package com.github.hunter0x7c7.sync.utils;
|
|
import java.io.BufferedInputStream;
|
import java.io.ByteArrayInputStream;
|
import java.io.ByteArrayOutputStream;
|
import java.io.FileInputStream;
|
import java.io.FilterInputStream;
|
import java.io.IOException;
|
import java.io.InputStream;
|
|
public class Base64Decoder extends FilterInputStream {
|
|
private static final char[] chars = {'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 mapping between char values and six-bit integers
|
private static final int[] ints = new int[128];
|
|
static {
|
for (int i = 0; i < 64; i++) {
|
ints[chars[i]] = i;
|
}
|
}
|
|
private int charCount;
|
private int carryOver;
|
|
/***
|
* Constructs a new Base64 decoder that reads input from the given
|
* InputStream.
|
*
|
* @param in
|
* the input stream
|
*/
|
public Base64Decoder(InputStream in) {
|
super(in);
|
}
|
|
/***
|
* Returns the next decoded character from the stream, or -1 if end of
|
* stream was reached.
|
*
|
* @return the decoded character, or -1 if the end of the input stream is
|
* reached
|
* @exception IOException
|
* if an I/O error occurs
|
*/
|
public int read() throws IOException {
|
// Read the next non-whitespace character
|
int x;
|
do {
|
x = in.read();
|
if (x == -1) {
|
return -1;
|
}
|
} while (Character.isWhitespace((char) x));
|
charCount++;
|
|
// The '=' sign is just padding
|
if (x == '=') {
|
return -1; // effective end of stream
|
}
|
|
// Convert from raw form to 6-bit form
|
x = ints[x];
|
|
// Calculate which character we're decoding now
|
int mode = (charCount - 1) % 4;
|
|
// First char save all six bits, go for another
|
if (mode == 0) {
|
carryOver = x & 63;
|
return read();
|
}
|
// Second char use previous six bits and first two new bits,
|
// save last four bits
|
else if (mode == 1) {
|
int decoded = ((carryOver << 2) + (x >> 4)) & 255;
|
carryOver = x & 15;
|
return decoded;
|
}
|
// Third char use previous four bits and first four new bits,
|
// save last two bits
|
else if (mode == 2) {
|
int decoded = ((carryOver << 4) + (x >> 2)) & 255;
|
carryOver = x & 3;
|
return decoded;
|
}
|
// Fourth char use previous two bits and all six new bits
|
else if (mode == 3) {
|
return ((carryOver << 6) + x) & 255;
|
}
|
return -1; // can't actually reach this line
|
}
|
|
/***
|
* Reads decoded data into an array of bytes and returns the actual number
|
* of bytes read, or -1 if end of stream was reached.
|
*
|
* @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 to read
|
* @return the actual number of bytes read, or -1 if the end of the input
|
* stream is reached
|
* @exception IOException
|
* if an I/O error occurs
|
*/
|
public int read(byte[] buf, int off, int len) throws IOException {
|
if (buf.length < (len + off - 1)) {
|
throw new IOException("The input buffer is too small: " + len
|
+ " bytes requested starting at offset " + off
|
+ " while the buffer " + " is only " + buf.length
|
+ " bytes long.");
|
}
|
|
// This could of course be optimized
|
int i;
|
for (i = 0; i < len; i++) {
|
int x = read();
|
if (x == -1 && i == 0) { // an immediate -1 returns -1
|
return -1;
|
} else if (x == -1) { // a later -1 returns the chars read so far
|
break;
|
}
|
buf[off + i] = (byte) x;
|
}
|
return i;
|
}
|
|
/***
|
* Returns the decoded form of the given encoded string, as a String. Note
|
* that not all binary data can be represented as a String, so this method
|
* should only be used for encoded String data. Use decodeToBytes()
|
* otherwise.
|
*
|
* @param encoded
|
* the string to decode
|
* @return the decoded form of the encoded string
|
*/
|
public static String decode(String encoded) {
|
return new String(decodeToBytes(encoded));
|
}
|
|
/***
|
* Returns the decoded form of the given encoded string, as bytes.
|
*
|
* @param encoded the string to decode
|
* @return the decoded form of the encoded string
|
*/
|
public static byte[] decodeToBytes(String encoded) {
|
byte[] bytes = null;
|
try {
|
bytes = encoded.getBytes("UTF-8");
|
} catch (Exception e) {
|
e.printStackTrace();
|
}
|
if (bytes != null) {
|
Base64Decoder in = new Base64Decoder(new ByteArrayInputStream(bytes));
|
ByteArrayOutputStream out = new ByteArrayOutputStream((int) (bytes.length * 0.67));
|
|
try {
|
byte[] buf = new byte[4 * 1024]; // 4K buffer
|
int bytesRead;
|
while ((bytesRead = in.read(buf)) != -1) {
|
out.write(buf, 0, bytesRead);
|
}
|
out.close();
|
|
return out.toByteArray();
|
} catch (Exception e) {
|
e.printStackTrace();
|
}
|
}
|
return null;
|
}
|
|
public static void main(String[] args) throws Exception {
|
if (args.length != 1) {
|
System.err.println("Usage: java Base64Decoder fileToDecode");
|
return;
|
}
|
|
Base64Decoder decoder = null;
|
try {
|
decoder = new Base64Decoder(new BufferedInputStream(new FileInputStream(args[0])));
|
byte[] buf = new byte[4 * 1024]; // 4K buffer
|
int bytesRead;
|
while ((bytesRead = decoder.read(buf)) != -1) {
|
System.out.write(buf, 0, bytesRead);
|
}
|
} finally {
|
if (decoder != null)
|
decoder.close();
|
}
|
}
|
}
|
