C++ (Cpp) IOStream::BytesLeftToRead Examples

Example #1

File: BackupStoreFileDiff.cpp Project: boxbackup/boxbackup

// --------------------------------------------------------------------------
//
// Function
//		Name:    BackupStoreFile::MoveStreamPositionToBlockIndex(IOStream &)
//		Purpose: Move the file pointer in this stream to just before the block index.
//				 Assumes that the stream is at the beginning, seekable, and
//				 reading from the stream is OK.
//		Created: 12/1/04
//
// --------------------------------------------------------------------------
void BackupStoreFile::MoveStreamPositionToBlockIndex(IOStream &rStream)
{
	// Size of file
	int64_t fileSize = rStream.BytesLeftToRead();

	// Get header
	file_StreamFormat hdr;

	// Read the header
	if(!rStream.ReadFullBuffer(&hdr, sizeof(hdr), 0 /* not interested in bytes read if this fails */, IOStream::TimeOutInfinite))
	{
		// Couldn't read header
		THROW_EXCEPTION(BackupStoreException, CouldntReadEntireStructureFromStream)
	}

	// Check magic number
	if(ntohl(hdr.mMagicValue) != OBJECTMAGIC_FILE_MAGIC_VALUE_V1
#ifndef BOX_DISABLE_BACKWARDS_COMPATIBILITY_BACKUPSTOREFILE
		&& ntohl(hdr.mMagicValue) != OBJECTMAGIC_FILE_MAGIC_VALUE_V0
#endif
		)
	{
		THROW_EXCEPTION(BackupStoreException, BadBackupStoreFile)
	}
	
	// Work out where the index is
	int64_t numBlocks = box_ntoh64(hdr.mNumBlocks);
	int64_t blockHeaderPosFromEnd = ((numBlocks * sizeof(file_BlockIndexEntry)) + sizeof(file_BlockIndexHeader));
	
	// Sanity check
	if(blockHeaderPosFromEnd > static_cast<int64_t>(fileSize - sizeof(file_StreamFormat)))
	{
		THROW_EXCEPTION(BackupStoreException, BadBackupStoreFile)
	}
	
	// Seek to that position
	rStream.Seek(0 - blockHeaderPosFromEnd, IOStream::SeekType_End);
	
	// Done. Stream now in right position (as long as the file is formatted correctly)
}