cannon: Add subcommand to convert from json state to binary witness

cannon/cmd/witness.go

+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/ethereum-optimism/optimism/cannon/mipsevm"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/urfave/cli/v2"
+)
+
+var (
+	WitnessInputFlag = &cli.PathFlag{
+		Name:      "input",
+		Usage:     "path of input JSON state.",
+		TakesFile: true,
+		Required:  true,
+	}
+	WitnessOutputFlag = &cli.PathFlag{
+		Name:      "output",
+		Usage:     "path to write binary witness.",
+		TakesFile: true,
+	}
+)
+
+func Witness(ctx *cli.Context) error {
+	input := ctx.Path(WitnessInputFlag.Name)
+	output := ctx.Path(WitnessOutputFlag.Name)
+	state, err := loadJSON[mipsevm.State](input)
+	if err != nil {
+		return fmt.Errorf("invalid input state (%v): %w", input, err)
+	}
+	witness := state.EncodeWitness()
+	h := crypto.Keccak256Hash(witness)
+	if output != "" {
+		if err := os.WriteFile(output, witness, 0755); err != nil {
+			return fmt.Errorf("writing output to %v: %w", output, err)
+		}
+	}
+	fmt.Println(h.Hex())
+	return nil
+}
+
+var WitnessCommand = &cli.Command{
+	Name:        "witness",
+	Usage:       "Convert a Cannon JSON state into a binary witness",
+	Description: "Convert a Cannon JSON state into a binary witness. The hash of the witness is written to stdout",
+	Action:      Witness,
+	Flags: []cli.Flag{
+		WitnessInputFlag,
+		WitnessOutputFlag,
+	},
+}

cannon/main.go

@@ -20,6 +20,7 @@ func main() {
 	app.Description = "MIPS Fault Proof tool"
 	app.Commands = []*cli.Command{
 		cmd.LoadELFCommand,
+		cmd.WitnessCommand,
 		cmd.RunCommand,
 	}
 	ctx, cancel := context.WithCancel(context.Background())