op-challenger: Add a translating trace provider.

op-challenger/game/fault/trace/translate.go

+package trace
+
+import (
+	"context"
+
+	"github.com/ethereum-optimism/optimism/op-challenger/game/fault/types"
+	"github.com/ethereum/go-ethereum/common"
+)
+
+type translatingProvider struct {
+	parentDepth uint64
+	provider    types.TraceProvider
+}
+
+func Translate(provider types.TraceProvider, parentDepth uint64) types.TraceProvider {
+	return &translatingProvider{
+		parentDepth: parentDepth,
+		provider:    provider,
+	}
+}
+
+func (p translatingProvider) Get(ctx context.Context, pos types.Position) (common.Hash, error) {
+	relativePos, err := pos.RelativeToAncestorAtDepth(p.parentDepth)
+	if err != nil {
+		return common.Hash{}, err
+	}
+	return p.provider.Get(ctx, relativePos)
+}
+
+func (p translatingProvider) GetStepData(ctx context.Context, pos types.Position) (prestate []byte, proofData []byte, preimageData *types.PreimageOracleData, err error) {
+	relativePos, err := pos.RelativeToAncestorAtDepth(p.parentDepth)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+	return p.provider.GetStepData(ctx, relativePos)
+}
+
+func (p translatingProvider) AbsolutePreStateCommitment(ctx context.Context) (hash common.Hash, err error) {
+	return p.provider.AbsolutePreStateCommitment(ctx)
+}
+
+var _ types.TraceProvider = (*translatingProvider)(nil)

op-challenger/game/fault/trace/translate_test.go

+package trace
+
+import (
+	"context"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum-optimism/optimism/op-challenger/game/fault/trace/alphabet"
+	"github.com/ethereum-optimism/optimism/op-challenger/game/fault/types"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTranslate(t *testing.T) {
+	orig := alphabet.NewTraceProvider("abcdefghij", 4)
+	translated := Translate(orig, 3)
+	// All nodes on the first translated layer, map to GIndex 1
+	for i := int64(8); i <= 15; i++ {
+		requireSameValue(t, orig, 1, translated, i)
+	}
+	// Nodes on the second translated layer map to GIndex 2 and 3 alternately
+	for i := int64(16); i <= 31; i += 2 {
+		requireSameValue(t, orig, 2, translated, i)
+		requireSameValue(t, orig, 3, translated, i+1)
+	}
+	// Nodes on the third translated layer map to GIndex 4, 5, 6 and 7
+	for i := int64(32); i <= 61; i += 4 {
+		requireSameValue(t, orig, 4, translated, i)
+		requireSameValue(t, orig, 5, translated, i+1)
+		requireSameValue(t, orig, 6, translated, i+2)
+		requireSameValue(t, orig, 7, translated, i+3)
+	}
+}
+
+func requireSameValue(t *testing.T, a types.TraceProvider, aGIdx int64, b types.TraceProvider, bGIdx int64) {
+	// Check Get returns the same results
+	aValue, err := a.Get(context.Background(), types.NewPositionFromGIndex(big.NewInt(aGIdx)))
+	require.NoError(t, err)
+	bValue, err := b.Get(context.Background(), types.NewPositionFromGIndex(big.NewInt(bGIdx)))
+	require.NoError(t, err)
+	require.Equal(t, aValue, bValue)
+
+	// Check GetStepData returns the same results
+	aPrestate, aProofData, aPreimageData, err := a.GetStepData(context.Background(), types.NewPositionFromGIndex(big.NewInt(aGIdx)))
+	require.NoError(t, err)
+	bPrestate, bProofData, bPreimageData, err := b.GetStepData(context.Background(), types.NewPositionFromGIndex(big.NewInt(bGIdx)))
+	require.NoError(t, err)
+	require.Equal(t, aPrestate, bPrestate)
+	require.Equal(t, aProofData, bProofData)
+	require.Equal(t, aPreimageData, bPreimageData)
+}
+
+func TestTranslate_AbsolutePreStateCommitment(t *testing.T) {
+	orig := alphabet.NewTraceProvider("abcdefghij", 4)
+	translated := Translate(orig, 3)
+	origValue, err := orig.AbsolutePreStateCommitment(context.Background())
+	require.NoError(t, err)
+	translatedValue, err := translated.AbsolutePreStateCommitment(context.Background())
+	require.NoError(t, err)
+	require.Equal(t, origValue, translatedValue)
+}