base64.java

pastry的java实现的2.0b版

/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

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********************************************************************************/
/**
 * Encodes and decodes to and from Base64 notation.
 *
 * <p>
 * Change Log:
 * </p>
 * <ul>
 *  <li>v2.0.2 - Now specifies UTF-8 encoding in places where the code fails on systems
 *   with other encodings (like EBCDIC).</li>
 *  <li>v2.0.1 - Fixed an error when decoding a single byte, that is, when the
 *   encoded data was a single byte.</li>
 *  <li>v2.0 - I got rid of methods that used booleans to set options. 
 *   Now everything is more consolidated and cleaner. The code now detects
 *   when data that's being decoded is gzip-compressed and will decompress it
 *   automatically. Generally things are cleaner. You'll probably have to
 *   change some method calls that you were making to support the new
 *   options format (<tt>int</tt>s that you "OR" together).</li>
 *  <li>v1.5.1 - Fixed bug when decompressing and decoding to a             
 *   byte[] using <tt>decode( String s, boolean gzipCompressed )</tt>.      
 *   Added the ability to "suspend" encoding in the Output Stream so        
 *   you can turn on and off the encoding if you need to embed base64       
 *   data in an otherwise "normal" stream (like an XML file).</li>  
 *  <li>v1.5 - Output stream pases on flush() command but doesn't do anything itself.
 *      This helps when using GZIP streams.
 *      Added the ability to GZip-compress objects before encoding them.</li>
 *  <li>v1.4 - Added helper methods to read/write files.</li>
 *  <li>v1.3.6 - Fixed OutputStream.flush() so that 'position' is reset.</li>
 *  <li>v1.3.5 - Added flag to turn on and off line breaks. Fixed bug in input stream
 *      where last buffer being read, if not completely full, was not returned.</li>
 *  <li>v1.3.4 - Fixed when "improperly padded stream" error was thrown at the wrong time.</li>
 *  <li>v1.3.3 - Fixed I/O streams which were totally messed up.</li>
 * </ul>
 *
 * <p>
 * I am placing this code in the Public Domain. Do with it as you will.
 * This software comes with no guarantees or warranties but with
 * plenty of well-wishing instead!
 * Please visit <a href="http://iharder.net/xmlizable">http://iharder.net/base64</a>
 * periodically to check for updates or to contribute improvements.
 * </p>
 *
 * @author Robert Harder
 * @author [e-mail]
 * @version 2.0
 */
package rice.p2p.util;

public class Base64
{
    
/* ********  P U B L I C   F I E L D S  ******** */   
    
    
    /** No options specified. Value is zero. */
    public final static int NO_OPTIONS = 0;
    
    /** Specify encoding. */
    public final static int ENCODE = 1;
    
    
    /** Specify decoding. */
    public final static int DECODE = 0;
    
    
    /** Specify that data should be gzip-compressed. */
    public final static int GZIP = 2;
    
    
    /** Don't break lines when encoding (violates strict Base64 specification) */
    public final static int DONT_BREAK_LINES = 8;
    
    
/* ********  P R I V A T E   F I E L D S  ******** */  
    
    
    /** Maximum line length (76) of Base64 output. */
    private final static int MAX_LINE_LENGTH = 76;
    
    
    /** The equals sign (=) as a byte. */
    private final static byte EQUALS_SIGN = (byte)'=';
    
    
    /** The new line character (\n) as a byte. */
    private final static byte NEW_LINE = (byte)'\n';
    
    
    /** Preferred encoding. */
    private final static String PREFERRED_ENCODING = "UTF-8";
    
    
    /** The 64 valid Base64 values. */
    private final static byte[] ALPHABET;
    private final static byte[] _NATIVE_ALPHABET = /* May be something funny like EBCDIC */
    {
        (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G',
        (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N',
        (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U', 
        (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z',
        (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g',
        (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n',
        (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u', 
        (byte)'v', (byte)'w', (byte)'x', (byte)'y', (byte)'z',
        (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', 
        (byte)'6', (byte)'7', (byte)'8', (byte)'9', (byte)'+', (byte)'/'
    };
    
    /** Determine which ALPHABET to use. */
    static
    {
        byte[] __bytes;
        try
        {
            __bytes = new String("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/").getBytes( PREFERRED_ENCODING );
        }   // end try
        catch (java.io.UnsupportedEncodingException use)
        {
            __bytes = _NATIVE_ALPHABET; // Fall back to native encoding
        }   // end catch
        ALPHABET = __bytes;
    }   // end static
    
    
    /** 
     * Translates a Base64 value to either its 6-bit reconstruction value
     * or a negative number indicating some other meaning.
     **/
    private final static byte[] DECODABET =
    {   
        -9,-9,-9,-9,-9,-9,-9,-9,-9,                 // Decimal  0 -  8
        -5,-5,                                      // Whitespace: Tab and Linefeed
        -9,-9,                                      // Decimal 11 - 12
        -5,                                         // Whitespace: Carriage Return
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 14 - 26
        -9,-9,-9,-9,-9,                             // Decimal 27 - 31
        -5,                                         // Whitespace: Space
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,              // Decimal 33 - 42
        62,                                         // Plus sign at decimal 43
        -9,-9,-9,                                   // Decimal 44 - 46
        63,                                         // Slash at decimal 47
        52,53,54,55,56,57,58,59,60,61,              // Numbers zero through nine
        -9,-9,-9,                                   // Decimal 58 - 60
        -1,                                         // Equals sign at decimal 61
        -9,-9,-9,                                      // Decimal 62 - 64
        0,1,2,3,4,5,6,7,8,9,10,11,12,13,            // Letters 'A' through 'N'
        14,15,16,17,18,19,20,21,22,23,24,25,        // Letters 'O' through 'Z'
        -9,-9,-9,-9,-9,-9,                          // Decimal 91 - 96
        26,27,28,29,30,31,32,33,34,35,36,37,38,     // Letters 'a' through 'm'
        39,40,41,42,43,44,45,46,47,48,49,50,51,     // Letters 'n' through 'z'
        -9,-9,-9,-9                                 // Decimal 123 - 126
        /*,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 127 - 139
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 140 - 152
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 153 - 165
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 166 - 178
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 179 - 191
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 192 - 204
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 205 - 217
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 218 - 230
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,     // Decimal 231 - 243
        -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9         // Decimal 244 - 255 */
    };
    
    private final static byte BAD_ENCODING    = -9; // Indicates error in encoding
    private final static byte WHITE_SPACE_ENC = -5; // Indicates white space in encoding
    private final static byte EQUALS_SIGN_ENC = -1; // Indicates equals sign in encoding

    
    /** Defeats instantiation. */
    private Base64(){}
    
    
    
/* ********  E N C O D I N G   M E T H O D S  ******** */    
    
    
    /**
     * Encodes the first three bytes of array <var>threeBytes</var>
     * and returns a four-byte array in Base64 notation.
     *
     * @param threeBytes the array to convert
     * @return four byte array in Base64 notation.
     * @since 1.3
     */
    private static byte[] encode3to4( byte[] threeBytes )
    {   
        return encode3to4( threeBytes, 3 );
    }   // end encodeToBytes
    
    
    
    /**
     * Encodes up to the first three bytes of array <var>threeBytes</var>
     * and returns a four-byte array in Base64 notation.
     * The actual number of significant bytes in your array is
     * given by <var>numSigBytes</var>.
     * The array <var>threeBytes</var> needs only be as big as
     * <var>numSigBytes</var>.
     *
     * @param threeBytes the array to convert
     * @param numSigBytes the number of significant bytes in your array
     * @return four byte array in Base64 notation.
     * @since 1.3
     */
    private static byte[] encode3to4( byte[] threeBytes, int numSigBytes )
    {  
        byte[] dest = new byte[4];
        encode3to4( threeBytes, 0, numSigBytes, dest, 0 );
        return dest;
    }
    
     /**
     * Encodes up to the first three bytes of array <var>threeBytes</var>
     * and returns a four-byte array in Base64 notation.
     * The actual number of significant bytes in your array is
     * given by <var>numSigBytes</var>.
     * The array <var>threeBytes</var> needs only be as big as
     * <var>numSigBytes</var>.
     * Code can reuse a byte array by passing a four-byte array as <var>b4</var>.
     *
     * @param b4 A reusable byte array to reduce array instantiation
     * @param threeBytes the array to convert
     * @param numSigBytes the number of significant bytes in your array
     * @return four byte array in Base64 notation.
     * @since 1.5.1
     */
    private static byte[] encode3to4( byte[] b4, byte[] threeBytes, int numSigBytes )
    {
        encode3to4( threeBytes, 0, numSigBytes, b4, 0 );
        return b4;
    }   // end encode3to4

    
    /**
     * Encodes up to three bytes of the array <var>source</var>
     * and writes the resulting four Base64 bytes to <var>destination</var>.
     * The source and destination arrays can be manipulated
     * anywhere along their length by specifying 
     * <var>srcOffset</var> and <var>destOffset</var>.
     * This method does not check to make sure your arrays
     * are large enough to accomodate <var>srcOffset</var> + 3 for
     * the <var>source</var> array or <var>destOffset</var> + 4 for
     * the <var>destination</var> array.
     * The actual number of significant bytes in your array is
     * given by <var>numSigBytes</var>.
     *
     * @param source the array to convert
     * @param srcOffset the index where conversion begins
     * @param numSigBytes the number of significant bytes in your array
     * @param destination the array to hold the conversion
     * @param destOffset the index where output will be put
     * @return the <var>destination</var> array
     * @since 1.3
     */
    private static byte[] encode3to4( 
     byte[] source, int srcOffset, int numSigBytes,
     byte[] destination, int destOffset )
    {
        //           1         2         3  
        // 01234567890123456789012345678901 Bit position
        // --------000000001111111122222222 Array position from threeBytes
        // --------|    ||    ||    ||    | Six bit groups to index ALPHABET
        //          >>18  >>12  >> 6  >> 0  Right shift necessary
        //                0x3f  0x3f  0x3f  Additional AND
        
        // Create buffer with zero-padding if there are only one or two
        // significant bytes passed in the array.
        // We have to shift left 24 in order to flush out the 1's that appear
        // when Java treats a value as negative that is cast from a byte to an int.
        int inBuff =   ( numSigBytes > 0 ? ((source[ srcOffset     ] << 24) >>>  8) : 0 )
                     | ( numSigBytes > 1 ? ((source[ srcOffset + 1 ] << 24) >>> 16) : 0 )
                     | ( numSigBytes > 2 ? ((source[ srcOffset + 2 ] << 24) >>> 24) : 0 );

        switch( numSigBytes )
        {
            case 3:
                destination[ destOffset     ] = ALPHABET[ (inBuff >>> 18)        ];
                destination[ destOffset + 1 ] = ALPHABET[ (inBuff >>> 12) & 0x3f ];
                destination[ destOffset + 2 ] = ALPHABET[ (inBuff >>>  6) & 0x3f ];
                destination[ destOffset + 3 ] = ALPHABET[ (inBuff       ) & 0x3f ];
                return destination;
                
            case 2:
                destination[ destOffset     ] = ALPHABET[ (inBuff >>> 18)        ];
                destination[ destOffset + 1 ] = ALPHABET[ (inBuff >>> 12) & 0x3f ];
                destination[ destOffset + 2 ] = ALPHABET[ (inBuff >>>  6) & 0x3f ];
                destination[ destOffset + 3 ] = EQUALS_SIGN;
                return destination;
                
            case 1:
                destination[ destOffset     ] = ALPHABET[ (inBuff >>> 18)        ];
                destination[ destOffset + 1 ] = ALPHABET[ (inBuff >>> 12) & 0x3f ];
                destination[ destOffset + 2 ] = EQUALS_SIGN;
                destination[ destOffset + 3 ] = EQUALS_SIGN;
                return destination;
                
            default:
                return destination;
        }   // end switch
    }   // end encode3to4
    
    
    
    /**
     * Serializes an object and returns the Base64-encoded
     * version of that serialized object. If the object
     * cannot be serialized or there is another error,
     * the method will return <tt>null</tt>.
     * The object is not GZip-compressed before being encoded.
     *
     * @param serializableObject The object to encode