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/* ____________________________________________________________________________
 * 
 * File:    UnicodeBOMInputStream.java
 * Author:  Gregory Pakosz.
 * Date:    02 - November - 2005    
 * ____________________________________________________________________________
 */
package javolution.xml.internal.stream;

import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;

/**
 * The UnicodeBOMInputStream class wraps any
 * InputStream and detects the presence of any Unicode BOM
 * (Byte Order Mark) at its beginning, as defined by
 * RFC 3629 - UTF-8, a transformation format of ISO 10646
 * 
 * 
The
 * Unicode FAQ
 * defines 5 types of BOMs:

 * 00 00 FE FF  = UTF-32, big-endian
 * FF FE 00 00  = UTF-32, little-endian
 * FE FF        = UTF-16, big-endian
 * FF FE        = UTF-16, little-endian
 * EF BB BF     = UTF-8
 * 

 * 
 * 
Use the {@link #getBOM()} method to know whether a BOM has been detected
 * or not.
 * 
 * Use the {@link #skipBOM()} method to remove the detected BOM from the
 * wrapped InputStream object.
 */
public class UnicodeBomInputStream extends InputStream {
    private final PushbackInputStream in;
    private final BOM bom;
    private boolean skipped = false;

    /**
     * Constructs a new UnicodeBOMInputStream that wraps the
     * specified InputStream.
     *
     * @param inputStream an InputStream.
     * @throws NullPointerException when inputStream is
     *                              null.
     * @throws IOException          on reading from the specified InputStream
     *                              when trying to detect the Unicode BOM.
     */
    public UnicodeBomInputStream(final InputStream inputStream) throws NullPointerException, IOException
    {
        if (inputStream == null)
            throw new NullPointerException("invalid input stream: null is not allowed");

        in = new PushbackInputStream(inputStream, 4);

        final byte bom[] = new byte[4];
        final int read = in.read(bom);

        switch (read) {
            case 4:
                if ((bom[0] == (byte) 0xFF) &&
                        (bom[1] == (byte) 0xFE) &&
                        (bom[2] == (byte) 0x00) &&
                        (bom[3] == (byte) 0x00)) {
                    this.bom = BOM.UTF_32_LE;
                    break;
                } else if ((bom[0] == (byte) 0x00) &&
                        (bom[1] == (byte) 0x00) &&
                        (bom[2] == (byte) 0xFE) &&
                        (bom[3] == (byte) 0xFF)) {
                    this.bom = BOM.UTF_32_BE;
                    break;
                }

            case 3:
                if ((bom[0] == (byte) 0xEF) &&
                        (bom[1] == (byte) 0xBB) &&
                        (bom[2] == (byte) 0xBF)) {
                    this.bom = BOM.UTF_8;
                    break;
                }

            case 2:
                if ((bom[0] == (byte) 0xFF) &&
                        (bom[1] == (byte) 0xFE)) {
                    this.bom = BOM.UTF_16_LE;
                    break;
                } else if ((bom[0] == (byte) 0xFE) &&
                        (bom[1] == (byte) 0xFF)) {
                    this.bom = BOM.UTF_16_BE;
                    break;
                }

            default:
                this.bom = BOM.NONE;
                break;
        }

        if (read > 0)
            in.unread(bom, 0, read);
    }

    /**
     * Returns the BOM that was detected in the wrapped
     * InputStream object.
     *
     * @return a BOM value.
     */
    public final BOM getBOM() {
        // BOM type is immutable.
        return bom;
    }

    /**
     * Skips the BOM that was found in the wrapped
     * InputStream object.
     *
     * @return this UnicodeBOMInputStream.
     * @throws IOException when trying to skip the BOM from the wrapped
     *                     InputStream object.
     */
    public final synchronized UnicodeBomInputStream skipBOM() throws IOException {
        if (!skipped) {
            in.skip(bom.bytes.length);
            skipped = true;
        }
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public int read() throws IOException {
        return in.read();
    }

    /**
     * {@inheritDoc}
     */
    public int read(final byte b[]) throws IOException,
            NullPointerException {
        return in.read(b, 0, b.length);
    }

    /**
     * {@inheritDoc}
     */
    public int read(final byte b[],
                    final int off,
                    final int len) throws IOException,
            NullPointerException {
        return in.read(b, off, len);
    }

    /**
     * {@inheritDoc}
     */
    public long skip(final long n) throws IOException {
        return in.skip(n);
    }

    /**
     * {@inheritDoc}
     */
    public int available() throws IOException {
        return in.available();
    }

    /**
     * {@inheritDoc}
     */
    public void close() throws IOException {
        in.close();
    }

    /**
     * {@inheritDoc}
     */
    public synchronized void mark(final int readlimit) {
        in.mark(readlimit);
    }

    /**
     * {@inheritDoc}
     */
    public synchronized void reset() throws IOException {
        in.reset();
    }

    /**
     * {@inheritDoc}
     */
    public boolean markSupported() {
        return in.markSupported();
    }

} // UnicodeBOMInputStream