C++ DataChunk::Set方法代码示例

/*! \param Buffer Pointer to data to be written
 *  \param Offset The offset within the KLV value field of the first byte to write
 *  \param Size The number of bytes to write
 *  \return Size if all OK, else != Size.  This may not equal the actual number of bytes written.
 *	The IV must have already been set.
 *  Only encrypted parts of the value may be written using this function (i.e. Offset >= PlaintextOffset)
 */
size_t KLVEObject::WriteCryptoDataTo(const UInt8 *Buffer, Position Offset, size_t Size)
{
	// Self-deleting store to allow us to extend working buffer if required
	DataChunk TempData;

	// Are we going to need to write padding bytes?
	bool AddPadding;
	if(static_cast<Length>(Offset + Size) >= ValueLength) AddPadding = true; else AddPadding = false;

	// Check if this is a "pointless" zero-byte write (rather than a request to write padding only)
	if((!AddPadding) && (Size == 0)) return 0;

	// Assume that the write will succeed and move the "next" pointer accordingly
	CurrentWriteOffset += Size;

	// Check if all the bytes will fit in the AwaitingEncryptionBuffer
	if((!AddPadding) && (Size < static_cast<size_t>(EncryptionGranularity - AwaitingEncryption)))
	{
		// Add to the end of the waiting buffer
		memcpy(&AwaitingEncryptionBuffer[AwaitingEncryption], Data.Data, Size);

		// All done
		return Size;
	}

	// Work out how many bytes we need to encrypt (estimate one - as many as offered)
	Length BytesToEncrypt = Size;

	// If there are any bytes waiting they need to be added to this write
	if(AwaitingEncryption)
	{
		// Build the full data in the temporary buffer
		TempData.ResizeBuffer(AwaitingEncryption + Size);

		// Start with "waiting" data
		TempData.Set(AwaitingEncryption, AwaitingEncryptionBuffer);

		// Copy in the new data
		TempData.Append(Size, Buffer);

		// Replace the working buffer pointer with a pointer to the temporary buffer
		Buffer = TempData.Data;

		// Update the offset (move it back to the first waiting byte)
		Offset -= AwaitingEncryption;

		// Record the revised size
		BytesToEncrypt = AwaitingEncryption + Size;
	}

	// Pad the data if required (i.e. if this is the last chunk of data)
	if(AddPadding)
	{
		if(Offset + BytesToEncrypt > ValueLength)
		{
			error("Attempted to write beyond the end of the encrypted value in KLVEObject::WriteCryptoDataTo()\n");
			return 0;
		}

		// Start by encrypting all but the last 16 bytes (including padding)
		Length StartSize = EncryptedLength - (EncryptionGranularity + Offset);

		// Sanity check the size of this chunk
		if((sizeof(size_t) < 8) && (StartSize > 0xffffffff))
		{
			error("Tried to encrypt > 4GBytes, but this platform can only handle <= 4GByte chunks\n");
			return 0;
		}

		// Don't write zero bytes
		if(StartSize)
		{
			// Encrypt by making a copy
			DataChunkPtr NewData = Encrypt->Encrypt(static_cast<size_t>(StartSize), Buffer);
			if(!NewData) return 0;

			// Write the encrypted data
			Base_WriteDataTo(NewData->Data, DataOffset + Offset, static_cast<size_t>(StartSize));

			// Update the current hash if we are calculating one
			// TODO: Sort the possible overflow here
			if(WriteHasher) WriteHasher->HashData(static_cast<size_t>(StartSize), NewData->Data);
		}

		// Buffer for last data to be encrypted
		UInt8 TempBuffer[EncryptionGranularity];

		// Copy in the remaining bytes from the end of the given buffer
		// Add padding bytes in a 16-byte version of the scheme defined in RFC 2898
		const UInt8 *pSrc = &Buffer[StartSize];
		UInt8 *pDst = TempBuffer;
		int i;
		int EncData = (int)(BytesToEncrypt - StartSize);
//.........这里部分代码省略.........