BASE64 Decoder Stream : Base64 Stream « File Input Output « Java





BASE64 Decoder Stream

   
/*
 * The contents of this file are subject to the terms 
 * of the Common Development and Distribution License 
 * (the "License").  You may not use this file except 
 * in compliance with the License.
 * 
 * You can obtain a copy of the license at 
 * glassfish/bootstrap/legal/CDDLv1.0.txt or 
 * https://glassfish.dev.java.net/public/CDDLv1.0.html. 
 * See the License for the specific language governing 
 * permissions and limitations under the License.
 * 
 * When distributing Covered Code, include this CDDL 
 * HEADER in each file and include the License file at 
 * glassfish/bootstrap/legal/CDDLv1.0.txt.  If applicable, 
 * add the following below this CDDL HEADER, with the 
 * fields enclosed by brackets "[]" replaced with your 
 * own identifying information: Portions Copyright [yyyy] 
 * [name of copyright owner]
 */

/*
 * @(#)BASE64DecoderStream.java 1.15 06/09/25
 *
 * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved.
 */


import java.io.*;

/**
 * This class implements a BASE64 Decoder. It is implemented as
 * a FilterInputStream, so one can just wrap this class around
 * any input stream and read bytes from this filter. The decoding
 * is done as the bytes are read out.
 * 
 * @author John Mani
 * @author Bill Shannon
 */

public class BASE64DecoderStream extends FilterInputStream {
    // buffer of decoded bytes for single byte reads
    private byte[] buffer = new byte[3];
    private int bufsize = 0;  // size of the cache
    private int index = 0;  // index into the cache

    // buffer for almost 8K of typical 76 chars + CRLF lines,
    // used by getByte method.  this buffer contains encoded bytes.
    private byte[] input_buffer = new byte[78*105];
    private int input_pos = 0;
    private int input_len = 0;;

    private boolean ignoreErrors = false;

    /** 
     * Create a BASE64 decoder that decodes the specified input stream.
     * The System property <code>mail.mime.base64.ignoreerrors</code>
     * controls whether errors in the encoded data cause an exception
     * or are ignored.  The default is false (errors cause exception).
     *
     * @param in  the input stream
     */
    public BASE64DecoderStream(InputStream in) {
  super(in);
  try {
      String s = System.getProperty("mail.mime.base64.ignoreerrors");
      // default to false
      ignoreErrors = s != null && !s.equalsIgnoreCase("false");
  } catch (SecurityException sex) {
      // ignore it
  }
    }

    /** 
     * Create a BASE64 decoder that decodes the specified input stream.
     *
     * @param in  the input stream
     * @param ignoreErrors  ignore errors in encoded data?
     */
    public BASE64DecoderStream(InputStream in, boolean ignoreErrors) {
  super(in);
  this.ignoreErrors = ignoreErrors;
    }

    /**
     * Read the next decoded byte from this input stream. The byte
     * is returned as an <code>int</code> in the range <code>0</code> 
     * to <code>255</code>. If no byte is available because the end of 
     * the stream has been reached, the value <code>-1</code> is returned.
     * This method blocks until input data is available, the end of the 
     * stream is detected, or an exception is thrown.
     *
     * @return     next byte of data, or <code>-1</code> if the end of the
     *             stream is reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public int read() throws IOException {
  if (index >= bufsize) {
      bufsize = decode(buffer, 0, buffer.length);
      if (bufsize <= 0) // buffer is empty
    return -1;
      index = 0; // reset index into buffer
  }
  return buffer[index++] & 0xff; // Zero off the MSB
    }

    /**
     * Reads up to <code>len</code> decoded bytes of data from this input stream
     * into an array of bytes. This method blocks until some input is
     * available.
     * <p>
     *
     * @param      buf   the buffer into which the data is read.
     * @param      off   the start offset of the data.
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the stream has been reached.
     * @exception  IOException  if an I/O error occurs.
     */
    public int read(byte[] buf, int off, int len) throws IOException {
  // empty out single byte read buffer
  int off0 = off;
  while (index < bufsize && len > 0) {
      buf[off++] = buffer[index++];
      len--;
  }
  if (index >= bufsize)
      bufsize = index = 0;

  int bsize = (len / 3) * 3;  // round down to multiple of 3 bytes
  if (bsize > 0) {
      int size = decode(buf, off, bsize);
      off += size;
      len -= size;

      if (size != bsize) {  // hit EOF?
    if (off == off0)  // haven't returned any data
        return -1;
    else      // returned some data before hitting EOF
        return off - off0;
      }
  }

  // finish up with a partial read if necessary
  for (; len > 0; len--) {
      int c = read();
      if (c == -1)  // EOF
    break;
      buf[off++] = (byte)c;
  }

  if (off == off0)  // haven't returned any data
      return -1;
  else      // returned some data before hitting EOF
      return off - off0;
    }

    /**
     * Tests if this input stream supports marks. Currently this class
     * does not support marks
     */
    public boolean markSupported() {
  return false; // Maybe later ..
    }

    /**
     * Returns the number of bytes that can be read from this input
     * stream without blocking. However, this figure is only
     * a close approximation in case the original encoded stream
     * contains embedded CRLFs; since the CRLFs are discarded, not decoded
     */ 
    public int available() throws IOException {
   // This is only an estimate, since in.available()
   // might include CRLFs too ..
   return ((in.available() * 3)/4 + (bufsize-index));
    }

    /**
     * This character array provides the character to value map
     * based on RFC1521.
     */  
    private final static char pem_array[] = {
  'A','B','C','D','E','F','G','H', // 0
  'I','J','K','L','M','N','O','P', // 1
  'Q','R','S','T','U','V','W','X', // 2
  'Y','Z','a','b','c','d','e','f', // 3
  'g','h','i','j','k','l','m','n', // 4
  'o','p','q','r','s','t','u','v', // 5
  'w','x','y','z','0','1','2','3', // 6
  '4','5','6','7','8','9','+','/'  // 7
    };

    private final static byte pem_convert_array[] = new byte[256];

    static {
  for (int i = 0; i < 255; i++)
      pem_convert_array[i] = -1;
  for (int i = 0; i < pem_array.length; i++)
      pem_convert_array[pem_array[i]] = (byte)i;
    }

    /**
     * The decoder algorithm.  Most of the complexity here is dealing
     * with error cases.  Returns the number of bytes decoded, which
     * may be zero.  Decoding is done by filling an int with 4 6-bit
     * values by shifting them in from the bottom and then extracting
     * 3 8-bit bytes from the int by shifting them out from the bottom.
     *
     * @param outbuf  the buffer into which to put the decoded bytes
     * @param pos position in the buffer to start filling
     * @param len the number of bytes to fill
     * @return    the number of bytes filled, always a multiple
     *      of three, and may be zero
     * @exception IOException if the data is incorrectly formatted
     */
    private int decode(byte[] outbuf, int pos, int len) throws IOException {
  int pos0 = pos;
  while (len >= 3) {
      /*
       * We need 4 valid base64 characters before we start decoding.
       * We skip anything that's not a valid base64 character (usually
       * just CRLF).
       */
      int got = 0;
      int val = 0;
      while (got < 4) {
    int i = getByte();
    if (i == -1 || i == -2) {
        boolean atEOF;
        if (i == -1) {
      if (got == 0)
          return pos - pos0;
      if (!ignoreErrors)
          throw new IOException("Error in encoded stream: " +
        "needed 4 valid base64 characters " +
        "but only got " + got + " before EOF" +
        recentChars());
      atEOF = true; // don't read any more
        } else {  // i == -2
      // found a padding character, we're at EOF
      // XXX - should do something to make EOF "sticky"
      if (got < 2 && !ignoreErrors)
          throw new IOException("Error in encoded stream: " +
        "needed at least 2 valid base64 characters," +
        " but only got " + got +
        " before padding character (=)" +
        recentChars());

      // didn't get any characters before padding character?
      if (got == 0)
          return pos - pos0;
      atEOF = false;  // need to keep reading
        }

        // pad partial result with zeroes

        // how many bytes will we produce on output?
        // (got always < 4, so size always < 3)
        int size = got - 1;
        if (size == 0)
      size = 1;

        // handle the one padding character we've seen
        got++;
        val <<= 6;

        while (got < 4) {
      if (!atEOF) {
          // consume the rest of the padding characters,
          // filling with zeroes
          i = getByte();
          if (i == -1) {
        if (!ignoreErrors)
            throw new IOException(
          "Error in encoded stream: " +
          "hit EOF while looking for " +
          "padding characters (=)" +
          recentChars());
          } else if (i != -2) {
        if (!ignoreErrors)
            throw new IOException(
          "Error in encoded stream: " +
          "found valid base64 character after " +
          "a padding character (=)" +
          recentChars());
          }
      }
      val <<= 6;
      got++;
        }

        // now pull out however many valid bytes we got
        val >>= 8;    // always skip first one
        if (size == 2)
      outbuf[pos + 1] = (byte)(val & 0xff);
        val >>= 8;
        outbuf[pos] = (byte)(val & 0xff);
        // len -= size; // not needed, return below
        pos += size;
        return pos - pos0;
    } else {
        // got a valid byte
        val <<= 6;
        got++;
        val |= i;
    }
      }

      // read 4 valid characters, now extract 3 bytes
      outbuf[pos + 2] = (byte)(val & 0xff);
      val >>= 8;
      outbuf[pos + 1] = (byte)(val & 0xff);
      val >>= 8;
      outbuf[pos] = (byte)(val & 0xff);
      len -= 3;
      pos += 3;
  }
  return pos - pos0;
    }

    /**
     * Read the next valid byte from the input stream.
     * Buffer lots of data from underlying stream in input_buffer,
     * for efficiency.
     *
     * @return  the next byte, -1 on EOF, or -2 if next byte is '='
     *    (padding at end of encoded data)
     */
    private int getByte() throws IOException {
  int c;
  do {
      if (input_pos >= input_len) {
    try {
        input_len = in.read(input_buffer);
    } catch (EOFException ex) {
        return -1;
    }
    if (input_len <= 0)
        return -1;
    input_pos = 0;
      }
      // get the next byte in the buffer
      c = input_buffer[input_pos++] & 0xff;
      // is it a padding byte?
      if (c == '=')
    return -2;
      // no, convert it
      c = pem_convert_array[c];
      // loop until we get a legitimate byte
  } while (c == -1);
  return c;
    }

    /**
     * Return the most recent characters, for use in an error message.
     */
    private String recentChars() {
  // reach into the input buffer and extract up to 10
  // recent characters, to help in debugging.
  String errstr = "";
  int nc = input_pos > 10 ? 10 : input_pos;
  if (nc > 0) {
      errstr += ", the " + nc +
          " most recent characters were: \"";
      for (int k = input_pos - nc; k < input_pos; k++) {
    char c = (char)(input_buffer[k] & 0xff);
    switch (c) {
    case '\r':  errstr += "\\r"; break;
    case '\n':  errstr += "\\n"; break;
    case '\t':  errstr += "\\t"; break;
    default:
        if (c >= ' ' && c < 0177)
      errstr += c;
        else
      errstr += ("\\" + (int)c);
    }
      }
      errstr += "\"";
  }
  return errstr;
    }

    /**
     * Base64 decode a byte array.  No line breaks are allowed.
     * This method is suitable for short strings, such as those
     * in the IMAP AUTHENTICATE protocol, but not to decode the
     * entire content of a MIME part.
     *
     * NOTE: inbuf may only contain valid base64 characters.
     *       Whitespace is not ignored.
     */
    public static byte[] decode(byte[] inbuf) {
  int size = (inbuf.length / 4) * 3;
  if (size == 0)
      return inbuf;

  if (inbuf[inbuf.length - 1] == '=') {
      size--;
      if (inbuf[inbuf.length - 2] == '=')
    size--;
  }
  byte[] outbuf = new byte[size];

  int inpos = 0, outpos = 0;
  size = inbuf.length;
  while (size > 0) {
      int val;
      int osize = 3;
      val = pem_convert_array[inbuf[inpos++] & 0xff];
      val <<= 6;
      val |= pem_convert_array[inbuf[inpos++] & 0xff];
      val <<= 6;
      if (inbuf[inpos] != '=') // End of this BASE64 encoding
    val |= pem_convert_array[inbuf[inpos++] & 0xff];
      else
    osize--;
      val <<= 6;
      if (inbuf[inpos] != '=') // End of this BASE64 encoding
    val |= pem_convert_array[inbuf[inpos++] & 0xff];
      else
    osize--;
      if (osize > 2)
    outbuf[outpos + 2] = (byte)(val & 0xff);
      val >>= 8;
      if (osize > 1)
    outbuf[outpos + 1] = (byte)(val & 0xff);
      val >>= 8;
      outbuf[outpos] = (byte)(val & 0xff);
      outpos += osize;
      size -= 4;
  }
  return outbuf;
    }

    /*** begin TEST program ***
    public static void main(String argv[]) throws Exception {
      FileInputStream infile = new FileInputStream(argv[0]);
  BASE64DecoderStream decoder = new BASE64DecoderStream(infile);
  int c;

  while ((c = decoder.read()) != -1)
      System.out.print((char)c);
  System.out.flush();
    }
    *** end TEST program ***/
}

   
    
    
  










Related examples in the same category

1.BASE64 Encoder Stream from Sun Microsystems
2.Base64 Character decoder as specified in RFC1113.
3.Base64 Character encoder as specified in RFC1113.
4.Performs Base-64 decoding on an underlying stream.
5.Class encodes the bytes written to the OutPutStream to a Base64 encoded string.
6.BASE64 Decoder Stream from Sun Microsystems
7.BASE64 Encoder Stream
8.Decode a BASE64 encoded input stream to some output stream
9.Hex dump
10.Dumps data in hexadecimal format
11.Apply a ASCII Hex encoding to the stream
12.Base64 Codec
13.Base64 encoding from DbUnit.org
14.Base64 provides Base64 encoding/decoding of strings and streams
15.Base64 - encode/decode data using the Base64 encoding scheme
16.Base64 from Eric Glass jcifs at samba dot org