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 huff_sym_table[];
extern const nghttp2_huff_decode huff_decode_table[][16];

/*
 * 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)
{
  size_t i;
  size_t nbits = 0;

  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)
{
  int rembits = 8;
  uint8_t *dest_first = dest;
  size_t i;

  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;
}

void nghttp2_hd_huff_decode_context_init(nghttp2_hd_huff_decode_context *ctx)
{
  ctx->state = 0;
  ctx->accept = 1;
}

ssize_t nghttp2_hd_huff_decode(nghttp2_hd_huff_decode_context *ctx,
                               nghttp2_buffer *dest,
                               const uint8_t *src, size_t srclen, int final)
{
  size_t i, j;
  int rv;
  /* We use the decoding algorithm described in
     http://graphics.ics.uci.edu/pub/Prefix.pdf */
  for(i = 0; i < srclen; ++i) {
    uint8_t in = src[i] >> 4;
    for(j = 0; j < 2; ++j) {
      const nghttp2_huff_decode *t = &huff_decode_table[ctx->state][in];
      if(t->state == -1) {
        return NGHTTP2_ERR_HEADER_COMP;
      }
      if(t->flags & NGHTTP2_HUFF_SYM) {
        rv = nghttp2_buffer_add_byte(dest, t->sym);
        if(rv != 0) {
          return rv;
        }
      }
      ctx->state = t->state;
      ctx->accept = (t->flags & NGHTTP2_HUFF_ACCEPTED) != 0;
      in = src[i] & 0xf;
    }
  }
  if(final && !ctx->accept) {
    return NGHTTP2_ERR_HEADER_COMP;
  }
  return i;
}