lnwire: allow longer failure messages

This fixes an incompatibility where lnd enforces a strict 256 byte
failure message, where as the spec sets this only as the recommended
length.

htlcswitch/failure_test.go

@@ -0,0 +1,86 @@
+package htlcswitch
+
+import (
+	"encoding/hex"
+	"encoding/json"
+	"os"
+	"testing"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	sphinx "github.com/lightningnetwork/lightning-onion"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/require"
+)
+
+// TestLongFailureMessage tests that longer failure messages can be interpreted
+// correctly.
+func TestLongFailureMessage(t *testing.T) {
+	t.Parallel()
+
+	var testData struct {
+		SessionKey string
+		Path       []string
+		Reason     string
+	}
+
+	// Use long 1024-byte test vector from BOLT 04.
+	testDataBytes, err := os.ReadFile("testdata/long_failure_msg.json")
+	require.NoError(t, err)
+	require.NoError(t, json.Unmarshal(testDataBytes, &testData))
+
+	sessionKeyBytes, _ := hex.DecodeString(testData.SessionKey)
+
+	reason, _ := hex.DecodeString(testData.Reason)
+
+	sphinxPath := make([]*btcec.PublicKey, len(testData.Path))
+	for i, sKey := range testData.Path {
+		bKey, err := hex.DecodeString(sKey)
+		require.NoError(t, err)
+
+		key, err := btcec.ParsePubKey(bKey)
+		require.NoError(t, err)
+
+		sphinxPath[i] = key
+	}
+
+	sessionKey, _ := btcec.PrivKeyFromBytes(sessionKeyBytes)
+
+	circuit := &sphinx.Circuit{
+		SessionKey:  sessionKey,
+		PaymentPath: sphinxPath,
+	}
+
+	errorDecryptor := &SphinxErrorDecrypter{
+		OnionErrorDecrypter: sphinx.NewOnionErrorDecrypter(circuit),
+	}
+
+	// Assert that the failure message can still be extracted.
+	failure, err := errorDecryptor.DecryptError(reason)
+	require.NoError(t, err)
+
+	incorrectDetails, ok := failure.msg.(*lnwire.FailIncorrectDetails)
+	require.True(t, ok)
+
+	var value varBytesRecordProducer
+
+	extraData := incorrectDetails.ExtraOpaqueData()
+	typeMap, err := extraData.ExtractRecords(&value)
+	require.NoError(t, err)
+	require.Len(t, typeMap, 1)
+
+	expectedValue := make([]byte, 300)
+	for i := range expectedValue {
+		expectedValue[i] = 128
+	}
+
+	require.Equal(t, expectedValue, value.data)
+}
+
+type varBytesRecordProducer struct {
+	data []byte
+}
+
+func (v *varBytesRecordProducer) Record() tlv.Record {
+	return tlv.MakePrimitiveRecord(34001, &v.data)
+}