~repos /gdx-studio

/*
 * 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.
   */
  @Override
  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.
   */
  @Override
  public int read(char[] cbuf, int off, int len) throws IOException {
    return internalIn.read(cbuf, off, len);
  }


}