com.generallycloud.baseio.codec.http2.hpack.HuffmanEncoder Maven / Gradle / Ivy
/*
* Copyright 2015-2017 GenerallyCloud.com
*
* 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.generallycloud.baseio.codec.http2.hpack;
import com.generallycloud.baseio.buffer.ByteBuf;
import com.generallycloud.baseio.buffer.ByteProcessor;
final class HuffmanEncoder {
private final int[] codes;
private final byte[] lengths;
private final EncodedLengthProcessor encodedLengthProcessor = new EncodedLengthProcessor();
private final EncodeProcessor encodeProcessor = new EncodeProcessor();
HuffmanEncoder() {
this(HpackUtil.HUFFMAN_CODES, HpackUtil.HUFFMAN_CODE_LENGTHS);
}
/**
* Creates a new Huffman encoder with the specified Huffman coding.
*
* @param codes the Huffman codes indexed by symbol
* @param lengths the length of each Huffman code
*/
private HuffmanEncoder(int[] codes, byte[] lengths) {
this.codes = codes;
this.lengths = lengths;
}
/**
* Compresses the input string literal using the Huffman coding.
*
* @param out the output stream for the compressed data
* @param data the string literal to be Huffman encoded
*/
public void encode(ByteBuf out, String data) {
encodeSlowPath(out, data);
}
private void encodeSlowPath(ByteBuf out, String data) {
long current = 0;
int n = 0;
for (int i = 0; i < data.length(); i++) {
int b = data.charAt(i) & 0xFF;
int code = codes[b];
int nbits = lengths[b];
current <<= nbits;
current |= code;
n += nbits;
while (n >= 8) {
n -= 8;
out.putByte((byte) (current >> n));
}
}
if (n > 0) {
current <<= 8 - n;
current |= 0xFF >>> n; // this should be EOS symbol
out.putByte((byte) current);
}
}
/**
* Returns the number of bytes required to Huffman encode the input string literal.
*
* @param data the string literal to be Huffman encoded
* @return the number of bytes required to Huffman encode data
*/
public int getEncodedLength(String data) {
return getEncodedLengthSlowPath(data);
}
private int getEncodedLengthSlowPath(String data) {
long len = 0;
for (int i = 0; i < data.length(); i++) {
len += lengths[data.charAt(i) & 0xFF];
}
return (int) ((len + 7) >> 3);
}
private final class EncodeProcessor implements ByteProcessor {
ByteBuf out;
private long current;
private int n;
@Override
public boolean process(byte value) {
int b = value & 0xFF;
int nbits = lengths[b];
current <<= nbits;
current |= codes[b];
n += nbits;
while (n >= 8) {
n -= 8;
out.putByte((byte) (current >> n));
}
return true;
}
void end() {
try {
if (n > 0) {
current <<= 8 - n;
current |= 0xFF >>> n; // this should be EOS symbol
out.putByte((byte) current);
}
} finally {
out = null;
current = 0;
n = 0;
}
}
}
private final class EncodedLengthProcessor implements ByteProcessor {
private long len;
@Override
public boolean process(byte value) {
len += lengths[value & 0xFF];
return true;
}
void reset() {
len = 0;
}
int length() {
return (int) ((len + 7) >> 3);
}
}
}