source: vbox/trunk/src/libs/liblzma-5.4.1/common/auto_decoder.c

///////////////////////////////////////////////////////////////////////////////
//
/// \file       auto_decoder.c
/// \brief      Autodetect between .xz, .lzma (LZMA_Alone), and .lz (lzip)
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "stream_decoder.h"
#include "alone_decoder.h"
#ifdef HAVE_LZIP_DECODER
#       include "lzip_decoder.h"
#endif


typedef struct {
        /// .xz Stream decoder, LZMA_Alone decoder, or lzip decoder
        lzma_next_coder next;

        uint64_t memlimit;
        uint32_t flags;

        enum {
                SEQ_INIT,
                SEQ_CODE,
                SEQ_FINISH,
        } sequence;
} lzma_auto_coder;


static lzma_ret
auto_decode(void *coder_ptr, const lzma_allocator *allocator,
                const uint8_t *restrict in, size_t *restrict in_pos,
                size_t in_size, uint8_t *restrict out,
                size_t *restrict out_pos, size_t out_size, lzma_action action)
{
        lzma_auto_coder *coder = coder_ptr;

        switch (coder->sequence) {
        case SEQ_INIT:
                if (*in_pos >= in_size)
                        return LZMA_OK;

                // Update the sequence now, because we want to continue from
                // SEQ_CODE even if we return some LZMA_*_CHECK.
                coder->sequence = SEQ_CODE;

                // Detect the file format. .xz files start with 0xFD which
                // cannot be the first byte of .lzma (LZMA_Alone) format.
                // The .lz format starts with 0x4C which could be the
                // first byte of a .lzma file but luckily it would mean
                // lc/lp/pb being 4/3/1 which liblzma doesn't support because
                // lc + lp > 4. So using just 0x4C to detect .lz is OK here.
                if (in[*in_pos] == 0xFD) {
                        return_if_error(lzma_stream_decoder_init(
                                        &coder->next, allocator,
                                        coder->memlimit, coder->flags));
#ifdef HAVE_LZIP_DECODER
                } else if (in[*in_pos] == 0x4C) {
                        return_if_error(lzma_lzip_decoder_init(
                                        &coder->next, allocator,
                                        coder->memlimit, coder->flags));
#endif
                } else {
                        return_if_error(lzma_alone_decoder_init(&coder->next,
                                        allocator, coder->memlimit, true));

                        // If the application wants to know about missing
                        // integrity check or about the check in general, we
                        // need to handle it here, because LZMA_Alone decoder
                        // doesn't accept any flags.
                        if (coder->flags & LZMA_TELL_NO_CHECK)
                                return LZMA_NO_CHECK;

                        if (coder->flags & LZMA_TELL_ANY_CHECK)
                                return LZMA_GET_CHECK;
                }

        // Fall through

        case SEQ_CODE: {
                const lzma_ret ret = coder->next.code(
                                coder->next.coder, allocator,
                                in, in_pos, in_size,
                                out, out_pos, out_size, action);
                if (ret != LZMA_STREAM_END
                                || (coder->flags & LZMA_CONCATENATED) == 0)
                        return ret;

                coder->sequence = SEQ_FINISH;
        }

        // Fall through

        case SEQ_FINISH:
                // When LZMA_CONCATENATED was used and we were decoding
                // a LZMA_Alone file, we need to check that there is no
                // trailing garbage and wait for LZMA_FINISH.
                if (*in_pos < in_size)
                        return LZMA_DATA_ERROR;

                return action == LZMA_FINISH ? LZMA_STREAM_END : LZMA_OK;

        default:
                assert(0);
                return LZMA_PROG_ERROR;
        }
}


static void
auto_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
{
        lzma_auto_coder *coder = coder_ptr;
        lzma_next_end(&coder->next, allocator);
        lzma_free(coder, allocator);
        return;
}


static lzma_check
auto_decoder_get_check(const void *coder_ptr)
{
        const lzma_auto_coder *coder = coder_ptr;

        // It is LZMA_Alone if get_check is NULL.
        return coder->next.get_check == NULL ? LZMA_CHECK_NONE
                        : coder->next.get_check(coder->next.coder);
}


static lzma_ret
auto_decoder_memconfig(void *coder_ptr, uint64_t *memusage,
                uint64_t *old_memlimit, uint64_t new_memlimit)
{
        lzma_auto_coder *coder = coder_ptr;

        lzma_ret ret;

        if (coder->next.memconfig != NULL) {
                ret = coder->next.memconfig(coder->next.coder,
                                memusage, old_memlimit, new_memlimit);
                assert(*old_memlimit == coder->memlimit);
        } else {
                // No coder is configured yet. Use the base value as
                // the current memory usage.
                *memusage = LZMA_MEMUSAGE_BASE;
                *old_memlimit = coder->memlimit;

                ret = LZMA_OK;
                if (new_memlimit != 0 && new_memlimit < *memusage)
                        ret = LZMA_MEMLIMIT_ERROR;
        }

        if (ret == LZMA_OK && new_memlimit != 0)
                coder->memlimit = new_memlimit;

        return ret;
}


static lzma_ret
auto_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
                uint64_t memlimit, uint32_t flags)
{
        lzma_next_coder_init(&auto_decoder_init, next, allocator);

        if (flags & ~LZMA_SUPPORTED_FLAGS)
                return LZMA_OPTIONS_ERROR;

        lzma_auto_coder *coder = next->coder;
        if (coder == NULL) {
                coder = lzma_alloc(sizeof(lzma_auto_coder), allocator);
                if (coder == NULL)
                        return LZMA_MEM_ERROR;

                next->coder = coder;
                next->code = &auto_decode;
                next->end = &auto_decoder_end;
                next->get_check = &auto_decoder_get_check;
                next->memconfig = &auto_decoder_memconfig;
                coder->next = LZMA_NEXT_CODER_INIT;
        }

        coder->memlimit = my_max(1, memlimit);
        coder->flags = flags;
        coder->sequence = SEQ_INIT;

        return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_auto_decoder(lzma_stream *strm, uint64_t memlimit, uint32_t flags)
{
        lzma_next_strm_init(auto_decoder_init, strm, memlimit, flags);

        strm->internal->supported_actions[LZMA_RUN] = true;
        strm->internal->supported_actions[LZMA_FINISH] = true;

        return LZMA_OK;
}