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com.squareup.okhttp.internal.spdy.Huffman Maven / Gradle / Ivy
/*
* Copyright 2013 Twitter, Inc.
*
* 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.squareup.okhttp.internal.spdy;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
/**
* This class was originally composed from the following classes in
* Twitter Hpack .
*
* {@code com.twitter.hpack.HuffmanEncoder}
* {@code com.twitter.hpack.HuffmanDecoder}
* {@code com.twitter.hpack.HpackUtil}
*
*/
class Huffman {
// Appendix C: Huffman Codes
// http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-07#appendix-C
private static final int[] CODES = {
0x3ffffba, 0x3ffffbb, 0x3ffffbc, 0x3ffffbd, 0x3ffffbe, 0x3ffffbf, 0x3ffffc0, 0x3ffffc1,
0x3ffffc2, 0x3ffffc3, 0x3ffffc4, 0x3ffffc5, 0x3ffffc6, 0x3ffffc7, 0x3ffffc8, 0x3ffffc9,
0x3ffffca, 0x3ffffcb, 0x3ffffcc, 0x3ffffcd, 0x3ffffce, 0x3ffffcf, 0x3ffffd0, 0x3ffffd1,
0x3ffffd2, 0x3ffffd3, 0x3ffffd4, 0x3ffffd5, 0x3ffffd6, 0x3ffffd7, 0x3ffffd8, 0x3ffffd9, 0x6,
0x1ffc, 0x1f0, 0x3ffc, 0x7ffc, 0x1e, 0x64, 0x1ffd, 0x3fa, 0x1f1, 0x3fb, 0x3fc, 0x65, 0x66,
0x1f, 0x7, 0x0, 0x1, 0x2, 0x8, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0xec, 0x1fffc, 0x27,
0x7ffd, 0x3fd, 0x7ffe, 0x67, 0xed, 0xee, 0x68, 0xef, 0x69, 0x6a, 0x1f2, 0xf0, 0x1f3, 0x1f4,
0x1f5, 0x6b, 0x6c, 0xf1, 0xf2, 0x1f6, 0x1f7, 0x6d, 0x28, 0xf3, 0x1f8, 0x1f9, 0xf4, 0x1fa,
0x1fb, 0x7fc, 0x3ffffda, 0x7fd, 0x3ffd, 0x6e, 0x3fffe, 0x9, 0x6f, 0xa, 0x29, 0xb, 0x70, 0x2a,
0x2b, 0xc, 0xf5, 0xf6, 0x2c, 0x2d, 0x2e, 0xd, 0x2f, 0x1fc, 0x30, 0x31, 0xe, 0x71, 0x72, 0x73,
0x74, 0x75, 0xf7, 0x1fffd, 0xffc, 0x1fffe, 0xffd, 0x3ffffdb, 0x3ffffdc, 0x3ffffdd, 0x3ffffde,
0x3ffffdf, 0x3ffffe0, 0x3ffffe1, 0x3ffffe2, 0x3ffffe3, 0x3ffffe4, 0x3ffffe5, 0x3ffffe6,
0x3ffffe7, 0x3ffffe8, 0x3ffffe9, 0x3ffffea, 0x3ffffeb, 0x3ffffec, 0x3ffffed, 0x3ffffee,
0x3ffffef, 0x3fffff0, 0x3fffff1, 0x3fffff2, 0x3fffff3, 0x3fffff4, 0x3fffff5, 0x3fffff6,
0x3fffff7, 0x3fffff8, 0x3fffff9, 0x3fffffa, 0x3fffffb, 0x3fffffc, 0x3fffffd, 0x3fffffe,
0x3ffffff, 0x1ffff80, 0x1ffff81, 0x1ffff82, 0x1ffff83, 0x1ffff84, 0x1ffff85, 0x1ffff86,
0x1ffff87, 0x1ffff88, 0x1ffff89, 0x1ffff8a, 0x1ffff8b, 0x1ffff8c, 0x1ffff8d, 0x1ffff8e,
0x1ffff8f, 0x1ffff90, 0x1ffff91, 0x1ffff92, 0x1ffff93, 0x1ffff94, 0x1ffff95, 0x1ffff96,
0x1ffff97, 0x1ffff98, 0x1ffff99, 0x1ffff9a, 0x1ffff9b, 0x1ffff9c, 0x1ffff9d, 0x1ffff9e,
0x1ffff9f, 0x1ffffa0, 0x1ffffa1, 0x1ffffa2, 0x1ffffa3, 0x1ffffa4, 0x1ffffa5, 0x1ffffa6,
0x1ffffa7, 0x1ffffa8, 0x1ffffa9, 0x1ffffaa, 0x1ffffab, 0x1ffffac, 0x1ffffad, 0x1ffffae,
0x1ffffaf, 0x1ffffb0, 0x1ffffb1, 0x1ffffb2, 0x1ffffb3, 0x1ffffb4, 0x1ffffb5, 0x1ffffb6,
0x1ffffb7, 0x1ffffb8, 0x1ffffb9, 0x1ffffba, 0x1ffffbb, 0x1ffffbc, 0x1ffffbd, 0x1ffffbe,
0x1ffffbf, 0x1ffffc0, 0x1ffffc1, 0x1ffffc2, 0x1ffffc3, 0x1ffffc4, 0x1ffffc5, 0x1ffffc6,
0x1ffffc7, 0x1ffffc8, 0x1ffffc9, 0x1ffffca, 0x1ffffcb, 0x1ffffcc, 0x1ffffcd, 0x1ffffce,
0x1ffffcf, 0x1ffffd0, 0x1ffffd1, 0x1ffffd2, 0x1ffffd3, 0x1ffffd4, 0x1ffffd5, 0x1ffffd6,
0x1ffffd7, 0x1ffffd8, 0x1ffffd9, 0x1ffffda, 0x1ffffdb
};
private static final byte[] CODE_LENGTHS = {
26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
26, 26, 26, 26, 26, 26, 26, 26, 26, 5, 13, 9, 14, 15, 6, 7, 13, 10, 9, 10, 10, 7, 7, 6, 5, 4,
4, 4, 5, 6, 6, 6, 6, 6, 6, 6, 8, 17, 6, 15, 10, 15, 7, 8, 8, 7, 8, 7, 7, 9, 8, 9, 9, 9, 7, 7,
8, 8, 9, 9, 7, 6, 8, 9, 9, 8, 9, 9, 11, 26, 11, 14, 7, 18, 5, 7, 5, 6, 5, 7, 6, 6, 5, 8, 8, 6,
6, 6, 5, 6, 9, 6, 6, 5, 7, 7, 7, 7, 7, 8, 17, 12, 17, 12, 26, 26, 26, 26, 26, 26, 26, 26, 26,
26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
26, 26, 26, 26, 26, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
25, 25, 25, 25, 25
};
private static final Huffman INSTANCE = new Huffman();
public static Huffman get() {
return INSTANCE;
}
private final Node root = new Node();
private Huffman() {
buildTree();
}
void encode(byte[] data, OutputStream out) throws IOException {
long current = 0;
int n = 0;
for (int i = 0; i < data.length; i++) {
int b = data[i] & 0xFF;
int code = CODES[b];
int nbits = CODE_LENGTHS[b];
current <<= nbits;
current |= code;
n += nbits;
while (n >= 8) {
n -= 8;
out.write(((int) (current >> n)));
}
}
if (n > 0) {
current <<= (8 - n);
current |= (0xFF >>> n);
out.write((int) current);
}
}
int encodedLength(byte[] bytes) {
long len = 0;
for (int i = 0; i < bytes.length; i++) {
int b = bytes[i] & 0xFF;
len += CODE_LENGTHS[b];
}
return (int) ((len + 7) >> 3);
}
byte[] decode(byte[] buf) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
Node node = root;
int current = 0;
int nbits = 0;
for (int i = 0; i < buf.length; i++) {
int b = buf[i] & 0xFF;
current = (current << 8) | b;
nbits += 8;
while (nbits >= 8) {
int c = (current >>> (nbits - 8)) & 0xFF;
node = node.children[c];
if (node.children == null) {
// terminal node
baos.write(node.symbol);
nbits -= node.terminalBits;
node = root;
} else {
// non-terminal node
nbits -= 8;
}
}
}
while (nbits > 0) {
int c = (current << (8 - nbits)) & 0xFF;
node = node.children[c];
if (node.children != null || node.terminalBits > nbits) {
break;
}
baos.write(node.symbol);
nbits -= node.terminalBits;
node = root;
}
return baos.toByteArray();
}
private void buildTree() {
for (int i = 0; i < CODE_LENGTHS.length; i++) {
addCode(i, CODES[i], CODE_LENGTHS[i]);
}
}
private void addCode(int sym, int code, byte len) {
Node terminal = new Node(sym, len);
Node current = root;
while (len > 8) {
len -= 8;
int i = ((code >>> len) & 0xFF);
if (current.children == null) {
throw new IllegalStateException("invalid dictionary: prefix not unique");
}
if (current.children[i] == null) {
current.children[i] = new Node();
}
current = current.children[i];
}
int shift = 8 - len;
int start = (code << shift) & 0xFF;
int end = 1 << shift;
for (int i = start; i < start + end; i++) {
current.children[i] = terminal;
}
}
private static final class Node {
// Null if terminal.
private final Node[] children;
// Terminal nodes have a symbol.
private final int symbol;
// Number of bits represented in the terminal node.
private final int terminalBits;
/** Construct an internal node. */
Node() {
this.children = new Node[256];
this.symbol = 0; // Not read.
this.terminalBits = 0; // Not read.
}
/**
* Construct a terminal node.
*
* @param symbol symbol the node represents
* @param bits length of Huffman code in bits
*/
Node(int symbol, int bits) {
this.children = null;
this.symbol = symbol;
int b = bits & 0x07;
this.terminalBits = b == 0 ? 8 : b;
}
}
}
