This class provides encoding of byte arrays into Base64-encoded strings, and decoding the other way. : Byte Array « File Input Output « Java
This class provides encoding of byte arrays into Base64-encoded strings, and decoding the other way.
package freenet.support;
/**
* This class provides encoding of byte arrays into Base64-encoded strings,
* and decoding the other way.
*
* <P>NOTE! This is modified Base64 with slightly different characters than
* usual, so it won't require escaping when used in URLs.
*
* <P>NOTE! This class only does the padding that's normal in Base64
* if the 'true' flag is given to the encode() method. This is because
* Base64 requires that the length of the encoded text be a multiple
* of four characters, padded with '='. Without the 'true' flag, we don't
* add these '=' characters.
*
* @author Stephen Blackheath
*/
public class Base64
{
private static char[] base64Alphabet = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
'w', 'x', 'y', 'z', '0', '1', '2', '3',
'4', '5', '6', '7', '8', '9', '~', '-'};
private static char[] base64StandardAlphabet = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
'w', 'x', 'y', 'z', '0', '1', '2', '3',
'4', '5', '6', '7', '8', '9', '+', '/'};
/**
* A reverse lookup table to convert base64 letters back into the
* a 6-bit sequence.
*/
private static byte[] base64Reverse;
private static byte[] base64StandardReverse;
// Populate the base64Reverse lookup table from the base64Alphabet table.
static {
base64Reverse = new byte[128];
base64StandardReverse = new byte[base64Reverse.length];
// Set all entries to 0xFF, which means that that particular letter
// is not a legal base64 letter.
for (int i = 0; i < base64Reverse.length; i++) {
base64Reverse[i] = (byte) 0xFF;
base64StandardReverse[i] = (byte) 0xFF;
}
for (int i = 0; i < base64Alphabet.length; i++) {
base64Reverse[base64Alphabet[i]] = (byte) i;
base64StandardReverse[base64StandardAlphabet[i]] = (byte) i;
}
}
/**
* Encode to our shortened (non-standards-compliant) format.
*/
public static String encode(byte[] in)
{
return encode(in, false);
}
/* FIXME: Figure out where this function is used and maybe remove it if its not
* used. Its old javadoc which has been here for a while fools the user into believing
* that the format is standard compliant */
/**
* Caller should specify equalsPad=true if they want a standards compliant padding,
* but not standard compliant encoding.
*/
public static String encode(byte[] in, boolean equalsPad) {
return encode(in, equalsPad, base64Alphabet);
}
/**
* Standard compliant encoding.
*/
public static String encodeStandard(byte[] in) {
return encode(in, true, base64StandardAlphabet);
}
/**
* Caller should specify equalsPad=true if they want a standards compliant encoding.
*/
private static String encode(byte[] in, boolean equalsPad, char[] alphabet)
{
char[] out = new char[((in.length+2)/3)*4];
int rem = in.length%3;
int o = 0;
for (int i = 0; i < in.length;) {
int val = (in[i++] & 0xFF) << 16;
if (i < in.length)
val |= (in[i++] & 0xFF) << 8;
if (i < in.length)
val |= (in[i++] & 0xFF);
out[o++] = alphabet[(val>>18) & 0x3F];
out[o++] = alphabet[(val>>12) & 0x3F];
out[o++] = alphabet[(val>>6) & 0x3F];
out[o++] = alphabet[val & 0x3F];
}
int outLen = out.length;
switch (rem) {
case 1: outLen -= 2; break;
case 2: outLen -= 1; break;
}
// Pad with '=' signs up to a multiple of four if requested.
if (equalsPad)
while (outLen < out.length)
out[outLen++] = '=';
return new String(out, 0, outLen);
}
/**
* Handles the standards-compliant padding (padded with '=' signs) as well as our
* shortened form.
* @throws IllegalBase64Exception
*/
public static byte[] decode(String inStr) throws Exception {
return decode(inStr, base64Reverse);
}
/**
* Handles the standards-compliant base64 encoding.
*/
public static byte[] decodeStandard(String inStr) throws Exception {
return decode(inStr, base64StandardReverse);
}
/**
* Handles the standards-compliant (padded with '=' signs) as well as our
* shortened form.
*/
private static byte[] decode(String inStr, byte[] reverseAlphabet)
throws Exception
{
try {
char[] in = inStr.toCharArray();
int inLength = in.length;
// Strip trailing equals signs.
while ((inLength > 0) && (in[inLength-1] == '='))
inLength--;
int blocks = inLength/4;
int remainder = inLength & 3;
// wholeInLen and wholeOutLen are the the length of the input and output
// sequences respectively, not including any partial block at the end.
int wholeInLen = blocks*4;
int wholeOutLen = blocks*3;
int outLen = wholeOutLen;
switch (remainder) {
case 1: throw new Exception("illegal Base64 length");
case 2: outLen = wholeOutLen+1; break;
case 3: outLen = wholeOutLen+2; break;
default: outLen = wholeOutLen;
}
byte[] out = new byte[outLen];
int o = 0;
int i;
for (i = 0; i < wholeInLen;) {
int in1 = reverseAlphabet[in[i]];
int in2 = reverseAlphabet[in[i+1]];
int in3 = reverseAlphabet[in[i+2]];
int in4 = reverseAlphabet[in[i+3]];
int orValue = in1|in2|in3|in4;
if ((orValue & 0x80) != 0)
throw new Exception("illegal Base64 character");
int outVal = (in1 << 18) | (in2 << 12) | (in3 << 6) | in4;
out[o] = (byte) (outVal>>16);
out[o+1] = (byte) (outVal>>8);
out[o+2] = (byte) outVal;
i += 4;
o += 3;
}
int orValue;
switch (remainder) {
case 2:
{
int in1 = reverseAlphabet[in[i]];
int in2 = reverseAlphabet[in[i+1]];
orValue = in1|in2;
int outVal = (in1 << 18) | (in2 << 12);
out[o] = (byte) (outVal>>16);
}
break;
case 3:
{
int in1 = reverseAlphabet[in[i]];
int in2 = reverseAlphabet[in[i+1]];
int in3 = reverseAlphabet[in[i+2]];
orValue = in1|in2|in3;
int outVal = (in1 << 18) | (in2 << 12) | (in3 << 6);
out[o] = (byte) (outVal>>16);
out[o+1] = (byte) (outVal>>8);
}
break;
default:
// Keep compiler happy
orValue = 0;
}
if ((orValue & 0x80) != 0)
throw new Exception("illegal Base64 character");
return out;
}
// Illegal characters can cause an ArrayIndexOutOfBoundsException when
// looking up reverseAlphabet.
catch (ArrayIndexOutOfBoundsException e) {
throw new Exception("illegal Base64 character");
}
}
}
/*
* This program 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 of the License, or
* (at your option) any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
package freenet.support;
import java.util.Arrays;
import java.util.Random;
import junit.framework.TestCase;
/**
* Test case for {@link freenet.support.Base64} class.
*
* @author Alberto Bacchelli <sback@freenetproject.org>
*/
public class Base64Test extends TestCase {
/**
* Test the encode(byte[]) method
* against a well-known example
* (see http://en.wikipedia.org/wiki/Base_64 as reference)
* to verify if it encode works correctly.
*/
public void testEncode() {
String toEncode = "Man is distinguished, not only by his reason, but by this singular " +
"passion from other animals, which is a lust of the mind, that by a perseverance " +
"of delight in the continued and indefatigable generation of knowledge, exceeds " +
"the short vehemence of any carnal pleasure.";
String expectedResult = "TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ" +
"1dCBieSB0aGlzIHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIG" +
"x1c3Qgb2YgdGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY" +
"29udGludWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRz" +
"IHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4";
byte[] aByteArrayToEncode = toEncode.getBytes();
assertEquals(Base64.encode(aByteArrayToEncode),expectedResult);
}
/**
* Test the decode(String) method
* against a well-known example
* (see http://en.wikipedia.org/wiki/Base_64 as reference)
* to verify if it decode an already encoded string correctly.
*/
public void testDecode() {
String toDecode = "TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ" +
"1dCBieSB0aGlzIHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIG" +
"x1c3Qgb2YgdGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY" +
"29udGludWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRz" +
"IHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=";
String expectedResult = "Man is distinguished, not only by his reason, but by this singular " +
"passion from other animals, which is a lust of the mind, that by a perseverance " +
"of delight in the continued and indefatigable generation of knowledge, exceeds " +
"the short vehemence of any carnal pleasure.";
try {
String decodedString = new String(Base64.decode(toDecode));
assertEquals(decodedString,expectedResult);
} catch (IllegalBase64Exception aException) {
fail("Not expected exception thrown : " + aException.getMessage()); }
}
/**
* Test encode(byte[] in)
* and decode(String inStr) methods,
* to verify if they work correctly together.
* It compares the string before encoding
* and with the one after decoding.
*/
public void testEncodeDecode() {
byte[] bytesDecoded;
byte[] bytesToEncode = new byte[5];
//byte upper bound
bytesToEncode[0] = 127;
bytesToEncode[1] = 64;
bytesToEncode[2] = 0;
bytesToEncode[3] = -64;
//byte lower bound
bytesToEncode[4] = -128;
String aBase64EncodedString = Base64.encode(bytesToEncode);
try {
bytesDecoded = Base64.decode(aBase64EncodedString);
assertTrue(Arrays.equals(bytesToEncode,bytesDecoded)); }
catch (IllegalBase64Exception aException) {
fail("Not expected exception thrown : " + aException.getMessage()); }
}
/**
* Test the encode(String,boolean)
* method to verify if the padding
* character '=' is correctly placed.
*/
public void testEncodePadding() {
byte[][] methodBytesArray = {
//three byte Array -> no padding char expected
{4,4,4},
//two byte Array -> one padding char expected
{4,4},
//one byte Array -> two padding-chars expected
{4}};
String encoded;
for (int i = 0; i<methodBytesArray.length; i++) {
encoded = Base64.encode(methodBytesArray[i],true);
if (i == 0)
//no occurrences expected
assertEquals(encoded.indexOf('='),-1);
else
assertEquals(encoded.indexOf('='),encoded.length()-i);
}
}
/**
* Test if the decode(String) method
* raise correctly an exception when
* providing a string with non-Base64
* characters.
*/
public void testIllegalBaseCharacter() {
// TODO: check many other possibile cases!
String illegalCharString = "abcd=fghilmn";
try {
Base64.decode(illegalCharString);
fail("Expected IllegalBase64Exception not thrown"); }
catch (IllegalBase64Exception exception) {
assertSame("illegal Base64 character",exception.getMessage()); }
}
/**
* Test if the decode(String) method
* raise correctly an exception when
* providing a string with a
* wrong Base64 length.
* (as we can consider not-padded strings too,
* the only wrong lengths are the ones
* where -> number MOD 4 = 1).
*/
public void testIllegalBaseLength() {
//most interesting case
String illegalLengthString = "a";
try {
Base64.decode(illegalLengthString);
fail("Expected IllegalBase64Exception not thrown"); }
catch (IllegalBase64Exception exception) {
assertSame("illegal Base64 length",exception.getMessage()); }
}
/**
* Random test
*
* @throws IllegalBase64Exception
*/
public void testRandom() throws IllegalBase64Exception {
int iter;
Random r = new Random(1234);
for (iter = 0; iter < 1000; iter++) {
byte[] b = new byte[r.nextInt(64)];
for (int i = 0; i < b.length; i++)
b[i] = (byte) (r.nextInt(256));
String encoded = Base64.encode(b);
byte[] decoded = Base64.decode(encoded);
assertEquals("length mismatch", decoded.length, b.length);
for (int i = 0; i < b.length; i++)
assertEquals("data mismatch: index " + i + " of " + b.length + " should be 0x"
+ Integer.toHexString(b[i] & 0xFF) + " was 0x" + Integer.toHexString(decoded[i] & 0xFF), b[i],
decoded[i]);
}
}
}
