external/nghttp2/nghttp2_hd_huffman.c

/*
 * nghttp2 - HTTP/2 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"

/*
 * 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 ssize_t huff_encode_sym(nghttp2_bufs *bufs, size_t *avail_ptr,
                               size_t rembits, const nghttp2_huff_sym *sym)
{
    int rv;
    size_t nbits = sym->nbits;
    uint32_t code = sym->code;

    /* We assume that sym->nbits <= 32 */
    if (rembits > nbits) {
        nghttp2_bufs_fast_orb_hold(bufs, (uint8_t)(code << (rembits - nbits)));
        return (ssize_t)(rembits - nbits);
    }

    if (rembits == nbits) {
        nghttp2_bufs_fast_orb(bufs, (uint8_t)code);
        --*avail_ptr;
        return 8;
    }

    nghttp2_bufs_fast_orb(bufs, (uint8_t)(code >> (nbits - rembits)));
    --*avail_ptr;

    nbits -= rembits;
    if (nbits & 0x7) {
        /* align code to MSB byte boundary */
        code <<= 8 - (nbits & 0x7);
    }

    if (*avail_ptr < (nbits + 7) / 8) {
        /* slow path */
        if (nbits > 24) {
            rv = nghttp2_bufs_addb(bufs, (uint8_t)(code >> 24));
            if (rv != 0) {
                return rv;
            }
            nbits -= 8;
        }
        if (nbits > 16) {
            rv = nghttp2_bufs_addb(bufs, (uint8_t)(code >> 16));
            if (rv != 0) {
                return rv;
            }
            nbits -= 8;
        }
        if (nbits > 8) {
            rv = nghttp2_bufs_addb(bufs, (uint8_t)(code >> 8));
            if (rv != 0) {
                return rv;
            }
            nbits -= 8;
        }
        if (nbits == 8) {
            rv = nghttp2_bufs_addb(bufs, (uint8_t)code);
            if (rv != 0) {
                return rv;
            }
            *avail_ptr = nghttp2_bufs_cur_avail(bufs);
            return 8;
        }

        rv = nghttp2_bufs_addb_hold(bufs, (uint8_t)code);
        if (rv != 0) {
            return rv;
        }
        *avail_ptr = nghttp2_bufs_cur_avail(bufs);
        return (ssize_t)(8 - nbits);
    }

    /* fast path, since most code is less than 8 */
    if (nbits < 8) {
        nghttp2_bufs_fast_addb_hold(bufs, (uint8_t)code);
        *avail_ptr = nghttp2_bufs_cur_avail(bufs);
        return (ssize_t)(8 - nbits);
    }

    /* handle longer code path */
    if (nbits > 24) {
        nghttp2_bufs_fast_addb(bufs, (uint8_t)(code >> 24));
        nbits -= 8;
    }

    if (nbits > 16) {
        nghttp2_bufs_fast_addb(bufs, (uint8_t)(code >> 16));
        nbits -= 8;
    }

    if (nbits > 8) {
        nghttp2_bufs_fast_addb(bufs, (uint8_t)(code >> 8));
        nbits -= 8;
    }

    if (nbits == 8) {
        nghttp2_bufs_fast_addb(bufs, (uint8_t)code);
        *avail_ptr = nghttp2_bufs_cur_avail(bufs);
        return 8;
    }

    nghttp2_bufs_fast_addb_hold(bufs, (uint8_t)code);
    *avail_ptr = nghttp2_bufs_cur_avail(bufs);
    return (ssize_t)(8 - nbits);
}

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;
}

int nghttp2_hd_huff_encode(nghttp2_bufs *bufs, const uint8_t *src,
                           size_t srclen)
{
    int rv;
    ssize_t rembits = 8;
    size_t i;
    size_t avail;

    avail = nghttp2_bufs_cur_avail(bufs);

    for (i = 0; i < srclen; ++i) {
        const nghttp2_huff_sym *sym = &huff_sym_table[src[i]];
        if (rembits == 8) {
            if (avail) {
                nghttp2_bufs_fast_addb_hold(bufs, 0);
            } else {
                rv = nghttp2_bufs_addb_hold(bufs, 0);
                if (rv != 0) {
                    return rv;
                }
                avail = nghttp2_bufs_cur_avail(bufs);
            }
        }
        rembits = huff_encode_sym(bufs, &avail, (size_t)rembits, sym);
        if (rembits < 0) {
            return (int)rembits;
        }
    }
    /* 256 is special terminal symbol, pad with its prefix */
    if (rembits < 8) {
        /* if rembits < 8, we should have at least 1 buffer space
           available */
        const nghttp2_huff_sym *sym = &huff_sym_table[256];
        assert(avail);
        /* Caution we no longer adjust avail here */
        nghttp2_bufs_fast_orb(
            bufs, (uint8_t)(sym->code >> (sym->nbits - (size_t)rembits)));
    }

    return 0;
}

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_buf *buf, const uint8_t *src,
                               size_t srclen, int final)
{
    size_t i;

    /* We use the decoding algorithm described in
       http://graphics.ics.uci.edu/pub/Prefix.pdf */
    for (i = 0; i < srclen; ++i) {
        const nghttp2_huff_decode *t;

        t = &huff_decode_table[ctx->state][src[i] >> 4];
        if (t->flags & NGHTTP2_HUFF_FAIL) {
            return NGHTTP2_ERR_HEADER_COMP;
        }
        if (t->flags & NGHTTP2_HUFF_SYM) {
            *buf->last++ = t->sym;
        }

        t = &huff_decode_table[t->state][src[i] & 0xf];
        if (t->flags & NGHTTP2_HUFF_FAIL) {
            return NGHTTP2_ERR_HEADER_COMP;
        }
        if (t->flags & NGHTTP2_HUFF_SYM) {
            *buf->last++ = t->sym;
        }

        ctx->state = t->state;
        ctx->accept = (t->flags & NGHTTP2_HUFF_ACCEPTED) != 0;
    }
    if (final && !ctx->accept) {
        return NGHTTP2_ERR_HEADER_COMP;
    }
    return (ssize_t)i;
}