Remove the assumption on BlockChain<T> has a block at least

[dahlia]

It's an idea which I came up with after reviewed the patch planetarium/libplanet-explorer#86.

After the patch #688 (and #746) was merged, BlockChain<T> became to guarantee it has a genesis block at least. This assumption purposes to prevent reorg/fork from the bottom by mistake.

However, IMHO the assumption that BlockChain<T>.Count is always greater than 0 is unnecessarily strong only for the purpose of preventing reorg from the bottom, and makes node apps (i.e., game clients) too complex to be deployed in reality, because each node has to bundle the whole data of the genesis block, which is hardly configurable by hand. For example, the patch planetarium/libplanet-explorer#86 adds an option -G/--genesis-block which takes a file, not a simple token/string, which is filled with the Bencodex-formatted genesis block. If you want to connect a Libplanet Explorer node to the existing network you need to extract a genesis block from the network first.

Instead of having such a strong assumption, to balance between the purpose and the complexity of deployment, I suggest BlockChain<T>() constructor to take only a HashDigest<SHA256> genesisHash instead of Block<T> genesisBlock. In this way, BlockChain<T> can be empty, but even if it has a genesis block it still guarantees what the genesis block is. We might be able to maintain the existing constructor taking Block<T> genesisBlock because it can be implemented by calling the basic constructor with genesisBlock.Hash and then immediately .Append(genesisBlock).

@planetarium/libplanet Opinions?

[longfin]

I agree with the claim that maintaining the genesis block is too hard to configure in some situations. but I also worry that containing genesis hash instead of the block can complicate operations because it can also be seen as adding a mode. (we can generate genesis hash from a block, but it's too hard to guess for given genesis hash. so BlockChain<T> that contains only genesis hash can be sort of 'no-mining mode' until receiving genesis block from the network)

Therefore, if we accept BlockChain<T> with only genesis hash, we also should indicate in some way that this BlockChain<T>.MineBlock() can't be used without the network. (Of course, libplanet-explorer is okay because it can't mine for other reasons. 😅 )

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.