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/* Base64InputStream.java -- base-64 input stream.

   Copyright (C) 2003, 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.java.io;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.FilterInputStream;

import java.io.IOException;

import java.io.InputStream;

/**

 * A filter input stream that decodes data encoded in the Base-64

 * encoding scheme.

 *

 * @author Casey Marshall (rsdio@metastatic.org)

 */

public class Base64InputStream extends FilterInputStream

{

  // Constants and fields.

  // ------------------------------------------------------------------------

  /** Base-64 digits. */

  private static final String BASE_64 =

    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  /** Base-64 padding character. */

  private static final char BASE_64_PAD = '=';

  /** Decoding state. */

  private int state;

  /** Intermediate decoded value. */

  private int temp;

  /** EOF flag. */

  private boolean eof;

  private final byte[] one = new byte[1];

  // Constructors.

  // ------------------------------------------------------------------------

  /**

   * Create a new Base-64 input stream. The input bytes must be the

   * ASCII characters A-Z, a-z, 0-9, + and /, with optional whitespace,

   * and will be decoded into a byte stream.

   *

   * @param in The source of Base-64 input.

   */

  public Base64InputStream(InputStream in)

  {

    super(in);

    state = 0;

    temp = 0;

    eof = false;

  }

  // Class method.

  // ------------------------------------------------------------------------

  /**

   * Decode a single Base-64 string to a byte array.

   *

   * @param base64 The Base-64 encoded data.

   * @return The decoded bytes.

   * @throws IOException If the given data do not compose a valid Base-64

   *  sequence.

   */

  public static byte[] decode(String base64) throws IOException

  {

    Base64InputStream in =

      new Base64InputStream(new ByteArrayInputStream(base64.getBytes()));

    ByteArrayOutputStream out =

      new ByteArrayOutputStream((int) (base64.length() / 0.666));

    byte[] buf = new byte[1024];

    int len;

    while ((len = in.read(buf)) != -1)

      out.write(buf, 0, len);

    return out.toByteArray();

  }

  // Instance methods.

  // ------------------------------------------------------------------------

  public int available()

  {

    return 0;

  }

  public int read() throws IOException

  {

    if (read(one) == 1)

      return one[0];

    return -1;

  }

  public int read(byte[] buf, int off, int len) throws IOException

  {

    if (eof)

      return -1;

    int count = 0;

    while (count < len)

      {

        int i;

        while (Character.isWhitespace((char) (i = in.read())));

        int pos = BASE_64.indexOf((char) i);

        if (pos >= 0)

          {

            switch (state)

              {

                case 0:

                  temp = pos << 2;

                  state = 1;

                  break;

                case 1:

                  buf[count++] = (byte) (temp | (pos >>> 4));

                  temp = (pos & 0x0F) << 4;

                  state = 2;

                  break;

                case 2:

                  buf[count++] = (byte) (temp | (pos >>> 2));

                  temp = (pos & 0x03) << 6;

                  state = 3;

                  break;

                case 3:

                  buf[count++] = (byte) (temp | pos);

                  state = 0;

                  break;

              }

          }

        else if (i == BASE_64_PAD)

          {

            switch (state)

              {

                case 0:

                case 1:

                  throw new IOException("malformed Base-64 input");

                case 2:

                  while (Character.isWhitespace((char) (i = in.read())));

                  if (i != BASE_64_PAD)

                    throw new IOException("malformed Base-64 input");

                case 3:

                  while (Character.isWhitespace((char) (i = in.read())));

              }

            eof = true;

            break;

          }

        else  // First non-Base-64 character, consider it end-of-stream.

          {

            if (state != 0)

              throw new IOException("malformed Base-64 input");

            eof = true;

            break;

          }

      }

      return count;

  }

  public boolean markSupported()

  {

    return false;

  }

  public void mark(int markLimit) { }

  public void reset() throws IOException

  {

    throw new IOException("reset not supported");

  }

  public long skip(long n) throws IOException

  {

    long skipped;

    for (skipped = 0; skipped < n; skipped++)

      if (read() == -1)

        break;

    return skipped;

  }

}