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
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
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
|
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package hpack
import (
"bytes"
"errors"
"io"
"sync"
)
var bufPool = sync.Pool{
New: func() interface{} { return new(bytes.Buffer) },
}
// HuffmanDecode decodes the string in v and writes the expanded
// result to w, returning the number of bytes written to w and the
// Write call's return value. At most one Write call is made.
func HuffmanDecode(w io.Writer, v []byte) (int, error) {
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
defer bufPool.Put(buf)
if err := huffmanDecode(buf, 0, v); err != nil {
return 0, err
}
return w.Write(buf.Bytes())
}
// HuffmanDecodeToString decodes the string in v.
func HuffmanDecodeToString(v []byte) (string, error) {
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
defer bufPool.Put(buf)
if err := huffmanDecode(buf, 0, v); err != nil {
return "", err
}
return buf.String(), nil
}
// ErrInvalidHuffman is returned for errors found decoding
// Huffman-encoded strings.
var ErrInvalidHuffman = errors.New("hpack: invalid Huffman-encoded data")
// huffmanDecode decodes v to buf.
// If maxLen is greater than 0, attempts to write more to buf than
// maxLen bytes will return ErrStringLength.
func huffmanDecode(buf *bytes.Buffer, maxLen int, v []byte) error {
rootHuffmanNode := getRootHuffmanNode()
n := rootHuffmanNode
// cur is the bit buffer that has not been fed into n.
// cbits is the number of low order bits in cur that are valid.
// sbits is the number of bits of the symbol prefix being decoded.
cur, cbits, sbits := uint(0), uint8(0), uint8(0)
for _, b := range v {
cur = cur<<8 | uint(b)
cbits += 8
sbits += 8
for cbits >= 8 {
idx := byte(cur >> (cbits - 8))
n = n.children[idx]
if n == nil {
return ErrInvalidHuffman
}
if n.children == nil {
if maxLen != 0 && buf.Len() == maxLen {
return ErrStringLength
}
buf.WriteByte(n.sym)
cbits -= n.codeLen
n = rootHuffmanNode
sbits = cbits
} else {
cbits -= 8
}
}
}
for cbits > 0 {
n = n.children[byte(cur<<(8-cbits))]
if n == nil {
return ErrInvalidHuffman
}
if n.children != nil || n.codeLen > cbits {
break
}
if maxLen != 0 && buf.Len() == maxLen {
return ErrStringLength
}
buf.WriteByte(n.sym)
cbits -= n.codeLen
n = rootHuffmanNode
sbits = cbits
}
if sbits > 7 {
// Either there was an incomplete symbol, or overlong padding.
// Both are decoding errors per RFC 7541 section 5.2.
return ErrInvalidHuffman
}
if mask := uint(1<<cbits - 1); cur&mask != mask {
// Trailing bits must be a prefix of EOS per RFC 7541 section 5.2.
return ErrInvalidHuffman
}
return nil
}
type node struct {
// children is non-nil for internal nodes
children *[256]*node
// The following are only valid if children is nil:
codeLen uint8 // number of bits that led to the output of sym
sym byte // output symbol
}
func newInternalNode() *node {
return &node{children: new([256]*node)}
}
var (
buildRootOnce sync.Once
lazyRootHuffmanNode *node
)
func getRootHuffmanNode() *node {
buildRootOnce.Do(buildRootHuffmanNode)
return lazyRootHuffmanNode
}
func buildRootHuffmanNode() {
if len(huffmanCodes) != 256 {
panic("unexpected size")
}
lazyRootHuffmanNode = newInternalNode()
for i, code := range huffmanCodes {
addDecoderNode(byte(i), code, huffmanCodeLen[i])
}
}
func addDecoderNode(sym byte, code uint32, codeLen uint8) {
cur := lazyRootHuffmanNode
for codeLen > 8 {
codeLen -= 8
i := uint8(code >> codeLen)
if cur.children[i] == nil {
cur.children[i] = newInternalNode()
}
cur = cur.children[i]
}
shift := 8 - codeLen
start, end := int(uint8(code<<shift)), int(1<<shift)
for i := start; i < start+end; i++ {
cur.children[i] = &node{sym: sym, codeLen: codeLen}
}
}
// AppendHuffmanString appends s, as encoded in Huffman codes, to dst
// and returns the extended buffer.
func AppendHuffmanString(dst []byte, s string) []byte {
rembits := uint8(8)
for i := 0; i < len(s); i++ {
if rembits == 8 {
dst = append(dst, 0)
}
dst, rembits = appendByteToHuffmanCode(dst, rembits, s[i])
}
if rembits < 8 {
// special EOS symbol
code := uint32(0x3fffffff)
nbits := uint8(30)
t := uint8(code >> (nbits - rembits))
dst[len(dst)-1] |= t
}
return dst
}
// HuffmanEncodeLength returns the number of bytes required to encode
// s in Huffman codes. The result is round up to byte boundary.
func HuffmanEncodeLength(s string) uint64 {
n := uint64(0)
for i := 0; i < len(s); i++ {
n += uint64(huffmanCodeLen[s[i]])
}
return (n + 7) / 8
}
// appendByteToHuffmanCode appends Huffman code for c to dst and
// returns the extended buffer and the remaining bits in the last
// element. The appending is not byte aligned and the remaining bits
// in the last element of dst is given in rembits.
func appendByteToHuffmanCode(dst []byte, rembits uint8, c byte) ([]byte, uint8) {
code := huffmanCodes[c]
nbits := huffmanCodeLen[c]
for {
if rembits > nbits {
t := uint8(code << (rembits - nbits))
dst[len(dst)-1] |= t
rembits -= nbits
break
}
t := uint8(code >> (nbits - rembits))
dst[len(dst)-1] |= t
nbits -= rembits
rembits = 8
if nbits == 0 {
break
}
dst = append(dst, 0)
}
return dst, rembits
}
|
