Evm integration

[pixelplex-dev]

Related requests:

filestar-project/specs-actors#7
filestar-project/geth#1
filestar-project/solidity#1

Background

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The main goal is to add ability of smart managing data in filestar network. Smart-contracts is a convinient and efficient solution for it. The idea is to add implementation of Ethereum Virtual Machine (EVM) and ways to communicate with it from FileStar.
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Proposal

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First of all, it's a EVM realization. It's located at evm-adapter library and play a key role in our model.

//create new stateDB 
func NewEVM(chain types.ChainAdapter, config *types.Config) (*EVM, error)
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//init with existing stateDB
func NewEVMWithStateDB(chain types.ChainAdapter, db types.StateDB, config *types.Config) (*EVM, error)

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The ChainAdapter provides access to chain functionality.
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type ChainAdapter interface {
	// Blockchain access
	//// Get block hash by block number
	GetBlockHashByNum(uint64) Hash
	// Address call suicide
	DeleteAddress(Address)
	// CallAddress
	CallAddress(Address, uint256.Int, []byte) ([]byte, error)
	// CreateContract
	CreateContract(from Address, code []byte, salt []byte, amount *big.Int) (ret []byte, contractAddr Address, leftOverGas uint64, err error)
	//  SetStateDB
	SetStateDB(StateDB)
	//  SetCleanPointer
	SetCleanPointer(bool)
​
	//Get Actor nonce
	GetNonce(Address) uint64
	//Set Actor nonce
	SetNonce(Address, uint64)
	// Balance managing
	//// Get balance by address
	GetBalance(Address) *big.Int
	//// Transfer tokens (from, to, value)
	TransferTokens(Address, Address, *big.Int)
}

• GetBlockHashByNum - get block hash by block number, used by Solidity (opcode BLOCKHASH)
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• DeleteAddress - delete actor by address (opcode SUICIDE)
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• CallAddress - call actor method by address with params(params serialized with cBor, opcode CALLACTOR)
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• CreateContract - create new actor (opcode opCreate)
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• SetStateDB - set shared stateDB for evms (used for CallAddress and CreateContract)
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• SetCleanPointer - set flag for cleaning shared stateDB
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• GetNonce - get nonce from address
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• SetNonce - set nonce for address
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• GetBalance - get balance by address
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• TransferTokens - transfer tokens from sender to reciever
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  To use EVM, at first, you need to implement this interface on your chain. It's like a bridge between lotus and EVM.
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  Another important moment is a CallActor - Actor, for whose we create this bridge.
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  actors/builtin/contract/contract_actor.go - here is new actor methods impl.
  And here is new structs:

type EvmLogs struct {
	// Consensus fields:
	// address of the contract that generated the event
	Address types.Address
	// list of topics provided by the contract.
	Topics []byte
	// supplied by the contract, usually ABI-encoded
	Data []byte
​
	// The Removed field is true if this log was reverted due to a chain reorganisation.
	// You must pay attention to this field if you receive logs through a filter query.
	Removed bool
}
​
// used as argument to new actor methods
type ContractParams struct {
	Code         []byte        // code of contract or call signature
	Value        lotusbig.Int  // value to transfer
	Salt         []byte        // salt if it is contract creation
	CommitStatus bool          // signaling, that need add changes to database
}
​
type ContractResult struct {
	Value   []byte          // return of evm call
	GasUsed int64           // amount of gas used
	Address types.Address   // address of new actor
	Logs    []EvmLogs       // logs generated by evm
}

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Also, we add extra functionality for EVM - new operation code CALLACTOR, special for FileStar network. Now it's possible to call specific actor from solidity code for your own purposes.
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Effect

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It's really important for FileStar ecosystem in the way of managing data. this improvement is aimed at users. Now they are able to store, manage or manipulate with data in a new smart way. Observing the success of Ethereum, we hope that this technology will show itself well in practice.