Add proof enhancer system with customda enhancers

validator/server_arb/proof_enhancer.go

@@ -0,0 +1,74 @@
+// Copyright 2025, Offchain Labs, Inc.
+// For license information, see https://github.com/OffchainLabs/nitro/blob/master/LICENSE.md
+package server_arb
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/offchainlabs/nitro/arbutil"
+)
+
+const (
+	// Enhancement flag in machine status byte
+	ProofEnhancementFlag = 0x80
+
+	// Marker bytes for different enhancement types
+	MarkerCustomDAReadPreimage        = 0xDA
+	MarkerCustomDAValidateCertificate = 0xDB
+)
+
+// ProofEnhancer enhances one-step proofs with additional data
+type ProofEnhancer interface {
+	// EnhanceProof checks if enhancement is needed and applies it
+	// Returns the enhanced proof or the original if no enhancement needed
+	EnhanceProof(ctx context.Context, messageNum arbutil.MessageIndex, proof []byte) ([]byte, error)
+}
+
+// ProofEnhancementManager manages multiple proof enhancers by marker type
+type ProofEnhancementManager struct {
+	enhancers map[byte]ProofEnhancer
+}
+
+// NewProofEnhancementManager creates a new proof enhancement manager
+func NewProofEnhancementManager() *ProofEnhancementManager {
+	return &ProofEnhancementManager{
+		enhancers: make(map[byte]ProofEnhancer),
+	}
+}
+
+// RegisterEnhancer registers an enhancer for a specific marker byte
+func (m *ProofEnhancementManager) RegisterEnhancer(marker byte, enhancer ProofEnhancer) {
+	m.enhancers[marker] = enhancer
+}
+
+// EnhanceProof implements ProofEnhancer interface
+func (m *ProofEnhancementManager) EnhanceProof(ctx context.Context, messageNum arbutil.MessageIndex, proof []byte) ([]byte, error) {
+	if len(proof) == 0 {
+		return proof, nil
+	}
+
+	// Check if enhancement flag is set
+	if proof[0]&ProofEnhancementFlag == 0 {
+		return proof, nil // No enhancement needed
+	}
+
+	// Find marker at end of proof
+	if len(proof) < 1 { // Need at least the marker byte
+		return nil, fmt.Errorf("proof too short for enhancement: %d bytes", len(proof))
+	}
+
+	marker := proof[len(proof)-1]
+	enhancer, exists := m.enhancers[marker]
+	if !exists {
+		return nil, fmt.Errorf("unknown enhancement marker: 0x%02x", marker)
+	}
+
+	// Remove enhancement flag from machine status
+	enhancedProof := make([]byte, len(proof))
+	copy(enhancedProof, proof)
+	enhancedProof[0] &= ^byte(ProofEnhancementFlag)
+
+	// Let specific enhancer handle the proof
+	return enhancer.EnhanceProof(ctx, messageNum, enhancedProof)
+}