Add proof enhancer system with customda enhancers

validator/server_arb/proof_enhancer.go

@@ -0,0 +1,100 @@
+// 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
+
+	// SequencerMessageHeaderSize is the size of the sequencer message header
+	// (MinTimestamp + MaxTimestamp + MinL1Block + MaxL1Block + AfterDelayedMessages = 8+8+8+8+8)
+	SequencerMessageHeaderSize = 40
+
+	// Sizes for proof enhancement marker data
+	CertificateHashSize      = 32 // Size of keccak256 hash of the certificate
+	OffsetSize               = 8  // Size of uint64 offset
+	MarkerSize               = 1  // Size of marker byte
+	CertificateSizeFieldSize = 8  // Size of uint64 certificate size field
+
+	// MinCertificateSize is the minimum size of a certificate (just the header byte).
+	// Real certificates will have more data, but the proof enhancer system doesn't
+	// put any further constraints on certificate structure.
+	MinCertificateSize = 1
+)
+
+// ProofMarker identifies the type of proof enhancement needed
+type ProofMarker byte
+
+// ProofEnhancer enhances one-step proofs with additional data.
+// For proving certain opcodes, like for CustomDA, Arbitrator doesn't have enough information
+// to generate the full proofs. In the case of CustomDA, daprovider implementations usually
+// need network access to talk to external DA systems to get full proof details. To indicate
+// that a proof needs enhancement, Arbitrator sets the ProofEnhancementFlag on the machine
+// status byte of the proof that it returns, and also appends one of the Marker bytes to
+// indicate which ProofEnhancer is required.
+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 allows registration of ProofEnhancers and provides forwarding of EnhanceProof
+// requests to the appropriate ProofEnhancer.
+type ProofEnhancementManager struct {
+	enhancers map[ProofMarker]ProofEnhancer
+}
+
+// NewProofEnhancementManager creates a new proof enhancement manager
+func NewProofEnhancementManager() *ProofEnhancementManager {
+	return &ProofEnhancementManager{
+		enhancers: make(map[ProofMarker]ProofEnhancer),
+	}
+}
+
+// RegisterEnhancer registers an enhancer for a specific marker byte
+func (m *ProofEnhancementManager) RegisterEnhancer(marker ProofMarker, enhancer ProofEnhancer) {
+	m.enhancers[marker] = enhancer
+}
+
+// EnhanceProof implements ProofEnhancer interface to forward EnhanceProof requests
+// to the appropriate registered ProofEnhancer implementation, if there is any
+// and proof enhancement was requested.
+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) < 2 { // Need at least the marker byte after the enhancement flag
+		return nil, fmt.Errorf("proof too short for enhancement: %d bytes", len(proof))
+	}
+	marker := ProofMarker(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)
+}