Qt的gzip模块实现

一直没找到Qt中方便的gzip模块,于是自己动手,调用zlib模块实现了一份.

目标: 

1.gzip的压缩与解压

2.内存中操作

3.方便的Qt接口

 

实现分析:

gzip 压缩算法为 deflate

inflateInit2时要求zlib库忽略zlib header 

gzip 在 deflate 的 raw data 前增加了 10 个字节的头，尾部添加了 8 个字节的校验字节（可选 crc32 和 adler32） 和长度标识字节

gzip 的 magic number 是 0x1f, 0x8b

zlib windowBits MAX_WBITS + 16 的时候，zlib 自己会产生一个 gzip 的头和尾，这种情况下 OS_CODE 被设置为 255（unknown），尾部校验使用 crc32

 

接口:

QByteArray gzipCompress(const QByteArray &in);

bool gzipUncompress(const QByteArray &data, QByteArray &out);

QByteArray gzipUncompress(const QByteArray &data); 

 

实现:

int httpgzdecompress(Byte *zdata, uLong nzdata, Byte *data, uLong *ndata)

{

    int err = 0;

    z_stream d_stream = {0}; /* decompression stream */

    static char dummy_head[2] =

    {

        0x8 + 0x7 * 0x10,

        (((0x8 + 0x7 * 0x10) * 0x100 + 30) / 31 * 31) & 0xFF,

    };

    d_stream.zalloc = (alloc_func)0;

    d_stream.zfree = (free_func)0;

    d_stream.opaque = (voidpf)0;

    d_stream.next_in  = zdata;

    d_stream.avail_in = 0;

    d_stream.next_out = data;

    if(inflateInit2(&d_stream, 47) != Z_OK) return -1;

    while (d_stream.total_out < *ndata && d_stream.total_in < nzdata) {

        d_stream.avail_in = d_stream.avail_out = 1; /* force small buffers */

        if((err = inflate(&d_stream, Z_NO_FLUSH)) == Z_STREAM_END) break;

        if(err != Z_OK )

        {

            if(err == Z_DATA_ERROR)

            {

                d_stream.next_in = (Bytef*) dummy_head;

                d_stream.avail_in = sizeof(dummy_head);

                if((err = inflate(&d_stream, Z_NO_FLUSH)) != Z_OK)

                {

                    return -1;

                }

            }

            else return -1;

        }

    }

    if(inflateEnd(&d_stream) != Z_OK) return -1;

    *ndata = d_stream.total_out;

    return 0;

}

 

int httpgzcompress(Bytef *data, uLong ndata, Bytef *zdata, uLong *nzdata)

{

    z_stream c_stream;

    int err = 0;

 

    if(data && ndata > 0)

    {

        c_stream.zalloc = (alloc_func)0;

        c_stream.zfree = (free_func)0;

        c_stream.opaque = (voidpf)0;

        if(deflateInit2(&c_stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED,

                        MAX_WBITS + 16, 8, Z_DEFAULT_STRATEGY) != Z_OK) return -1;

        c_stream.next_in  = data;

        c_stream.avail_in  = ndata;

        c_stream.next_out = zdata;

        c_stream.avail_out  = *nzdata;

        while (c_stream.avail_in != 0 && c_stream.total_out < *nzdata)

        {

            if(deflate(&c_stream, Z_NO_FLUSH) != Z_OK) return -1;

        }

        if(c_stream.avail_in != 0) return c_stream.avail_in;

        for (;;) {

            if((err = deflate(&c_stream, Z_FINISH)) == Z_STREAM_END) break;

            if(err != Z_OK) return -1;

        }

        if(deflateEnd(&c_stream) != Z_OK) return -1;

        *nzdata = c_stream.total_out;

        return 0;

    }

    return -1;

}

 

QByteArray gzipCompress(const QByteArray &in)

{

    QByteArray dest(compressBound(in.size()) + 7, 0);

    uLongf destLen = dest.size();

    int r1 = httpgzcompress((Bytef*)in.data(), in.size(), (Bytef*)dest.data(),&destLen);

    dest.resize(destLen);

    return dest;

}

 

 

bool gzipUncompress(const QByteArray &data, QByteArray &out)

{

    if (data.size()<=8)

    {

        return false;

    }

 

    ulong orign_crc = *((ulong*)(data.data() + data.length() - 8));

    ulong len =*((ulong*)(data.data() + data.length() - 4));

 

    out.resize(len);

    int ret = httpgzdecompress((Bytef *)data.data(), data.length(),(Bytef *)out.data(), &len); //(Bytef *)(data.data()+10), data.length()-10-8);

    if (ret!=Z_OK)

    {

        qWarning("gzipUncompress error: %d", ret);

        return false;

    }

    uLong crc = crc32(0L, Z_NULL, 0);

    crc = crc32(crc, (Bytef *)(out.data()), out.length());

 

    if (crc==orign_crc)

    {

        return true;

    }

    else{

        qWarning("gzipUncompress crc check sum fail");

        out.clear();

        return false;

    }

}

 

QByteArray gzipUncompress(const QByteArray &data)

{

    QByteArray out;

    gzipUncompress(out);

    return out;

}

 

还有一份之前使用的qCompress的压缩实现(效率比较低)

QByteArray gzip(const QByteArray &in)
{
    QByteArray uncompress=qCompress(in);
    uncompress.remove(0,4);//去除qCompress头
    uncompress.remove(0, 2); //去除zlib头
    uncompress.remove(uncompress.size() - 4, 4); //去除zlib尾
    uint len=in.size();
    unsigned long crc=GetCrc32((unsigned char *)in.data(),len);
    const unsigned char gzipheader[10]={0x1f,0x8b,8,0,0,0,0,0,2,255};
    QByteArray out;
    out.append((char *)gzipheader,10);
    out.append(uncompress);
    out.append((char *)&crc,4);
    out.append((char *)&len,4);
    return out;
}