @param defaultEncoding The encoding to use if no recognized BOM is
     *        found.  If this value is <code>null</code>, a system default
     *        is used.
     * @throws IOException If an error occurs when checking for/reading the
     *         BOM.
     */
    public UnicodeReader(InputStream in, String defaultEncoding)
                                    throws IOException {
        init(in, defaultEncoding);
    }


    /**
     * Closes this reader.
     */
    public void close() throws IOException {
        internalIn.close();
    }


    /**
     * Returns the encoding being used to read this input stream (i.e., the
     * encoding of the file).  If a BOM was recognized, then the specific
     * Unicode type is returned; otherwise, either the default encoding passed
     * into the constructor or the system default is returned.
     *
     * @return The encoding of the stream.
     */
    public String getEncoding() {
        return encoding;
    }


    /**
     * Read-ahead four bytes and check for BOM marks. Extra bytes are
     * unread back to the stream, only BOM bytes are skipped.
     *
     * @param defaultEncoding The encoding to use if no BOM was recognized.  If
     *        this value is <code>null</code>, then a system default is used.
     * @throws IOException If an error occurs when trying to read a BOM.
     */
    protected void init(InputStream in, String defaultEncoding)
                                            throws IOException {

        PushbackInputStream tempIn = new PushbackInputStream(in, BOM_SIZE);

        byte bom[] = new byte[BOM_SIZE];
        int n, unread;
        n = tempIn.read(bom, 0, bom.length);

        if ((bom[0]==(byte)0x00) && (bom[1]==(byte)0x00) &&
                (bom[2]==(byte)0xFE) && (bom[3]==(byte)0xFF)) {
            encoding = "UTF-32BE";
            unread = n - 4;
        }

        else if (n==BOM_SIZE && // Last 2 bytes are 0; could be an empty UTF-16
                (bom[0]==(byte)0xFF) && (bom[1]==(byte)0xFE) &&
                (bom[2]==(byte)0x00) && (bom[3]==(byte)0x00)) {
            encoding = "UTF-32LE";
            unread = n - 4;
        }
        
        else if ((bom[0]==(byte)0xEF) &&
            (bom[1]==(byte)0xBB) &&
            (bom[2]==(byte)0xBF)) {
            encoding = "UTF-8";
            unread = n - 3;
        }

        else if ((bom[0]==(byte)0xFE) && (bom[1] == (byte)0xFF)) {
            encoding = "UTF-16BE";
            unread = n - 2;
        }

        else if ((bom[0]==(byte)0xFF) && (bom[1]== (byte)0xFE)) {
            encoding = "UTF-16LE";
            unread = n - 2;
        }

        else {
            // Unicode BOM mark not found, unread all bytes
            encoding = defaultEncoding;
            unread = n;
        }

        if (unread > 0)
            tempIn.unread(bom, (n - unread), unread);
        else if (unread < -1)
            tempIn.unread(bom, 0, 0);

        // Use given encoding
        if (encoding == null) {
            internalIn = new InputStreamReader(tempIn);
            encoding = internalIn.getEncoding(); // Get the default.
        }
        else {
            internalIn = new InputStreamReader(tempIn, encoding);
        }

    }


    /**
     * Read characters into a portion of an array. This method will block until
     * some input is available, an I/O error occurs, or the end of the stream
     * is reached.
     *
     * @param cbuf The buffer into which to read.
     * @param off The offset at which to start storing characters.
     * @param len The maximum number of characters to read.
     *
     * @return The number of characters read, or <code>-1</code> if the end
     *         of the stream has been reached.
     */
    public int read(char[] cbuf, int off, int len) throws IOException {
        return internalIn.read(cbuf, off, len);
    }


}