C++ LZMA SDK：解压LZMA2压缩文件的函数

Question

我正在尝试创建一个函数，用于解压缩 LZAM2 压缩数据。我受到了这个教程的启发：（链接），它对于 LZMA 工作得非常好，我试图将其适应于 LZMA2。我已经成功地创建了 LZMA2 的压缩函数，但是对于解压缩函数却没有成功。

以下是压缩函数：

static void Compress2Inc(std::vector<unsigned char> &outBuf,
                         const std::vector<unsigned char> &inBuf)
{
    CLzma2EncHandle enc = Lzma2Enc_Create(&SzAllocForLzma, &SzAllocForLzma2);
    assert(enc);

    CLzma2EncProps props;
    Lzma2EncProps_Init(&props);
    props.lzmaProps.writeEndMark = 1; // 0 or 1

    SRes res = Lzma2Enc_SetProps(enc, &props);
    assert(res == SZ_OK);

    unsigned propsSize = LZMA_PROPS_SIZE;
    outBuf.resize(propsSize);

    res = Lzma2Enc_WriteProperties(enc);
    //cout << res;
    //assert(res == SZ_OK && propsSize == LZMA_PROPS_SIZE);

    VectorInStream inStream = { &VectorInStream_Read, &inBuf, 0 };
    VectorOutStream outStream = { &VectorOutStream_Write, &outBuf };

    res = Lzma2Enc_Encode(enc,
        (ISeqOutStream*)&outStream, (ISeqInStream*)&inStream,
        0);
    assert(res == SZ_OK);

    Lzma2Enc_Destroy(enc);
}

在哪里：

static void *AllocForLzma2(void *, size_t size) { return BigAlloc(size); }
static void FreeForLzma2(void *, void *address) { BigFree(address); }
static ISzAlloc SzAllocForLzma2 = { AllocForLzma2, FreeForLzma2 };

static void *AllocForLzma(void *, size_t size) { return MyAlloc(size); }
static void FreeForLzma(void *, void *address) { MyFree(address); }
static ISzAlloc SzAllocForLzma = { AllocForLzma, FreeForLzma };

typedef struct
{
    ISeqInStream SeqInStream;
    const std::vector<unsigned char> *Buf;
    unsigned BufPos;
} VectorInStream;

SRes VectorInStream_Read(void *p, void *buf, size_t *size)
{
    VectorInStream *ctx = (VectorInStream*)p;
    *size = min(*size, ctx->Buf->size() - ctx->BufPos);
    if (*size)
        memcpy(buf, &(*ctx->Buf)[ctx->BufPos], *size);
    ctx->BufPos += *size;
    return SZ_OK;
}

typedef struct
{
    ISeqOutStream SeqOutStream;
    std::vector<unsigned char> *Buf;
} VectorOutStream;

size_t VectorOutStream_Write(void *p, const void *buf, size_t size)
{
    VectorOutStream *ctx = (VectorOutStream*)p;
    if (size)
    {
        unsigned oldSize = ctx->Buf->size();
        ctx->Buf->resize(oldSize + size);
        memcpy(&(*ctx->Buf)[oldSize], buf, size);
    }
    return size;
}

这是目前我写的解压函数，但是Lzma2Dec_DecodeToBuf函数返回错误码1(SZ_ERROR_DATA)，我在网上没有找到任何有关此问题的信息。

static void Uncompress2Inc(std::vector<unsigned char> &outBuf,
                           const std::vector<unsigned char> &inBuf)
{
    CLzma2Dec dec;
    Lzma2Dec_Construct(&dec);

    SRes res = Lzma2Dec_Allocate(&dec, outBuf.size(), &SzAllocForLzma);
    assert(res == SZ_OK);

    Lzma2Dec_Init(&dec);

    outBuf.resize(UNCOMPRESSED_SIZE);
    unsigned outPos = 0, inPos = LZMA_PROPS_SIZE;
    ELzmaStatus status;
    const unsigned BUF_SIZE = 10240;
    while (outPos < outBuf.size())
    {
        unsigned destLen = min(BUF_SIZE, outBuf.size() - outPos);
        unsigned srcLen  = min(BUF_SIZE, inBuf.size() - inPos);
        unsigned srcLenOld = srcLen, destLenOld = destLen;

        res = Lzma2Dec_DecodeToBuf(&dec,
                                   &outBuf[outPos], &destLen,
                                   &inBuf[inPos], &srcLen,
                                   (outPos + destLen == outBuf.size()) ? LZMA_FINISH_END : LZMA_FINISH_ANY,
                                   &status);

        assert(res == SZ_OK);
        inPos += srcLen;
        outPos += destLen;
        if (status == LZMA_STATUS_FINISHED_WITH_MARK)
            break;
    }

    Lzma2Dec_Free(&dec, &SzAllocForLzma);
    outBuf.resize(outPos);
}

我正在使用从这里下载的LZMA SDK和Visual Studio 2008。有人在这里遇到了完全相同的问题，但我无法运用他的代码...

有人曾经成功地使用LZMA SDK解压缩LZMA2压缩文件吗？

请帮忙！

- Jacob Krieg

---

你可能会发现查看p7zip的源代码是有益的。 - Elliott Frisch

据我所知，p7zip是7zip的GNU/Linux POSIX版本。我需要在Windows上使用它。 - Jacob Krieg

这里也遇到了同样的问题。解压缩时报错码1。 你解决了吗？ - Michael Chourdakis

Answer 1

一个临时的解决方法是将SRes res = Lzma2Dec_Allocate(&dec, outBuf.size(), &SzAllocForLzma);替换为SRes res = Lzma2Dec_Allocate(&dec, 8, &SzAllocForLzma);在Uncompress2Inc函数中，其中8是一个神奇的数字...

然而这不是解决问题的正确方法...

第一个错误是Lzma2Enc_WriteProperties并没有返回结果，而是一个属性字节，该属性字节必须作为第二个参数用于Uncompress2Inc函数中的Lzma2Dec_Allocate调用。因此，我们用属性字节替换神奇数字8，一切都按预期工作。

为了实现这一点，必须向编码数据添加5字节头，该头将在解码函数中提取。以下是一个在VS2008中工作的示例(不是最完美的代码，但它可以工作...我会在以后有时间的时候回来，提供更好的示例):

void Lzma2Benchmark::compressChunk(std::vector<unsigned char> &outBuf, const std::vector<unsigned char> &inBuf)
{
    //! \todo This is a temporary workaround, size needs to be added to the 
    m_uncompressedSize = inBuf.size();

    std::cout << "Uncompressed size is: " << inBuf.size() << std::endl;

    DWORD tickCountBeforeCompression = GetTickCount();

    CLzma2EncHandle enc = Lzma2Enc_Create(&m_szAllocForLzma, &m_szAllocForLzma2);
    assert(enc);

    CLzma2EncProps props;
    Lzma2EncProps_Init(&props);
    props.lzmaProps.writeEndMark = 1; // 0 or 1
    props.lzmaProps.level = 9;
    props.lzmaProps.numThreads = 3;
    //props.numTotalThreads = 2;

    SRes res = Lzma2Enc_SetProps(enc, &props);
    assert(res == SZ_OK);

    // LZMA_PROPS_SIZE == 5 bytes
    unsigned propsSize = LZMA_PROPS_SIZE;
    outBuf.resize(propsSize);

    // I think Lzma2Enc_WriteProperties returns the encoding properties in 1 Byte
    Byte properties = Lzma2Enc_WriteProperties(enc);

    //! \todo This is a temporary workaround
    m_propByte = properties;

    //! \todo Here m_propByte and m_uncompressedSize need to be added to outBuf's 5 byte header so simply add those 2 values to outBuf and start the encoding from there.

    BenchmarkUtils::VectorInStream inStream = { &BenchmarkUtils::VectorInStream_Read, &inBuf, 0 };
    BenchmarkUtils::VectorOutStream outStream = { &BenchmarkUtils::VectorOutStream_Write, &outBuf };

    res = Lzma2Enc_Encode(enc,
                          (ISeqOutStream*)&outStream,
                          (ISeqInStream*)&inStream,
                          0);

    std::cout << "Compress time is: " << GetTickCount() - tickCountBeforeCompression << " milliseconds.\n";

    assert(res == SZ_OK);

    Lzma2Enc_Destroy(enc);

    std::cout << "Compressed size is: " << outBuf.size() << std::endl;
}

void Lzma2Benchmark::unCompressChunk(std::vector<unsigned char> &outBuf, const std::vector<unsigned char> &inBuf)
{
    DWORD tickCountBeforeUncompression = GetTickCount();

    CLzma2Dec dec;
    Lzma2Dec_Construct(&dec);

    //! \todo Heere the property size and the uncompressed size need to be extracted from inBuf, which is the compressed data.

    // The second parameter is a temporary workaround.
    SRes res = Lzma2Dec_Allocate(&dec, m_propByte/*8*/, &m_szAllocForLzma);
    assert(res == SZ_OK);

    Lzma2Dec_Init(&dec);

    outBuf.resize(m_uncompressedSize);
    unsigned outPos = 0, inPos = LZMA_PROPS_SIZE;
    ELzmaStatus status;
    const unsigned BUF_SIZE = 10240;

    while(outPos < outBuf.size())
    {
        SizeT destLen = std::min(BUF_SIZE, outBuf.size() - outPos);
        SizeT srcLen  = std::min(BUF_SIZE, inBuf.size() - inPos);
        SizeT srcLenOld = srcLen, destLenOld = destLen;

        res = Lzma2Dec_DecodeToBuf(&dec,
                                   &outBuf[outPos],
                                   &destLen,
                                   &inBuf[inPos],
                                   &srcLen,
                                   (outPos + destLen == outBuf.size()) ? LZMA_FINISH_END : LZMA_FINISH_ANY,
                                   &status);

        assert(res == SZ_OK);
        inPos += srcLen;
        outPos += destLen;

        if(status == LZMA_STATUS_FINISHED_WITH_MARK)
        {
            break;
        }
    }

    Lzma2Dec_Free(&dec, &m_szAllocForLzma);

    outBuf.resize(outPos);

    std::cout << "Uncompress time is: " << GetTickCount() - tickCountBeforeUncompression << " milliseconds.\n";
}

- Jacob Krieg