watchtower/wtwire/init: add CheckRemoteInit method

watchtower/wtwire/init.go

@@ -1,6 +1,7 @@
 package wtwire
 
 import (
+	"fmt"
 	"io"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -72,3 +73,67 @@ func (msg *Init) MaxPayloadLength(uint32) uint32 {
 
 // A compile-time constraint to ensure Init implements the Message interface.
 var _ Message = (*Init)(nil)
+
+// CheckRemoteInit performs basic validation of the remote party's Init message.
+// This method checks that the remote Init's chain hash matches our advertised
+// chain hash and that the remote Init does not contain any required feature
+// bits that we don't understand.
+func (msg *Init) CheckRemoteInit(remoteInit *Init,
+	featureNames map[lnwire.FeatureBit]string) error {
+
+	// Check that the remote peer is on the same chain.
+	if msg.ChainHash != remoteInit.ChainHash {
+		return NewErrUnknownChainHash(remoteInit.ChainHash)
+	}
+
+	remoteConnFeatures := lnwire.NewFeatureVector(
+		remoteInit.ConnFeatures, featureNames,
+	)
+
+	// Check that the remote peer doesn't have any required connection
+	// feature bits that we ourselves are unaware of.
+	unknownConnFeatures := remoteConnFeatures.UnknownRequiredFeatures()
+	if len(unknownConnFeatures) > 0 {
+		return NewErrUnknownRequiredFeatures(unknownConnFeatures...)
+	}
+
+	return nil
+}
+
+// ErrUnknownChainHash signals that the remote Init has a different chain hash
+// from the one we advertised.
+type ErrUnknownChainHash struct {
+	hash chainhash.Hash
+}
+
+// NewErrUnknownChainHash creates an ErrUnknownChainHash using the remote Init's
+// chain hash.
+func NewErrUnknownChainHash(hash chainhash.Hash) *ErrUnknownChainHash {
+	return &ErrUnknownChainHash{hash}
+}
+
+// Error returns a human-readable error displaying the unknown chain hash.
+func (e *ErrUnknownChainHash) Error() string {
+	return fmt.Sprintf("remote init has unknown chain hash: %s", e.hash)
+}
+
+// ErrUnknownRequiredFeatures signals that the remote Init has required feature
+// bits that were unknown to us.
+type ErrUnknownRequiredFeatures struct {
+	unknownFeatures []lnwire.FeatureBit
+}
+
+// NewErrUnknownRequiredFeatures creates an ErrUnknownRequiredFeatures using the
+// remote Init's required features that were unknown to us.
+func NewErrUnknownRequiredFeatures(
+	unknownFeatures ...lnwire.FeatureBit) *ErrUnknownRequiredFeatures {
+
+	return &ErrUnknownRequiredFeatures{unknownFeatures}
+}
+
+// Error returns a human-readable error displaying the unknown required feature
+// bits.
+func (e *ErrUnknownRequiredFeatures) Error() string {
+	return fmt.Sprintf("remote init has unknown required features: %v",
+		e.unknownFeatures)
+}