evm: implement vm.GetHashFn

x/evm/types/state_transition.go

@@ -47,11 +47,30 @@ type ExecutionResult struct {
 	GasInfo GasInfo
 }
 
+// GetHashFn implements vm.GetHashFunc for Ethermint. It casts the current
+// tendermint header hash to an ethereum Hash format. If the context block height
+// doesn't match the requested height, it will return an empty hash.
+func GetHashFn(ctx sdk.Context) vm.GetHashFunc {
+	return func(height uint64) common.Hash {
+		if ctx.BlockHeight() != int64(height) {
+			return common.Hash{}
+		}
+
+		// cast the ABCI header to tendermint Header type
+		tmHeader := AbciHeaderToTendermint(ctx.BlockHeader())
+
+		// get the Tendermint block hash from the current header
+		tmBlockHash := tmHeader.Hash()
+		return common.BytesToHash(tmBlockHash.Bytes())
+	}
+}
+
 func (st StateTransition) newEVM(ctx sdk.Context, csdb *CommitStateDB, gasLimit uint64, gasPrice *big.Int, config ChainConfig) *vm.EVM {
 	// Create context for evm
 	context := vm.Context{
 		CanTransfer: core.CanTransfer,
 		Transfer:    core.Transfer,
+		GetHash:     GetHashFn(ctx),
 		Origin:      st.Sender,
 		Coinbase:    common.Address{}, // there's no benefitiary since we're not mining
 		BlockNumber: big.NewInt(ctx.BlockHeight()),

x/evm/types/utils.go

@@ -8,6 +8,10 @@ import (
 	"github.com/pkg/errors"
 	"golang.org/x/crypto/sha3"
 
+	abci "github.com/tendermint/tendermint/abci/types"
+	tmtypes "github.com/tendermint/tendermint/types"
+	"github.com/tendermint/tendermint/version"
+
 	"github.com/cosmos/cosmos-sdk/codec"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
@@ -152,3 +156,36 @@ func recoverEthSig(R, S, Vb *big.Int, sigHash ethcmn.Hash) (ethcmn.Address, erro
 
 	return addr, nil
 }
+
+// AbciHeaderToTendermint is a util function to parse a tendermint ABCI Header to
+// tendermint types Header.
+func AbciHeaderToTendermint(header abci.Header) tmtypes.Header {
+	return tmtypes.Header{
+		Version: version.Consensus{
+			Block: version.Protocol(header.Version.Block),
+			App:   version.Protocol(header.Version.App),
+		},
+		ChainID: header.ChainID,
+		Height:  header.Height,
+		Time:    header.Time,
+
+		LastBlockID: tmtypes.BlockID{
+			Hash: header.LastBlockId.Hash,
+			PartsHeader: tmtypes.PartSetHeader{
+				Total: int(header.LastBlockId.PartsHeader.Total),
+				Hash:  header.LastBlockId.PartsHeader.Hash,
+			},
+		},
+		LastCommitHash: header.LastCommitHash,
+		DataHash:       header.DataHash,
+
+		ValidatorsHash:     header.ValidatorsHash,
+		NextValidatorsHash: header.NextValidatorsHash,
+		ConsensusHash:      header.ConsensusHash,
+		AppHash:            header.AppHash,
+		LastResultsHash:    header.LastResultsHash,
+
+		EvidenceHash:    header.EvidenceHash,
+		ProposerAddress: header.ProposerAddress,
+	}
+}