Compress Data

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• Download test application files - 48 Kb

Introduction

This code will compress/decompress data from ISequentialStream to ISequentialStream. It also has functions to compress/decompress CFile and CByteArray.

Background

While developing software, sometimes I need to compress data to decrease size. The gzip library does compression for me, but it is not ready to handle in-memory or CFile in MFC. So, here is the class that assists me compressing data.

Using the code

The class Flate does compression/decompression for ISquentialStream, CFile, CByteArray. Compression for CByteArray is done by another small utility class CBAStreamReader/CBAStreamWriter.

//
// class Flate declaration.
//
class Flate
{
public:
    Flate()
    {
    }

    void Inflate(ISequentialStream* pOutput, ISequentialStream* pInput);
    void Deflate(ISequentialStream* pOutput, ISequentialStream* pInput);

    void Inflate(CFile* pOutput, CFile* pInput);
    void Deflate(CFile* pOutput, CFile* pInput);

    BOOL    Compress(CByteArray& dst, const CByteArray& src)
    {
        return Compress(dst, src.GetData(), src.GetSize());
    }

    BOOL    Compress(CByteArray& dst, const BYTE* src, UINT srcLen);

    BOOL    Uncompress(CByteArray& dst, const CByteArray& src)
    {
        return Uncompress(dst, src.GetData(), src.GetSize());
    }

    BOOL    Uncompress(CByteArray& dst, const BYTE* src, UINT srcLen);
};

Here is one function that compresses CFile data. The internal function uses z_stream to support custom streams. First, it reads data from input CFile, compresses it by deflate method and saves it to output CFile.

//
// Deflate method compresses CFile based data.
//

void Flate::Deflate(CFile* pOutput, CFile* pInput)
{
    z_stream zstm;
    memset(&zstm,0,sizeof(z_stream));

    BYTE zBufIn[UNCOMP_BUFSIZE];
    BYTE zBufOut[COMP_BUFSIZE];

    deflateInit(&zstm, Z_DEFAULT_COMPRESSION);

    int err = Z_OK;
    while ( TRUE )
    {
        UINT cbRead = 0;
        cbRead = pInput->Read(zBufIn, sizeof(zBufIn));
        if ( cbRead == 0 )
            break;

        zstm.next_in = (Bytef*)zBufIn;
        zstm.avail_in = (uInt)cbRead;

        while ( TRUE )
        {
            zstm.next_out = (Bytef*)zBufOut;
            zstm.avail_out = sizeof(zBufOut);

            err = deflate(&zstm, Z_SYNC_FLUSH);
            if (err != Z_OK)
                break;

            UINT cbWrite = sizeof(zBufOut) - zstm.avail_out;
            if ( cbWrite == 0 )
                break;
            pOutput->Write(zBufOut, cbWrite);

            if ( zstm.avail_out != 0 )
                break;
        }
    }

    err = deflateEnd(&zstm);
}

Here is the other function that uncompresses CFile data. It is almost same as Inflate.

//
// Inflate methods uncompresses CFile based data.
//

void Flate::Inflate(CFile* pOutput, CFile* pInput)
{
    z_stream zstm;
    memset(&zstm,0,sizeof(z_stream));

    BYTE zBufIn[COMP_BUFSIZE];
    BYTE zBufOut[UNCOMP_BUFSIZE];

    inflateInit(&zstm);

    int err = Z_OK;
    while ( TRUE )
    {
        UINT cbRead = 0;
        cbRead = pInput->Read(zBufIn, sizeof(zBufIn));
        if ( cbRead == 0 )
            break;

        zstm.next_in = (Bytef*)zBufIn;
        zstm.avail_in = (uInt)cbRead;

        while ( TRUE )
        {
            zstm.next_out = (Bytef*)zBufOut;
            zstm.avail_out = sizeof(zBufOut);

            err = inflate(&zstm, Z_SYNC_FLUSH);
            if (err != Z_OK)
                break;

            UINT cbWrite = sizeof(zBufOut) - zstm.avail_out;
            if ( cbWrite == 0 )
                break;
            pOutput->Write(zBufOut, cbWrite);

            if ( zstm.avail_out != 0 )
                break;
        }
    }

    err = inflateEnd(&zstm);
}