feat: vm.PrecompileEnvironment access to block info (ethereum#27)

Author: ARR4N

core/evm.go

@@ -73,6 +73,7 @@ func NewEVMBlockContext(header *types.Header, chain ChainContext, author *common
 		BlobBaseFee: blobBaseFee,
 		GasLimit:    header.GasLimit,
 		Random:      random,
+		Header:      header,
 	}
 }
 

core/vm/contracts.libevm.go

@@ -2,10 +2,12 @@ package vm
 
 import (
 	"fmt"
+	"math/big"
 
 	"github.com/holiman/uint256"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/libevm"
 	"github.com/ethereum/go-ethereum/params"
 )
@@ -99,6 +101,10 @@ type PrecompileEnvironment interface {
 	// ReadOnlyState will always be non-nil.
 	ReadOnlyState() libevm.StateReader
 	Addresses() *libevm.AddressContext
+
+	BlockHeader() (types.Header, error)
+	BlockNumber() *big.Int
+	BlockTime() uint64
 }
 
 //
@@ -152,6 +158,24 @@ func (args *evmCallArgs) Addresses() *libevm.AddressContext {
 	}
 }
 
+func (args *evmCallArgs) BlockHeader() (types.Header, error) {
+	hdr := args.evm.Context.Header
+	if hdr == nil {
+		// Although [core.NewEVMBlockContext] sets the field and is in the
+		// typical hot path (e.g. miner), there are other ways to create a
+		// [vm.BlockContext] (e.g. directly in tests) that may result in no
+		// available header.
+		return types.Header{}, fmt.Errorf("nil %T in current %T", hdr, args.evm.Context)
+	}
+	return *hdr, nil
+}
+
+func (args *evmCallArgs) BlockNumber() *big.Int {
+	return new(big.Int).Set(args.evm.Context.BlockNumber)
+}
+
+func (args *evmCallArgs) BlockTime() uint64 { return args.evm.Context.Time }
+
 var (
 	// These lock in the assumptions made when implementing [evmCallArgs]. If
 	// these break then the struct fields SHOULD be changed to match these

core/vm/contracts.libevm_test.go

@@ -3,6 +3,8 @@ package vm_test
 import (
 	"fmt"
 	"math/big"
+	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/holiman/uint256"
@@ -11,6 +13,8 @@ import (
 	"golang.org/x/exp/rand"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/libevm"
@@ -79,6 +83,31 @@ func TestPrecompileOverride(t *testing.T) {
 	}
 }
 
+type statefulPrecompileOutput struct {
+	Caller, Self            common.Address
+	StateValue              common.Hash
+	ReadOnly                bool
+	BlockNumber, Difficulty *big.Int
+	BlockTime               uint64
+	Input                   []byte
+}
+
+func (o statefulPrecompileOutput) String() string {
+	var lines []string
+	out := reflect.ValueOf(o)
+	for i, n := 0, out.NumField(); i < n; i++ {
+		name := out.Type().Field(i).Name
+		fld := out.Field(i).Interface()
+
+		verb := "%v"
+		if _, ok := fld.([]byte); ok {
+			verb = "%#x"
+		}
+		lines = append(lines, fmt.Sprintf("%s: "+verb, name, fld))
+	}
+	return strings.Join(lines, "\n")
+}
+
 func TestNewStatefulPrecompile(t *testing.T) {
 	rng := ethtest.NewPseudoRand(314159)
 	precompile := rng.Address()
@@ -87,20 +116,27 @@ func TestNewStatefulPrecompile(t *testing.T) {
 	const gasLimit = 1e6
 	gasCost := rng.Uint64n(gasLimit)
 
-	makeOutput := func(caller, self common.Address, input []byte, stateVal common.Hash, readOnly bool) []byte {
-		return []byte(fmt.Sprintf(
-			"Caller: %v Precompile: %v State: %v Read-only: %t, Input: %#x",
-			caller, self, stateVal, readOnly, input,
-		))
-	}
 	run := func(env vm.PrecompileEnvironment, input []byte, suppliedGas uint64) ([]byte, uint64, error) {
 		if got, want := env.StateDB() != nil, !env.ReadOnly(); got != want {
 			return nil, 0, fmt.Errorf("PrecompileEnvironment().StateDB() must be non-nil i.f.f. not read-only; got non-nil? %t; want %t", got, want)
 		}
+		hdr, err := env.BlockHeader()
+		if err != nil {
+			return nil, 0, err
+		}
 
 		addrs := env.Addresses()
-		val := env.ReadOnlyState().GetState(precompile, slot)
-		return makeOutput(addrs.Caller, addrs.Self, input, val, env.ReadOnly()), suppliedGas - gasCost, nil
+		out := &statefulPrecompileOutput{
+			Caller:      addrs.Caller,
+			Self:        addrs.Self,
+			StateValue:  env.ReadOnlyState().GetState(precompile, slot),
+			ReadOnly:    env.ReadOnly(),
+			BlockNumber: env.BlockNumber(),
+			BlockTime:   env.BlockTime(),
+			Difficulty:  hdr.Difficulty,
+			Input:       input,
+		}
+		return []byte(out.String()), suppliedGas - gasCost, nil
 	}
 	hooks := &hookstest.Stub{
 		PrecompileOverrides: map[common.Address]libevm.PrecompiledContract{
@@ -109,11 +145,18 @@ func TestNewStatefulPrecompile(t *testing.T) {
 	}
 	hooks.Register(t)
 
+	header := &types.Header{
+		Number:     rng.BigUint64(),
+		Time:       rng.Uint64(),
+		Difficulty: rng.BigUint64(),
+	}
 	caller := rng.Address()
 	input := rng.Bytes(8)
 	value := rng.Hash()
 
-	state, evm := ethtest.NewZeroEVM(t)
+	state, evm := ethtest.NewZeroEVM(t, ethtest.WithBlockContext(
+		core.NewEVMBlockContext(header, nil, rng.AddressPtr()),
+	))
 	state.SetState(precompile, slot, value)
 
 	tests := []struct {
@@ -155,12 +198,21 @@ func TestNewStatefulPrecompile(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			wantReturnData := makeOutput(caller, precompile, input, value, tt.wantReadOnly)
+			wantReturnData := statefulPrecompileOutput{
+				Caller:      caller,
+				Self:        precompile,
+				StateValue:  value,
+				ReadOnly:    tt.wantReadOnly,
+				BlockNumber: header.Number,
+				BlockTime:   header.Time,
+				Difficulty:  header.Difficulty,
+				Input:       input,
+			}.String()
 			wantGasLeft := gasLimit - gasCost
 
 			gotReturnData, gotGasLeft, err := tt.call()
 			require.NoError(t, err)
-			assert.Equal(t, string(wantReturnData), string(gotReturnData))
+			assert.Equal(t, wantReturnData, string(gotReturnData))
 			assert.Equal(t, wantGasLeft, gotGasLeft)
 		})
 	}

core/vm/evm.go

@@ -79,6 +79,8 @@ type BlockContext struct {
 	BaseFee     *big.Int       // Provides information for BASEFEE (0 if vm runs with NoBaseFee flag and 0 gas price)
 	BlobBaseFee *big.Int       // Provides information for BLOBBASEFEE (0 if vm runs with NoBaseFee flag and 0 blob gas price)
 	Random      *common.Hash   // Provides information for PREVRANDAO
+
+	Header *types.Header // libevm addition; not guaranteed to be set
 }
 
 // TxContext provides the EVM with information about a transaction.

libevm/ethtest/evm.go

@@ -19,13 +19,13 @@ import (
 // arguments to [vm.NewEVM] are the zero values of their respective types,
 // except for the use of [core.CanTransfer] and [core.Transfer] instead of nil
 // functions.
-func NewZeroEVM(tb testing.TB) (*state.StateDB, *vm.EVM) {
+func NewZeroEVM(tb testing.TB, opts ...EVMOption) (*state.StateDB, *vm.EVM) {
 	tb.Helper()
 
 	sdb, err := state.New(common.Hash{}, state.NewDatabase(rawdb.NewMemoryDatabase()), nil)
 	require.NoError(tb, err, "state.New()")
 
-	return sdb, vm.NewEVM(
+	vm := vm.NewEVM(
 		vm.BlockContext{
 			CanTransfer: core.CanTransfer,
 			Transfer:    core.Transfer,
@@ -35,4 +35,27 @@ func NewZeroEVM(tb testing.TB) (*state.StateDB, *vm.EVM) {
 		&params.ChainConfig{},
 		vm.Config{},
 	)
+	for _, o := range opts {
+		o.apply(vm)
+	}
+
+	return sdb, vm
+}
+
+// An EVMOption configures the EVM returned by [NewZeroEVM].
+type EVMOption interface {
+	apply(*vm.EVM)
+}
+
+type funcOption func(*vm.EVM)
+
+var _ EVMOption = funcOption(nil)
+
+func (f funcOption) apply(vm *vm.EVM) { f(vm) }
+
+// WithBlockContext overrides the default context.
+func WithBlockContext(c vm.BlockContext) EVMOption {
+	return funcOption(func(vm *vm.EVM) {
+		vm.Context = c
+	})
 }

libevm/ethtest/rand.go

@@ -1,6 +1,8 @@
 package ethtest
 
 import (
+	"math/big"
+
 	"golang.org/x/exp/rand"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -40,3 +42,8 @@ func (r *PseudoRand) Bytes(n uint) []byte {
 	r.Read(b) //nolint:gosec,errcheck // Guaranteed nil error
 	return b
 }
+
+// Big returns [rand.Rand.Uint64] as a [big.Int].
+func (r *PseudoRand) BigUint64() *big.Int {
+	return new(big.Int).SetUint64(r.Uint64())
+}