Add fraud proof gossiping logic to light clients (cosmos#724)

Resolves rollkit/rollkit#673.

---------

Co-authored-by: Manav Aggarwal <manavaggarwal1234@gmail.com>

node/full.go

@@ -369,7 +369,7 @@ func (n *FullNode) newHeaderValidator() p2p.GossipValidator {
 func (n *FullNode) newFraudProofValidator() p2p.GossipValidator {
 	return func(fraudProofMsg *p2p.GossipMessage) bool {
 		n.Logger.Debug("fraud proof received", "from", fraudProofMsg.From, "bytes", len(fraudProofMsg.Data))
-		var fraudProof abci.FraudProof
+		fraudProof := abci.FraudProof{}
 		err := fraudProof.Unmarshal(fraudProofMsg.Data)
 		if err != nil {
 			n.Logger.Error("failed to deserialize fraud proof", "error", err)

node/light.go

@@ -1,20 +1,115 @@
 package node
 
 import (
+	"context"
+
+	ds "github.com/ipfs/go-datastore"
+	"github.com/libp2p/go-libp2p/core/crypto"
+	abciclient "github.com/tendermint/tendermint/abci/client"
+	abci "github.com/tendermint/tendermint/abci/types"
+	"github.com/tendermint/tendermint/libs/log"
 	"github.com/tendermint/tendermint/libs/service"
 	rpcclient "github.com/tendermint/tendermint/rpc/client"
+	tmtypes "github.com/tendermint/tendermint/types"
+
+	"github.com/rollkit/rollkit/config"
+	"github.com/rollkit/rollkit/p2p"
+	"github.com/rollkit/rollkit/store"
 )
 
 var _ Node = &LightNode{}
 
 type LightNode struct {
 	service.BaseService
+
+	P2P *p2p.Client
+
+	app abciclient.Client
+
+	ctx context.Context
 }
 
-func (n *LightNode) GetClient() rpcclient.Client {
-	return NewLightClient(n)
+func (ln *LightNode) GetClient() rpcclient.Client {
+	return NewLightClient(ln)
+}
+
+func newLightNode(
+	ctx context.Context,
+	conf config.NodeConfig,
+	p2pKey crypto.PrivKey,
+	appClient abciclient.Client,
+	genesis *tmtypes.GenesisDoc,
+	logger log.Logger,
+) (*LightNode, error) {
+	datastore, err := openDatastore(conf, logger)
+	if err != nil {
+		return nil, err
+	}
+	client, err := p2p.NewClient(conf.P2P, p2pKey, genesis.ChainID, datastore, logger.With("module", "p2p"))
+	if err != nil {
+		return nil, err
+	}
+
+	node := &LightNode{
+		P2P: client,
+		app: appClient,
+		ctx: ctx,
+	}
+
+	node.P2P.SetTxValidator(node.falseValidator())
+	node.P2P.SetHeaderValidator(node.falseValidator())
+	node.P2P.SetFraudProofValidator(node.newFraudProofValidator())
+
+	node.BaseService = *service.NewBaseService(logger, "LightNode", node)
+
+	return node, nil
 }
 
-func newLightNode() (Node, error) {
-	return &LightNode{}, nil
+func openDatastore(conf config.NodeConfig, logger log.Logger) (ds.TxnDatastore, error) {
+	if conf.RootDir == "" && conf.DBPath == "" { // this is used for testing
+		logger.Info("WARNING: working in in-memory mode")
+		return store.NewDefaultInMemoryKVStore()
+	}
+	return store.NewDefaultKVStore(conf.RootDir, conf.DBPath, "rollkit-light")
+}
+
+func (ln *LightNode) OnStart() error {
+	if err := ln.P2P.Start(ln.ctx); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Dummy validator that always returns a callback function with boolean `false`
+func (ln *LightNode) falseValidator() p2p.GossipValidator {
+	return func(*p2p.GossipMessage) bool {
+		return false
+	}
+}
+
+func (ln *LightNode) newFraudProofValidator() p2p.GossipValidator {
+	return func(fraudProofMsg *p2p.GossipMessage) bool {
+		ln.Logger.Info("fraud proof received", "from", fraudProofMsg.From, "bytes", len(fraudProofMsg.Data))
+		fraudProof := abci.FraudProof{}
+		err := fraudProof.Unmarshal(fraudProofMsg.Data)
+		if err != nil {
+			ln.Logger.Error("failed to deserialize fraud proof", "error", err)
+			return false
+		}
+
+		resp, err := ln.app.VerifyFraudProofSync(abci.RequestVerifyFraudProof{
+			FraudProof:           &fraudProof,
+			ExpectedValidAppHash: fraudProof.ExpectedValidAppHash,
+		})
+		if err != nil {
+			return false
+		}
+
+		if resp.Success {
+			panic("received valid fraud proof! halting light client")
+		}
+
+		return false
+	}
 }

node/node.go

@@ -40,6 +40,13 @@ func NewNode(
 			logger,
 		)
 	} else {
-		return newLightNode()
+		return newLightNode(
+			ctx,
+			conf,
+			p2pKey,
+			appClient,
+			genesis,
+			logger,
+		)
 	}
 }