Bitcoin core tutorial & code walk through (Part 8) - blockchain

In part 8, we will look at code that handles blockchain.

In validation.cpp,
ProcessNewBlockHeaders(std::vector<CBlockHeader>&, CValidationState&, CChainParams&, CBlockIndex**) loops through the CBlockHeaders, for each header, it calls AcceptBlockHeader().

**ProcessNewBlockHeaders() is called in ProcessMessage() in net_processing.cpp.

ProcessNewBlock(CChainParams&, std::shared_ptr<const CBlock>, bool, bool) calls CheckBlock(), if that is successful, it calls AcceptBlock(). Then, the best chain is activated using ActivateBestChain().

**ProcessNewBlock() is called in ProcessMessage() in net_processing.cpp.

AcceptBlock(std::shared_ptr<const CBlock>&, CValidationState&, CChainParams&, CBlockIndex**, bool, CDiskBlockPos*, bool) calls AcceptBlockHeader(). It checks if it already has the block and the block has more work to advance blockchain tip. It also checks for block height if the block is too too ahead for blockchain pruning. If the above conditions are fulfilled, it calls CheckBlock(). If header is valid and there is sufficient work, merkle tree and segwit merkle tree are good, calls NewPowValidBlock() to announce new block to peer nodes. Then, it calls WriteBlockToDisk(). Finally, the ReceivedBlockTransactions() is called to connect the new block to the chain.

AcceptBlockHeader(CBlockHeader&, CValidationState&, CChainParams&, CBlockIndex**) firstly checks for genesis block. If block header is already known, the block is not accepted. It checks for previous block and bad block. It calls CheckBlockIndex().

CheckBlockIndex(Consensus::Params&) iterates over the entire blockchain, and checks for consistency using CBlockIndex *pindex. For example, it checks for block height, the chainwork length. tree validity.

CheckBlock(CBlock&, CValidationState&, Consensus::Params&, bool, bool) calls CheckBlockHeader() for checking header validity. Next, it check merkle root. After that, it checks for size limits, duplicate coinbase. The transactions is checked using CheckTransaction().

In consensus/tx_verify.cpp.
CheckTransaction(CTransaction&, CValidationState&, bool) firstly check for empty vin and vout. Then, it checks for negative or too large output value, duplicate inputs.