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();
}
void Gunzip::ProcessTail()
{
assert(tailLen == 8);
word32 calculatedCrc = crc.GetCrc();
if ((((word32)tail[0]) | ((word32)tail[1] << 8) | ((word32)tail[2] << 16) | ((word32)tail[3] << 24)) != calculatedCrc)
throw CrcErr();
if ((((word32)tail[4]) | ((word32)tail[5] << 8) | ((word32)tail[6] << 16) | ((word32)tail[7] << 24)) != totalLen)
throw LengthErr();
tailLen = 9; // signal TailProcesser to bypass everything from now on
}
// - - - P a r s e P k t - - - //
// Read one packet from RX and //
// extract payload //
// Inputs: //
// *pktBfr - ptr to payload //
// data from RX //
// Outputs: //
// Payload passed by ref //
/////////////////////////////////
void ParsePkt(void *payloadBfr)
{
ParserState state = P1;
CPU_INT16S c;
CPU_INT08S checksum = 0;
CPU_INT08U i = 0;
PktBfr *pktBfr = payloadBfr;
while(1)
{
//Receive a byte
c = GetByte();
//XOR byte with current checksum
checksum ^= c;
switch(state)
{
case P1: //Preamble 1
if(c == P1Char)
state = P2;
else
{
//Error if wrong char
PreambleErr(state);
state = ER;
}
break;
case P2: //Preamble 2
if(c == P2Char)
state = P3;
else
{
//Error if wrong char
PreambleErr(state);
state = ER;
}
break;
case P3: //Preamble 3
if(c == P3Char)
state = L;
else
{
//Error if wrong char
PreambleErr(state);
state = ER;
}
break;
case L: //Length
//Check that it is a valid length
if(c<PacketMinLength)
{
//If length is invalid, error
LengthErr();
state = ER;
}
else
{
//Read in length field
pktBfr->payloadLen = c - HeaderLength;
state = D;
i = 0;
}
break;
case D: //Data
//Read in Data until payloadLen is reached
pktBfr->data[i++] = c;
if(i >= pktBfr->payloadLen-1)
state = C;
break;
case C: //Checksum
//Check that the final bitwise XOR of packet = 0
if(!(checksum))
return;
//Otherwise, report an error
CheckErr();
state = ER;
break;
case ER: //Error State 1
//Clear checksum
checksum = 0;
//If we have a valid preamble char, progress to next error state
if(c==P1Char)
{
state = ER2;
//Don't lose a checksum char!
checksum ^= P1Char;
}
break;
case ER2: //Error State 2
//If we have a valid preamble char, progress to next error state
if(c==P2Char)
state = ER3;
//Otherwise, return to first error state
else
state = ER;
break;
case ER3: //Error State 3
//If we have a valid preamble char, we have a real message.
//Progress to Length state.
if(c==P3Char)
state=L;
//Otherwise, fall back to first error state
else
state=ER;
break;
}
}
}