Skip to content

Instantly share code, notes, and snippets.

@mumayank

mumayank/Base64.java

Created June 12, 2017 15:42
Show Gist options
  • Save mumayank/3481ddb87cf1a2fd1ac37e5b7c47eda4 to your computer and use it in GitHub Desktop.
Save mumayank/3481ddb87cf1a2fd1ac37e5b7c47eda4 to your computer and use it in GitHub Desktop.
Download ZIP
Raw
Base64.java
import java.io.UnsupportedEncodingException;
/**
* Utilities for encoding and decoding the Base64 representation of
* binary data. See RFCs <a
* href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a
* href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.
*/
public class Base64 {
/**
* Default values for encoder/decoder flags.
*/
public static final int DEFAULT = 0;
/**
* Encoder flag bit to omit the padding '=' characters at the end
* of the output (if any).
*/
public static final int NO_PADDING = 1;
/**
* Encoder flag bit to omit all line terminators (i.e., the output
* will be on one long line).
*/
private static final int NO_WRAP = 2;
/**
* Encoder flag bit to indicate lines should be terminated with a
* CRLF pair instead of just an LF. Has no effect if {@code
* NO_WRAP} is specified as well.
*/
private static final int CRLF = 4;
/**
* Encoder/decoder flag bit to indicate using the "URL and
* filename safe" variant of Base64 (see RFC 3548 section 4) where
* {@code -} and {@code _} are used in place of {@code +} and
* {@code /}.
*/
private static final int URL_SAFE = 8;
// --------------------------------------------------------
// shared code
// --------------------------------------------------------
private static abstract class Coder {
byte[] output;
int op;
}
// --------------------------------------------------------
// decoding
// --------------------------------------------------------
/**
* Decode the Base64-encoded data in input and return the data in
* a new byte array.
*
* <p>The padding '=' characters at the end are considered optional, but
* if any are present, there must be the correct number of them.
*
* @param str the input String to decode, which is converted to
* bytes using the default charset
* @param flags controls certain features of the decoded output.
* Pass {@code DEFAULT} to decode standard Base64.
*
* @throws IllegalArgumentException if the input contains
* incorrect padding
*/
public static byte[] decode(String str, int flags) {
return decode(str.getBytes(), flags);
}
/**
* Decode the Base64-encoded data in input and return the data in
* a new byte array.
*
* <p>The padding '=' characters at the end are considered optional, but
* if any are present, there must be the correct number of them.
*
* @param input the input array to decode
* @param flags controls certain features of the decoded output.
* Pass {@code DEFAULT} to decode standard Base64.
*
* @throws IllegalArgumentException if the input contains
* incorrect padding
*/
private static byte[] decode(byte[] input, int flags) {
return decode(input, 0, input.length, flags);
}
/**
* Decode the Base64-encoded data in input and return the data in
* a new byte array.
*
* <p>The padding '=' characters at the end are considered optional, but
* if any are present, there must be the correct number of them.
*
* @param input the data to decode
* @param offset the position within the input array at which to start
* @param len the number of bytes of input to decode
* @param flags controls certain features of the decoded output.
* Pass {@code DEFAULT} to decode standard Base64.
*
* @throws IllegalArgumentException if the input contains
* incorrect padding
*/
private static byte[] decode(byte[] input, int offset, int len, int flags) {
// Allocate space for the most data the input could represent.
// (It could contain less if it contains whitespace, etc.)
Decoder decoder = new Decoder(flags, new byte[len*3/4]);
if (!decoder.process(input, offset, len, true)) {
throw new IllegalArgumentException("bad base-64");
}
// Maybe we got lucky and allocated exactly enough output space.
if (decoder.op == decoder.output.length) {
return decoder.output;
}
// Need to shorten the array, so allocate a new one of the
// right size and copy.
byte[] temp = new byte[decoder.op];
System.arraycopy(decoder.output, 0, temp, 0, decoder.op);
return temp;
}
private static class Decoder extends Coder {
/**
* Lookup table for turning bytes into their position in the
* Base64 alphabet.
*/
private static final int DECODE[] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};
/**
* Decode lookup table for the "web safe" variant (RFC 3548
* sec. 4) where - and _ replace + and /.
*/
private static final int DECODE_WEBSAFE[] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63,
-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};
/** Non-data values in the DECODE arrays. */
private static final int SKIP = -1;
private static final int EQUALS = -2;
/**
* States 0-3 are reading through the next input tuple.
* State 4 is having read one '=' and expecting exactly
* one more.
* State 5 is expecting no more data or padding characters
* in the input.
* State 6 is the error state; an error has been detected
* in the input and no future input can "fix" it.
*/
private int state; // state number (0 to 6)
private int value;
final private int[] alphabet;
Decoder(int flags, byte[] output) {
this.output = output;
alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
state = 0;
value = 0;
}
/**
* Decode another block of input data.
*
* @return true if the state machine is still healthy. false if
* bad base-64 data has been detected in the input stream.
*/
boolean process(byte[] input, int offset, int len, boolean finish) {
if (this.state == 6) return false;
int p = offset;
len += offset;
// Using local variables makes the decoder about 12%
// faster than if we manipulate the member variables in
// the loop. (Even alphabet makes a measurable
// difference, which is somewhat surprising to me since
// the member variable is final.)
int state = this.state;
int value = this.value;
int op = 0;
final byte[] output = this.output;
final int[] alphabet = this.alphabet;
while (p < len) {
// Try the fast path: we're starting a new tuple and the
// next four bytes of the input stream are all data
// bytes. This corresponds to going through states
// 0-1-2-3-0. We expect to use this method for most of
// the data.
//
// If any of the next four bytes of input are non-data
// (whitespace, etc.), value will end up negative. (All
// the non-data values in decode are small negative
// numbers, so shifting any of them up and or'ing them
// together will result in a value with its top bit set.)
//
// You can remove this whole block and the output should
// be the same, just slower.
if (state == 0) {
while (p+4 <= len &&
(value = ((alphabet[input[p] & 0xff] << 18) |
(alphabet[input[p+1] & 0xff] << 12) |
(alphabet[input[p+2] & 0xff] << 6) |
(alphabet[input[p+3] & 0xff]))) >= 0) {
output[op+2] = (byte) value;
output[op+1] = (byte) (value >> 8);
output[op] = (byte) (value >> 16);
op += 3;
p += 4;
}
if (p >= len) break;
}
// The fast path isn't available -- either we've read a
// partial tuple, or the next four input bytes aren't all
// data, or whatever. Fall back to the slower state
// machine implementation.
int d = alphabet[input[p++] & 0xff];
switch (state) {
case 0:
if (d >= 0) {
value = d;
++state;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 1:
if (d >= 0) {
value = (value << 6) | d;
++state;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 2:
if (d >= 0) {
value = (value << 6) | d;
++state;
} else if (d == EQUALS) {
// Emit the last (partial) output tuple;
// expect exactly one more padding character.
output[op++] = (byte) (value >> 4);
state = 4;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 3:
if (d >= 0) {
// Emit the output triple and return to state 0.
value = (value << 6) | d;
output[op+2] = (byte) value;
output[op+1] = (byte) (value >> 8);
output[op] = (byte) (value >> 16);
op += 3;
state = 0;
} else if (d == EQUALS) {
// Emit the last (partial) output tuple;
// expect no further data or padding characters.
output[op+1] = (byte) (value >> 2);
output[op] = (byte) (value >> 10);
op += 2;
state = 5;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 4:
if (d == EQUALS) {
++state;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 5:
if (d != SKIP) {
this.state = 6;
return false;
}
break;
}
}
if (!finish) {
// We're out of input, but a future call could provide
// more.
this.state = state;
this.value = value;
this.op = op;
return true;
}
// Done reading input. Now figure out where we are left in
// the state machine and finish up.
switch (state) {
case 0:
// Output length is a multiple of three. Fine.
break;
case 1:
// Read one extra input byte, which isn't enough to
// make another output byte. Illegal.
this.state = 6;
return false;
case 2:
// Read two extra input bytes, enough to emit 1 more
// output byte. Fine.
output[op++] = (byte) (value >> 4);
break;
case 3:
// Read three extra input bytes, enough to emit 2 more
// output bytes. Fine.
output[op++] = (byte) (value >> 10);
output[op++] = (byte) (value >> 2);
break;
case 4:
// Read one padding '=' when we expected 2. Illegal.
this.state = 6;
return false;
case 5:
// Read all the padding '='s we expected and no more.
// Fine.
break;
}
this.state = state;
this.op = op;
return true;
}
}
// --------------------------------------------------------
// encoding
// --------------------------------------------------------
/**
* Base64-encode the given data and return a newly allocated
* String with the result.
*
* @param input the data to encode
* @param flags controls certain features of the encoded output.
* Passing {@code DEFAULT} results in output that
* adheres to RFC 2045.
*/
public static String encodeToString(byte[] input, int flags) {
try {
return new String(encode(input, flags), "US-ASCII");
} catch (UnsupportedEncodingException e) {
// US-ASCII is guaranteed to be available.
throw new AssertionError(e);
}
}
/**
* Base64-encode the given data and return a newly allocated
* byte[] with the result.
*
* @param input the data to encode
* @param flags controls certain features of the encoded output.
* Passing {@code DEFAULT} results in output that
* adheres to RFC 2045.
*/
private static byte[] encode(byte[] input, int flags) {
return encode(input, 0, input.length, flags);
}
/**
* Base64-encode the given data and return a newly allocated
* byte[] with the result.
*
* @param input the data to encode
* @param offset the position within the input array at which to
* start
* @param len the number of bytes of input to encode
* @param flags controls certain features of the encoded output.
* Passing {@code DEFAULT} results in output that
* adheres to RFC 2045.
*/
private static byte[] encode(byte[] input, int offset, int len, int flags) {
Encoder encoder = new Encoder(flags, null);
// Compute the exact length of the array we will produce.
int output_len = len / 3 * 4;
// Account for the tail of the data and the padding bytes, if any.
if (encoder.do_padding) {
if (len % 3 > 0) {
output_len += 4;
}
} else {
switch (len % 3) {
case 0: break;
case 1: output_len += 2; break;
case 2: output_len += 3; break;
}
}
// Account for the newlines, if any.
if (encoder.do_newline && len > 0) {
output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *
(encoder.do_cr ? 2 : 1);
}
encoder.output = new byte[output_len];
encoder.process(input, offset, len, true);
assert encoder.op == output_len;
return encoder.output;
}
private static class Encoder extends Coder {
/**
* Emit a new line every this many output tuples. Corresponds to
* a 76-character line length (the maximum allowable according to
* <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
*/
static final int LINE_GROUPS = 19;
/**
* Lookup table for turning Base64 alphabet positions (6 bits)
* into output bytes.
*/
private static final byte ENCODE[] = {
'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', '+', '/',
};
/**
* Lookup table for turning Base64 alphabet positions (6 bits)
* into output bytes.
*/
private static final byte ENCODE_WEBSAFE[] = {
'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', '-', '_',
};
final private byte[] tail;
/* package */ int tailLen;
private int count;
final boolean do_padding;
final boolean do_newline;
final boolean do_cr;
final private byte[] alphabet;
Encoder(int flags, byte[] output) {
this.output = output;
do_padding = (flags & NO_PADDING) == 0;
do_newline = (flags & NO_WRAP) == 0;
do_cr = (flags & CRLF) != 0;
alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;
tail = new byte[2];
tailLen = 0;
count = do_newline ? LINE_GROUPS : -1;
}
void process(byte[] input, int offset, int len, boolean finish) {
// Using local variables makes the encoder about 9% faster.
final byte[] alphabet = this.alphabet;
final byte[] output = this.output;
int op = 0;
int count = this.count;
int p = offset;
len += offset;
int v = -1;
// First we need to concatenate the tail of the previous call
// with any input bytes available now and see if we can empty
// the tail.
switch (tailLen) {
case 0:
// There was no tail.
break;
case 1:
if (p+2 <= len) {
// A 1-byte tail with at least 2 bytes of
// input available now.
v = ((tail[0] & 0xff) << 16) |
((input[p++] & 0xff) << 8) |
(input[p++] & 0xff);
tailLen = 0;
}
break;
case 2:
if (p+1 <= len) {
// A 2-byte tail with at least 1 byte of input.
v = ((tail[0] & 0xff) << 16) |
((tail[1] & 0xff) << 8) |
(input[p++] & 0xff);
tailLen = 0;
}
break;
}
if (v != -1) {
output[op++] = alphabet[(v >> 18) & 0x3f];
output[op++] = alphabet[(v >> 12) & 0x3f];
output[op++] = alphabet[(v >> 6) & 0x3f];
output[op++] = alphabet[v & 0x3f];
if (--count == 0) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
count = LINE_GROUPS;
}
}
// At this point either there is no tail, or there are fewer
// than 3 bytes of input available.
// The main loop, turning 3 input bytes into 4 output bytes on
// each iteration.
while (p+3 <= len) {
v = ((input[p] & 0xff) << 16) |
((input[p+1] & 0xff) << 8) |
(input[p+2] & 0xff);
output[op] = alphabet[(v >> 18) & 0x3f];
output[op+1] = alphabet[(v >> 12) & 0x3f];
output[op+2] = alphabet[(v >> 6) & 0x3f];
output[op+3] = alphabet[v & 0x3f];
p += 3;
op += 4;
if (--count == 0) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
count = LINE_GROUPS;
}
}
if (finish) {
// Finish up the tail of the input. Note that we need to
// consume any bytes in tail before any bytes
// remaining in input; there should be at most two bytes
// total.
if (p-tailLen == len-1) {
int t = 0;
v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
tailLen -= t;
output[op++] = alphabet[(v >> 6) & 0x3f];
output[op++] = alphabet[v & 0x3f];
if (do_padding) {
output[op++] = '=';
output[op++] = '=';
}
if (do_newline) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
}
} else if (p-tailLen == len-2) {
int t = 0;
v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |
(((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
tailLen -= t;
output[op++] = alphabet[(v >> 12) & 0x3f];
output[op++] = alphabet[(v >> 6) & 0x3f];
output[op++] = alphabet[v & 0x3f];
if (do_padding) {
output[op++] = '=';
}
if (do_newline) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
}
} else if (do_newline && op > 0 && count != LINE_GROUPS) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
}
assert tailLen == 0;
assert p == len;
} else {
// Save the leftovers in tail to be consumed on the next
// call to encodeInternal.
if (p == len-1) {
tail[tailLen++] = input[p];
} else if (p == len-2) {
tail[tailLen++] = input[p];
tail[tailLen++] = input[p+1];
}
}
this.op = op;
this.count = count;
}
}
private Base64() { } // don't instantiate
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment