Improve transactions verification process in `WithVerifyBlock` dBFT callback

[AnnaShaleva]

After #87 there's a proper WithVerifyBlock dBFT callback implemented. During block verification it performs basic transactions correctness checks (while processing transactions states):

go-ethereum/core/state_processor.go

Lines 90 to 93 in d1dd299

	receipt, err := applyTransaction(msg, p.config, gp, statedb, blockNumber, blockHash, tx, usedGas, vmenv)
	if err != nil {
	return nil, nil, 0, fmt.Errorf("could not apply tx %d [%v]: %w", i, tx.Hash().Hex(), err)
	}

and

go-ethereum/core/state_processor.go

Lines 113 to 117 in d1dd299

	// Apply the transaction to the current state (included in the env).
	result, err := ApplyMessage(evm, msg, gp)
	if err != nil {
	return nil, err
	}

and

go-ethereum/core/state_transition.go

Lines 174 to 183 in d1dd299

	// ApplyMessage computes the new state by applying the given message
	// against the old state within the environment.
	//
	// ApplyMessage returns the bytes returned by any EVM execution (if it took place),
	// the gas used (which includes gas refunds) and an error if it failed. An error always
	// indicates a core error meaning that the message would always fail for that particular
	// state and would never be accepted within a block.
	func ApplyMessage(evm *vm.EVM, msg *Message, gp *GasPool) (*ExecutionResult, error) {
	return NewStateTransition(evm, msg, gp).TransitionDb()
	}

and

go-ethereum/core/state_transition.go

Lines 342 to 364 in d1dd299

	// TransitionDb will transition the state by applying the current message and
	// returning the evm execution result with following fields.
	//
	// - used gas: total gas used (including gas being refunded)
	// - returndata: the returned data from evm
	// - concrete execution error: various EVM errors which abort the execution, e.g.
	// ErrOutOfGas, ErrExecutionReverted
	//
	// However if any consensus issue encountered, return the error directly with
	// nil evm execution result.
	func (st *StateTransition) TransitionDb() (*ExecutionResult, error) {
	// First check this message satisfies all consensus rules before
	// applying the message. The rules include these clauses
	//
	// 1. the nonce of the message caller is correct
	// 2. caller has enough balance to cover transaction fee(gaslimit * gasprice)
	// 3. the amount of gas required is available in the block
	// 4. the purchased gas is enough to cover intrinsic usage
	// 5. there is no overflow when calculating intrinsic gas
	// 6. caller has enough balance to cover asset transfer for **topmost** call
	// Check clauses 1-3, buy gas if everything is correct
	if err := st.preCheck(); err != nil {

So basic checks for proposed in-block transactions are there and seems that we don't need a separate mempool to verify in-block transactions. But, there should be some policy checks implemented, as @chenquanyu mentioned in #87 (comment).

[roman-khimov]

seems that we don't need a separate mempool to verify in-block transactions

The problem is to get them from peers while creating a block (not going into CV because of missing tx).

[AnnaShaleva]

seems that we don't need a separate mempool to verify in-block transactions

The problem is to get them from peers while creating a block (not going into CV because of missing tx).

For this we have a separate designated #98 (comment). And this issue is about additional in-block transactions verification.

[AnnaShaleva]

Replaced by #314, not relevant anymore.