Add precompiles to access validator set (#441)

consensus/clique/clique.go

@@ -30,6 +30,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/consensus/istanbul"
 	"github.com/ethereum/go-ethereum/consensus/misc"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -268,6 +269,10 @@ func (c *Clique) Author(header *types.Header) (common.Address, error) {
 	return ecrecover(header, c.signatures)
 }
 
+func (c *Clique) GetValidators(blockNumber *big.Int, headerHash common.Hash) []istanbul.Validator {
+	return []istanbul.Validator{}
+}
+
 // VerifyHeader checks whether a header conforms to the consensus rules.
 func (c *Clique) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
 	return c.verifyHeader(chain, header, nil)

consensus/consensus.go

@@ -21,6 +21,7 @@ import (
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus/istanbul"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/ethdb"
@@ -102,6 +103,9 @@ type Engine interface {
 	// that a new block should have.
 	CalcDifficulty(chain ChainReader, time uint64, parent *types.Header) *big.Int
 
+	// GetValidators returns the list of current validators.
+	GetValidators(blockNumber *big.Int, headerHash common.Hash) []istanbul.Validator
+
 	// APIs returns the RPC APIs this consensus engine provides.
 	APIs(chain ChainReader) []rpc.API
 

consensus/ethash/consensus.go

@@ -28,6 +28,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/math"
 	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/consensus/istanbul"
 	"github.com/ethereum/go-ethereum/consensus/misc"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -80,6 +81,10 @@ func (ethash *Ethash) Author(header *types.Header) (common.Address, error) {
 	return header.Coinbase, nil
 }
 
+func (ethash *Ethash) GetValidators(blockNumber *big.Int, headerHash common.Hash) []istanbul.Validator {
+	return []istanbul.Validator{}
+}
+
 // VerifyHeader checks whether a header conforms to the consensus rules of the
 // stock Ethereum ethash engine.
 func (ethash *Ethash) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {

consensus/istanbul/backend/backend.go

@@ -156,6 +156,11 @@ func (sb *Backend) Validators(proposal istanbul.Proposal) istanbul.ValidatorSet
 	return sb.getValidators(proposal.Number().Uint64(), proposal.Hash())
 }
 
+func (sb *Backend) GetValidators(blockNumber *big.Int, headerHash common.Hash) []istanbul.Validator {
+	validatorSet := sb.getValidators(blockNumber.Uint64(), headerHash)
+	return validatorSet.FilteredList()
+}
+
 // Broadcast implements istanbul.Backend.Broadcast
 func (sb *Backend) Broadcast(valSet istanbul.ValidatorSet, payload []byte) error {
 	// send to others

core/chain_makers.go

@@ -91,7 +91,7 @@ func (b *BlockGen) AddTx(tx *types.Transaction) {
 // further limitations on the content of transactions that can be
 // added. If contract code relies on the BLOCKHASH instruction,
 // the block in chain will be returned.
-func (b *BlockGen) AddTxWithChain(bc *BlockChain, tx *types.Transaction) {
+func (b *BlockGen) AddTxWithChain(bc ChainContext, tx *types.Transaction) {
 	if b.gasPool == nil {
 		b.SetCoinbase(common.Address{})
 	}

core/evm.go

@@ -57,6 +57,11 @@ func NewEVMContext(msg Message, header *types.Header, chain ChainContext, author
 		beneficiary = *author
 	}
 
+	var engine consensus.Engine
+	if chain != nil {
+		engine = chain.Engine()
+	}
+
 	return vm.Context{
 		CanTransfer: CanTransfer,
 		Transfer:    Transfer,
@@ -68,6 +73,7 @@ func NewEVMContext(msg Message, header *types.Header, chain ChainContext, author
 		Difficulty:  new(big.Int).Set(header.Difficulty),
 		GasLimit:    header.GasLimit,
 		GasPrice:    new(big.Int).Set(msg.GasPrice()),
+		Engine:      engine,
 	}
 }
 

core/vm/contracts.go

@@ -57,6 +57,8 @@ var requestAttestationAddress = common.BytesToAddress(append([]byte{0}, CeloPrec
 var transferAddress = common.BytesToAddress(append([]byte{0}, (CeloPrecompiledContractsAddressOffset - 2)))
 var fractionMulExpAddress = common.BytesToAddress(append([]byte{0}, (CeloPrecompiledContractsAddressOffset - 3)))
 var proofOfPossessionAddress = common.BytesToAddress(append([]byte{0}, (CeloPrecompiledContractsAddressOffset - 4)))
+var getValidatorAddress = common.BytesToAddress(append([]byte{0}, (CeloPrecompiledContractsAddressOffset - 5)))
+var numberValidatorsAddress = common.BytesToAddress(append([]byte{0}, (CeloPrecompiledContractsAddressOffset - 6)))
 
 // PrecompiledContractsByzantium contains the default set of pre-compiled Ethereum
 // contracts used in the Byzantium release.
@@ -75,6 +77,8 @@ var PrecompiledContractsByzantium = map[common.Address]PrecompiledContract{
 	transferAddress:           &transfer{},
 	fractionMulExpAddress:     &fractionMulExp{},
 	proofOfPossessionAddress:  &proofOfPossession{},
+	getValidatorAddress:       &getValidator{},
+	numberValidatorsAddress:   &numberValidators{},
 }
 
 // RunPrecompiledContract runs and evaluates the output of a precompiled contract.
@@ -588,3 +592,48 @@ func (c *proofOfPossession) Run(input []byte, caller common.Address, evm *EVM, g
 
 	return true32Byte, gas, nil
 }
+
+type getValidator struct{}
+
+func (c *getValidator) RequiredGas(input []byte) uint64 {
+	return params.GetValidatorGas
+}
+
+func (c *getValidator) Run(input []byte, caller common.Address, evm *EVM, gas uint64) ([]byte, uint64, error) {
+	index := (&big.Int{}).SetBytes(input[0:32])
+	blockNumber := evm.Context.BlockNumber
+	validators := evm.Context.Engine.GetValidators(blockNumber, evm.Context.GetHash(blockNumber.Uint64()))
+	gas, err := debitRequiredGas(c, input, gas)
+	if err != nil {
+		return nil, gas, err
+	}
+
+	if index.Cmp(big.NewInt(int64(len(validators)))) >= 0 {
+		return nil, gas, ErrValidatorsOutOfBounds
+	}
+
+	validatorAddress := validators[index.Uint64()].Address()
+	addressBytes := common.LeftPadBytes(validatorAddress[:], 32)
+
+	return addressBytes, gas, nil
+}
+
+type numberValidators struct{}
+
+func (c *numberValidators) RequiredGas(input []byte) uint64 {
+	return params.GetValidatorGas
+}
+
+func (c *numberValidators) Run(input []byte, caller common.Address, evm *EVM, gas uint64) ([]byte, uint64, error) {
+	blockNumber := evm.Context.BlockNumber
+	validators := evm.Context.Engine.GetValidators(blockNumber, evm.Context.GetHash(blockNumber.Uint64()))
+	gas, err := debitRequiredGas(c, input, gas)
+	if err != nil {
+		return nil, gas, err
+	}
+
+	numberValidators := big.NewInt(int64(len(validators))).Bytes()
+	numberValidatorsBytes := common.LeftPadBytes(numberValidators[:], 32)
+
+	return numberValidatorsBytes, gas, nil
+}

core/vm/errors.go

@@ -27,4 +27,5 @@ var (
 	ErrInsufficientBalance      = errors.New("insufficient balance for transfer")
 	ErrContractAddressCollision = errors.New("contract address collision")
 	ErrNoCompatibleInterpreter  = errors.New("no compatible interpreter")
+	ErrValidatorsOutOfBounds    = errors.New("getValidators out of bounds")
 )

core/vm/evm.go

@@ -25,6 +25,7 @@ import (
 	"github.com/ethereum/go-ethereum/accounts/abi"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/consensus"
 	"github.com/ethereum/go-ethereum/contract_comm/errors"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto"
@@ -99,6 +100,8 @@ type Context struct {
 	Difficulty  *big.Int       // Provides information for DIFFICULTY
 
 	Header *types.Header
+
+	Engine consensus.Engine
 }
 
 // EVM is the Ethereum Virtual Machine base object and provides

params/protocol_params.go

@@ -98,6 +98,7 @@ const (
 	FractionMulExpGas uint64 = 1050 // Cost of performing multiplication and exponentiation of fractions to an exponent of up to 10^3.
 	// TODO(kobigurk):  Figure out what the actual gas cost of this contract should be.
 	ProofOfPossessionGas uint64 = 1050 // Cost of verifying a BLS proof of possession.
+	GetValidatorGas      uint64 = 5000 // Cost of reading a validator's address
 )
 
 var (