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#include "FlowDecoder.h"
#include <assert.h>
#include <stdio.h>
#include <string.h>
CFlowDecoder::CFlowDecoder() : m_nBytesInBuffer(0)
, m_pCurrentReadPointer(0)
, m_pBufferStart(0)
, m_pBufferEnd(0)
, m_DecoderState(E_WAITING_FOR_HEADER)
, m_nSynchronized(false)
{
}
void CFlowDecoder::DecodeFlow(BYTE* pBuffer, unsigned long nLen)
{
if (NULL == pBuffer || 0 ==nLen)
return;
InitializeBuffer(pBuffer, nLen);
// The decoder state machine
bool bWaitForNewData = false;
//::OutputDebugString(_T("Enter FlowDecoder!\n") );
// Stay in state machine until all data has been consumed and no overflow occured
while (!bWaitForNewData)
{
// Now process data in Buffer
switch (m_DecoderState)
{
case E_WAITING_FOR_HEADER:
switch (ReceiveHeader() )
{
case E_STATE_NEEDS_MORE_DATA:
// We need more data... we do nothing... just wait
bWaitForNewData = true;
break;
case E_STATE_GOT_WRONG_DATA:
m_nSynchronized = false;
break;
case E_STATE_OK:
// We found a header... now we wait for the payload
m_DecoderState = E_WAITING_FOR_PACKET_DATA;
break;
default:
case E_STATE_UNDEFINED:
assert(false);
break;
}
break;
case E_WAITING_FOR_PACKET_DATA:
switch (ReceivePacket() )
{
case E_STATE_NEEDS_MORE_DATA:
// We need more data... we do nothing... just wait
bWaitForNewData = true;
break;
case E_STATE_GOT_WRONG_DATA:
case E_STATE_OK:
// Now we wait for the next header
m_DecoderState = E_WAITING_FOR_HEADER;
break;
default:
case E_STATE_UNDEFINED:
assert(false);
break;
}
break;
default:
assert(false);
m_DecoderState = E_WAITING_FOR_HEADER;
break;
}
}
}
void CFlowDecoder::Reset()
{
InitializeBuffer(0, 0);
m_DecoderState = E_WAITING_FOR_HEADER;
}
void CFlowDecoder::InitializeBuffer(BYTE* pBuffer, unsigned long nLen)
{
m_nBytesInBuffer = nLen;
m_pCurrentReadPointer = pBuffer;
m_pBufferStart = pBuffer;
m_pBufferEnd = &pBuffer[nLen];
}
unsigned long CFlowDecoder::GetNumberOfBytesInBuffer() const
{
return m_nBytesInBuffer;
}
unsigned long CFlowDecoder::GetNumberOfMemoryChunks() const
{
return (&m_pCurrentReadPointer[m_nBytesInBuffer] <= m_pBufferEnd) ? 1 : 2;
}
bool CFlowDecoder::GetMemoryChunk(unsigned long nNum, BYTE*& pReadPointer, unsigned long& nBytesAvailable) const
{
// Valid chunk number?
if (nNum >= GetNumberOfMemoryChunks() )
return false;
// Calculate number of bytes at end of buffer
nBytesAvailable = static_cast<unsigned long>(m_pBufferEnd - m_pCurrentReadPointer);
if (nNum == 0)
{
pReadPointer = m_pCurrentReadPointer;
}
else // if (nNum == 1)
{
pReadPointer = m_pBufferStart;
// Reuse already calculated number of bytes at end of buffer to calc number of bytes at start
nBytesAvailable = static_cast<unsigned long>(m_nBytesInBuffer - nBytesAvailable);
}
return true;
}
bool CFlowDecoder::CopyFromBuffer(BYTE* pTarget, unsigned long len) const
{
if (len > GetNumberOfBytesInBuffer() )
return false;
BYTE* pBufferStart;
unsigned long nBytesAvailable;
// Chunk zero always exists
GetMemoryChunk(0, pBufferStart, nBytesAvailable);
// Now check if the whole packet is in first chunk; Do we need to get 2nd chunk?
if (nBytesAvailable >= len)
{
// Copy first part
::memcpy(pTarget, pBufferStart, len);
}
else
{
// Merge first and 2nd chunk
// Copy first part
::memcpy(pTarget, pBufferStart, nBytesAvailable);
pTarget = &pTarget[nBytesAvailable];
len -= nBytesAvailable;
// Now get 2nd part and merge
bool bRetVal = GetMemoryChunk(1, pBufferStart, nBytesAvailable);
assert(bRetVal);
::memcpy(pTarget, pBufferStart, len);
}
return true;
}
bool CFlowDecoder::RemoveBytesFromBuffer(unsigned long len)
{
if (len > m_nBytesInBuffer)
{
assert(false);
return false;
}
if (GetNumberOfMemoryChunks() == 1)
{
// Advance pointer in chunk 0
m_pCurrentReadPointer = &m_pCurrentReadPointer[len];
}
else
{
// Calculate number of bytes at end of buffer (i.e. chunk 0)
unsigned long nBytesAtEnd = static_cast<unsigned long>(m_pBufferEnd - m_pCurrentReadPointer);
if (len >= nBytesAtEnd)
{
m_pCurrentReadPointer = &m_pBufferStart[len - nBytesAtEnd];
}
else
{
// Advance pointer in chunk 0
m_pCurrentReadPointer = &m_pCurrentReadPointer[len];
}
}
m_nBytesInBuffer -= len;
assert(m_pCurrentReadPointer >= m_pBufferStart);
assert(m_pCurrentReadPointer <= m_pBufferEnd);
return true;
}
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