nghttp2/lib/nghttp2_hd_huffman.c

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/*
* nghttp2 - HTTP/2.0 C Library
*
* Copyright (c) 2013 Tatsuhiro Tsujikawa
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include "nghttp2_hd_huffman.h"
#include <string.h>
#include <assert.h>
#include "nghttp2_hd.h"
extern const nghttp2_huff_sym req_huff_sym_table[];
extern const int16_t req_huff_decode_table[][256];
extern const nghttp2_huff_sym res_huff_sym_table[];
extern const int16_t res_huff_decode_table[][256];
/*
* Returns next 8 bits of data from |in|, starting |bitoff| bits
* offset. If there are fewer bits left than |bitoff|, the left bits
* with padded with 0 are returned. The |bitoff| must be strictly less
* than 8.
*/
static uint8_t get_prefix_byte(const uint8_t *in, size_t len, size_t bitoff)
{
uint8_t b;
size_t bitleft;
if(bitoff == 0) {
return *in;
}
bitleft = 8 - bitoff;
b = (*in & ((1 << bitleft) - 1)) << bitoff;
if(len > 1) {
b |= *(in + 1) >> bitleft;
}
return b;
}
/*
* Decodes next byte from input |in| with length |len|, starting
* |bitoff| bit offset.
*
* This function returns the decoded symbol number (0-255 and 256 for
* special terminal symbol) if it succeeds, or -1.
*/
static int huff_decode(const uint8_t *in, size_t len, size_t bitoff,
const nghttp2_huff_sym *huff_sym_table,
const huff_decode_table_type *huff_decode_table)
{
int rv = 0;
size_t len_orig = len;
if(len == 0) {
return -1;
}
for(;;) {
rv = huff_decode_table[rv][get_prefix_byte(in, len, bitoff)];
if(rv >= 0) {
break;
}
/* Negative return value means we need to lookup next table. */
rv = -rv;
++in;
--len;
if(len == 0) {
return -1;
}
}
if(bitoff + huff_sym_table[rv].nbits > len_orig * 8) {
return -1;
}
return rv;
}
/*
* Returns next LSB aligned |nbits| bits from huffman symbol |sym|,
* starting |codebitoff| bit offset (from beginning of code sequence,
* so it could be more than 8).
*/
static uint8_t huff_get_lsb_aligned(const nghttp2_huff_sym *sym,
size_t codebitoff,
size_t nbits)
{
uint8_t a = sym->code[codebitoff/8];
size_t localbitoff = codebitoff & 0x7;
size_t bitleft = 8 - localbitoff;
if(bitleft >= nbits) {
return (a >> (bitleft - nbits)) & ((1 << nbits) - 1);
} else {
uint8_t b = 0;
a &= ((1 << bitleft) - 1);
a <<= nbits - bitleft;
if((sym->nbits + 7) / 8 > codebitoff / 8 + 1) {
b = sym->code[codebitoff / 8 + 1] >> (8 - (nbits - bitleft));
}
return a | b;
}
}
/*
* Encodes huffman code |sym| into |*dest_ptr|,starting |bitoff|
* offset. The |bitoff| must be strictly less than 8. At the end of
* the process, the |*dest_ptr| is updated and points where next
* output should be placed. The bit offset of the pointed location is
* returned.
*/
static size_t huff_encode_sym(uint8_t **dest_ptr, size_t bitoff,
const nghttp2_huff_sym *sym)
{
size_t b = 0;
if(bitoff == 0) **dest_ptr = 0;
**dest_ptr |= huff_get_lsb_aligned(sym, b, 8 - bitoff);
b += 8 - bitoff;
++*dest_ptr;
for(; b < sym->nbits; b += 8, ++*dest_ptr) {
**dest_ptr = huff_get_lsb_aligned(sym, b, 8);
}
bitoff = 8 - (b - sym->nbits);
if(bitoff > 0) {
--*dest_ptr;
}
return bitoff;
}
size_t nghttp2_hd_huff_encode_count(const uint8_t *src, size_t len,
nghttp2_hd_side side)
{
size_t i;
size_t nbits = 0;
const nghttp2_huff_sym *huff_sym_table;
if(side == NGHTTP2_HD_SIDE_REQUEST) {
huff_sym_table = req_huff_sym_table;
} else {
huff_sym_table = res_huff_sym_table;
}
for(i = 0; i < len; ++i) {
nbits += huff_sym_table[src[i]].nbits;
}
/* pad the prefix of EOS (256) */
return (nbits + 7) / 8;
}
ssize_t nghttp2_hd_huff_encode(uint8_t *dest, size_t destlen,
const uint8_t *src, size_t srclen,
nghttp2_hd_side side)
{
int bitoff = 0;
uint8_t *dest_first = dest;
size_t i;
const nghttp2_huff_sym *huff_sym_table;
if(side == NGHTTP2_HD_SIDE_REQUEST) {
huff_sym_table = req_huff_sym_table;
} else {
huff_sym_table = res_huff_sym_table;
}
for(i = 0; i < srclen; ++i) {
const nghttp2_huff_sym *sym = &huff_sym_table[src[i]];
bitoff = huff_encode_sym(&dest, bitoff, sym);
}
/* 256 is special terminal symbol, pad with its prefix */
if(bitoff > 0) {
*dest |= huff_sym_table[256].code[0] >> bitoff;
}
return dest - dest_first + (bitoff > 0);
}
ssize_t nghttp2_hd_huff_decode_count(const uint8_t *src, size_t srclen,
nghttp2_hd_side side)
{
size_t bitoff = 0;
size_t i, j;
const nghttp2_huff_sym *huff_sym_table;
const huff_decode_table_type *huff_decode_table;
if(side == NGHTTP2_HD_SIDE_REQUEST) {
huff_sym_table = req_huff_sym_table;
huff_decode_table = req_huff_decode_table;
} else {
huff_sym_table = res_huff_sym_table;
huff_decode_table = res_huff_decode_table;
}
j = 0;
for(i = 0; i < srclen;) {
int rv = huff_decode(src + i, srclen - i, bitoff,
huff_sym_table, huff_decode_table);
if(rv == -1) {
/* TODO Check prefix of EOS */
if(i + 1 == srclen && bitoff > 0) {
break;
}
return -1;
}
if(rv == 256) {
/* 256 is special terminal symbol */
break;
}
j++;
bitoff += huff_sym_table[rv].nbits;
i += bitoff / 8;
bitoff &= 0x7;
}
return j;
}
ssize_t nghttp2_hd_huff_decode(uint8_t *dest, size_t destlen,
const uint8_t *src, size_t srclen,
nghttp2_hd_side side)
{
size_t bitoff = 0;
size_t i, j;
const nghttp2_huff_sym *huff_sym_table;
const huff_decode_table_type *huff_decode_table;
if(side == NGHTTP2_HD_SIDE_REQUEST) {
huff_sym_table = req_huff_sym_table;
huff_decode_table = req_huff_decode_table;
} else {
huff_sym_table = res_huff_sym_table;
huff_decode_table = res_huff_decode_table;
}
j = 0;
for(i = 0; i < srclen;) {
int rv = huff_decode(src + i, srclen - i, bitoff,
huff_sym_table, huff_decode_table);
if(rv == -1) {
/* TODO Check prefix of EOS */
if(i + 1 == srclen && bitoff > 0) {
break;
}
return -1;
}
if(rv == 256) {
/* 256 is special terminal symbol */
break;
}
dest[j++] = rv;
bitoff += huff_sym_table[rv].nbits;
i += bitoff / 8;
bitoff &= 0x7;
}
return j;
}