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Yu is a highly customizable blockchain framework.

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Overall Structure

Introduction

By using Yu, you can customize three levels to develop your own blockchain. The Tripod is for developers to customize their own bussiness.
First level is define Exection and Query on chain.
Second level is define blockchain lifecycle. ( including customizable Consensus Algorithm )
Third level is define basic components, such as block data structures, blockchain, blockbase, txpool.

• Define your Exection and Query on chain.
  Execution is like Transaction in Ethereum but not only for transfer of Token, it changes the state on the chain and must be consensus on all nodes.
  Query is like query in Ethereum, it doesn't change state, just query some data from the chain.

type (
	Execution func(*context.Context, currentBlock IBlock, *chain_env.ChainEnv) error
	
	Query func(ctx *context.Context, env *chain_env.ChainEnv, blockHash common.Hash) (respObj interface{}, err error)
)

• Define Your blockchain lifecycle, this function is in Tripod interface.
  CheckTxn defines the rules for checking transactions(Executions) before inserting txpool.
  VerifyBlock defines the rules for verifying blocks.
  InitChain defines bussiness when the blockchain starts up. You should use it to define Genesis Block.
  StartBlock defines bussiness when a new block starts. In this func, you can set some attributes( including pack txns from txpool, mining ) in the block, then you should tell the framework whether broadcast the block to other nodes or not.
  EndBlock defines bussiness when all nodes accept the new block, usually we execute the txns of new block and append block into the chain.
  FinalizeBlock defines bussiness when the block is finalized in the chain by all nodes.

type Tripod interface {

    ......
    
    CheckTxn(*txn.SignedTxn)    

    VerifyBlock(block IBlock, env *ChainEnv) bool

    InitChain(env *ChainEnv, land *Land) error

    StartBlock(block IBlock, env *ChainEnv, land *Land) (needBroadcast bool, err error)

    EndBlock(block IBlock, env *ChainEnv, land *Land) error

    FinalizeBlock(block IBlock, env *ChainEnv, land *Land) error
}

Examples

Asset Tripod
Asset Tripod imitates an Asset function, it has transfer accounts, create accounts.
QueryBalance queries someone's account balance. It implements type func Query.

func (a *Asset) QueryBalance(ctx *context.Context, env *ChainEnv, _ Hash) (interface{}, error) {
	account := ctx.GetAddress("account")
	amount := a.getBalance(env, account)
	return amount, nil
}

CreateAccount creates an account. It implements type func Execution.
EmitEvent will emit an event out of the chain.
The error returned will emit out of the chain.

func (a *Asset) CreateAccount(ctx *context.Context, _ IBlock, env *ChainEnv) error {
	addr := ctx.Caller
	amount := ctx.GetUint64("amount")

	if a.exsitAccount(env, addr) {
		_ = ctx.EmitEvent("Account Exists!")
		return nil
	}

	a.setBalance(env, addr, Amount(amount))
	_ = ctx.EmitEvent("Account Created Success!")
	return nil
}

We need use SetExec and SetQueries to set Execution and Query into Asset Tripod.
When we set a Execution, we need declare how much Lei(耜) it consumes. (Lei is the same as gas in ethereum )

func NewAsset(tokenName string) *Asset {
	df := NewDefaultTripod("asset")

	a := &Asset{df, tokenName}
	a.SetExec(a.Transfer, 100).SetExec(a.CreateAccount, 10)
	a.SetQueries(a.QueryBalance)

	return a
}

Finally set Asset Tripod into land in main func.

func main() {
    startup.StartUp(pow.NewPow(1024), asset.NewAsset("YuCoin"))
}

Pow Tripod
Pow Tripod imitates a Consensus algorithm for proof of work. It customizes the lower-level code.

• Start a new block
  If there are no verified blocks from P2P network, we pack some txns, mine a new block and broadcast it to P2P network.

func (p *Pow) StartBlock(block IBlock, env *ChainEnv, _ *Land) (needBroadcast bool, err error) {
    ......

    // get validated blocks from P2P network, if exists, use it and return.
    pbsht, err := chain.TakeP2pBlocks(height)
    if err != nil {
   	logrus.Errorf("get p2p-blocks error: %s", err.Error())
    }
    if len(pbsht) > 0 {
   	block.CopyFrom(pbsht[0])
   	logrus.Infof("USE P2P block(%s)", block.GetHash().String())
   	env.StartBlock(block.GetHash())
   	return
    }
    
    // if there are no validated blocks from P2P network, we need to mine a block.
    needBroadcast = true

    ......

    // pack transactions(Executions) from txpool
    txns, err := pool.Pack(p.pkgTxnsLimit)
    if err != nil {
    	return
    }

    ......

    // mine a hash for the new block
    nonce, hash, err := spow.Run(block, p.target, p.targetBits)
    if err != nil {
        return
    }

    block.(*Block).SetNonce(uint64(nonce))
    block.SetHash(hash)

    ......

    return 
}

• End the block
  We execute the txns of the block and append the block into the chain.

func (*Pow) EndBlock(block IBlock, env *ChainEnv, land *Land) error {
        ......

        // execute the txns of the block
	err := node.ExecuteTxns(block, env, land)
	if err != nil {
		return err
	}

        // append the block into chain
	err = chain.AppendBlock(block)
	if err != nil {
		return err
	}

        ......
        // flush the txpool to prepare for new txns of the next block   
        return pool.Flush()   
}

• Finalize the block
  poW does not need finalize stage, so the FinalizeBlock has no implements.

Same as Asset Tripod , finally set Pow Tripod into land in main function.

func main() {
	startup.StartUp(pow.NewPow(1024), asset.NewAsset("YuCoin"))
}