BaseNCodec.java
/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.facebook.presto.common.type.encoding;
import java.util.Arrays;
/**
* Abstract superclass for Base-N encoders and decoders.
*
* <p>
* This class is thread-safe.
* </p>
*
* @version $Id: BaseNCodec.java 1634404 2014-10-26 23:06:10Z ggregory $
*/
public abstract class BaseNCodec
{
/**
* Holds thread context so classes can be thread-safe.
* <p>
* This class is not itself thread-safe; each thread must allocate its own copy.
*
* @since 1.7
*/
static class Context
{
/**
* Place holder for the bytes we're dealing with for our based logic.
* Bitwise operations store and extract the encoding or decoding from this variable.
*/
int ibitWorkArea;
/**
* Place holder for the bytes we're dealing with for our based logic.
* Bitwise operations store and extract the encoding or decoding from this variable.
*/
long lbitWorkArea;
/**
* Buffer for streaming.
*/
byte[] buffer;
/**
* Position where next character should be written in the buffer.
*/
int pos;
/**
* Position where next character should be read from the buffer.
*/
int readPos;
/**
* Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless,
* and must be thrown away.
*/
boolean eof;
/**
* Variable tracks how many characters have been written to the current line. Only used when encoding. We use
* it to make sure each encoded line never goes beyond lineLength (if lineLength > 0).
*/
int currentLinePos;
/**
* Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This
* variable helps track that.
*/
int modulus;
Context()
{
}
/**
* Returns a String useful for debugging (especially within a debugger.)
*
* @return a String useful for debugging.
*/
@SuppressWarnings("boxing") // OK to ignore boxing here
@Override
public String toString()
{
return String.format("%s[buffer=%s, currentLinePos=%s, eof=%s, ibitWorkArea=%s, lbitWorkArea=%s, " +
"modulus=%s, pos=%s, readPos=%s]", this.getClass().getSimpleName(), Arrays.toString(buffer),
currentLinePos, eof, ibitWorkArea, lbitWorkArea, modulus, pos, readPos);
}
}
/**
* EOF
*
* @since 1.7
*/
static final int EOF = -1;
private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;
/**
* Defines the default buffer size - currently {@value}
* - must be large enough for at least one encoded block+separator
*/
private static final int DEFAULT_BUFFER_SIZE = 8192;
/**
* Mask used to extract 8 bits, used in decoding bytes
*/
protected static final int MASK_8BITS = 0xff;
/**
* Byte used to pad output.
*/
protected static final byte PAD_DEFAULT = '='; // Allow static access to default
protected final byte pad; // instance variable just in case it needs to vary later
/**
* Number of bytes in each full block of encoded data, e.g. 3 for Base64 and 8 for Base32
*/
private final int encodedBlockSize;
/**
* Chunksize for encoding. Not used when decoding.
* A value of zero or less implies no chunking of the encoded data.
* Rounded down to nearest multiple of encodedBlockSize.
*/
protected final int lineLength;
/**
* Note <code>lineLength</code> is rounded down to the nearest multiple of {@link #encodedBlockSize}
* If <code>chunkSeparatorLength</code> is zero, then chunking is disabled.
*
* @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
* @param lineLength if > 0, use chunking with a length <code>lineLength</code>
* @param chunkSeparatorLength the chunk separator length, if relevant
*/
protected BaseNCodec(final int encodedBlockSize,
final int lineLength, final int chunkSeparatorLength)
{
this(encodedBlockSize, lineLength, chunkSeparatorLength, PAD_DEFAULT);
}
/**
* Note <code>lineLength</code> is rounded down to the nearest multiple of {@link #encodedBlockSize}
* If <code>chunkSeparatorLength</code> is zero, then chunking is disabled.
*
* @param encodedBlockSize the size of an encoded block (e.g. Base64 = 4)
* @param lineLength if > 0, use chunking with a length <code>lineLength</code>
* @param chunkSeparatorLength the chunk separator length, if relevant
* @param pad byte used as padding byte.
*/
BaseNCodec(final int encodedBlockSize,
final int lineLength, final int chunkSeparatorLength, final byte pad)
{
this.encodedBlockSize = encodedBlockSize;
final boolean useChunking = lineLength > 0 && chunkSeparatorLength > 0;
this.lineLength = useChunking ? (lineLength / encodedBlockSize) * encodedBlockSize : 0;
this.pad = pad;
}
/**
* Returns the amount of buffered data available for reading.
*
* @param context the context to be used
* @return The amount of buffered data available for reading.
*/
private int available(final Context context)
{ // package protected for access from I/O streams
return context.buffer != null ? context.pos - context.readPos : 0;
}
/**
* Get the default buffer size. Can be overridden.
*
* @return {@link #DEFAULT_BUFFER_SIZE}
*/
private int getDefaultBufferSize()
{
return DEFAULT_BUFFER_SIZE;
}
/**
* Increases our buffer by the {@link #DEFAULT_BUFFER_RESIZE_FACTOR}.
*
* @param context the context to be used
*/
private byte[] resizeBuffer(final Context context)
{
if (context.buffer == null) {
context.buffer = new byte[getDefaultBufferSize()];
context.pos = 0;
context.readPos = 0;
}
else {
final byte[] b = new byte[context.buffer.length * DEFAULT_BUFFER_RESIZE_FACTOR];
System.arraycopy(context.buffer, 0, b, 0, context.buffer.length);
context.buffer = b;
}
return context.buffer;
}
/**
* Ensure that the buffer has room for <code>size</code> bytes
*
* @param size minimum spare space required
* @param context the context to be used
* @return the buffer
*/
byte[] ensureBufferSize(final int size, final Context context)
{
if ((context.buffer == null) || (context.buffer.length < context.pos + size)) {
return resizeBuffer(context);
}
return context.buffer;
}
/**
* Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
* bytes. Returns how many bytes were actually extracted.
* <p>
* Package protected for access from I/O streams.
*
* @param b byte[] array to extract the buffered data into.
* @param bPos position in byte[] array to start extraction at.
* @param bAvail amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
* @param context the context to be used
* @return The number of bytes successfully extracted into the provided byte[] array.
*/
int readResults(final byte[] b, final int bPos, final int bAvail, final Context context)
{
if (context.buffer != null) {
final int len = Math.min(available(context), bAvail);
System.arraycopy(context.buffer, context.readPos, b, bPos, len);
context.readPos += len;
if (context.readPos >= context.pos) {
context.buffer = null; // so hasData() will return false, and this method can return -1
}
return len;
}
return context.eof ? EOF : 0;
}
/**
* Checks if a byte value is whitespace or not.
* Whitespace is taken to mean: space, tab, CR, LF
*
* @param byteToCheck the byte to check
* @return true if byte is whitespace, false otherwise
*/
protected static boolean isWhiteSpace(final byte byteToCheck)
{
switch (byteToCheck) {
case ' ':
case '\n':
case '\r':
case '\t':
return true;
default:
return false;
}
}
/**
* Encodes a byte[] containing binary data, into a String containing characters in the appropriate alphabet.
* Uses UTF8 encoding.
*
* @param pArray a byte array containing binary data
* @return String containing only character data in the appropriate alphabet.
*/
public String encodeAsString(final byte[] pArray)
{
return StringUtils.newStringUtf8(encode(pArray));
}
/**
* Decodes a String containing characters in the Base-N alphabet.
*
* @param pArray A String containing Base-N character data
* @return a byte array containing binary data
*/
public byte[] decode(final String pArray)
{
return decode(StringUtils.getBytesUtf8(pArray));
}
/**
* Decodes a byte[] containing characters in the Base-N alphabet.
*
* @param pArray A byte array containing Base-N character data
* @return a byte array containing binary data
*/
public byte[] decode(final byte[] pArray)
{
if (pArray == null || pArray.length == 0) {
return pArray;
}
final Context context = new Context();
decode(pArray, 0, pArray.length, context);
decode(pArray, 0, EOF, context); // Notify decoder of EOF.
final byte[] result = new byte[context.pos];
readResults(result, 0, result.length, context);
return result;
}
/**
* Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
*
* @param pArray a byte array containing binary data
* @return A byte array containing only the base-n alphabetic character data
*/
public byte[] encode(final byte[] pArray)
{
if (pArray == null || pArray.length == 0) {
return pArray;
}
final Context context = new Context();
encode(pArray, 0, pArray.length, context);
encode(pArray, 0, EOF, context); // Notify encoder of EOF.
final byte[] buf = new byte[context.pos - context.readPos];
readResults(buf, 0, buf.length, context);
return buf;
}
// package protected for access from I/O streams
abstract void encode(byte[] pArray, int i, int length, Context context);
// package protected for access from I/O streams
abstract void decode(byte[] pArray, int i, int length, Context context);
/**
* Returns whether or not the <code>octet</code> is in the current alphabet.
* Does not allow whitespace or pad.
*
* @param value The value to test
* @return <code>true</code> if the value is defined in the current alphabet, <code>false</code> otherwise.
*/
protected abstract boolean isInAlphabet(byte value);
/**
* Tests a given byte array to see if it contains any characters within the alphabet or PAD.
* <p>
* Intended for use in checking line-ending arrays
*
* @param arrayOctet byte array to test
* @return <code>true</code> if any byte is a valid character in the alphabet or PAD; <code>false</code> otherwise
*/
boolean containsAlphabetOrPad(final byte[] arrayOctet)
{
if (arrayOctet == null) {
return false;
}
for (final byte element : arrayOctet) {
if (pad == element || isInAlphabet(element)) {
return true;
}
}
return false;
}
}