1 /*
2  * nghttp2 - HTTP/2 C Library
3  *
4  * Copyright (c) 2013 Tatsuhiro Tsujikawa
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining
7  * a copy of this software and associated documentation files (the
8  * "Software"), to deal in the Software without restriction, including
9  * without limitation the rights to use, copy, modify, merge, publish,
10  * distribute, sublicense, and/or sell copies of the Software, and to
11  * permit persons to whom the Software is furnished to do so, subject to
12  * the following conditions:
13  *
14  * The above copyright notice and this permission notice shall be
15  * included in all copies or substantial portions of the Software.
16  *
17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
19  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
20  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
21  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
22  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
23  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
24  */
25 #ifndef NGHTTP2_HD_HUFFMAN_H
26 #define NGHTTP2_HD_HUFFMAN_H
27 
28 #ifdef HAVE_CONFIG_H
29 #include <config.h>
30 #endif /* HAVE_CONFIG_H */
31 
32 #include "nghttp2.h"
33 
34 typedef enum {
35     /* FSA accepts this state as the end of huffman encoding
36        sequence. */
37     NGHTTP2_HUFF_ACCEPTED = 1,
38     /* This state emits symbol */
39     NGHTTP2_HUFF_SYM = (1 << 1),
40     /* If state machine reaches this state, decoding fails. */
41     NGHTTP2_HUFF_FAIL = (1 << 2)
42 } nghttp2_huff_decode_flag;
43 
44 typedef struct {
45     /* huffman decoding state, which is actually the node ID of internal
46        huffman tree.  We have 257 leaf nodes, but they are identical to
47        root node other than emitting a symbol, so we have 256 internal
48        nodes [1..255], inclusive. */
49     uint8_t state;
50     /* bitwise OR of zero or more of the nghttp2_huff_decode_flag */
51     uint8_t flags;
52     /* symbol if NGHTTP2_HUFF_SYM flag set */
53     uint8_t sym;
54 } nghttp2_huff_decode;
55 
56 typedef nghttp2_huff_decode huff_decode_table_type[16];
57 
58 typedef struct {
59     /* Current huffman decoding state. We stripped leaf nodes, so the
60        value range is [0..255], inclusive. */
61     uint8_t state;
62     /* nonzero if we can say that the decoding process succeeds at this
63        state */
64     uint8_t accept;
65 } nghttp2_hd_huff_decode_context;
66 
67 typedef struct {
68     /* The number of bits in this code */
69     uint32_t nbits;
70     /* Huffman code aligned to LSB */
71     uint32_t code;
72 } nghttp2_huff_sym;
73 
74 extern const nghttp2_huff_sym huff_sym_table[];
75 extern const nghttp2_huff_decode huff_decode_table[][16];
76 
77 #endif /* NGHTTP2_HD_HUFFMAN_H */
78