nghttp2/lib/nghttp2_hd_huffman.c

/*
 * 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 <stdio.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;
  if(bitoff == 0) {
    return *in;
  }
  b = *in << bitoff;
  if(len > 1) {
    b |= *(in + 1) >> (8 - bitoff);
  }
  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;
}
/*
 * Encodes huffman code |sym| into |*dest_ptr|, whose least |rembits|
 * bits are not filled yet.  The |rembits| must be in range [1, 8],
 * inclusive.  At the end of the process, the |*dest_ptr| is updated
 * and points where next output should be placed. The number of
 * unfilled bits in the pointed location is returned.
 */
static size_t huff_encode_sym(uint8_t **dest_ptr, size_t rembits,
                              const nghttp2_huff_sym *sym)
{
  size_t nbits = sym->nbits;
  for(;;) {
    if(rembits > nbits) {
      **dest_ptr |= sym->code << (rembits - nbits);
      rembits -= nbits;
      break;
    }
    **dest_ptr |= sym->code >> (nbits - rembits);
    ++*dest_ptr;
    nbits -= rembits;
    rembits = 8;
    if(nbits == 0) {
      break;
    }
    **dest_ptr = 0;
  }
  return rembits;
}

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 rembits = 8;
  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]];
    if(rembits == 8) {
      *dest = 0;
    }
    rembits = huff_encode_sym(&dest, rembits, sym);
  }
  /* 256 is special terminal symbol, pad with its prefix */
  if(rembits < 8) {
    const nghttp2_huff_sym *sym = &huff_sym_table[256];
    *dest |= sym->code >> (sym->nbits - rembits);
    ++dest;
  }
  return dest - dest_first;
}

static int check_last_byte(const uint8_t *src, size_t srclen, size_t idx,
                           size_t bitoff)
{
  uint8_t last_mask = (1 << (8 - bitoff)) - 1;
  return idx + 1 == srclen && bitoff > 0 &&
    (src[idx] & last_mask) == last_mask;
}

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) {
      if(check_last_byte(src, srclen, i, bitoff)) {
        break;
      }
      return -1;
    }
    if(rv == 256) {
      /* 256 is special terminal symbol and it should not encoded in
         byte string. */
      return -1;
    }
    j++;
    bitoff += huff_sym_table[rv].nbits;
    i += bitoff / 8;
    bitoff &= 0x7;
  }
  return j;
}

ssize_t nghttp2_hd_huff_decode(uint8_t **dest_ptr,
                               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;
  uint8_t *dest = NULL;
  size_t destlen = 0;
  int rv;

  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;) {
    rv = huff_decode(src + i, srclen - i, bitoff,
                     huff_sym_table, huff_decode_table);
    if(rv == -1) {
      if(check_last_byte(src, srclen, i, bitoff)) {
        break;
      }
      rv = NGHTTP2_ERR_HEADER_COMP;
      goto fail;
    }
    if(rv == 256) {
      /* 256 is special terminal symbol and it should not encoded in
         byte string. */
      rv = NGHTTP2_ERR_HEADER_COMP;
      goto fail;
    }
    if(j == destlen) {
      size_t new_len = j == 0 ? 32 : j * 2;
      uint8_t *new_dest = realloc(dest, new_len);
      if(new_dest == NULL) {
        rv = NGHTTP2_ERR_NOMEM;
        goto fail;
      }
      dest = new_dest;
      destlen = new_len;
    }
    dest[j++] = rv;
    bitoff += huff_sym_table[rv].nbits;
    i += bitoff / 8;
    bitoff &= 0x7;
  }
  *dest_ptr = dest;
  return j;
 fail:
  free(dest);
  return rv;
}