gzip.cpp

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// gzip.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "gzip.h"

NAMESPACE_BEGIN(CryptoPP)

void Gzip::WritePrestreamHeader()
{
        m_totalLen = 0;
        m_crc.Restart();

        AttachedTransformation()->Put(MAGIC1);
        AttachedTransformation()->Put(MAGIC2);
        AttachedTransformation()->Put(DEFLATED);
        AttachedTransformation()->Put(0);               // general flag
        AttachedTransformation()->PutWord32(0); // time stamp
        byte extra = byte((GetDeflateLevel() == 1) ? FAST : ((GetDeflateLevel() == 9) ? SLOW : 0));
        AttachedTransformation()->Put(extra);
        AttachedTransformation()->Put(GZIP_OS_CODE);
}

void Gzip::ProcessUncompressedData(const byte *inString, size_t length)
{
        m_crc.Update(inString, length);
        m_totalLen += (word32)length;
}

void Gzip::WritePoststreamTail()
{
        SecByteBlock crc(4);
        m_crc.Final(crc);
        AttachedTransformation()->Put(crc, 4);
        AttachedTransformation()->PutWord32(m_totalLen, LITTLE_ENDIAN_ORDER);
}

// *************************************************************

Gunzip::Gunzip(BufferedTransformation *attachment, bool repeat, int propagation)
        : Inflator(attachment, repeat, propagation), m_length(0)
{
}

void Gunzip::ProcessPrestreamHeader()
{
        m_length = 0;
        m_crc.Restart();

        byte buf[6];
        byte b, flags;

        if (m_inQueue.Get(buf, 2)!=2) throw HeaderErr();
        if (buf[0] != MAGIC1 || buf[1] != MAGIC2) throw HeaderErr();
        if (!m_inQueue.Skip(1)) throw HeaderErr();       // skip extra flags
        if (!m_inQueue.Get(flags)) throw HeaderErr();
        if (flags & (ENCRYPTED | CONTINUED)) throw HeaderErr();
        if (m_inQueue.Skip(6)!=6) throw HeaderErr();    // Skip file time, extra flags and OS type

        if (flags & EXTRA_FIELDS)       // skip extra fields
        {
                word16 length;
                if (m_inQueue.GetWord16(length, LITTLE_ENDIAN_ORDER) != 2) throw HeaderErr();
                if (m_inQueue.Skip(length)!=length) throw HeaderErr();
        }

        if (flags & FILENAME)   // skip filename
                do
                        if(!m_inQueue.Get(b)) throw HeaderErr();
                while (b);

        if (flags & COMMENTS)   // skip comments
                do
                        if(!m_inQueue.Get(b)) throw HeaderErr();
                while (b);
}

void Gunzip::ProcessDecompressedData(const byte *inString, size_t length)
{
        AttachedTransformation()->Put(inString, length);
        m_crc.Update(inString, length);
        m_length += (word32)length;
}

void Gunzip::ProcessPoststreamTail()
{
        SecByteBlock crc(4);
        if (m_inQueue.Get(crc, 4) != 4)
                throw TailErr();
        if (!m_crc.Verify(crc))
                throw CrcErr();

        word32 lengthCheck;
        if (m_inQueue.GetWord32(lengthCheck, LITTLE_ENDIAN_ORDER) != 4)
                throw TailErr();
        if (lengthCheck != m_length)
                throw LengthErr();
}

NAMESPACE_END