Add tests for witness generation

rvgo/cmd/test_data/state.json

@@ -0,0 +1,7 @@
+{
+  "pc": 0,
+  "exited": false,
+  "step": 0,
+  "witness": "wOSi8Cm62dDmKt1OGwxlLrSznk6zE4ghp7evP1rfrXYAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAIGCAAAAAAAAAAAAAAAAB/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
+  "stateHash": "0x03216fdc4a7bfd4c7160fa946d1bfe451d13ff32da496609fe18355282b910c6"
+}

rvgo/cmd/witness_test.go

@@ -0,0 +1,120 @@
+package cmd
+
+import (
+	"compress/gzip"
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/ethereum-optimism/asterisc/rvgo/fast"
+	"github.com/ethereum-optimism/optimism/cannon/mipsevm"
+)
+
+//go:embed test_data/state.json
+var testState []byte
+
+var asteriscWitnessLen = 362
+
+func TestLoadState(t *testing.T) {
+	t.Run("Uncompressed", func(t *testing.T) {
+		dir := t.TempDir()
+		path := filepath.Join(dir, "state.json")
+		require.NoError(t, os.WriteFile(path, testState, 0644))
+
+		state, err := fast.LoadVMStateFromFile(path)
+		require.NoError(t, err)
+
+		var expected fast.VMState
+		require.NoError(t, json.Unmarshal(testState, &expected))
+		require.Equal(t, &expected, state)
+	})
+
+	t.Run("Gzipped", func(t *testing.T) {
+		dir := t.TempDir()
+		path := filepath.Join(dir, "state.json.gz")
+		f, err := os.OpenFile(path, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0644)
+		require.NoError(t, err)
+		defer f.Close()
+		writer := gzip.NewWriter(f)
+		_, err = writer.Write(testState)
+		require.NoError(t, err)
+		require.NoError(t, writer.Close())
+
+		state, err := fast.LoadVMStateFromFile(path)
+		require.NoError(t, err)
+
+		var expected fast.VMState
+		require.NoError(t, json.Unmarshal(testState, &expected))
+		require.Equal(t, &expected, state)
+	})
+
+	t.Run("InvalidStateWitness", func(t *testing.T) {
+		invalidWitnessLen := asteriscWitnessLen - 1
+		state := &fast.VMState{
+			Step:    10,
+			Exited:  true,
+			Witness: make([]byte, invalidWitnessLen),
+		}
+		err := validateState(state)
+		require.ErrorContains(t, err, "invalid witness")
+	})
+
+	t.Run("InvalidStateHash", func(t *testing.T) {
+		state := &fast.VMState{
+			Step:    10,
+			Exited:  true,
+			Witness: make([]byte, asteriscWitnessLen),
+		}
+		// Unknown exit code
+		state.StateHash[0] = 37
+		err := validateState(state)
+		require.ErrorContains(t, err, "invalid stateHash: unknown exitCode")
+		// Exited but ExitCode is VMStatusUnfinished
+		state.StateHash[0] = 3
+		err = validateState(state)
+		require.ErrorContains(t, err, "invalid stateHash: invalid exitCode")
+		// Not Exited but ExitCode is not VMStatusUnfinished
+		state.Exited = false
+		for exitCode := 0; exitCode < 3; exitCode++ {
+			state.StateHash[0] = byte(exitCode)
+			err = validateState(state)
+			require.ErrorContains(t, err, "invalid stateHash: invalid exitCode")
+		}
+	})
+}
+
+// validateState performs verification of state; it is not perfect.
+// It does not recalculate whether witness nor stateHash is correctly set from state.
+func validateState(state *fast.VMState) error {
+	if err := validateStateHash(state); err != nil {
+		return err
+	}
+	if err := validateWitness(state); err != nil {
+		return err
+	}
+	return nil
+}
+
+func validateStateHash(state *fast.VMState) error {
+	exitCode := state.StateHash[0]
+	if exitCode >= 4 {
+		return fmt.Errorf("invalid stateHash: unknown exitCode %d", exitCode)
+	}
+	if (state.Exited && exitCode == mipsevm.VMStatusUnfinished) || (!state.Exited && exitCode != mipsevm.VMStatusUnfinished) {
+		return fmt.Errorf("invalid stateHash: invalid exitCode %d", exitCode)
+	}
+	return nil
+}
+
+func validateWitness(state *fast.VMState) error {
+	witnessLen := len(state.Witness)
+	if witnessLen != asteriscWitnessLen {
+		return fmt.Errorf("invalid witness: Length must be 362 but got %d", witnessLen)
+	}
+	return nil
+}